Abstract: Greenhouse and growth chamber experiments were conducted to study glyphosate efficacy, rainfastness, absorption, and translocation in redvine. Glyphosate at 0, 0.56, 1.12, 2.24, and 4.48 kg ai/ha was applied to redvine plants raised from rootstocks at the five- to seven-leaf stage (about 25 cm tall). Redvine control ranged from 55% at 0.56 kg/ha glyphosate to 98% at 4.48 kg/ha. Glyphosate at rates above 1.12 kg/ha, greatly reduced regrowth from rootstocks of treated plants. A simulated rainfall of 2.5 cm (7.5 cm/h intensity) within 24 h of glyphosate application reduced efficacy by 23% compared with no simulated rainfall. Absorption of ¹⁴C-glyphosate in redvine increased from 1.8 to 21.9%, and translocation increased from 0.1 to 8.1% from 6 to 192 h after application, respectively. Translocation was both acropetal and basipetal, and by 96 h of exposure, the ¹⁴C radioactivity was widely distributed throughout the plant. Absorption and translocation was greatly affected by posttreatment temperature. Absorption and translocation were highest (34.9 and 10.6%, respectively) in plants maintained at 35/30 C (14/10 h, day/night), followed by 15/10 C (21.2 and 4.9%, respectively), and was lowest (7.8 and 1.6%, respectively) in plants maintained at 25/20 C. Results suggest that longer periods of leaf exposure to the herbicide and high temperatures could increase glyphosate absorption, translocation to redvine rootstocks, and subsequent control. These data also suggest that effective control of redvine in the field will require glyphosate rates higher than those recommended for use in glyphosate-resistant crops.

Nomenclature: Glyphosate; isopropylamine salt; redvine, Brunnichia ovata (Walt.) Shinners #³ BRVCI.

Additional index words: Rainfastness, regrowth, temperature, uptake, BRVCI.

Abbreviations: HAA, hours after application; WAT, weeks after treatment.

Abstract: Three experiments were conducted in the field using common cocklebur as a test species to identify weed growth differences due to propagation method and weed age when transplanted (with no crop and with soybean). Two experiments involved weed establishment in noncrop areas using four propagation methods (direct seeded–transplanted, peat tablets, peat pots, and plastic inserts) in a factorial arrangement with three transplant timings (at the cotyledon stage, at two true leaves, and at four true leaves). A direct-seeded method was also included as a check. Propagation methods and transplant timings were contrasted to the direct-seeded method because it was the “most natural” method of those tested. Based on results from the first year, the peat tablet method at the three transplant timings plus the direct-seeded method were used to establish the weed in a field experiment with soybean. In 1996 at 4 wk after emergence (WAE), 8 WAE, and senescence, weeds planted in peat tablets and transplanted at the cotyledon stage were most similar to the direct-seeded method. Peat pots and plastic inserts displayed an intermediate number of differences, whereas direct-seeded–transplanted weeds exhibited the most differences of any propagation method. Transplanting at the two-leaf stage showed more differences, with the four-leaf stage showing even more. In 1997 at 4 WAE, few propagation methods or transplant timings were different from the direct-seeded method. Results from harvests at 8 WAE and at senescence were comparable to those in the previous year. Differences between years at 4 WAE were attributed to greater heat stress and less moisture early in 1996. When common cocklebur was grown in soybean, no differences were detected at 4 WAE between peat tablets transplanted at the cotyledon stage vs. direct-seeded weeds and only one difference when transplanted at the two- and four-leaf stages. At 8 WAE, the early transplant was again the most comparable treatment to direct-seeded weeds, with many differences at the later transplant timings. At senescence, weed differences were no longer apparent. Patterns established for peat tablets with the weed growing alone largely held true when it was grown with soybean.

Nomenclature: Common cocklebur, Xanthium strumarium L. #³ XANST; soybean, Glycine max (L.) Merr. ‘Manokin’.

Additional index words: Propagation methods, transplant timings, direct seeded, peat tablet, peat pot, plastic insert, weed ecology, competition, interference, XANST.

Abbreviations: POST, postemergence; WAE, weeks after emergence.

Abstract: A field study evaluated the effects of green kyllinga establishment method (seed vs. stolon), two mowing heights (2.5 and 5.0 cm), and three nitrogen (N) rates (0, 24, and 49 kg/ha/mo) on green kyllinga infestation in ‘Tifway’ bermudagrass turf. The study was initiated in vigorous and newly established or “weak” bermudagrass turf in May 1997 and continued until December 1998. The green kyllinga area was measured periodically each year and plant dry weight (g/500 cm²) was calculated in December 1997 and 1998. In 1997, stolon established green kyllinga plots were twice as large as seeded plots in vigorous turf and four times larger in weak turf. Method of establishment, however, was less important in 1998 as seedling populations became more established. In weak turf, increasing N rate to 49 kg/ha/mo decreased green kyllinga spread by 50% in 1997 and by 40% in 1998 compared to no N. In vigorous turf, mowing height influenced green kyllinga infestation more than N. Low mowing height (2.5 cm) increased green kyllinga infestations nearly twofold in vigorous turf in 1997 and more than fivefold in 1998. Golf course fairways are often maintained at clipping heights shorter than 2.5 cm, and green kyllinga is a prevalent weed at these sites. Green kyllinga may gain a competitive advantage in bermudagrass turf at lower mowing heights.

Nomenclature: Green kyllinga, Kyllinga brevifolia Rottb.; bermudagrass, Cynodon dactylon Burtt-Davey × C. transvaalensis L. Pers. Tifway.

Additional index words: Turfgrass cultural practices, weed competition, weed ecology.

Abbreviations: N, nitrogen.

Abstract: Absorption and translocation of nicosulfuron and dicamba applied alone and combined was studied in 25-cm-high hemp dogbane originating from lateral roots that had overwintered. Absorption of ¹⁴C-nicosulfuron by hemp dogbane was not affected by applications of 70 g ai/ha unlabeled dicamba. Upward translocation of ¹⁴C-nicosulfuron in hemp dogbane was 86% greater 6 d after treatment (DAT) when dicamba was tank mixed with nicosulfuron, compared to nicosulfuron applied alone. Combinations of nicosulfuron plus dicamba increased translocation of nicosulfuron to hemp dogbane crown and roots 237 and 130%, 1 and 6 DAT, respectively, compared to nicosulfuron applied alone. Absorption of ¹⁴C-dicamba by hemp dogbane was not affected by the addition of 31 g ai/ha nicosulfuron. Upward translocation of dicamba in hemp dogbane was 42% greater 6 DAT for nicosulfuron plus dicamba compared to dicamba applied alone. Increased hemp dogbane control with nicosulfuron plus dicamba compared to either herbicide applied alone can be explained by enhanced translocation of both herbicides.

Nomenclature: Dicamba; hemp dogbane, Apocynum cannabinum L.#³ APCCA.

Additional index words: Absorption, interaction, tank mixture, APCCA.

Abbreviations: DAT, days after treatment.

Abstract: Glyphosate is often mixed with residual herbicides to control emerged weeds in no-till crop production systems. Field studies were conducted in Ohio from 1992 to 1994 to evaluate the weed control provided by residual herbicides and reduced rates of glyphosate in full-season, no-till soybean. Herbicide treatments were applied at two timings to examine the effect of weed size. At 4 wk after treatment, greater than 85% Pennsylvania smartweed control was obtained with metribuzin plus chlorimuron and linuron plus chlorimuron applied with 280 g ai/ha glyphosate and with imazethapyr and imazaquin applied with 560 g/ha glyphosate. All residual herbicides provided at least 85% common lambsquarters control when applied with 560 g/ha glyphosate. In 1992, the early application of residual herbicides provided this level of common lambsquarters control without glyphosate due to the small weed size at the time of application. Residual herbicides applied with 280 g/ha glyphosate controlled giant foxtail 85% or greater. Higher glyphosate rates were needed to control barnyardgrass. The performance of reduced glyphosate rates was dependent on weed species and weed size.

Nomenclature: Chlorimuron; glyphosate; imazaquin; imazethapyr; linuron; metribuzin; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; common lambsquarters, Chenopodium album L. # CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY; soybean, Glycine max (L.) Merr.

Additional index words: Tank mixtures, CHEAL, ECHCG, POLPY, SETFA.

Abbreviations: WAT, weeks after treatment.

Abstract: Glyphosate was applied to pepper as single or sequential applications to assess the consequences of drift or other accidental exposures. Foliar injury increased and plant vigor declined with increased rates of glyphosate and were exacerbated by a second application. Single applications at flowering (stage 1) were more damaging than single applications after fruit set (stage 2). Decline in marketable yield with increased glyphosate rate was greater with stage 1 applications, except in spring 1987 when marketable yields with single applications of glyphosate at stage 1 or stage 2 were statistically similar. Sequential applications resulted in the lowest marketable yields. Total yields declined with increased glyphosate rate and decline was more pronounced with sequential applications than with single applications. Total yield was affected to a greater extent when glyphosate was applied at stage 1 than at stage 2. Yield was more sensitive to two successive exposures than to single applications. Mean fruit weight was reduced by glyphosate in two of the four experiments.

Nomenclature: Glyphosate; pepper, Capsicum annuum L.

Additional index words: Simulated drift, herbicide injury.

Abbreviations: DAT, days after treatment; WAT, weeks after treatment.

Abstract: Field experiments were conducted in 1997 and 1998 near Columbia and Novelty, MO, and at Urbana, IL, to evaluate corn injury, weed control, corn yield, and estimated economic returns with weed management programs in glufosinate-resistant corn. Herbicide programs included acetochlor preemergence (PRE) followed by glufosinate alone or with atrazine postemergence (POST) and total POST programs consisting of single and sequential applications of glufosinate alone or tank mixed with acetochlor, atrazine, or acetochlor plus atrazine. Metolachlor PRE followed by dicamba plus atrazine early POST (EPOST) and metolachlor plus atrazine PRE were included for comparison. In the total POST treatments, mid-POST applications controlled shattercane and common cocklebur better than EPOST applications. However, yield reductions as high as 23% occurred because of early-season weed interference, although weeds were controlled later in the season. Applying atrazine with glufosinate generally increased control of giant foxtail, common cocklebur, morningglory species, and common waterhemp compared to glufosinate alone, but did not increase control of common lambsquarters, velvetleaf, or Pennsylvania smartweed. Corn yield was positively correlated with weed control (r = 0.88) and more strongly dependent on grass (r = 0.82) than broadleaf (r = 0.70) weed control. Net incomes were positively correlated to corn yield (r = 0.73). Four of the top six net income-producing treatments included two herbicide applications. Three of the treatments were PRE followed by POST programs, and the fourth was a sequential POST treatment of glufosinate.

Nomenclature: Acetochlor; atrazine; dicamba; glufosinate; metolachlor; common cocklebur, Xanthium strumarium L. #³ XANST; common lambsquarters, Chenopodium album L. # CHEAL; common waterhemp, Amaranthus rudis Sauer # AMATA; giant foxtail, Setaria faberi (L.) Herrm. # SETFA; morningglory, Ipomoea spp.; Pennsylvania smartweed, Polygonum pensylvanicum L. # POLPY; shattercane, Sorghum bicolor (L.) Moench. # SORVU; velvetleaf, Abutilon theophrasti (L.) Medikus # ABUTH; corn, Zea mays L. # ZEAMX ‘Pioneer 34A55’.

Additional index words: Corn yield, economic returns, glufosinate-resistant crop, AMATA, ABUTH, CHEAL, POLPY, SETFA, SORVU, XANST, ZEAMX.

Abbreviations: ALS, acetolactate synthase; CV, coefficient of variation; EPOST, early postemergence; MPOST, mid-postemergence; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

Abstract: Field experiments were conducted in southern Wisconsin from 1996 to 1998 to evaluate the effects of acetochlor applied preemergence (PRE) followed by nicosulfuron or sethoxydim applied postemergence (POST) and of cultivation on woolly cupgrass control, corn grain yield, and woolly cupgrass seed production. Sethoxydim treatments provided greater woolly cupgrass control than nicosulfuron treatments in 1997 and similar control to nicosulfuron treatments in 1996 and 1998. However, neither herbicide killed all emerged woolly cupgrass plants, regardless of herbicide rate or POST application timing. Late postemergence treatments provided greater season-long control than early postemergence treatments in 1996 and 1998, but there was no difference in control between timings in 1997. Acetochlor applied PRE at 1,800 g ai/ha (1×) followed by nicosulfuron (35 g ai/ha) or sethoxydim (213 g ai/ha) at the registered rate (1×) or at one half of the registered rate (0.5×) consistently provided sufficient woolly cupgrass control to maximize corn yield, regardless of cultivation or POST herbicide application timing. Acetochlor PRE treatments, cultivated and noncultivated, followed by sethoxydim POST and cultivated acetochlor PRE treatments followed by nicosulfuron POST treatments provided sufficient control in each year to limit woolly cupgrass seed production to a level that decreased the predicted future seedbank density, regardless of herbicide rate or POST herbicide application timing. However, noncultivated acetochlor treatments followed by nicosulfuron applied at 1× followed by 0.5× or at 0.5× followed by 0.5× did not consistently reduce seed production to a level that decreased the predicted future seedbank density. These results suggest that the rate of sethoxydim can be reduced to 0.5× if a full rate of acetochlor is applied PRE with little effect on corn yield or woolly cupgrass seedbank density. However, reducing the rate of nicosulfuron to 0.5× following an application of acetochlor at the full rate or reducing both the acetochlor and nicosulfuron or sethoxydim rate to 0.5× is recommended only if a cultivation is planned.

Nomenclature: Acetochlor; nicosulfuron; sethoxydim; woolly cupgrass, Eriochloa villosa (Thunb.) Kunth #³ ERBVI; corn, Zea mays L. ‘DeKalb SR404’, ‘DeKalb DK493SR’.

Additional index words: Acetochlor, herbicide rate, herbicide application timing, nicosulfuron, sethoxydim, sethoxydim-resistant corn, woolly cupgrass seed production.

Abbreviations: COC, crop oil concentrate; DAT, days after treatment; EPOST, early postemergence; LPOST, late postemergence; OM, organic matter; POST, postemergence; PRE, preemergence; UAN, urea ammonium nitrate.

Abstract: Eurasian watermilfoil, an aquatic invasive weed, has been identified recently at a number of sites in western Nevada and northeastern California, including Lake Tahoe. Because Eurasian watermilfoil is easily spread by fragments, transport on boats and boating equipment plays a key role in contaminating new water bodies. This is an important means of the potential spread of this weed throughout key recreational and agricultural areas surrounding Lake Tahoe. Unless the weed is controlled, significant alterations of aquatic ecosystems, with associated degradation of natural resources and economic damages to human uses of those resources, may occur. This research uses the economic valuation approach known as benefits transfer to estimate the value of a portion of the recreational service flows that society currently enjoys in the Truckee River watershed below Lake Tahoe. The lower-bound estimates of baseline water-based recreation value at a subset of sites in the watershed range from $30 to $45 million/yr. Impacts from the continued spread of Eurasian watermilfoil in the watershed could be significant; for example, even a 1% decrease in recreation values would correspond to roughly $500,000/yr as a lower bound.

Nomenclature: Eurasian watermilfoil, Myriophyllum spicatum L. #³ MYPSP.

Additional index words: Aquatic weeds, economic impacts, invasive species, recreation, MYPSP.

Abstract: Studies were conducted from 1995 to 1997 near Tifton, GA, to evaluate shallow tillage implements and tillage frequency for stale seedbed weed control in peanut. Tillage implements evaluated were a power tiller, disk harrow, field conditioner, and sweep cultivator. Plots for each implement were tilled once or twice prior to planting peanut. Results from midseason weed counts and peanut yield showed similar responses among implements and frequency of tillage. These results indicate no advantage of any shallow tillage implement for stale seedbed weed control, although peanut yields were generally greater in plots with tilled stale seedbeds than in the nontilled control. The implement of choice should be based on cost of operation and compatibility with the overall peanut production system.

Nomenclature: Peanut, Arachis hypogaea L., ‘Georgia Runner’.

Key index words: Cultural weed control, groundnut.

Abbreviations: DAE, days after emergence; POST, postemergence; PRE, preemergence.

Abstract: Greenhouse experiments were conducted in Greece to evaluate the level of propanil resistance in three barnyardgrass biotypes collected from rice fields where propanil had been used for around 25 yr. Suspected resistant biotypes were not controlled by propanil at 2.6, 5.2, 10.4, and 20.8 kg ai/ha, with the highest rate five times greater than the recommended rate. Control was reduced even more when propanil application was delayed until the three- to five-leaf stage. The susceptible barnyardgrass biotype collected from a nontreated propanil area was controlled with 2.6 kg/ha propanil. All barnyardgrass biotypes were effectively controlled by quinclorac (0.75 kg ai/ha) applied either alone at the two- to three-leaf stage or in mixture with propanil (3.5 kg/ha) at the three- to five-leaf stage. Only two of the resistant barnyardgrass biotypes were effectively controlled by azimsulfuron (0.02 kg ai/ha) applied alone at the two- to three-leaf stage, but all biotypes were controlled with the addition of propanil (3.5 kg/ha) at the three- to five-leaf stage. The resistant barnyardgrass biotype, which required the highest rate of propanil to reduce biomass by 50%, also tended to exhibit the most growth potential 7 to 22 d after emergence when compared with the other resistant biotypes or the susceptible biotype. Results clearly show that varying levels of barnyardgrass resistance to propanil exist but that effective control alternatives are available.

Nomenclature: Azimsulfuron; propanil; quinclorac; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; rice, Oryza sativa L.

Additional index words: Herbicide resistance, resistant biotype.

Abbreviations: DAE, days after emergence; R-BYG, resistant barnyardgrass; S-BYG, susceptible barnyardgrass.

Abstract: Sicklepod (Senna obtusifolia), hemp sesbania (Sesbania exaltata), and pitted morningglory (Ipomoea lacunosa) seed production and viability in early-maturing soybean (Glycine max) were evaluated following preharvest desiccation. The herbicide combinations 1.1 kg ai/ha glyphosate plus 6.7 kg ai/ha sodium chlorate, 2.2 kg/ha glyphosate plus 3.4 kg/ha sodium chlorate, and 0.3 kg ai/ha paraquat plus 6.7 kg/ha sodium chlorate reduced sicklepod germination, emergence, and seedling growth in most cases. Oxyfluorfen at 0.3 kg ai/ha plus 3.4 or 6.7 kg/ha sodium chlorate also reduced sicklepod germination and growth. Glufosinate from 0.8 to 1.4 kg ai/ha reduced sicklepod germination but did not have a consistent effect on other seedling growth parameters. Bromoxynil at 1.1 kg ai/ha plus 3.4 kg/ha sodium chlorate reduced sicklepod germination but did not have a consistent effect on most growth parameters. A wide range of treatments reduced hemp sesbania germination, emergence, and growth to very low levels. All desiccant applications reduced pitted morningglory seed production compared to the untreated check. Glyphosate at 1.1 kg/ha plus 6.7 kg/ha sodium chlorate, 0.3 kg/ha oxyfluorfen plus 3.4 kg/ha sodium chlorate, and 0.8 or 1.1 kg/ha glufosinate reduced pitted morningglory seed production and desiccated weeds effectively. Most treatments reduced emergence in 1996, when seeds were smaller and less mature than those collected in 1995. When application volume of paraquat alone or in tank mixture decreased, germination and growth of sicklepod was reduced, indicating increased paraquat efficacy.

Nomenclature: Bromoxynil; glufosinate; glyphosate; oxyfluorfen; paraquat; sodium chlorate; pitted morningglory, Ipomoea lacunosa L. #³ IPOLA; hemp sesbania, Sesbania exaltata (Raf.) ex A. W. Hill # SEBEX; sicklepod, Senna obtusifolia (L.) Irwin et Barnaby # CASOB; soybean, Glycine max (L.) Merr. ‘NK 4260’.

Additional index words: Desiccation, germination, early-maturing soybean.

Abbreviations: DAT, days after treatment.

Abstract: Digital imagery from satellites and airborne remote sensing offer an opportunity to accurately detect weed infestations. Image resolution and plant growth stage are critical factors for maximum weed detection with low errors. Data analysis in traditional image assessment has relied on agreement measures, such as Cohen's kappa and asymptotic procedures, that compare what is on the image but not on the ground and what is on the ground but not on the image. Statistical comparisons of multispectral images, however, require some knowledge of the variability of the image classification results to determine significant differences among agreement measures. Bayesian methods were used to develop probability distributions for an agreement measure, conditional kappa, and were then subsequently applied to assess and compare image resolutions and plant growth stages. Results showed that images of a study site known to have yellow starthistle populations could identify the noninfested areas with greater accuracy than infested areas at spatial resolutions of 0.5, 1.0, 2.0, and 4.0 m. The detection accuracy of yellow starthistle in the images taken either prebloom or at flowering with 4.0-m spatial resolution usually was equal to or better than spatial resolutions of 0.5, 1.0, and 2.0 m for the cover classes that were not, moderately (31 to 70%), and highly (71 to 100%) infested. The 0.5-m resolution was better than 4.0-m spatial resolution when detecting the moderate cover class, but both resolutions had high omissional and commissional errors. Contrasting the best detection resolution for finding yellow starthistle colonies across flight times indicated that flying at flowering stage with the 4.0-m spatial resolution provided the best detection of the yellow starthistle cover classes considered. In the cases where different spatial resolutions resulted in equal detection accuracy, the larger spatial resolution was selected because of lower costs of acquiring and processing the data.

Nomenclature: Yellow starthistle, Centaurea solstitialis L. #³ CENSO.

Additional index words: Airborne charge-coupled devices, conditional kappa, image analysis, remote sensing, videography, weed detection.

Abbreviations:K̂_i, conditional kappa, where i denotes the image classification category (high, moderate, and none).

Abstract: Field trials were conducted with spring-sown rye and field pea cover crops to determine the effect of five rye–pea proportions and three seeding rates (high, medium, and low) on weed suppression during cover crop growth. Measurements on weed and cover crop growth were taken approximately 2 mo after seeding when cover crops were killed. Cover crops were killed by mowing in 1996 and by undercutting in 1997 and 1998. Cover crop biomass, averaged over rye–pea proportion, was highest in 1998 at 4.3 million tons (MT)/ha (high seeding rate) and lowest in 1997 at 1.5 MT/ha (low seeding rate). Cover crops of pure rye or rye–pea mixes suppressed weeds more effectively than did pure pea. Dominant weeds were ladysthumb, smooth pigweed, smallflower galinsoga, and common lambsquarters. Ground cover by weeds ranged from a low of 2% (rye–pea mixes) to a maximum of 73% (pure pea). Cover crop mixes of 50% or more rye seeded at the high rate gave the best weed suppression.

Nomenclature: Ladysthumb, Polygonum persicaria L. #³ POLPE; smooth pigweed, Amaranthus hybridus L. # AMACH; smallflower galinsoga, Galinsoga parviflora Cav. # GASPA; common lambsquarters, Chenopodium album L. # CHEAL; field pea, Pisum sativum L.; rye, Secale cereale L. ‘Wheeler’.

Additional index words: Allelopathy, mixed cropping, undercutting, AMACH, CHEAL, GASPA, POLPE.

Abbreviations: DAS, days after seeding.

Abstract: Competition from large crabgrass is often responsible for the establishment failure of spring-seeded cool-season turfgrasses. The objective of this study was to determine how soon after seedling emergence dithiopyr could be applied without causing unacceptable damage to Kentucky bluegrass. Dithiopyr at 0.28 and 0.56 kg/ha was applied at various times prior to seeding and after emergence of Kentucky bluegrass in the field and greenhouse. Dithiopyr damaged Kentucky bluegrass seedlings in the greenhouse when applied earlier than 10 d after emergence (DAE) at 0.28 kg/ha and 14 DAE at 0.56 kg/ha. In the field study with heavy large crabgrass infestation, no significant phytotoxicity or long-term thinning occurred with any application of dithiopyr after emergence of Kentucky bluegrass. Dithiopyr applied as early as 3 DAE improved cover of Kentucky bluegrass by reducing competition from large crabgrass. When seeding is done early in spring before large crabgrass germination, dithiopyr could be applied at 0.28 kg/ha 10 DAE or at 0.56 kg/ha 14 DAE without risk of injury. Dithiopyr could be applied as early as 3 DAE on sites with heavy large crabgrass pressure or to late spring seedings when large crabgrass is germinating because the risk of turf thinning is warranted given the benefit of reduced large crabgrass competition for the desired turf.

Nomenclature: Dithiopyr; large crabgrass, Digitaria sanguinalis (L.) Scop. #³ DIGSA; Kentucky bluegrass, Poa pratensis L. ‘America’, # POAPR.

Additional index words: Preemergence herbicides.

Abbreviations: DAE, days after emergence; POST, postemergence; PRE, preemergence; WAE, weeks after emergence.

Abstract: Greenhouse experiments evaluated azafenidin and thiazopyr applied separately, as a tank mix, or in rapid succession, for preemergence control of yellow nutsedge (Cyperus esculentus) and hairy beggarticks (Bidens pilosa). Average of yellow nutsedge shoot dry weights at 21 and 42 d after treatment (DAT), indicated that azafenidin at 0.28, 0.56, and 1.12 kg ai/ha controlled 70, 86, and 90%, respectively, and thiazopyr at 1.12 kg/ha controlled 10% of yellow nutsedge. However, when thiazopyr at 1.12 kg/ha was tank-mixed with azafenidin at 0.28, 0.56, and 1.12 kg/ha, yellow nutsedge control averaged for 21 and 42 DAT was reduced to 41, 69, and 78%, respectively. Root plus tuber dry weight of yellow nutsedge increased threefold when 1.12 kg/ha thiazopyr was mixed with 0.28 kg/ha azafenidin, compared to azafenidin applied alone at the above rate. When the herbicides were applied sequentially, within minutes of each other, the antagonistic responses were reproduced, independent of the order of herbicide application. Thiazopyr applied at 0.56 and 1.12 kg/ha stimulated the emergence and establishment of hairy beggarticks and antagonized azafenidin for the control of yellow nutsedge based on a mathematical model. Although thiazopyr reduced the preemergence herbicidal efficacy of azafenidin on hairy beggarticks control, antagonism could not be determined because of the stimulatory effects of thiazopyr on hairy beggarticks emergence.

Nomenclature: Azafenidin; thiazopyr; hairy beggarticks, Bidens pilosa L. #³ BIDPI; yellow nutsedge, Cyperus esculentus L. # CYPES.

Additional index words: Herbicide interaction, stimulation, scarification, antagonism, spanish needles, Bidens alba, Bidens leucantha.

Abbreviations: DAT, days after treatment; PRE, preemergence; WAT, weeks after treatment.

Abstract: A greenhouse study was conducted to determine the effects of sublethal dicamba concentrations in the nutrient media on hydroponically grown tomato plants. Tomato leaf area was the most sensitive vegetative growth parameter measured in response to dicamba concentrations, ranging from 0 to 22 µg/L. Leaf area was reduced 31 and 76%, and specific leaf weights, a relative measure of leaf thickness (g/cm²), increased 26 and 121% after 30-d exposure to dicamba concentrations of 2.2 and 22 µg/L, respectively. In long-term experiments conducted until plants produced first ripe fruit, regression analysis indicated leaf area reductions of 8 and 66% from initial dicamba concentrations of 1 and 10 µg/L, respectively. Reductions in total fruit fresh weight were highly correlated (r = 0.93) with leaf area reductions caused by dicamba. A hyperbolic regression model gave predicted losses in fruit fresh weight per plant of 6% at 1 µg/L dicamba and 73% at 10 µg/L dicamba (r² = 0.87). Results generally indicated that the level of dicamba in the nutrient media of hydroponically grown tomatoes that produced no observable effect was ≤ 1 µg/L.

Nomenclature: Dicamba; tomato, Lycopersicon esculentum L. ‘Trust’.

Additional index words: Groundwater contamination, herbicide bioassay.

Abbreviations: CID, centimeter inside diameter; DAT, days after transplant; EC, electrical conductivity; PI, plant introduction.

Abstract: Field experiments were conducted in 1996 and 1997 near Arlington, WI, to compare the efficacy of glyphosate applied below registered rates in sequential and tank-mix combinations with residual herbicides to no-till, narrow-row, glyphosate-resistant soybean. In the sequential combinations of preplant (PP) residual herbicides and postemergence (POST) glyphosate study, glyphosate followed one of eight burndown treatments. Clomazone applied PP controlled 86% of common lambsquarters in 1996 when followed by 420 g ae/ha glyphosate early POST (EPOST). All other herbicide treatments controlled 94% or greater regardless of weed species, PP treatment, glyphosate timing, or glyphosate rate. The greatest soybean yields occurred in EPOST glyphosate applications in 1996 and late POST (LPOST) glyphosate applications in 1997. The only time PP residual herbicides were beneficial was prior to the LPOST glyphosate application in 1996. In the tank-mix POST combinations of glyphosate and residual herbicides study, glyphosate was applied alone or in combination with four residual herbicides. Soybean injury did not exceed 5% except in the glyphosate and imazethapyr combination in 1997. Control of common lambsquarters, velvetleaf, and giant foxtail was 90% or greater when averaged across all residual combinations and glyphosate timings and rates. Imazethapyr alone controlled velvetleaf 99% and giant foxtail 92% in 1997. When glyphosate was applied alone, soybean yields were similar at all glyphosate rates and application timings, except the 630 g/ha glyphosate LPOST resulted in a lower yield than 420 g/ha glyphosate LPOST. Only one residual herbicide, SAN 582, combined with glyphosate produced yields equivalent to the highest yielding treatments when averaged over both glyphosate rates and timings. Cloransulam added to 420 g/ha glyphosate EPOST and chlorimuron plus thifensulfuron and imazethapyr added to 420 g/ha glyphosate LPOST resulted in lower soybean yields compared to the same rate of glyphosate applied alone at the respective timings. Thus, no herbicide combination preformed better than glyphosate applied in a timely manner alone. However, in situations where early-season weed competition is severe and a timely glyphosate application is not possible, a PP residual herbicide may be beneficial.

Nomenclature: Chlorimuron; clomazone; cloransulam; glyphosate; imazethapyr; pendimethalin; SAN 582 (proposed name dimethenamid), 2-chloro-N-(2,4-dimethyl-3-thienyl)-N-(2-methoxy-1-methylethyl)-acetamide; thifensulfuron; common lambsquarters, Chenopodium album L. #³ CHEAL; giant foxtail, Setaria faberi Herrm. # SETFA; velvetleaf, Abutilon theophrasti Medicus # ABUTH; soybean, Glycine max (L.) Merr.

Additional index words: Combinations, sequential, tank-mixed.

Abbreviations: EPOST, early postemergence; 7DPP, 7 d prior to planting; DAP, days after planting; fb, followed by; LPOST, late postemergence; POST, postemergence; PP, preplant.

Abstract: The development of glufosinate-resistant corn represents a new weed management system for corn growers. Field experiments were conducted from 1995 to 1997 at four locations in southwestern Ontario. The objective of this study was to determine the effect of timing of weed control relative to the growth stage of corn with glufosinate applied alone or in combination with residual herbicides. Control of all species tested improved with the addition of atrazine plus dicamba to glufosinate, applied from the two- to eight-leaf stage of corn growth. Based on a 90% weed dry matter reduction, glufosinate with atrazine plus dicamba controlled common ragweed, common lambsquarters, and pigweed species at the three-leaf stage of corn and yellow foxtail, barnyardgrass, and large crabgrass at the two-, four-, and eight-leaf stage of corn, respectively. Weed control with glufosinate alone was improved when applied at the later growth stages of corn. Glufosinate applied alone at the four-leaf stage of corn controlled common ragweed and common lambsquarters, whereas pigweed species were controlled effectively at the eight-leaf stage of corn growth. Corn grain yield was consistently higher when glufosinate was applied in combination with residual herbicides, compared to glufosinate alone. Glufosinate in combination with residual herbicides applied to corn at the three- to five-leaf stage may represent the best timing for weed control. Our data suggested that a tank mixture of glufosinate with other postemergence residual herbicides or a split application of glufosinate in combination with cultivation may be required for weed control in glufosinate-resistant corn.

Nomenclature: Atrazine; dicamba; SAN 582 (proposed name, dimethenamid), 2-chloro-N-[(1-methyl-2-methoxy)ethyl]-N-(2,4-dimethyl-thien-3-yl)-acetamide; glufosinate; metolachlor; redroot pigweed, Amaranthus retroflexus L. #³ AMARE; common lambsquarters, Chenopodium album L. # CHEAL; yellow foxtail, Setaria glauca (L.) Beauv. # SETGL; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; barnyardgrass, Echinochloa crus-galli (L.) Beauv. # ECHCR; common ragweed, Ambrosia artemisiifolia L. # AMBEL; corn, Zea mays L.

Additional index words: Integrated weed management.

Abbreviations: DAE, days after emergence; DM, dry matter; HRC, herbicide-resistant crops; IWM, integrated weed management; POST, postemergence; PRE, preemergence.

Abstract: The objective of this study was to compare the consistency and accuracy of visually estimated weed biomass and weed control data to data obtained through image analysis. Weed biomass and weed control were evaluated in soybean herbicide efficacy trials conducted at the University of Nebraska–Lincoln during 1992 and 1993. Measurements were based on visual estimates and on aerial photographs taken at a height of 3.5 m above the soil surface. Photographs were digitized and classified, producing pixel values for broadleaf weeds, grass weeds, soybean, and soil. Percent weed cover was calculated in relation to the crop canopy, based on the respective number of pixels per image. Visual and photographic ratings of weed biomass and of weed control were not closely correlated. In the first year the visual method discriminated between more treatments than the photographic method, but the opposite occurred in the second year. The photographic method predicted yield more closely than the visual estimates. We concluded that visual estimates were less consistent and more subject to observer bias than measurements obtained with the photographic method.

Nomenclature: Soybean, Glycine max (L.) Merr.

Additional index words: Image analysis, canopy.

Abbreviations: POST, postemergence; PPI, preplant incorporated; PRE, preemergence.

Abstract: Field experiments were conducted to evaluate pyridine herbicides for Virginia buttonweed control and turfgrass tolerance. Treatments included clopyralid and fluroxypyr applied at 35, 70, 140, 280, and 560 g ae/ha, compared to a three-way combination of 2,4-D plus dichlorprop plus dicamba (840 840 210 g ae/ha, respectively). Fluroxypyr applied at 140 g/ha or greater controlled Virginia buttonweed 80% or greater through 10 wk after treatment. A second experiment evaluated 280 g/ha clopyralid or 140 g/ha fluroxypyr alone or in combination with 0.25 or 0.50% (v/v) nonionic surfactant, compared to 280 g/ha dicamba or 1,120 g/ha 2,4-D alone or in combination with nonionic surfactant. The addition of nonionic surfactant to clopyralid or fluroxypyr did not increase Virginia buttonweed control. Fluroxypyr at 280 g/ha and higher produced 22 to 53% injury to bermudagrasses 2 wk after treatment. Common centipedegrass was injured through 3 wk after treatment with 4,470 g/ha fluroxypyr or greater. Zoysiagrass exhibited injury with 4,470 g/ha fluroxypyr at 2 wk after treatment; however, injury was less than 8% at 3 wk. Common St. Augustinegrass was severely injured with 2,235 g/ha or greater fluroxypyr through 7 wk after treatment. Clopyralid did not cause injury to any turfgrass species.

Nomenclature: Clopyralid; dicamba; dichlorprop; fluroxypyr; 2,4-D; common bermudagrass, Cynodon dactylon (L.) Pers. #³ CYNDA; common centipedegrass, Eremochloa ophiuroides (Munro) Hack. # ERLOP; common St. Augustinegrass, Stenotaphrum secundatum (Walt.) Ktze. # STPSE; hybrid bermudagrass, Cynodon dactylon × C. transvaalensis Burtt-Davy ‘Tifway’, ‘Tifgreen’; Virginia buttonweed, Diodia virginiana L. # DIQVI; Zoysiagrass, Zoysia japonica Steud. ‘Meyer’ # ZOYMA.c

Additional index words: CYNDA, DIQVI, ERLOP, STPSE, ZOYMA.

Abbreviations: MHE, methylheptyl ester.

Abstract: Understanding the effects of previous herbicide applications on cover crops is important if cover crops are to be successfully established during the same growing season. Greenhouse research was conducted to evaluate the sensitivity of annual ryegrass (Lolium multiflorum), oat (Avena sativa), crimson clover (Trifolium incarnatum), and medium red clover (Trifolium pratense) to EPTC plus R-29148, pendimethalin, and metolachlor plus CGA-154281 in a loam soil with 2.5% organic matter. Annual ryegrass density was reduced 96% by EPTC at 4.48 kg ai/ha and metolachlor at 2.24 kg ai/ha, whereas oat density was reduced 99% and 35%, respectively, from the two treatments. Pendimethalin at 1.68 kg ai/ha reduced annual ryegrass density 14%, but not oat density. Crimson clover biomass was reduced 33% by EPTC, 45% by metolachlor, and 15% by pendimethalin. All herbicides reduced the density of medium red clover > 25%, but biomass was reduced only by metolachlor. Field trials were conducted to determine whether persistence of these herbicides would affect the seeding time for annual ryegrass and crimson clover establishment. Annual ryegrass was successfully established following application of EPTC at 4.48 kg/ha when seeding was delayed 35 to 40 d after treatment (DAT). Pendimethalin at 1.68 kg/ha injured annual ryegrass > 15%, and annual ryegrass was severely injured by metolachlor at 1.68 kg/ha regardless of seeding time. Successful establishment of crimson clover following all herbicides was possible when seeding timings were delayed. Pendimethalin injured crimson clover less than 13% 15 to 17 DAT, and EPTC injured crimson clover less than 5% 28 to 35 DAT. Crimson clover injury from metolachlor was less than 16% 35 to 40 DAT. Herbicides with longer reported soil persistence generally require more time between herbicide application and cover crop seeding for safe establishment of the cover crop, particularly if the cover crop species is sensitive to the herbicide.

Nomenclature: CGA-154281, 4-(dichloroacetyl)-3,4-dihydro-3-methyl-2H-1,4-benzoxazine; EPTC; metolachlor; pendimethalin; R-29148, 3-(dichloroacetyl)-2,2,5-trimethyloxazolidine; annual ryegrass, Lolium multiflorum L.; crimson clover, Trifolium incarnatum L. #³ TRFIN; oat, Avena sativa L. # AVESA; red clover, Trifolium pratense L. # TRFPR.

Additional index words: Interseeded cover crops, overseeded cover crops.

Abbreviations: DAS, days after seeding; DAT, days after treatment.

Abstract: Producers in the semiarid Great Plains are seeking management strategies to delay development of herbicide resistance. The objective of this study was to determine if cultural systems could control weeds in proso millet (Panicum miliaceum), thus eliminating the need for herbicides and removing selection pressure. Initially, we evaluated individual cultural practices for improving competitiveness of proso millet. Increasing seeding rate, banding N fertilizer with the seeds, growing a taller cultivar, and eliminating tillage favored proso millet over redroot pigweed (Amaranthus retroflexus). Combining several cultural practices with delayed planting in a cultural system reduced biomass and seed production of two pigweed species 85% or more in both tilled and no-till systems, subsequently eliminating proso millet yield loss. Density of the two pigweed species was sevenfold greater in the tilled system, yet the cultural system approach was still effective. Cultural system impact on seed production suggests that pigweed densities will not increase over time. With cultural systems, producers can minimize selection pressure, thus delaying development of herbicide resistance.

Nomenclature: Redroot pigweed, Amaranthus retroflexus L. #³ AMARE; proso millet, Panicum miliaceum L. ‘Cope’, ‘Sunup’.

Additional index words: Delayed planting, increased seeding rate, nitrogen placement, tillage, AMARE.

Abstract: Wild oat (Avena fatua) control often is an integral management practice in cropping systems that include cereal crops. Experiments were conducted at two locations in Saskatchewan (Saskatoon and Scott), Canada, from 1994 to 1997 to determine the influence of ICIA 0604 rate (50, 100, 150, and 200 g ai/ha), water volume (30, 50, and 100 L/ha), spray mixture pH (unbuffered, close to pH 7.0; reduced, pH 4.0), late morning and evening application times, and sodium bicarbonate concentration of water source (Saskatoon water, negligible; Scott water, 695 mg/L) on wild oat fresh weight and wheat (Triticum aestivum) grain yield. Reducing ICIA 0604 rate below the recommended label rate (200 g/ha) increased wild oat fresh weight by 22% and decreased wheat grain yield by 7% when applied with 50 or 100 L/ha of water. Applications with 30 L/ha of water resulted in more wild oat growth (19%) and less wheat yield (6%), regardless of the ICIA 0604 rates. Spray mixture pH or time of application did not modify the effects of ICIA 0604 rate and water volume on wild oat fresh weight and wheat yield at Saskatoon. At Scott, the negative effects of ICIA 0604 rates lower than 200 g/ha applied with 50 or 100 L/ha of water were most apparent when applications were made in the morning, especially with an unbuffered spray mixture. ICIA 0604 applications made in the evening with 50 or 100 L/ha of water resulted in the lowest wild oat fresh weights and greatest wheat yields, regardless of the ICIA 0604 rate or spray mixture pH. Antagonism between sodium bicarbonate in the unbuffered water from Scott, as indicated by the spray mixture pH effect, and the time of application effect were important factors controlling treatment responses at Scott. Lower than recommended ICIA 0604 rates often maintained net returns, even though wheat yield responded negatively to reduced ICIA 0604 rates. Understanding the effects of water quality on wild oat control will allow producers to make prudent decisions regarding the optimal application parameters for ICIA 0604.

Nomenclature: ICIA 0604 (proposed common name, tralkoxydim), 2-[1-(ethoxyimino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)cyclohex-2-enone; wild oat, Avena fatua L. #³ AVEFA; hard red spring wheat, Triticum aestivum L.

Additional index words: Water volume, spray mixture pH, time of application, weed interference, AVEFA.

Abstract: Field research was conducted at three locations in Mississippi to evaluate CGA-277476 tank mixtures with four broadleaf herbicides for possible improvement of broadleaf weed control. Tank mixtures in this research were typically additive, although some instances of antagonism were noted. Control of morningglory (Ipomoea) species and hemp sesbania (Sesbania exaltata) was not consistently improved by the addition of acifluorfen, chlorimuron, fomesafen, or imazaquin to 59 or 79 g ai/ha CGA-277476. However, when a large population of weeds was present, the addition of acifluorfen, chlorimuron, or fomesafen to 59 or 79 g/ha CGA-277476 improved control over CGA-277476 alone. Prickly sida (Sida spinosa) was not controlled more than 68% with any treatment in this study; however, horse purslane (Trianthema portulacastrum) was controlled at least 90% with either 79 g/ha CGA-277476 alone or tank-mixed with acifluorfen, fomesafen, chlorimuron, or imazaquin. The addition of CGA-277476 to acifluorfen or fomesafen did not improve control over acifluorfen or fomesafen alone on any of the weeds evaluated; however, the addition of CGA-277476 to imazaquin improved hemp sesbania control over imazaquin alone. Tank mixtures did not result in yields greater than CGA-277476 alone in areas with moderate weed pressure, whereas in areas with severe weed pressure, tank mixtures improved soybean (Glycine max) yield over CGA-277476 alone.

Nomenclature: CGA-277476, 2-[[[[(4,6-dimethyl-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl] benzoic acid; entireleaf morningglory, Ipomoea hederacea var. integriuscula Gray #³ IPOHG; hemp sesbania, Sesbania exaltata (Raf.) Rydb. ex A.W. Hill # SEBEX; horse purslane, Trianthema portulacastrum L. # TRTPO; pitted morningglory, Ipomoea lacunosa L. # IPOLA; prickly sida, Sida spinosa L. # SIDSP; soybean, Glycine max (L.) Merr. ‘Hartz 4994’, ‘Pioneer 9592’.

Additional index words: Tank mixture, acifluorfen, chlorimuron, fomesafen, imazaquin, IPOHG, IPOLA, SEBEX, SIDSP, TRTPO.

Abbreviations: Grn, Greenville; POST, postemergence; Stk-N, Starkville-North; Stk-S, Starkville-South; WAT, weeks after treatment.

Abstract: Field experiments were conducted at Vegreville and Lacombe, AB, to determine the influence of barley (Hordeum vulgare) variety and seeding rate on interference of wild oat (Avena fatua) with barley. Barley variety and seeding rate affected barley density, height at maturity, and seed yield, as well as wild oat shoot dry weight and seed yield in most experiments, but there was no variety by seeding rate interaction. As expected, the semidwarf varieties Falcon and CDC Earl were the shortest. Barley seedling emergence and subsequent plant densities varied among varieties, locations, and years. The hull-less varieties Falcon and CDC Dawn had the poorest emergence in most cases, whereas AC Lacombe and Seebe had the highest emergence. Wild oat shoot dry matter and seed production was highest in the Falcon, CDC Dawn, and CDC Earl plots, suggesting that these were the least competitive with wild oat. Barley yield loss from wild oat interference also tended to be highest in these varieties. Poor emergence of Falcon and CDC Dawn and the shorter stature of Falcon and CDC Earl likely contributed to their relatively poor competitiveness with wild oat. Increasing the seeding rate improved the competitiveness of all varieties, as evidenced by reduced wild oat shoot dry matter and seed production and, in some cases, improved barley yields.

Nomenclature: Wild oat, Avena fatua L. #³ AVEFA; barley, Hordeum vulgare L. ‘Falcon’, ‘Phoenix’, ‘AC Lacombe’, ‘Seebe’, ‘CDC Earl’, ‘Harrington’, ‘CDC Dawn’.

Additional index words: Hull-less barley, semidwarf barley, wild oat competition.

Abstract: Producers in the semiarid Great Plains are including corn (Zea mays) in dryland rotations; however, weed management is difficult because the corn canopy is not competitive with weeds. My objective was to determine if cultural practices can enhance corn's competitiveness with weeds, thus supplementing current weed management strategies. Cultural systems, comprised of different row spacing, plant population, and nitrogen placement, were evaluated for effects on foxtail millet (Setaria italica) growth during three growing seasons. A cultural system comprised of 38-cm row spacing, 47,000 plants/ha, and N banded near the seeds reduced foxtail millet biomass 60% compared with the conventional system of 76-cm row spacing, 37,000 plants/ha, and N broadcast. Narrow rows had the greatest effect on foxtail millet growth. Corn's tolerance to foxtail millet interference also was improved, as yield loss in the system with narrow rows, high population, and banded fertilizer was reduced threefold compared with the conventional system. Integrating cultural systems with rotation design and residue management will further strengthen weed management in semiarid corn production.

Nomenclature: Corn, Zea mays L. ‘Pioneer 3893’; foxtail millet, Setaria italica (L.) Beauv. ‘Golden German’.

Additional index words: Increased seeding rate, nitrogen placement, row spacing.

Abstract: This study assessed the tolerance of ‘Midlawn’ (Cynodon dactylon × C. transvaalensis) and ‘OKS 91-11’ (C. dactylon) bermudagrass to commonly used postemergence herbicides and compared visual assessment with vehicle-mounted optical sensing (V-MOS) for evaluating herbicide phytotoxicity. Two postemergence herbicides were applied to mature stands of Midlawn and OKS 91-11 at two and four times label rates, and seven postemergence herbicides were applied at standard and two times label rates. Visual evaluation and spectral assessments were made for turf color 2, 7, 14, and 21 d after treatment (DAT). Triclopyr and triclopyr plus clopyralid at 2× and 4× label rates caused significant damage on OKS 91-11 and Midlawn bermudagrass in both July and September experiments. MSMA at 2× rate and MSMA metribuzin at 1× and 2× rate caused up to 73% color reductions that disappeared within 21 DAT in both cultivars. During July, 2,4-D plus mecoprop plus dicamba at the 2× rate caused at least 18% injury to Midlawn bermudagrass for 21 d. Metribuzin was safe at the 1× rate but caused significant injury for up to 7 d at the 2× rate. Imazaquin and halosulfuron-methyl each caused significant damage on one rating date. Pronamide caused no change in color regardless of rate or time of application. OKS 91-11 tolerated 2× rates of 2,4-D plus mecoprop plus dicamba better than Midlawn, but cultivar responses to other herbicide treatments were similar. V-MOS was effective for measuring green color reduction on bermudagrass turf. V-MOS and visual evaluation were linearly related (P < 0.01) at a strength of r = 0.58. Statistical results obtained using visual rating and V-MOS were the same in 86% of all cases.

Nomenclature: 2,4-D; bentazon; dicamba; halosulfuron-methyl; imazaquin; mecoprop; metribuzin; MSMA; prodiamine; pronamide; triclopyr; common bermudagrass, Cynodon dactylon (L.) Pers. OKS 91-11; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davy, Midlawn.

Additional index words: NDVI, phytotoxicity, postemergence herbicide, spectral acquisition, turfgrass injury, turfgrass quality, variable-rate technology.

Abbreviations: CA, commercially available; DAT, days after treatment; NDVI, normalized difference vegetative index; NIR, near infrared; OSU, Oklahoma State University; R, red; V-MOS, vehicle-mounted optical sensing.

Abstract: Leafy spurge (Euphorbia esula) along long distances of railroad right-of-ways is often treated with the least expensive herbicides available that only control top growth. The objective of this research was to evaluate flea beetles, Aphthona nigriscutis and a mixed population of A. czwalinae and A. lacertosa, for establishment and potential to reduce leafy spurge infestations along railroad right-of-ways. In separate experiments, both Aphthona species established the first year following release, and the rate of spread was similar regardless of the initial number released. Aphthona nigriscutis reduced leafy spurge approximately 65% up to 16 m from the release point by 3 to 5 yr after release. The mixed population of A. czwalinae and A. lacertosa reduced leafy spurge density over 95% within 4 yr of release. Biological control is an alternative to chemical control for leafy spurge along railroad right-of-ways, and establishment at these sites could facilitate biological control agent movement into remote areas.

Nomenclature: Leafy spurge, Euphorbia esula L. #³ EPHES; flea beetles, Aphthona spp.

Additional index words: Invasive weed control, biocontrol.

Abstract: A Research Committee was established by the Weed Science Society of America to outline the direction of weed science research during the next decade. Weeds adversely affect humans in both agricultural and nonagricultural environments. It is the opinion of the research committee that weed science will be advantageously positioned for the future if research focuses on research decision processes, weed biology and ecology, weed control and management practices, herbicide resistance, issues related to transgenic plants, environmental issues, and potential benefits of weeds. These future weed science research directions endorse those of the commodity and grower input group Coalition for Research on Plant Systems (CROPS)'99, a U.S. Department of Agriculture (USDA)-supported initiative. The future of weed science is dependent on a joint effort from industry, government regulators, and the public sector consisting of grower groups, as well as USDA, Agriculture and Agri-Food Canada (AAFC), and university researchers. It is our opinion that efforts spent on these research areas will benefit not only growers, commodity groups, homeowners, and industry, but society at large, through the maintenance and improvement of the food and fiber production system, and the environment in North America.

Abbreviations: AAFC, Agriculture and Agri-Food Canada; CROPS'99, Coalition for Research on Plant Systems (1999); EWRS, European Weed Research Society; GPS, global positioning systems; HRC, herbicide-resistant crops; IWM, integrated weed management; KBDSS, knowledge-based decision support strategies; USDA, U.S. Department of Agriculture; WSSA, Weed Science Society of America.