Biennial wormwood has become a problem for soybean producers in the northern Great Plains of the United States. Research was conducted to evaluate control of biennial wormwood with preemergence (PRE) herbicides alone or followed by postemergence (POST) herbicides in 2000 and 2001 at Fargo, Leonard, and Wyndmere, ND. Favorable soil moisture conditions at Leonard resulted in continual emergence and greater densities of biennial wormwood, whereas the soil at Fargo and Wyndmere was dry and few biennial wormwood seedlings emerged at these locations. Biennial wormwood control with PRE herbicides was greater than 89% at Fargo and Wyndmere but was 80% or lower at Leonard. PRE biennial wormwood control was higher with flumetsulam than with sulfentrazone. When POST treatments were applied after PRE herbicides, biennial wormwood control 4 wk after treatment was 92% or better at Fargo and Wyndmere but was 76% or less at Leonard. The combination of PRE and POST herbicide treatments did not improve control greatly at Fargo or Wyndmere but at Leonard reduced the number of biennial wormwood plants.

Technology is now available to create herbicide-tolerant crops. This technology, when combined with environmentally and toxicologically sound herbicides and when used wisely in an integrated weed management program, can contribute positively to crop production. However, it is unlikely that herbicide-tolerant crops will revolutionize weed management. Instead, they will complement existing weed management practices and provide additional options to growers. Adoption and success of herbicide-tolerant crops will be dependent on several technical, environmental, business, economic, and societal issues. Industries that are developing herbicide-tolerant crops need to openly communicate and discuss both the value that their technology brings to agriculture and society and the strategies for ensuring its responsible use.

Some annual weeds, perennial herbs, and suffrutescent half shrubs are unique in that their populations are cyclic in nature and relatively short-lived. This variability presents a confounding factor that makes management decisions about control of these weeds difficult. This paper presents a procedure, using Markov processes, that gives additional information for managing cyclic weed populations. The Markov chain model is used to evaluate the interyear patterns of broom snakeweed survival when growing on New Mexico rangeland.

I, too, would like to add my welcome to each of you on behalf of the 32nd annual Weed Science Society of America meeting. I would especially like to recognize our special guest this morning, Dr. C. Everett Koop. I know each of you will find the Clarion Plaza facilities and the program to be excellent due to an outstanding effort by Joe Antognini and the Program Committee and Joan Dusky and the Local Arrangements Committee. We owe all of these folks a tremendous debt of gratitude for the success of this meeting.

Experiments were conducted over 2 yr and at two locations in Central Georgia to determine the influence of paraquat applied for weed control in the spring and following first harvest on alfalfa yield and crown carbohydrate content. Paraquat at 0.28 and 0.56 kg ai ha-1 controlled most annual cool-season weeds at 20 d after March treatment. These rates controlled annual warm-season weeds when applied as early as 7 d after first harvest. Treatments applied during March and as late as 7 d after first harvest did not influence alfalfa production or crown carbohydrate content. However, paraquat applied 14 d after first harvest reduced alfalfa yield 40% and significantly decreased crown carbohydrate content at second harvest but the alfalfa had fully recovered by the third harvest. This indicates that alfalfa is resilient to chemical defoliation by paraquat applied for weed control.

Fifty irrigated cornfields in five eastern Colorado counties were sampled for their seedbanks and annual weed seedlings and mature populations between 1988 and 1992. Fourteen annual broadleaf species and seven annual grass species were identified in the 50 seedbanks sampled after the fields were tilled in the fall. Redroot pigweed and a mixture of green and yellow foxtail were the weed species encountered most, occurring in 90 and 54% of the fields, respectively. The single-plant populations of broadleaf and grass species in June and September were similar to those observed in the seedbanks. The number of weed species as seeds in the seedbank, June seedlings, and September plants per field ranged from zero to five grass species and zero to eight broadleaf species.

Undesirable stands of hybrid corn often result in a decision to replant; removal of the initial corn is recommended to reduce competition for available resources. Because much of the hybrid corn is glyphosate-resistant (GR), the particular herbicide and timing for control is challenging. No-till field trials were established in central and northeast Missouri in 2009 and 2010 to determine the efficacy of glufosinate POST in glufosinate-resistant corn or imazethapyr plus imazapyr POST in imidazolinone-resistant corn for the control of GR corn. Separate blocks of glufosinate-resistant and imidazolinone-resistant corn were planted in 76 cm rows, with GR corn established between rows at densities of 1 (low) and 4 (high) plants m−2. Herbicides were broadcast at corn heights of 10, 20, and 40 cm. Visual estimates of control rated 5 wk after treatment were highest for the 20 cm application height, ranging from 81 to 84% and 72 to 79% with glufosinate or imazethapyr plus imazapyr, respectively. Control was unacceptable at 10 and 40 cm, ranging from 26 to 62% and 24 to 83%. Dry weights per plant indicated that applications at all heights reduced GR corn biomass a minimum of 94 and 82% with glufosinate or imazethapyr plus imazapyr, respectively. Although control of GR corn with single applications of glufosinate and imazethapyr plus imazapyr was unacceptable for two of three application heights, reductions in corn biomass indicate applications were effective.

Control of broadleaf weeds in caladium is difficult due in part to a lack of selective POST herbicides. Cultivation is not an option due to the dense canopy and potential for tuber injury. As a result, growers currently rely on preemergence (PRE) herbicide and hand-weeding. The objective of this research was to evaluate the control of four common broadleaf weeds of field grown caladium with POST applications of halosulfuron, thifensulfuron-methyl, and trifloxysulfuron, and determine the tolerance of caladium cultivars ‘Florida Fantasy’ and ‘Florida cardinal’ to POST applications of halosulfuron. At 4 weeks after treatment (WAT), thifensufluron-methyl at 28 g ai ha−1 and trifloxysulfuron at 84 g ai ha−1 provided approximately 90 and 70% common purslane control, respectively, while halosulfuron at 210 g ai ha−1 provided 55% suppression. Trifloxysulfuron controlled ≥90% spotted spurge at 42 g ha−1, whereas the highest rate of halosulfuron and thifensulfuron-methyl only achieved 60% suppression. In field experiments, the evaluated sulfonylurea (SU) herbicides were less efficacious on hairy indigo and sharppod morningglory as control never exceeded 65 and 50%, respectively. In greenhouse experiments, the evaluated halosulfuron rates ranging from 26 to 420 g ha−1 did not significantly reduce caladium tuber weight from the nontreated control. Averaged over halosulfuron rates, ‘Florida Fantasy’ damage was 5 and 6% at 2 and 4 WAT, respectively, while ‘Florida Cardinal’ damage was 11%. We conclude that none of the herbicide treatments effectively controlled all species evaluated. Sequential treatments, higher rates, or tank-mixtures may be necessary to adequately control these species. We also conclude that caladium cultivars ‘Florida Fantasy’ and ‘Florida Cardinal’ have acceptable tolerance to POST applications of halosulfuron. Further research is needed to evaluate caladium tolerance to other SU herbicides.

The objective of this research was to describe proportional differences across time and region in management practices among southern cotton farmers who experienced glyphosate-resistant (GR) weeds on their farms earlier than those who experienced them later and among farmers who were closest to one of four historical outbreak epicenters: Lauderdale County, TN; Macon County, GA; Edgecombe County, NC; and Terry County, TX. A mail survey was conducted with cotton farmers in 2012 from 13 southern, cotton-producing states. Survey responses on practices used by farmers were classified into three broad categories of labor, mechanical/tillage/chemical (MTC), and cultural. Proportions of respondents using practices from each category were identified by time and region; across which, proportional-difference tests were conducted. Results indicated respondents encountering GR weeds earlier were more likely than farmers who experienced them later to use the three broad-category practices (labor, 98 vs. 92%; MTC, 95 vs. 89%; and cultural, 86 vs. 76%) and specific practices, including hooded sprayers (76 vs. 58%), in-season herbicide change (83 vs. 60%), and field-border management (60 vs. 35%). Also, respondents closest to Lauderdale County were more likely than farmers closest to Edgecombe County to use broad-labor practices (99 vs. 91%) and specific practices, including hand hoeing (96 vs. 84%), hand spraying (49 vs. 31%), spot spraying (76 vs. 59%), wick applicator (13 vs. 11%), and field-border management (58 vs. 39%). Education programs on weed management can be developed and tailored according to the time and regional differences to provide effective information and communication channels to farmers.

Clover inclusion may increase the sustainability of certain low-maintenance turfgrasses. However, selective weed control within mixed turfgrass–clover swards proves problematic because of clover susceptibility to herbicides. Research was conducted to identify common turf herbicides that are tolerated by three Trifolium species, including white clover, ball clover, and small hop clover, within low-maintenance turfgrass. Leaf and flower density, as well as plant height, were measured 4 wk after treatment as indicators of clover response to 14 herbicides. The three Trifolium spp. were moderately tolerant of bentazon (< 35% decrease in leaf density, height, or flowering). Simazine was well tolerated by white clover (< 5% decrease in all response variables), yet moderate injury to ball clover and small hop clover was observed (> 32% decrease in leaf density and > 27% decrease in flower density). Pronamide was well tolerated by white and ball clovers, with no effect on measured response variables; however, pronamide decreased small hop clover height and flower density (38 and 42%, respectively). Imazethapyr and imazamox were moderately well tolerated by white clover and small hop clover (< 39% decrease by all response variables), yet ball clover may be more susceptible to these herbicides than was anticipated based on previously reported tolerance. The herbicides 2,4-DB, halosulfuron, and metribuzin were well tolerated by white clover, with no effect on measured response variables; however, results suggest ball and small hop clovers were less tolerant. Clopyralid, 2,4-D, glyphosate, imazaquin, metsulfuron-methyl, and nicosulfuron resulted in varying degrees of injury across clover species and response variables, but, in general, these herbicides may not be viable options when attempting to maintain any of the three clover species tested. Further research is needed to quantify long-term effects of herbicide application on sward composition and clover succession.

Quinclorac is a systemic herbicide registered to control annual grass and broadleaf weeds in rice. Field research was conducted to determine the most effective quinclorac treatment for leafy spurge control. Leafy spurge control 12 mo after treatment (MAT) averaged 38 and 77% when quinclorac was applied at 0.56 and 1.7 kg ae/ha, respectively. Quinclorac applied with the crop-oil-based adjuvant Scoil provided similar leafy spurge control compared to quinclorac applied alone. Quinclorac plus Scoil applied with picloram provided better leafy spurge control than quinclorac plus Scoil alone. The optimum date for fall treatment with quinclorac is broad. Quinclorac at 1.1 kg/ha plus Scoil at 2.3 L/ha applied on September 1, September 15, October 1, and October 15 provided similar leafy spurge control and averaged 56% 12 MAT.

Field experiments were conducted in 1997 and 1998 to evaluate the effects of gypsum (GYP), anionic polyacrylamide (PAM), and dolomitic lime (DL) on atrazine and acetochlor efficacy and leaching. Surface-applied treatments of PAM (20 kg/ha), GYP (1,000 kg/ha), PAM + GYP (20 + 1,000 kg/ha), and DL (1,000 kg/ha), plus an unamended control, were evaluated at two locations, i.e., West Lafayette, IN (sites A and B) and Bourbon, IN (sites C and D). Sites A and C were evaluated in 1997 and 1998, while sites B and D were evaluated only in 1998. West Lafayette experiments were on a Raub silt loam (fine-silty, mixed, mesic, aquic Arguidolls) soil, and Bourbon experiments were on a Rensselaer silt loam (fine-silty, mixed, mesic, Typic Arguidolls) soil. Atrazine and acetochlor efficacy was reduced on GYP-amended plots at site A in 1997 where the total weed density was significantly higher (P = 0.10) compared with all other treatments. The results were not significant at this site in 1998; however, weed density tended to be higher with the GYP treatment. Weed density was significantly higher with DL amendments than with the other treatments at site B in 1998. Weed control was not reduced with any treatment at site C or site D in 1997 and 1998. The very strong weed pressures at these sites may have hidden potential differences. Rainfall within hours of amendment and herbicide application resulted in increased atrazine and acetochlor leaching below 15 cm under GYP-amended plots compared with all the treatments at site C in 1997. Atrazine and acetochlor concentrations in the soil were similar among treatments at all other sites, sampling times, and in both years. The application of GYP increased herbicide leaching only when heavy rainfall occurred immediately after application.

CGA-362622 has been registered for postemergence (POST) over-the-top or POST-directed application in cotton. Research was conducted during 1998 in Texas to determine potential cotton phytotoxicity after POST application of CGA-362622 alone and with the insecticides acephate, dicrotophos, azinphos methyl, oxamyl, thiamethoxam, dimethoate, and malathion and to determine the response of four cotton cultivars to CGA-362622 applied alone. CGA-362622 applied with malathion injured cotton more than either pesticide applied alone, and yield was reduced in one of four locations when the pesticides were applied in mixture compared with nontreated cotton. Pyrithiobac or CGA-362622 mixed with malathion injured cotton similarly. The other insecticides tank mixed with CGA-362622 generally did not adversely affect cotton. The cotton cultivars ‘Delta and Pine Land 50’, ‘Paymaster 1220’, ‘Paymaster 1220RR’, and ‘Stoneville 474’ responded similarly to CGA-362622 applied alone or with insecticides.

Common windgrass is an increasing winter wheat weed problem in Michigan. Postplant incorporated trifluralin, applied at 0.56 kg/ha, reduced common windgrass density by 85% in small plot research and by 70% or greater in production scale sites. In 1994–1995, incorporation implements had no effect on initial wheat density. However in a spring 1995 evaluation, significant wheat injury and stand reduction occurred in response to trifluralin incorporation. Incorporation implement effects on wheat injury were in the order: flex-tine harrow > spike tooth drag > rotary hoe. When trifluralin was shallowly incorporated over wheat planted at least 5 cm deep, no significant wheat injury was observed at any site. Injury from postplant incorporated trifluralin was related to shallow planting depth.

Field experiments were conducted in southwestern Oklahoma near Colony in 2000 and near Ft. Cobb in 2001 to quantify the effect of time of removal of a natural population of crownbeard on peanut yield. Weed densities and dry weed weights were measured at eight weed-removal times, and in-shell peanut yields were determined at harvest. Crownbeard was removed at 0 (the weed-free check), 4, 6, 8, 10, 12, 14, and 16 wk (full season) after crop emergence (WAE). Weed density was a poor predictor for dry weed weight and peanut yield; however, dry weed weight and time of removal were good predictors for peanut yield. Weed growth was minimal up to 4 WAE and increased linearly after that time. For each week of weed growth, a 0.52 kg/plot increase in dry weed weight was measured. Peanut yield decreased linearly because of crownbeard competition. For each kilogram per plot increase in dry weed weight, a 129 kg/ha or 5.1% peanut yield reduction took place. For each week of weed interference, a 75 kg/ha or 2.8% peanut yield reduction occurred. Crownbeard removal by or before 4 WAE will minimize losses in peanut yield because of interference.

Field studies were conducted in 2002 and 2003 in New Jersey to determine the length of time after a bispyribac-sodium application at which creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded. Bispyribac at 148 or 296 g ai/ha was applied 6, 4, 2, or 1 week before seeding (WBS). Bispyribac at 148 g/ha applied 1 WBS reduced ground cover of creeping bentgrass and Kentucky bluegrass at 3 weeks after seeding (WAS) by 30 and 42% as compared to the nontreated check, respectively. Reductions in Kentucky bluegrass and creeping bentgrass ground cover from bispyribac at 296 g/ha applied 1 WBS were evident at 28 WAS, whereas perennial ryegrass recovered from initial reductions in ground cover by this time. Applications made 6 to 2 weeks before seeding did not adversely affect ground cover of any species at any evaluation date as compared to the nontreated check. These studies suggest creeping bentgrass, Kentucky bluegrass, and perennial ryegrass can be safely reseeded 2 weeks after a bispyribac application. However, ground cover may be reduced by bispyribac applied 1 WBS.

Field experiments conducted in 1992 and 1993 evaluated transplanted watermelon tolerance to ethalfluralin applied PPI, PRE (before transplanting), and POST (immediately after transplanting) at 1.2 or 2.4 kg ai/ha. Other treatments for comparison included the registered herbicides ethalfluralin POST-directed spray (PDS), ethalfluralin PDS followed by (fb) naptalam POST, bensulide plus naptalam PPI, and a nontreated check. All treatments controlled common lambsquarters and goosegrass 83 to 100% 2 and 6 weeks after treatment (WAT). Watermelon was injured 30 to 77% in 1992 and 14 to 83% in 1993 by ethalfluralin PPI or PRE at 1.2 or 2.4 kg/ha. Ethalfluralin POST was not injurious to watermelon. In 1992, watermelon treated with ethalfluralin POST at 1.2 and 2.4 kg/ha yielded 52 to 62% more fruit than watermelon from the nontreated check. In 1993, yield of transplanted watermelon treated with ethalfluralin POST was similar to that in the nontreated check.

Three field experiments were conducted to evaluate efficacy of BAS 625, cyhalofop, and fenoxaprop plus isoxadifen when applied alone or with acifluorfen plus bentazon, acifluorfen, bentazon, triclopyr, bensulfuron, halosulfuron, carfentrazone, and propanil. Broadleaf signalgrass control with fenoxaprop plus isoxadifen was reduced by triclopyr and halosufuron. None of these herbicides reduced Amazon sprangletop control by fenoxaprop plus isoxadifen. Barnyardgrass control with fenoxaprop plus isoxadifen was reduced by halosulfuron and propanil. Barnyardgrass and Amazon sprangletop control by cyhalofop was reduced by bentazon plus acifluorfen, bentazon, acifluorfen, triclopyr, bensulfuron, or halosulfuron. Broadleaf signalgrass control with cyhalofop was reduced by triclopyr and halosulfuron. Amazon sprangletop control by cyhalofop was reduced by all herbicides. Barnyardgrass control with BAS 625 was reduced when applied with propanil, bentazon, or bentazon plus acifluorfen. Broadleaf signalgrass control with BAS 625 was reduced when applied with bentazon plus acifluorfen. Amazon sprangletop control with BAS 625 was reduced when applied with bentazon, acifluorfen, halosulfuron, or propanil.

Studies were conducted in 1996 and 1997 to determine the effect of irrigation systems used to produce transplants on subsequent tolerance of banana and bell pepper (Capsicum annuum) transplants to field-applied herbicides. The irrigation systems were overhead (OH), ebb and flood (EF), and float (F). At 2 and 4 wk, banana and bell pepper injury was greatest from clomazone (1.1 kg/ha) treatments. Banana and bell pepper yield were not influenced by herbicide treatment. Although crop injury was greater in 1997, there was no herbicide or irrigation system interaction with year. OH and EF irrigated banana pepper and OH irrigated bell pepper produced the greatest total yield over two harvests, whereas F irrigated pepper yielded the least. F irrigated bell pepper plants had reduced early total yield and fancy fruits relative to other irrigation treatments. F irrigated plants yielded 32 and 22% less than OH irrigated plants in banana and bell pepper, respectively. Stand counts at 3 wk after planting (WAP) show that, unlike OH and EF treatments, F treatments lost 240 to 330 plants/ha. Differences in stand among treatments were greater in 1997 than 1996. Based on our study, the OH irrigated system appears to be the best system for producing bell pepper transplants with the greatest total yield. With banana pepper, both OH and EF irrigated systems appear to produce banana pepper transplants with the greatest total yield. Also, pepper transplant tolerance to herbicides is not affected by the irrigation system used to produce transplants.

Common cocklebur is an adaptable and competitive weed with variable morphology. To learn how the rate of net photosynthesis (Pn) by common cocklebur relates to traits that may influence competitiveness, we compared Pn, accumulation of biomass (shoot mass, root mass, and total plant mass), and total leaf area among six accessions of common cocklebur grown in a greenhouse. There were highly significant (P ≤ 0.01) differences among accessions for all measured traits. Correlations of each measure of biomass with total leaf area were positive and highly significant, but correlations of Pn with each biomass measure and with total leaf area were negative. The negative correlations were largely a result of relatively low biomass accumulation by the two accessions with the highest Pn. This contrasted with results from a previous experiment on field-grown common cocklebur plants, in which the correlation of Pn with shoot mass was positive (r = 0.64). Despite the negative Pn-to-biomass correlations in the greenhouse study, the rank among accessions for Pn in the greenhouse was nearly the same as with the field-grown plants (Spearman rank correlation r = 0.89). We conclude that the relative Pn rates among common cocklebur accessions grown in the greenhouse may be used to predict their relative Pn rates in the field, but relationships of Pn with biomass or leaf area observed in the greenhouse may not be a reliable indicator of relationships in the field.