In field studies conducted over 2 yr, POST applications of chlorimuron, imazaquin, fomesafen, or acifluorfen following PRE applications of clomazone, metribuzin, or metribuzin plus chlorimuron enhanced wild poinsettia control when compared with the PRE herbicides applied alone. Wild poinsettia control was highest for imazaquin compared with other PRE treatments and with the exception of fomesafen, applications of POST herbicides following imazaquin PRE did not improve weed control. With the addition of POST herbicides, soybean yields were generally not increased, but moisture content in one year and foreign material content both years were reduced. In other studies, early POST applications (2 to 8 cm) of fomesafen, imazaquin, acifluorfen, lactofen, and chlorimuron controlled wild poinsettia better than late POST applications (10 to 15 cm) in only one year. Soybean yields both years were generally similar regardless of herbicide application time.

Downy brome serves as an alternative host for Russian wheat aphid (RWA) in winter wheat. In field studies, downy brome infestations of 5 and 39 plants per m2 increased RWA-infested winter wheat tillers 1.4 to 2.8 times that seen in non-infested plots, respectively. RWA-infested winter wheat tillers were not reduced consistently by fertilization. Chlorpyrifos reduced the number of RWA-infested winter wheat tillers to 15 to 43% of untreated wheat. Insecticide efficacy was not influenced by downy brome infestation or by fertilizer either band- or broadcast-applied.

This study was designed to develop a protocol for using a biologically-based system to detect and tract airborne herbicides. Common bean, lentil, and pea were selected for their quasi-diagnostic sensitivity to chlorsulfuron, thifensulfuron, metsulfuron, tribenuron, paraquat, glyphosate, bromoxynil, 2,4-D, and dicamba. Plants were grown in the greenhouse at Prosser, WA, and placed at 25 exposure sites at weekly intervals between Apr. 2 and Oct. 15, 1991. After 1 wk of field exposure plants were brought back and observed for herbicide symptoms over a 28-d period. Symptoms that developed were compared with symptoms caused by disease, insects, adverse weather conditions, and herbicides applied at different rates under controlled conditions on these species. In addition, if herbicide symptoms were observed, herbicide spray records and weather data in the area were used in a computer model to determine the source of potential herbicide drift. This study demonstrates that indicator plant species selected for high sensitivity to herbicides can be used to monitor the occurrence of herbicide movement.

Field studies were conducted in 1991 and 1992 to determine potential soybean injury due to 2,4-D ester at 560, 1120, and 1680 g ai/ha applied 0, 7, and 14 d before planting (DBP). Delayed emergence and increased injury of soybean were observed as 2,4-D rate increased and interval between application and planting decreased. Delay in emergence ranged from 0 to 67% and 0 to 50% in 1991 and 1992, respectively. Injury at 15 days after planting (DAP) combined over years ranged from 0 to 61%. Minimal (0 to 8%) delay in emergence and minimal (0 to 5%) injury at 15, 30, 45, and 60 DAP occurred when 2,4-D at 560 or 1120 g/ha was applied 7 or 14 DBP. No significant yield reduction occurred due to 2,4-D rate, application timing, or their interaction.

Torpedograss has invaded fine turfgrasses in the Southern U.S. due to its tolerance to most commonly used turfgrass herbicides. Research was conducted to determine torpedograss and ‘Tifway’ bermudagrass tolerance to quinclorac and tank-mix combinations with other turf herbicides. Quinclorac rates in excess of 2.2 kg ai/ha were required for control (≥ 80%) of torpedograss. Sequential applications were more effective than single applications. Generally, sequential applications made 3 wk after the initial were more effective than delaying sequential applications until 4 wk after the initial application. Tifway bermudagrass injury from quinclorac applied at 4.5 kg/ha, or at 2.2 kg/ha followed by a sequential application of 1.1 or 2.2 kg/ha, was observed at 4 to 10 wk; however, turf recovered thereafter. Sequential applications of quinclorac plus imazaquin (1.1 + 0.6 kg/ha) increased torpedograss control (approximate 35%) as compared to quinclorac plus MSMA (1.1 + 1.1 kg/ha) but also decreased turf quality versus quinclorac applied alone or in combination with MSMA. Quinclorac applied at 2.2 kg/ha followed by 1.1 kg/ha applied 3 or 6 wk after the initial controlled torpedograss best with least reduction in bermudagrass quality. Quinclorac is the first herbicide reported to selectively control torpedograss in bermudagrass turf.

Quackgrass biotypes collected from 15 locations exhibited differential response to primisulfuron at 20 g ha−1 in field experiments at Hudson, NY during 1990 and 1991. Quackgrass control ranged from 23 to 100% 77 days after application (DAA) in 1990 and from 38 to 100% 88 DAA in 1991. The biotype from Montpelier, OH was the most tolerant both years. Differential response of quackgrass biotypes from five locations was confirmed in greenhouse experiments. The primisulfuron rate required to reduce shoot regrowth by 50% in the greenhouse was estimated at 15, 15, 17, 17, and 37 g ha−1 for biotypes from Amherst, MA; Mahnomen MN; Fargo, ND; State College, PA; and Montpelier, OH, respectively. Quackgrass shoot regrowth was reduced more when primisulfuron was applied with the linear alcohol ethoxylate additive 1412-70 compared with Scoil, Sylgard 309, Agridex, or X-77.

Preemergence (PRE) and postemergence (POST) herbicides were sequentially applied to common bermudagrass over a two-year period to determine the lowest herbicide rates required to maintain acceptable large crabgrass and goosegrass control. Large crabgrass control was consistently higher in late August when MSMA at 2.2 kg ha−1 was applied to plots previously treated with dithiopyr at 0.3 kg ha−1 (99%) in 1991, and either pendimethalin at 1.1 kg ha−1 (95%) or oxadiazon at 1.1 kg ha−1 (94%) in 1992 than when either herbicide was applied alone (≤ 79%). Goosegrass control was also higher in late August when MSMA plus metribuzin at 2.0 + 0.14 kg ha−1 was applied to plots treated with pendimethalin at 1.7 kg ha−1 (71%) in 1991, with oxadiazon at ≤ 2.2 kg ha−1 (≤ 89%) in 1992, and with dithiopyr at 0.4 kg ha−1 (≤ 96%) both years than when the herbicides were applied alone. Diclofop at 1.1 kg ha−1 applied alone as POST controlled ≥ 96% goosegrass throughout the two-year period.

PRE and POST herbicides were evaluated for their effects on root growth of Kentucky bluegrass and tall fescue turf. All PRE treatments, bensulide at 14.0 kg ai ha−1, DCPA at 11.8 kg ha−1, dithiopyr at 0.4 kg ha−1, pendimethalin at 1.7 kg ha−1, and prodiamine at 0.6 kg ha−1, inhibited root growth when cores, 10 cm in diam and 2.5 cm deep, of herbicide-treated Kentucky bluegrass were placed into pots of perlite. Only prodiamine inhibited tall fescue rooting. None of the PRE treatments reduced rooting of grasses when 10-cm diam and 16-cm deep cores were sampled from the field. No differences in rooting were observed among any of the POST treatments on either species.

Experiments were conducted in the greenhouse and the field to determine if a seaweed extract and its component alginates could enhance the activity of sethoxydim on barley (five- to six-leaf stage). In greenhouse trials, sethoxydim with 0.5% oil concentrate was applied at 0.05, 0.1, and 0.15 kg ai/ha; in field trials, sethoxydim with 0.5% oil concentrate was applied at 0.1, 0.2, and 0.3 kg/ha. In both sets of trials the seaweed extract was applied at a rate of 1 and 2 L/ha, and the alginates were applied at 250 and 500 g/ha. When either the seaweed extract, or the calcium ammonium salt of alginic acid was used as an adjuvant a significant increase in sethoxydim activity was usually observed. At the highest rates of these adjuvants, sethoxydim (0.2 kg/ha) activity increased from 59% control (1321 g/m2 fresh weight) with only oil concentrate, to 87% control (224 g/m2 fresh weight) with seaweed extract, or 89% control (184 g/m2 fresh weight) with the calcium ammonium salt of alginic acid. Sodium salts of alginic acid, both low and medium viscosity, were much less effective.

Field studies were conducted at Charleston, SC to evaluate the effects of six chemical treatments on bahiagrass and the potential of these treatments to reduce mowing operations. Sulfometuron, maleic hydrazide, and imazethapyr plus imazapyr, in decreasing order of effectiveness, were the most consistent treatments evaluated during the 2-yr study. Sulfometuron reduced bahiagrass vegetative height (23%) for 6 to 8 WAT and suppressed 87 to 92% of seedheads without adversely affecting turf quality. All treatments temporarily discolored turf; however, effects were not objectionable for medium- to low-quality turf settings. Sulfometuron, maleic hydrazide, and imazethapyr plus imazapyr controlled growth and maintained acceptable turf quality for an average of 9, 9, and 8 wk, respectively; thereby reducing mowing operations by an average 29%. Mefluidide plus fluazifop-P, mefluidide plus sulfometuron, and chlorosulfuron were the least effective and/or consistent treatments evaluated.

Sicklepod seed production and germination were evaluated in density and weed-free period studies without herbicide treatment and after imazaquin or metribuzin plus chlorimuron were applied PRE in soybean. Neither herbicide nor sicklepod density affected sicklepod seed germination, but delaying emergence of sicklepod from 0 wk to 8 wk after soybean emergence reduced subsequent sicklepod seed germination from 92% to 48%. Increasing sicklepod density from two to eight plants per row m reduced sicklepod seeds per plant, but increased sicklepod seeds per m2, regardless of herbicide. Extending the weed-free period from 0 to 8 wk reduced sicklepod seeds per plant and seeds per m2. Imazaquin and chlorimuron plus metribuzin reduced sicklepod seeds per m2 more than 50% at 0 or 2 wk weed-free intervals, compared with nontreated plants at these same intervals.

When formulated and sprayed in an invert emulsion (IE), conidia of the mycoherbicide, Colletotrichum truncatum, controlled hemp sesbania in the absence of dew. To optimize hemp sesbania control, formulation droplet size influence upon the pathogen's germination and pathogenicity was investigated. Conidia germination in manually produced IE droplets decreased from 46% to 5% as droplet diameter decreased from 2700 to 900 μm. Droplet size did not affect appressoria formation. On a per conidium basis, 900-μm droplets were more pathogenic to detached hemp sesbania leaves than were 2100-μm droplets. An air-assist spray system produced droplet spectra with volume median diameters of 421 and 104 μm, respectively. The spectrum of smaller droplets covered the target better than did that of larger droplets. When applied to whole hemp sesbania plants in greenhouse trials, conidia in the smaller and larger droplet spectra gave 90 and 94% control, respectively. Sufficient conidia germinated in IE droplets of a variety of sizes to control hemp sesbania excellently.

Field studies were conducted in 1986-87 and 1988-89 to compare chiseling, disking, and skewtreading to no-till and to compare 0.3 and 0.4 kg ai ha−1 pronamide applied before or after fall tillages for weed control in fallow. Chiseling or disking in October 1986 when weeds were emerged reduced the dry weight of volunteer wheat about 90% the following spring; however, only disking reduced the dry weight of downy brome 90%. Disking or skewtreading in October 1988 before weeds germinated reduced the dry weight of volunteer wheat about 95% 6 mo later, but none of the three tillages reduced the dry weight of downy brome. Pronamide applied at 0.3 and 0.4 kg ha−1 to emerged downy brome and volunteer wheat with either chiseling or disking before or after herbicide application reduced the dry weight of both species 90% or more 6 mo later compared with tillage alone. If weeds did not emerge until early November, then only pronamide at 0.4 kg ha−1 applied in no-till or after fall tillage controlled both species at least 90%.

In field studies conducted over two years, soybean cultivars ‘Deltapine 415’, ‘Forrest’, ‘Asgrow 6785’, ‘Centennial’, 'Sharkey’, ‘Terra Vig 616’, ‘Hartz 6686’, and ‘Pioneer 9791’ responded similarly to POST application of AC 263,222. With supplemental overhead irrigation of 5.1 cm weekly for 4 wk initiated 21 d after herbicide applications, mature soybean height for the cultivars averaged 18% less than that of the untreated check for 27 g/ha AC 263,222, but only 8% less when not irrigated. Although nonirrigated soybean seed yield following AC 263,222 application the first year was not reduced compared with the untreated check, with irrigation seed yield reductions of 12 and 32% were noted for 13 and 27 g/ha AC 263,222, respectively. Seed yield the second year was not negatively affected with herbicide application whether soybean was irrigated or not irrigated. For individual years, seed yield for the untreated irrigated and nonirrigated checks was similar. In the first year soybean yield following AC 263,222 at 13 and 27 g/ha with irrigation was 16 and 30% lower, respectively, than when soybean was not irrigated. Decreases in soybean 100-seed weight accompanied the yield reductions.

Field experiments were conducted in central Missouri in 1989 and 1990 to evaluate weed control practices in conjunction with cover crops and cover management systems in reduced tillage corn. There was no difference in weed control among soybean stubble, hairy vetch, and rye soil cover when averaged over cover management systems and herbicide treatments. However, mowed hairy vetch and rye covers provided greater weed control in the no-till plots than soybean stubble when no herbicide was used. Differences in weed control among cover management systems were reduced or eliminated when a PRE herbicide was applied. corn population and height were reduced by hairy vetch and rye soil cover. Corn grain yield was reduced in rye plots both years. There was no difference in grain yield between tilled and no-till plots.

Field applications of the rhizobacterium, Pseudomonas fluorescens strain D7 (D7), have selectively suppressed downy brome in winter wheat test plots. A phytotoxin produced by D7 inhibits downy brome root growth. An assay system was developed for future investigations of the mechanism of action of this and other phytotoxins that inhibit root growth. A crude preparation of the phytotoxin, cell-free supernatant (CFS), had little activity on downy brome root elongation in a sand-petri plate system. CFS was very active in a hydroponic system, in which a 6% (v/v) concentration inhibited root elongation within 1.5 h. Inhibition of root elongation was reversible in this system. Root elongation of downy brome seedlings resumed within 3 h after removal from a 9-h incubation in 8% CFS. CFS from genetic variants of D7 did not substantially inhibit root growth and a semi-crystallized precipitation product from D7 CFS inhibited root growth similarly to D7 CFS, indicating that the phytotoxin present in the CFS was responsible for growth inhibition.

Field investigations were conducted for 2 yr to characterize the responses of wheat, kidney bean, field corn, squash, okra, potato, and banana to soil-applied hexazinone, imazapyr, tebuthiuron, and triclopyr at rates used for control of woody perennial plants. Test species were planted at seven selected intervals through the first and second years after herbicide applications to assess residual herbicide activity. Tebuthiuron treatments of 2.2 kg ai ha−1 were not tolerated by any bioassay species planted 436 d after application (DAA). Only potato was tolerant of residual hexazinone 436 DAA. All species except banana generally tolerated residual imazapyr and triclopyr by the second growing season. Indigenous plants repopulated all herbicide-treated areas, except those treated with tebuthiuron, by the third growing season. Plots treated with tebuthiuron were 90% free of indigenous plants 40 mo after herbicide application.

Woolly cupgrass control with acetochlor, alachlor, and metolachlor in corn was evaluated at Stratford, IA from 1985 through 1990. Averaged over application techniques, acetochlor at 3.4 kg/ha controlled more than 85% of woolly cupgrass five out of six years, whereas alachlor at 4.5 kg/ha and metolachlor at 3.4 kg/ha controlled more than 85% of this weed one and two years out of six, respectively. Herbicide incorporation did not consistently improve woolly cupgrass control. PRE applications were more effective than incorporated treatments in years with greater than 7 mm rainfall occurring within 3 d after application.

The acetolactate synthase-inhibiting herbicides chlorimuron and imazaquin, and the diphenylether herbicides acifluorfen and lactofen, were applied alone and in all possible combinations to the foliage of common cocklebur, pitted morningglory, and prickly sida to evaluate interacting effects on absorption and translocation. The addition of unlabeled acifluorfen to 14C-chlorimuron increased absorption in common cocklebur, pitted morningglory, and prickly sida. Lactofen also increased absorption of 14C-imazaquin in all species. Conversely, imazaquin reduced absorption or translocation of 14C-acifluorfen in common cocklebur or pitted morningglory, respectively. In all species, absorption was lower when unlabeled chlorimuron or imazaquin was combined with 14C-lactofen than when applied alone.

Studies were conducted for 3 yr to evaluate herbicides and herbicide combinations for triazine-resistant smooth pigweed (TR-AMACH) control in field corn. Of the PRE treatments, combinations of atrazine plus acetochlor, metolachlor plus dicamba, and atrazine plus alachlor provided the most complete control of this weed (77 to 81%). The best early postemergence (EP) combination was pendimethalin plus atrazine plus dicamba (93% control). Pyridate plus atrazine applied POST provided a four-site average of 98% control. The most effective sequential herbicide treatments consisted of either metolachlor or pendimethalin PRE followed by POST treatments containing either pyridate, thifensulfuron, bromoxynil, or dicamba.