A study was conducted in 1995 and 1996 to determine the effect of soybean planting date, tillage level, and glyphosate application on sicklepod control and seed production. Soybean was planted in April, May, June, and July into conventional and no-till seedbeds. Herbicide programs evaluated were metribuzin plus chlorimuron preemergence (PRE) followed by (fb) chlorimuron postemergence (POST) (standard program [STD]), metribuzin plus chlorimuron PRE fb glyphosate POST as-needed, and glyphosate POST as-needed. Control was similar across planting dates in both years with slight variations due to weather. The July planting date had the lowest total sicklepod seed production over the 2-yr study. Sicklepod control was better in conventional tillage, but soybean yields were greater in no-till. Herbicide programs that included glyphosate provided greater sicklepod control, lower sicklepod seed production, and higher soybean yields than the STD. Use of glyphosate in combination with later planting dates, especially July, has the potential to prevent sicklepod seed accumulation in the soil while maintaining yields in a dryland soybean production system.

Nomenclature: Chlorimuron; glyphosate; metribuzin; sicklepod, Senna obtusifolia (L.) Irwin and Barnaby #³ CASOB; soybean, Glycine max (L.) Merr.

Additional index words: CASOB, no-till, planting date, Roundup Ready soybean, sicklepod seedbank.

Abbreviations: fb, followed by; POST, postemergence; PRE, preemergence; STD, standard program; WAE, weeks after emergence.

Experiments were conducted to determine peanut tolerance to CGA-362622 applied preemergence (PRE) and postemergence (POST) and to determine the potential for CGA-362622 applied PRE and POST to cotton to injure peanut grown in rotation the following year. CGA-362622 at 3.75 and 7.5 g ai/ha applied PRE visually injured peanut 11 and 16%, respectively, at 5 wk after treatment (WAT) but did not influence peanut yield. POST treatments at 3.75 and 7.5 g/ha injured peanut 63 and 93%, respectively, at 4 WAT and reduced peanut stand by 53 and 89% at 11 WAT, respectively. Peanut pod yield was reduced 73.1 and 97.9% by CGA-362622 POST at 3.75 and 7.5 g/ha, respectively, compared with the untreated weed-free control. CGA-362622 PRE at 3.75 and 7.5 g/ha reduced peanut pod yield 7.5 and 12.6%, respectively. Cotton was injured 9% or less by CGA-362622 PRE or POST at 3.75 or 7.5 g/ha and up to 25% with CGA-362622 POST at 15 g/ha. However, CGA-362622 did not influence weed-free cotton lint yields, regardless of method or rate of application. Peanuts grown in rotation were not injured, and yields were not influenced by CGA-362622 applied PRE or POST the previous year to cotton.

Nomenclature: CGA-362622, N-[4,6-dimethoxy-(2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; cotton, Gossypium hirsutum L.; peanut, Arachis hypogaea L.

Additional index words: Carryover, crop injury, sulfonylurea herbicide.

Abbreviations: ALS, acetolactate synthase; EPOST, early postemergence; LPOST, late postemergence; MPOST, mid postemergence; POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

The effect of spurred anoda competition in narrow- (35 cm) and wide-row (70 cm) soybean was studied in field experiments for 2 yr. Vigorous early soybean growth in narrow- compared with wide-row soybean resulted in lower radiation transmitted through the canopy, which can partially account for greater competitiveness of narrow-row than wide-row soybean. Soybean plant height was not significantly influenced by the row spacing. Relative yield total (RYT), which is the relationship between yield in mixtures and in monocultures of the crop or the weed and indicates resource complementarity, was equal to 1 with 12 spurred anoda/m² in the year with less precipitation. Regardless of the row spacing, spurred anoda gave resource use complementarity with the crop (RYT > 1) in all other treatments; therefore, partial avoidance of competition in mixed species was evident. Soybean aggressivity, which takes into account the effect of competition on both the crop and the weed and indicates competitive ability, decreased with weed density in both row spacings. Soybean yield loss at harvest was linearly related to relative dry weight 40 d after planting. Weed-free narrow- and wide-row soybean produced similar yields. In the presence of the spurred anoda, soybean yield was greater in narrow-row compared with wide-row soybean only in the most humid year. A management system that uses quick canopy closure with narrow-row soybean can provide excellent soybean yield and suppression of low spurred anoda densities.

Nomenclature: Soybean, Glycine max (L.) Merr.; spurred anoda, Anoda cristata (L.) Schlecht. #³ ANVCR.

Additional index words: Aggressivity, competition, crop and weed biomass, row spacing, weed density.

Abbreviations: DAP, days after planting; PPF, photosynthetic photon flux; RDW, relative dry weights; RYT, relative yield total.

Field research was conducted during 3 yr to evaluate response of rice and corn to simulated drift rates representing 12.5, 6.3, 3.2, 1.6, and 0.8% of the usage rates of 1,120 g ai/ha glyphosate (140, 70, 35, 18, and 9 g/ha, respectively) and 420 g ai/ha glufosinate (53, 26, 13, and 4 g/ha, respectively). Early-postemergence applications were made to two- to three-leaf rice and six-leaf corn, and late-postemergence applications to rice at panicle differentiation and to corn at nine-leaf stage (1 wk before tasseling). Crop injury was generally greater for the two highest rates of both herbicides when applied early. Little to no reduction in rice or corn height was observed with glufosinate. Glyphosate consistently reduced rice plant height when the two highest rates were applied early, and heading was delayed 2 to 5 d. In 2 of 3 yr, the highest rate of glyphosate reduced rice yield 99 and 67% when applied early and 54 and 29% when applied late. Germination of rice seeds from glyphosate-treated plants was reduced in 1 of 2 yr and for only the highest rate. For glufosinate, rice yield was reduced 30% and in only one year when applied late at the highest rate. Early application of glyphosate reduced corn yield an average of 22 to 78% for the three highest rates, but only for the highest rate at the late timing (33%). Corn yield was reduced an average of 13 and 11% for the highest rate of glufosinate at the early and late timings, respectively. In greenhouse studies, five rice varieties were equally sensitive, as were five corn varieties, to reduced rates of glyphosate and glufosinate.

Nomenclature: Glufosinate; glyphosate; corn, Zea mays L. ‘Asgrow 897’, ‘Dekalb 687’, ‘Mycogen 8460’, ‘Pioneer 3223’, ‘Terral 2930’; rice, Oryza sativa L. ‘Bengal’, ‘Cocodrie’, ‘Cypress’, ‘Drew’, ‘Jefferson’.

Additional index words: Crop injury, herbicide drift, off-target movement, rice germination, rice vigor.

Abbreviations: DAP, days after plating; DAT, days after treatment.

Field studies were conducted from 1996 through 1998 to evaluate control of broadleaf signalgrass and slender amaranth by clethodim, fluazifop-P-butyl, and fluazifop-P-butyl plus fenoxaprop-P-ethyl applied alone, in combination with pyrithiobac, or sequentially with pyrithiobac. Broadleaf signalgrass control with graminicides alone was 75 to 100%. Although broadleaf signalgrass control with clethodim was not reduced by pyrithiobac, control with fluazifop-P-butyl and fluazifop-P-butyl plus fenoxaprop-P-ethyl was reduced by pyrithiobac. Pyrithiobac controlled slender amaranth 85 to 100% when applied alone. However, slender amaranth control by pyrithiobac was inconsistent when pyrithiobac was applied in mixture or sequentially with graminicides. A reduction in slender amaranth control may have resulted from a combination of reduced graminicide efficacy and interference caused by broadleaf signalgrass with slender amaranth (pyrithiobac alone). Cotton yields were highest when pyrithiobac was applied 24 h after graminicides.

Nomenclature: Clethodim; fenoxaprop-P-ethyl; fluazifop-P-butyl; pyrithiobac; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash #³ BRAPP; slender amaranth, Amaranthus gracilis Desf. # AMAVI; cotton, Gossypium hirsutum L. ‘Deltapine 50’, ‘Paymaster H-1215’, ‘DP5690RR’.

Additional index words: Amaranthus gracilis, AMAVI, antagonism, Brachiaria platyphylla, BRAPP, herbicide interaction.

Abbreviations: POST, postemergence; PRE, preemergence; WAT, weeks after treatment.

A survey of 174 fields was conducted during August and September of 1998 to investigate effects of cultural and herbicide practices on postharvest weed control in winter wheat stubble fields across western and southern Nebraska. Seventy-four percent of the fields were seeded at rates of 67 to 100 kg/ha, with 60% of the wheat seeded in rows spaced 25 cm apart. Wheat seeded in east–west rows contained 98% more stinkgrass and 82% more tumble pigweed than wheat seeded in north–south rows. Sixty-nine percent of winter wheat stubble fields were rated excellent for weed control. Postharvest weed control with herbicides was not affected by row spacing. In western Nebraska, density of tumble pigweed and Russian thistle was greater when wheat seeding rate was 50 kg/ha than at higher seeding rates. Short-stature winter wheat cultivars had greater densities of Pennsylvania smartweed and toothed spurge than taller cultivars. The most common winter wheat cultivars were ‘Arapahoe’ (34%) and ‘Alliance’ (17%). Weed control was positively correlated with number of winter wheat stems per square meter (r = 0.22**). Density of several weed species was greater in fields seeded with a disk than with a hoe drill. The most common crop rotations sampled were winter wheat–corn–fallow (50%), winter wheat–fallow (18%), and winter wheat–corn–soybean (13%). Winter wheat yields and wheat stem densities were greater and weed density was less when winter wheat was seeded after an 11- to 14-mo fallow period rather than a 0- to 5-mo period.

Nomenclature: Green foxtail, Setaria viridis (L.) Beauv. #³ SETVI; kochia, Kochia scoparia (L.) Schrad. # KCHSC; Pennsylvania smartweed, Polygoncum pensylvanicum P. # POLPY; Russian thistle, Salsola iberica Sennen & Pau # SASKR; stinkgrass, Eragrostis cilianensis (All.) E. Mosher # ERACN; toothed spurge, Euphorbia dentata Michx. # EPHDE; tumble pigweed, Amaranthus albus L. # AMAAL; corn, Zea mays L.; soybean, Glycine max (L.) Merr.; winter wheat, Triticum aestivum L.

Additional index words: Atrazine, crop rotations, ecofallow, ecofarming, glyphosate, no-till, weed management.

Abbreviations: W–C or Sor, winter wheat–corn or sorghum; W–C–F, winter wheat–corn–fallow; W–C–Soy, winter wheat–corn–soybean; W–C–Spgr, winter wheat–corn–spring grains; W–F, winter wheat–fallow; W–W, winter wheat–winter wheat.

A survey of 174 fields was conducted to investigate performance of herbicides applied after winter wheat harvest on weeds across western and southern Nebraska during August and September 1998. Glyphosate plus 2,4-D plus atrazine was applied on 32%, glyphosate plus 2,4-D or dicamba on 24%, paraquat plus atrazine on 23%, glyphosate on 8%, ICIA0224 plus 2,4-D or atrazine on 10%, and atrazine plus 2,4-D on 3% of the fields. These treatments controlled 85 to 100% of the weeds except atrazine plus 2,4-D, which controlled 30%. The frequency of occurrence of the most prevalent summer annual grasses was as follows: green foxtail, 65%; barnyardgrass, 46%; stinkgrass, 41%; witchgrass, 39%; and longspine sandbur, 36%. The most common broadleaf weeds and their frequency were redroot pigweed, 32%; tumble pigweed, 30%; tall waterhemp, 28%; and kochia, 25%. Virginia groundcherry, 22%; common milkweed, 11%; yellow woodsorrel, 9%; and field bindweed, 6% were the most common perennial weeds. The five most difficult weeds to control were yellow nutsedge, spotted spurge, Virginia groundcherry, common milkweed, and toothed spurge, with control ratings of 0, 3, 17, 26, and 33%, respectively. These weeds were not controlled with glyphosate or mixtures containing glyphosate. Only 35% of the fields were treated before summer annual grasses had headed. Late applications required higher herbicides rates for effective control.

Nomenclature: Atrazine; 2,4-D; dicamba; glyphosate; ICIA0224 (glyphosate trimethylsulfonium salt); paraquat; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; common milkweed, Asclepias syriaca L. # ASCYS; field bindweed, Convolvulus arvensis L. # CONAR; green foxtail, Setaria viridis (L.) Beauv. # SETVI; kochia, Kochia scoparia (L.) Schrad # KCHSC; longspine sandbur, Cenchrus longispinus (Hack.) Fern. # CCHPA; redroot pigweed, Amaranthus retroflexus L. # AMARE; spotted spurge, Euphorbia maculata L. # EPHMA; stinkgrass, Eragrostis cilianensis (All.) E. Mosher # ERACN; tall waterhemp, Amaranthus tuberculatus (Moq.) J. D. Sauer # AMATA; toothed spurge, Euphorbia dentata Michx. # EPHDE; tumble pigweed, Amaranthus albus L. # AMAAL; Virginia groundcherry, Physalis virginiana Mill. # PHYLC; witchgrass, Panicum capillare L. # PANCA; yellow nutsedge, Cyperus esculentus L. # CYPES; yellow woodsorrel, Oxalis stricta L. # OXAST; winter wheat, Triticum aestivum L.

Additional index words: AMAAL, AMARE, atrazine, conservation tillage, CYPES, 2,4-D, dicamba, ECHCG, ecofallow, ecofarming, ERACN, glyphosate, KCHSC, KSHSC, no-till, OXAST, PANCA, paraquat, SETVI, weed management.

Five field studies on sandy soils with ≤ 1% organic matter in south Texas showed that halosulfuron at 0.066 kg/ha preemergence (PRE) controlled ≥ 92% purple nutsedge and at 0.066 kg/ha postemergence (POST) controlled purple nutsedge 77 to 95%. Sulfentrazone at 0.11 to 0.28 kg/ha PRE or POST controlled purple nutsedge < 65% at one location but > 75% at two other locations. Poor control at the one location may have been due to a lack of early-season rainfall or irrigation. Potatoes were stunted 5 to 26% with halosulfuron PRE, whereas POST treatments caused 7 to 40% stunting. Sulfentrazone at 0.11 to 0.28 kg/ha applied PRE or POST caused 2 to 38% stunting. ‘Atlantic’ potato stunting with sulfentrazone POST at 0.14 to 0.28 kg/ha was ≥ 20%, whereas ‘Snowden’ and ‘1625’ potatoes were stunted ≤ 20%. Potato yields were reduced 65 and 39% with sulfentrazone and halosulfuron POST, respectively, at the high rates, but yield reductions occurred with all POST treatments on Atlantic potatoes 10- to 20-cm tall. Halosulfuron PRE at 0.033 kg/ha and sulfentrazone PRE at 0.14 kg/ha did not reduce yields; however, all other treatments of halosulfuron and sulfentrazone reduced potato yields.

Nomenclature: Halosulfuron; sulfentrazone; purple nutsedge, Cyperus rotundus L. #³ CYPRO; potato, Solanum tubersum L., ‘Atlantic’, ‘Snowden’, ‘1625’.

Additional index words: Preemergence, postemergence.

Abbreviations: OM, organic matter; POST, postemergence; PPI, preplant incorporated; PRE, preemergence; WAP, weeks after planting.

Preharvest applications of glyphosate can be useful in controlling perennial weeds. Experiments were conducted from 1996 to 1999 to determine whether preharvest glyphosate applications are affected by differences in the amount of soybean canopy present at the time of application by measuring spray deposition and subsequently horsenettle or Canada thistle control. Soybean leaf interference levels were achieved by use of three soybean cultivars with different maturity groups to achieve no leaf interference, moderate leaf interference, and maximum leaf interference, and soybean was planted in three row spacings ranging from 19 to 76 cm. As soybean leaf interference increased, spray coverage of spray deposition cards decreased. There was a similar trend for relative spray volume, determined by intensity of the color change with water-sensitive cards. Row spacing did not influence spray coverage or relative spray volume. Percent change in horsenettle or Canada thistle stems from fall to spring counts was inconsistent. Differences detected in spray coverage did not influence weed control or weed stem density the following spring.

Nomenclature: Glyphosate; Canada thistle, Cirsium arvense (L.) Scop. #³ CIRAR; horsenettle, Solanum carolinense L. # SOLCA; soybean, Glycine max (L.) Merr.

Additional index words: CIRAR, Cirsium arvense, cultural practices, integrated weed management, perennial weed control, Solanum carolinense, SOLCA, spray deposition.

Studies were conducted in 1999, 2000, and 2001 to evaluate broadleaf weed control in cotton with postemergence applications of bromoxynil and bromoxynil plus CGA 362622. Bromoxynil was applied at 280 and 560 g ai/ha, and CGA 362622 was applied at 0, 3.8, and 7.5 g ai/ha in a factorial treatment arrangement. Cotton injury 7 d after treatment (DAT) during the 3 yr was 11 to 35% with the herbicide mixtures, but injury did not exceed 2% 28 DAT when averaged over years. CGA 362622 plus bromoxynil controlled velvetleaf, smooth pigweed, common ragweed, and common cocklebur at least 77% 28 DAT. Control of morningglory species was at least 87% with herbicide combinations, except in 2001 when control was only 60% with 280 g/ha bromoxynil plus 3.8 g/ha CGA 362622. Bromoxynil also controlled jimsonweed, but CGA 362622 did not. Spurred anoda control pooled over years did not exceed 53% with bromoxynil or bromoxynil plus CGA 362622 mixtures. Cotton yields generally reflected the level of weed control from the herbicide treatments. In these studies, mixtures of CGA 362622 with bromoxynil controlled several broadleaf weeds better than did either herbicide alone.

Nomenclature: Bromoxynil; CGA 362622 (proposed common name trifloxysulfuron sodium), N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluoroethoxy)-pyridin-2-sulfonamide sodium salt; annual morningglory species, Ipomoea spp.; common cocklebur, Xanthium strumarium L. #³ XANST; common ragweed, Ambrosia artemisiifolia L. # AMBEL; jimsonweed, Datura stramonium L. # DATST; smooth pigweed, Amaranthus hybridus L. # AMACH; spurred anoda, Anoda cristata (L.) Schlecht. # ANVCR; velvetleaf, Abutilon theophrasti Medicus # ABUTH; cotton, Gossypium hirsutum L.

Additional index words: IPOHE, IPOLA, Ipomoea hederacea (L.) Jacq., Ipomoea lacunosa L., Ipomoea purpurea (L.) Roth, IPOPU, ivyleaf morningglory, pitted morningglory, tall morningglory.

Abbreviations: DAT, days after treatment; POSD, postdirected; POST, postemergence; PRE, preemergence.

Field experiments were conducted in 2000 and 2001 in Virginia to evaluate the incidence and severity of maize chlorotic dwarf virus and maize dwarf mosaic virus in response to postemergence (POST) johnsongrass control in two corn hybrids. Previous research demonstrated the increased disease severity in virus-susceptible corn hybrids as an indirect effect of POST johnsongrass control. The increased disease severity resulted from greater transmission by insect vectors, which moved from dying johnsongrass to the crop. Recent observations have indicated a lack of virus tolerance in glyphosate-tolerant corn hybrids commercially available in Virginia. A transgenic glyphosate-tolerant hybrid and a nontransgenic virus-tolerant hybrid, similar in growth characteristics and maturity, were subjected to POST treatments of nicosulfuron, whereas the glyphosate-tolerant hybrid was also treated with glyphosate. Both nicosulfuron and glyphosate, broadcast or directed, provided essentially complete johnsongrass control, although initial johnsongrass control was greater with glyphosate treatments. Little or no disease incidence occurred in the virus-tolerant hybrid. With the virus-susceptible hybrid, significant increases in disease incidence were observed in response to any herbicide treatment applied to johnsongrass-containing plots relative to the same treatment applied to weed-free plots. Johnsongrass control with nicosulfuron or glyphosate caused similar disease incidence and severity in this hybrid, regardless of application method. Results of these experiments indicated that growers' choice of hybrid genetics should focus primarily on disease resistance rather than on herbicide resistance in fields that are infested with johnsongrass.

Nomenclature: Glyphosate; nicosulfuron; johnsongrass, Sorghum halepense (L.) Pers. #³ SORHA; corn, Zea mays (L). ZEAMX.

Abbreviations: DAT, days after treatment; MCD, maize chlorotic dwarf; MDM, maize dwarf mosaic; MCDV, maize chlorotic dwarf virus; MDMV, maize dwarf mosaic virus; POST, postemergence; SS, Southern States; WAT, weeks after treatment; WF, weed-free.

The potential weediness of hybrid bermudagrass cultivars in nontarget areas is an important factor when considering the development of herbicide-resistant cultivars. Field studies evaluated the response of common bermudagrass, hexaploid hybrid ‘Tifton-10’, and two triploid hybrid bermudagrass cultivars (‘TifEagle’ and ‘TifSport’) to clethodim, fluazifop-p, glufosinate, glyphosate, and quizalofop-p. Glyphosate was more consistent than clethodim and clethodim plus glyphosate in controlling common bermudagrass. The triploid cultivars were equally sensitive to each of these treatments, whereas Tifton-10 control was highest with treatments that included glyphosate. Variability between years in control of common bermudagrass was attributed to differences in plant size at application, with greater control of smaller plants. All herbicides reduced common bermudagrass plant diameters ≥ 93% in 1999 when grown without a crop. However, in 2001, only herbicide treatments that included two applications of 1.1 kg ai/ha glyphosate reduced plant diameters 6 to 59%. None of the other treatments reduced common bermudagrass plant diameters compared with pretreatment values. When grown with cotton, fluazifop-p and 4.5 kg/ha glyphosate were the only treatments consistent across cultivars and years. All herbicide treatments reduced triploid hybrid bermudagrass plant diameters ≥ 90%, whereas Tifton-10 plant diameters were reduced > 86% by all treatments, with the exception of clethodim. As in the non-cropland study, common bermudagrass plant diameters were reduced ≥ 97% by herbicides in 1999, whereas in 2001, only fluazifop-p and glyphosate treatments reduced plant diameters compared with the nontreated control. Both the lack of aggressiveness and susceptibility to common herbicides of the triploid hybrid cultivars relative to common bermudagrass indicates that these non–pollen-producing or -receiving cultivars are reasonable candidates for the introduction of herbicide resistance.

Nomenclature: Clethodim; fluazifop-p; glufosinate; glyphosate; quizalofop-p; common bermudagrass, Cynodon dactylon (L.) Pers. #³ CYNDA ‘Tifton-10’; hybrid bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davy ‘TifEagle’, ‘TifSport’; cotton, Gossypium hirsutum L.

Additional index words: Transgenic turfgrass, turfgrass weed management.

Abbreviations: fb, followed by; triploid hybrid cultivars, grouping of TifEagle and TifSport bermudagrass cultivars; WAP, weeks after transplanting.

Field studies were conducted during the 2000 to 2001 growing seasons to evaluate winter annual weed control and crop tolerance with fall-applied herbicides in corn at Belleville, IL. Atrazine, simazine, and rimsulfuron plus thifensulfuron applied in the fall controlled mouseear chickweed, henbit, and Carolina foxtail 93% or greater at planting the following spring. Flumetsulam controlled mouseear chickweed and henbit 98 and 93%, respectively, at planting. Metribuzin controlled mouseear chickweed and henbit 100 and 97%, respectively. CGA-152005 controlled mouseear chickweed, henbit, and wild garlic 93 to 100%. CGA-152005 provided the greatest control of wild garlic, with control ranging from 94 to 100% at planting. CGA-152005 plus simazine controlled 99 to 100% of all winter annual weeds evaluated. Reducing winter annual weed vegetation did not increase soil temperatures at 5-cm depth in May. CGA-152005 caused discoloration and height reduction of corn. CGA-152005 at the highest rate (60 g ai/ha) reduced corn plant height by 7% and grain yield by 8%.

Nomenclature: Atrazine; CGA-152005, 1-(4-methoxy-6-methyl-triazin-2-yl)-3-[[2-(3,3,3-trifluoropropyl)-phenylsulfonyl]]-urea; flumetsulam; metribuzin; rimsulfuron; simazine; thifensulfuron; Carolina foxtail, Alopercurus carolinianus Walt. #³ ALOCA; henbit, Lamium amplexicaule L. # LAMAM; mouseear chickweed, Cerastium vulgatum L. # CERVU; wild garlic, Allium vineale L. # ALLVI; corn, Zea mays (L.) ‘Pioneer 33G28 LL’.

Additional index words: Discoloration, height reduction, preemergence.

Abbreviations: DAP, days after planting; DAT, days after treatment; POST, postemergence.

Studies examined the effect of herbicides on the quality and root strength of winter-installed tall fescue and hybrid bermudagrass sod. Sod was installed in February and treated approximately 30 to 45 d after installation with a variety of preemergence (PRE) and postemergence (POST) herbicides. Tall fescue quality was not affected by any herbicide treatment in 2000 or 2001. Root strength reduction occurred only in 2001 by dithiopyr applied PRE at 2.5 kg ai/ha, which is 4.5 times the maximum use rate. No other herbicides decreased tall fescue root strength in either year. Bermudagrass quality was decreased by triclopyr plus clopyralid applied POST, which resulted in 22 and 6% injury 42 d after initial treatment (DAIT) in 2000 and 2001, respectively. However, POST herbicides did not affect bermudagrass root strength in either year. PRE herbicide treatments did not reduce root development in bermudagrass in 2000. However, dithiopyr applied at 0.84 and 2.5 kg/ha reduced bermudagrass rooting by 59 and 70%, 60 DAIT, in 2001. Pendimethalin reduced root development of bermudagrass by 62% when applied at 10.2 kg/ha, three times the maximum use rate, in 2001. However, by 120 DAIT, only dithiopyr applied at 2.5 kg/ha decreased bermudagrass root development.

Nomenclature: Clopyralid; 2,4-D; dicamba; dithiopyr; MCPP; oxadiazon; pendimethalin; pronamide; simazine; triclopyr; hybrid bermudagrass, Cynodon transvaalensis Burtt-Davy × Cynodon dactylon (L.) Pers. ‘Tifway II’; tall fescue, Festuca arundinacea Schreb. #³ FESAR ‘Rebel II’.

Additional index words: Dynamometer, root strength.

Abbreviations: DAIT, days after initial treatment; fb, followed by; POST, postemergence; PRE, preemergence; 3×, three times the maximum labeled use rate; 4.5×, four and a half times the maximum labeled use rate.

Experiments were conducted at two locations in Texas during 2000 and 2001 to compare barnyardgrass, broadleaf signalgrass, and red rice control; rice tolerance; and grain yield after single and sequential applications of imazethapyr in imidazolinone-tolerant rice. Red rice and barnyardgrass control on a clay soil at Beaumont was at least 94% with imazethapyr at 70, 90, and 100 g ai/ha applied preplant incorporated (PPI) or preemergence (PRE) followed by (fb) at least 40 g/ha of imazethapyr applied early postemergence (EPOST). Broadleaf signalgrass control on a very fine sandy loam soil at Eagle Lake was at least 86% when imazethapyr was applied PPI or PRE fb EPOST applications of imazethapyr. Sequential postemergence applications at Beaumont resulted in at least 95% red rice and barnyardgrass control when 40 g/ha applied late postemergence followed any EPOST application. Sequential postemergence applications at Eagle Lake controlled broadleaf signalgrass 98% during both years. Imazethapyr applied postemergence injured rice 0 to 34% up to 12 d after treatment. Rice yield reductions were correlated to weed control and most likely were not associated with early-season rice injury.

Nomenclature: Imazethapyr; imidazolinone; barnyardgrass, Echinochloa crus-galli (L.) Beauv. #³ ECHCG; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; red rice, Oryza sativa L. # ORYSA; rice, Oryza sativa L. # ORYSA.

Additional index words: CLEARFIELD* rice, Newpath.

Abbreviations: EPOST, early postemergence; fb, followed by; LPOST, late postemergence; PD, panicle differentiation; PPI, preplant incorporated; PRE, preemergence.

Field experiments were conducted in Virginia in 2000 and 2001 to determine the response of wheat and Italian ryegrass biotypes to postemergence applications of diclofop-methyl compared with several experimental and registered herbicides. Control of diclofop-methyl–sensitive Italian ryegrass by AE F130060 03 was similar to control by diclofop-methyl and was greater than that by chlorsulfuron plus metsulfuron, chlorsulfuron plus metribuzin, MON 37560, ICIA 0604, and CGA 184927. AE F130060 03 also controlled diclofop-methyl–resistant Italian ryegrass better than the other herbicides. Late-season spike density of diclofop-methyl–resistant Italian ryegrass was reduced 91 to 98% by AE F130060 03. Despite injury ranging from 10 to 24%, grain yield from wheat treated with AE F130060 03 was similar to or greater than yield from wheat treated with the other herbicides. Italian ryegrass control, spike density, and grain yield were not influenced by AE F130060 03 rate or addition of methylated seed oil.

Nomenclature: AE F130060 03 {8.3:1.7 mixture of AE F130060 00, proposed common name mesosulfuron-methyl, 2-[(4,6-dimethoxypyrimidin-2-yl carbamoyl)sulfamoyl]-4-methanesulfonamido-p-toluic acid, plus AE F115008 00, proposed common name iodosulfuron-methyl-sodium, 4-iodo-2-[3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)ureidosulfonyl]benzoic acid}; CGA 184927, proposed common name clodinafop-propargyl, (R)-2-[4-[(5-chloro-3-fluoro-2-pyridinyl)oxy]phenoxy]propanoic acid 5-chloro-8-quinolinoxyacetic acid-1-methylester; chlorsulfuron; diclofop-methyl; ICIA 0604, proposed common name tralkoxydim, 2-[1-(ethoxyamino)propyl]-3-hydroxy-5-(2,4,6-trimethylphenyl)-2-cyclohexen-1-one; metribuzin; metsulfuron; MON 37560, proposed common name sulfosulfuron, 1-(4,6-dimethoxypyrimidin-2-yl)-3-[(ethanesulfonyl-imidazo[1,2-a]-pyridine-3-yl)sulfonyl]urea; Italian ryegrass, Lolium multiflorum Lam. #³ LOLMU; winter wheat, Triticum aestivum L. ‘Pioneer 2643’, ‘Pioneer 26R24’, ‘Pocohontas’.

Additional index words: Diclofop-methyl resistance, resistance management.

Abbreviations: ACCase, acetyl coenzyme A carboxylase (EC 6.4.1.2); ALS, acetolactate synthase (EC 4.1.3.18); MSO, methylated seed oil; POST, postemergence; PRE, preemergence; WAT, weeks after treatment; WBT, weeks before treatment.

Yellow nutsedge, a weed commonly present in Florida vegetable fields, may substantially reduce crop yields when not controlled. Soil fumigation with methyl bromide effectively controls nutsedges, but methyl bromide is being phased out of production and use in the United States. Therefore, nutsedge management in bell pepper is a cause for concern. An experiment was conducted during four seasons (spring and fall of 1999 and 2000) to determine the tolerance of bell pepper grown at two in-row spacings (23 and 31 cm) to interference resulting from planted yellow nutsedge tuber densities (0 to 120 tubers/m²). Relative to yields with no nutsedge, pepper fruit yields in each season were reduced 10% with fewer than 5 planted tubers/m². Yield losses increased more rapidly with an increase in initial nutsedge density from 0 to 30 than from 30 to 120 tubers/m². With 30 nutsedge tubers/m², large fruit yield was reduced 54 to 74% compared to that with no nutsedge. Nutsedge shoots overtopped the pepper plants as early as 6 wk after treatment when, with 15 planted tubers/m², nutsedge interference reduced pepper plant biomass by 10 to 47%. In the absence of methyl bromide, weed control strategies with high efficacy against yellow nutsedge will be needed for bell pepper production.

Nomenclature: Methyl bromide; yellow nutsedge, Cyperus esculentus L. #³ CYPES; bell pepper, Capsicum annuum L. ‘X3R Camelot’.

Additional index words: Weed interference, yellow nutsedge competition, yield loss.

Abbreviations: No., number; WAT, weeks after treatment.

Bahiagrass is used for roadsides, pastures, and lawns in the southeastern United States mainly because of drought and nematode tolerance. Metsulfuron is a sulfonylurea herbicide, which selectively controls bahiagrass in bermudagrass. Certain cultivars of bahiagrass were observed to be tolerant to recommended rates of metsulfuron. Therefore, research was conducted to investigate the susceptibility of five major bahiagrass cultivars to metsulfuron applied at increasing rates to 42 g ai/ha. Five bahiagrass cultivars were evaluated: ‘Pensacola’, ‘Tifton-9’, ‘Argentine’, ‘Common’, and ‘Paraguayan’. Argentine, Common, and Paraguayan cultivars showed a four- to fivefold increased tolerance to metsulfuron compared with Pensacola. Because of yearly inconsistencies, results for Tifton-9 were inconclusive.

Nomenclature: Metsulfuron; Argentine bahiagrass, Paspalum notatum Fluegge var. notatum ‘Argentine’; bermudagrass, Cynodon dactylon (L.) Pers; Common bahiagrass, Paspalum notatum Fluegge var. notatum ‘Common’; Paraguayan bahiagrass, Paspalum notatum Fluegge var. notatum ‘Paraguayan’; Pensacola bahiagrass, Paspalum notatum Fluegge var. saurae Parodi ‘Pensacola’; Tifton-9 bahiagrass, Paspalum notatum Fluegge var. saurae Parodi ‘Tifton-9’.

Abbreviations: GR₅₀, metsulfuron rate required to reduce regrowth to 50% of untreated; OM, organic matter; WAT, weeks after treatment.

Greenhouse studies were conducted to evaluate shoot number, shoot weight, and root weight reduction of yellow and purple nutsedge to three placement levels (soil, foliar, and soil foliar applied) and four herbicide treatments (CGA-362622, imazaquin, MSMA, and imazaquin MSMA). Soil-applied CGA-362622 reduced shoot number, shoot weight, and root weight greater than foliar-applied CGA-362622. Foliar-applied imazaquin and soil-applied MSMA achieved little reduction in measured variables compared with the nontreated control. Foliar-applied imazaquin and soil-applied MSMA reduced shoot number, shoot weight, and root weight less than imazaquin MSMA applied in a similar manner. Averaged over placement levels, imazaquin reduced shoot weight of yellow nutsedge greater than purple nutsedge. Averaged over herbicide treatments, soil-applied treatments were more effective in reducing purple nutsedge shoot number, whereas foliar-applied treatments were more effective in reducing yellow nutsedge shoot number.

Nomenclature: CGA-362622, N-[(4,6-dimethoxy-2-pyrimidinyl)carbamoyl]-3-(2,2,2-trifluroethoxy)-pyridin-2-sulfonamide sodium salt; imazaquin; MSMA; purple nutsedge, Cyperus rotundus L. #³ CYPRO; yellow nutsedge, Cyperus esculentus L. # CYPES.

Additional index words: Foliar absorption, root absorption.

Abbreviations: DAP, days after planting; DAT, days after treatment; NIS, nonionic surfactant; POST, postemergence.

Studies were conducted in 2000 and 2001 to investigate responses of glyphosate-resistant cotton, glyphosate-resistant soybean, and selected weed species to postemergence applications of isopropylamine (Ipa) and diammonium (Dia) salts of glyphosate at selected rates ranging from 0.42 to 3.36 kg ae/ha. No differences were detected between either glyphosate salts or application timings for cotton injury, cotton lint yield, micronaire, fiber length, fiber strength, or fiber uniformity. In a weed-free soybean study, no differences in soybean injury occurred between early-postemergence treatments of the two glyphosate salts. Injury from late-postemergence treatments did not exceed 12% with glyphosate-Ipa or 9% with glyphosate-Dia at 3.36 kg/ha. Soybean treated with glyphosate-Ipa yielded 3,050 kg/ha, whereas soybean treated with glyphosate-Dia yielded 2,880 kg/ha, when averaged over glyphosate rate and application timing. In a soybean study that included weed control as a variable, weed control at 14 d after treatment (DAT), and soybean yield was independent of glyphosate salt. Control of common ragweed, ivyleaf morningglory, pitted morningglory, and large crabgrass at 28 DAT was similar at 0.84 kg/ha of either glyphosate salt.

Nomenclature: Glyphosate; common ragweed, Ambrosia artemisiifolia L. #³ AMBEL; ivyleaf morningglory, Ipomoea hederacea (L.) Jacq. # IPOHE; large crabgrass, Digitaria sanguinalis (L.) Scop. # DIGSA; pitted morningglory, Ipomoea lacunosa L. # IPOLA; cotton, Gossypium hirsutum L. ‘PM1218 BG/RR’; soybean, Glycine max (L.) Merr. ‘Asgrow 5401RR’.

Additional index words: Diammonium, glyphosate formulation, glyphosate salt, isopropylamine.

Abbreviations: DAT, days after treatment; Dia, diammonium; EPOST, early postemergence; Ipa, isopropylamine; LPOST, late postemergence; POST, postemergence; PRE, preemergence; Tms, trimethylsulfonium.

At 10.4 mM bentazon treatment, the tolerance index of susceptible (S) inbred corn, line TN89, at one-leaf stage decreased to 27% of that of the control, whereas > 90% of tolerance index of control was maintained in tolerant (T) line LU21. More than fourfold of malondialdehyde (MDA) accumulated in S line within 7 d after treatment (DAT), but only a slight accumulation of MDA was found in T line. ¹⁴C-Bentazon application experiment indicated that there was no difference in bentazon absorption between T and S lines. However, bentazon metabolism in T line was more active than that in susceptible TN89. The metabolite, 6-glucose-bentazon in T line rapidly accumulated to the maximum 3 DAT, whereas this conjugate actually decreased in S line. Assay of in vitro activity of bentazon-6-hydroxylase showed that it was decreased in both lines with development and that this activity in T line at two-leaf stage was ca. 50% higher than that in S line. It is suggested that the higher bentazon tolerance in LU21 is primarily associated with an active bentazon metabolism, partially due to a higher bentazon-6-hydroxylase activity coupled with glucosylation.

Nomenclature: Bentazon; corn, Zea mays (L.). #³ ZEAMX.

Additional index words: Hydroxylase, inbred line, Taiwan.

Abbreviations: DAT, days after treatment; HPLC, high-performance liquid chromatography; MDA, malondialdehyde; S, susceptible; T, tolerant; TLC, thin-layer chromatography.

Response of glyphosate-resistant cotton to various rates of topically applied glyphosate was investigated in growth chamber experiments to determine the relationship between glyphosate rate and boll abscission. Glyphosate at 0, 0.56, 1.12, or 2.24 kg ai/ha was applied to all exposed foliage at the 12-leaf growth stage. Immediately after this treatment, ¹⁴C-glyphosate was applied to the three uppermost fully expanded leaves at 0, 37, 74, or 148 kBq per leaf for the 0, 0.56, 1.12, or 2.24 kg/ha treatment, respectively. After glyphosate application, glyphosate accumulated in reproductive tissue, and bolls were abscised. Abscission increased as the amount of glyphosate translocated to fruiting sites increased.

Nomenclature: Glyphosate; cotton, Gossypium hirsutum L., ‘Delta & Pine Land 5690RR’.

Additional index words: Boll abscission; transgenic crops.

Abbreviations: EPSPS, 5-enolpyruvylshikimate-3-phosphate synthase (EC 2.5.1.19); GR, glyphosate resistant; WAT, weeks after treatment.

Glyphosate and glufosinate are now options for postemergence weed control in herbicide-resistant corn and soybean. Velvetleaf is one of the more difficult to control annual weeds with these herbicides at commonly used rates. Ammonium sulfate (AMS) is generally used with these herbicides to overcome hard water antagonism and to increase herbicide activity. Greenhouse and field trials were conducted with commercial adjuvants that might substitute for AMS. The adjuvants were evaluated in deionized water, tap water, and deionized water containing 500 mg/L CaCO₃. In the absence of AMS, hard water reduced velvetleaf control with both herbicides. Regardless of water source, AMS increased velvetleaf control with both glyphosate and glufosinate. Several adjuvants increased velvetleaf control with either herbicide; however, none were superior to 2% w/v AMS. Other adjuvants decreased velvetleaf control with either herbicide.

Nomenclature: Ammonium sulfate; glufosinate; glyphosate; velvetleaf, Abutilon theophrasti Medic #³ ABUTH; corn, Zea mays L. # ZEAMA; soybean, Glycine max (L.) Merr. # GLYMA.

Additional index words: Ammonium sulfate, glufosinate, glyphosate.

Laboratory and greenhouse experiments were conducted to determine quinclorac efficacy as influenced by surfactants, methylated seed oil (MSO), basic pH compounds, and salts in the spray carrier water. Quinclorac efficacy for green foxtail control generally increased with an increase in linear alcohol ethoxylate (LAE) surfactant carbon-chain length and percentage of ethoxylation. With LAE surfactants, quinclorac phytotoxicity to green foxtail was nearly doubled (average from 44 to 81%) when triethanolamine (TEA) was included in the spray mixture. Combination of LAE surfactants with TEA also enhanced quinclorac absorption. Enhancement of quinclorac absorption and phytotoxicity by LAE surfactants and TEA was related to spray deposits that had close contact with the cuticle and without apparent quinclorac crystals. Sodium and calcium ions strongly antagonized quinclorac efficacy when applied with a block copolymer surfactant or MSO. Ammonium sulfate or ammonium nitrate adjuvants were more effective than urea–ammonium nitrate liquid fertilizer in overcoming antagonism from salts in spray carrier waters. These results demonstrate the potential for maximizing quinclorac efficacy by careful selection of surfactants, nitrogen fertilizer, and basic pH additives.

Nomenclature: Quinclorac; green foxtail, Setaria viridis (L.) P. Beauv. #³ SETVI.

Additional index words: Herbicide absorption, nitrogen fertilizer, nonionic surfactant, pH, spray deposit.

Abbreviations: AMS, ammonium sulfate; AN, ammonium nitrate; DEA, diethanolamine; EO, ethylene oxide chain; LAE, linear alcohol ethoxylate; MEA, monoethanolamine; MSO, methylated seed oil; TEA, triethanolamine; UAN, urea–ammonium nitrate (28% N) liquid fertilizer.

Field experiments were conducted to examine the influence of spray volume on glyphosate efficacy in relation to glyphosate rate, formulation, ammonium sulfate addition, and type of sprayer nozzle. Using several grass species it was shown that glyphosate efficacy increased as spray volume decreased from 190 to 23 L/ha. To obtain equal efficacy, glyphosate rates can be reduced by at least one-third when glyphosate is applied in 23 or 47 L/ha spray volume compared with 94 or 190 L/ha. The amount of surfactant in formulated glyphosate at 35 to 140 g ae/ha rates was insufficient when glyphosate was applied in 94 or 190 L/ha spray volumes. Additional surfactant enhanced glyphosate efficacy at these rates when applied in 94 or 190 L/ha spray volume, but efficacy was still less than when applied in 23 or 47 L/ha without additional surfactant. Thus, low spray volumes maximized glyphosate efficacy primarily through high herbicide concentration in the spray deposit and reduced salts from the carrier to antagonize efficacy. Glyphosate applied in 23 L/ha spray volume with drift-reducing nozzles provided control equal to that provided by glyphosate applied with standard flat-fan nozzles. Grass control also was equal from several glyphosate formulations that contained surfactants, regardless of spray volume.

Nomenclature: Glyphosate.

Additional index words: Adjuvant, application methods, spray deposit, spray droplet.

Abbreviations: AMS, ammonium sulfate; DAT, days after treatment; NIS, nonionic surfactant.

Field experiments were conducted at three locations in 2000 and 2001 to evaluate what effect soil characteristics have on sensitivity of two corn hybrids to soil-applied isoxaflutole plus flufenacet. Soil types were a Flanagan silt loam with 3.9% organic matter (OM), a Drummer silty clay loam with 5.0% OM, and a Cisne silt loam with 2.1% OM. Soil pH was adjusted to four target levels, < 6.0, 6.0 to 6.5, 6.6 to 7.0, and > 7.0, at each location. Isoxaflutole plus flufenacet treatments consisted of the recommended rate (1 ×) and two times (2 ×), and four times (4 ×) the recommended rates based on soil type. Additional treatments included 1 × and 2 × isoxaflutole plus flufenacet with 1.1 kg/ha atrazine and S-metolachor plus atrazine as a control treatment. Corn hybrid ‘Garst 8366’ (G8366) was more sensitive to soil-applied isoxaflutole plus flufenacet compared with ‘Garst 8600’ (G8600). Corn injury occurred only at two of three locations. Addition of atrazine to the 1 × and 2 × isoxaflutole plus flufenacet treatments showed a trend (P = 0.15) toward increased injury and reduced yield only for the G8366 on the Cisne soil. The 4 × rate of the premixture reduced yield 9 to 49% at two locations. Yields were reduced at the low-OM (2.1%) location, regardless of hybrid or application rate. At two locations, there was a negative linear relationship between soil pH and corn grain yield, particularly at the 4 × rate. Corn visual injury and yield reductions were greatest from herbicide applications to low-OM soils with high pH levels.

Nomenclature: Atrazine; flufenacet; isoxaflutole; S-metolachor; corn, Zea mays L. ‘Garst 8600’ (G8600), ‘Garst 8366’ (G8366).

Additional index words: Acetamide, crop safety, isoxazole, phytotoxicity, soil pH, soil OM.

Abbreviations: CEC, cation exchange capacity; DAP, days after planting; OM, organic matter; UAN, urea–ammonium nitrate.

The classification of herbicides by site of action, published in 1997, has been revised. The classification system uses a numbering system for a herbicide's site of action, chemical family, and common name. Regulatory agencies in the United States and Canada have published labeling guidelines based on the classification to aid in herbicide resistance management.

Abbreviations: EPA, Environmental Protection Agency; HRAC, Herbicide Resistance Action Committee; PMRA, Pest Management Regulatory Agency.

Herbicide-resistant cultivars may improve some aspects of weed management in wheat. However, negative consequences such as gene transfer among species, increased development of resistant weeds, or less effective volunteer wheat control may result from their use. Therefore, we reviewed literature on volunteer (self-sown) wheat seedling emergence and seed longevity in soil for insight in managing herbicide-resistant wheat. Data from classical burial studies suggested that wheat seeds were short-lived in soil, persisting less than 1 yr. Yet, in field studies, volunteer wheat seedlings were still emerging 16 mo after harvest; occasionally, seedlings have been observed 2 yr after harvest. Volunteer wheat emergence was extremely variable; causes of the variability are numerous and include genotypic, environmental, and production factors. This variability makes it difficult to predict volunteer wheat infestations in future years. Diverse cropping systems will enable producers to accrue the benefits of herbicide-resistant cultivars and yet still manage wheat volunteers, minimize gene flow by pollen, and avoid transfer of herbicide resistance. In regions where alternative crops are not viable, a key concern will be controlling volunteers and gene transfer in the next wheat crop.

Nomenclature: Wheat, Triticum aestivum L.

Additional index words: Dormancy, environment, gene transfer, herbicide resistance.

Red rice has long been a troublesome, conspecific weed of cultivated rice. Rice varieties carrying certain herbicide-resistant traits acquired through genetic modification (herbicide-resistant varieties) now offer new options for red rice control. In concert with this innovation is the risk of gene flow, which can result in the transfer of that specific herbicide resistance to red rice and thus render this weed control measure ineffective. Gene flow in concept is simple, however, the parameters that determine the establishment of a new trait in a weed population are complex. Cross-pollination to make hybrid seed and the subsequent fate of those hybrid families in the general weed population are some of the biological factors that influence gene flow between red rice and cultivated rice. Natural outcrossing among rice plants is generally low. Most of the pollen dispersal studies published to date indicated that rice × rice outcrossing rates were less than 1.0%. Numerous reports summarized in this study suggest that outcrossing rates between rice and red rice can be highly variable but usually are similar to or lower than this level. However, once hybrids form, they may introgress into a red rice population within only a few generations. If hybrid seed families are to persist and establish herbicide-resistant red rice populations, they must successfully compete in the crop–weed complex. The ability to survive a herbicide applied to a herbicide-resistant rice variety would be a strong selective advantage for these hybrid families. Thus, the well-established principles of weed resistance management appear to be relevant for herbicide-resistant crop systems and should be used in combination with practices to minimize coincident flowering to mitigate the potential impact of gene flow from herbicide-resistant rice into red rice. For the rice–red rice crop–weed complex, there are both biological factors and agricultural practices that can work together to preserve these new weed control options.

Nomenclature: Red rice, Oryza sativa L. #³ ORYSA; rice, Oryza sativa L.

Additional index words: Genetically modified organism, glufosinate, glyphosate, herbicide tolerant, imazethapyr, introgression, outcrossing, pollen transfer, transgenic rice.

Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); bar, bialophos resistant; EPA, Environmental Protection Agency; GMO, genetically modified organism; PCR, polymerase chain reaction; USDA, U.S. Department of Agriculture.