The efficacy of reduced rates of metolachlor plus cyanazine for weed control in sweet corn was evaluated over a 2-yr period. Early postemergence (POST) and POST herbicide applications at reduced rates gave control of broadleaf weeds comparable to control at the 1 × rate, except for the early POST application at the ¼ × rate in 1993. Preplant incorporated (PPI) and preemergence (PRE) herbicide applications at reduced rates gave poor broadleaf weed control, except for the PRE application at the ½ × rate in 1993. Early POST applications at the ¼ × rate resulted in significantly reduced grass control in 1994, while POST applications at the ¼ × rate gave significantly reduced grass control both years. Generally, POST applications controlled broadleaf weeds better than early POST applications, while grass control with early POST applications was superior to POST applications at reduced rates. Preemergence and PPI applications at reduced rates gave poor broadleaf weed control but satisfactory grass control. Preplant incorporated applications at reduced rates resulted in reduced yield both years, while PRE applications at reduced rates reduced yield only in 1994. Early POST and POST applications at reduced rates did not affect sweet corn yield. The addition of adjuvants to the ¼ × application rate had no effect on weed control or yield.

The Southern Weed Science Society has conducted an annual survey of the most troublesome weeds in several major crops since 1971. The objective of this summary was to characterize shifts in weed populations over a 22-yr period in four major agronomic crops. For corn, soybean, cotton, and peanut, the largest increases in rank as the most troublesome weeds were found with sicklepod and bermudagrass. The largest decreases were found with johnsongrass, crab-grasses, and common cocklebur. Morningglories and nutsedges remained relatively constant weed problems over the 22-yr period. Sicklepod, nutsedges, and morningglories were the three most troublesome weeds averaged over all crops because they are so well established and relatively difficult to control. Pigweeds (Palmer amaranth, sandhills amaranth, tumble pigweed, and water-hemps) have become increasingly important in soybean, peanut, and cotton in a limited number of states.

Three Group V soybean cultivars were grown in the greenhouse to quantify interference when planted at various intervals with sicklepod, and the effects of chlorimuron and imazaquin POST on this interspecific interference. Soybean shoot height or fresh weight was not affected by sicklepod interference when sicklepod was planted 10 d after soybean in most cases. ‘Asgrow 5979’ soybean shoot height was not reduced when planted with sicklepod, but was reduced when planted 10 d after sicklepod and no herbicide treatment was added. When sicklepod was planted 10 d before Asgrow 5979 and ‘9592 Pioneer’ soybean, shoot height was reduced more than ‘Hutcheson,’ regardless of herbicide treatment. The cultivar 9592 Pioneer was more effective in reducing sicklepod shoot height than Asgrow 5979 when no herbicide treatment was used. Chlorimuron or imazaquin had little or no effect on sicklepod interference with soybean under these conditions.

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.

Eleven sweet corn hybrids representing a wide range of injury with imazethapyr in a greenhouse study were evaluated in simulated imazethapyr carryover field studies conducted at Arlington, WI. Imazethapyr at 0, 11, 22, and 44 g ai/ha was applied and incorporated 15 d prior to planting sweet corn. The greatest injury occurred 28 d after planting, with reductions in height ranging from 0 to 25%. Reductions in corn ear yields were similar all years for 10 of the 11 hybrids. Reductions in corn ear yield for ‘Crisp N’ Sweet 710,’ ‘Cornucopia,’ ‘Super Sweet Jubilee,’ ‘Excellency,’ and ‘DMC 20–35′ were less than for ‘Natural Sweet 9000,’ ‘Jubilee,’ ‘Zenith,’ ‘Green Giant 40,’ and ‘Green Giant 97.’ In 1992, plots were prepared for an actual imazethapyr carryover study by applying imazethapyr PPI at 70 and 140 g/ha and planting soybean. In 1993, four sweet corn hybrids were planted. Corn ear yield of Green Giant 97 was reduced following previous-year applications of 140 g/ha imazethapyr. Corn ear yields of Excellency, Super Sweet Jubilee, and Jubilee were not reduced at either actual carryover rate. These studies indicate variability among sweet corn hybrids in susceptibility to imazethapyr. Greenhouse results were indicative of field responses and may be useful as a rapid test to determine hybrid susceptibility.

Dodder is a serious parasitic weed of cranberry bogs. Investigations were undertaken to determine if applications of sand to cranberry bogs might be useful as a control strategy for dodder. Sand is regularly applied to bogs as a cultural practice. In greenhouse studies, applications of sand reduced the seedling emergence, but did not affect survival time of dodder seedlings. At least 2.5 cm of sand was needed to reduce the emergence of dodder seedlings. Sanding may be used as part of a program consisting of combinations of multiple management methods directed toward the control of dodder. In addition, potential exists for using sand as a nonchemical means for obtaining some control, should present herbicidal control methods become unavailable.

The objective of this paper was to evaluate the effect of preplant applications of trifluralin on barley stand and yield, and control of grass weeds in field experiments during 1992 and 1993. Factors examined were: (1) crop planting patterns (conventional drill with rows 15 cm apart and deep-seeder drill with rows 25 cm apart), (2) herbicide application times (22 d before sowing and immediately before sowing), and (3) herbicide application. During 1993, hand-weeded plots also were established. Trifluralin applied preplant at 528 g ai/ha reduced weed density and biomass. Weed control was higher under conventional planting than under the deep planting pattern, and there was no effect of the time of application on herbicide efficacy. There was no herbicide injury to the crop, and grain yield was higher in treated than in untreated plots due to successful weed control.

Field experiments were conducted in 1994 and 1995 to determine if the sodium salt of pyrithiobac or bromoxynil applied in a low-volume, air-assist spray system controlled entireleaf morningglory, pitted morningglory, and smallflower morningglory as well as treatments applied with a conventional hydraulic fan spraying system, and to determine if herbicide rates could be reduced when using the low-volume spraying system. Pyrithiobac at 0.035 and 0.071 kg ai/ha and bromoxynil at 0.56 and 1.12 kg ai/ha were applied alone and in combination with DSMA at 1.7 kg ai/ha or MSMA at 1.7 kg ai/ha. Spraying systems were calibrated to deliver 26 L/ha and 140 L/ha for the low-volume and conventional systems, respectively. No significant differences in control were noted between low-volume and conventional spray systems when herbicides were applied at the suggested use rates of 0.071 and 1.12 kg ai/ha for pyrithiobac and bromoxynil, respectively. Morningglory control was reduced when pyrithiobac and bromoxynil were applied at one-half the suggested use rate regardless of the spraying systems. Bromoxynil alone generally controlled pitted and entireleaf morningglory better than pyrithiobac alone regardless of rate and application method. However, pyrithiobac generally provided better control of smallflower morningglory than bromoxynil. Adding MSMA or DSMA to bromoxynil and pyrithiobac increased control of both weed species.

Releasing Tyta luctuosa on hedge bindweed in cornfields did not increase defoliation more than endemic herbivores. Larvae of T. luctuosa were rarely found after release, indicating they suffered high mortality or dispersed from test plants. Eleven species of endemic insects were found feeding on bindweed, all of which are known to be generalists feeding, in some cases, on economically important plants. Oidaematophorus monodactylus (L.) (Lepidoptera: Pterophoridae) was the most damaging species to the bindweed.

In field studies in 1991, 1992, and 1993, rimsulfuron at 26 and 35 g ai/ha, sequentially at 26 g/ha, at 26 g/ha plus metribuzin at 280 g ai/ha, and metribuzin at 280 g/ha were evaluated POST for weed control in transplanted ‘Agriset’ tomato. Common lambsquarters was controlled by rimsulfuron at 35 g/ha. Rimsulfuron plus metribuzin gave consistent control of common ragweed, but jimsonweed control was inconsistent and goosegrass control was generally low. Rimsulfuron treatments caused slight (< 12%) temporary injury to new terminal growth of tomato. Yield of tomato fruit was consistently high in the metribuzin, metribuzin plus rimsulfuron, and rimsulfuron sequential treatments. In greenhouse studies, giant foxtail and large crabgrass control by rimsulfuron was above 95 and 85%, respectively, but goosegrass was not controlled. Height of four tomato cultivars was not reduced, but dry weight of ‘Floradade’ and ‘Sunbeam’ was reduced by rimsulfuron.

Experiments were conducted in 1991 and 1992 to evaluate the weed control effectiveness from several rates of AC 263,222 applied PPI and PRE (36 and 72 g ai/ha), early POST (EPOST) (18, 36, 54, or 72 g/ha), POST (18, 36, 54, or 72 g/ha), and EPOST followed by (fb) POST (27 fb 27 g/ha or 36 fb 36 g/ha). These treatments were compared to the commercial standard of bentazon at 0.28 kg ai/ha plus paraquat at 0.14 kg ai/ha EPOST fb bentazon at 0.56 kg/ha plus paraquat at 0.14 kg/ha plus 2,4-DB at 0.28 kg ae/ha. Application method had little effect on weed control with AC 263,222. In contrast, application rate affected control. Purple nutsedge, yellow nutsedge, prickly sida, smallflower morningglory, bristly starbur, common cocklebur, and coffee senna were controlled at least 82% with AC 263,222 at 36 g/ha (one-half the maximum registered use rate) regardless of application method. AC 263,222 at 72 g/ha (registered use rate) controlled sicklepod 84 to 93%, Florida beggarweed 65 to 100%, and Ipomoea morningglory species 89 to 99%. A single application of AC 263,222 at 36 g/ha or more controlled all weeds (with the exception of Florida beggarweed) as well or greater than sequential applications of bentazon plus paraquat fb bentazon, paraquat, and 2,4-DB. All rates of AC 263,222 applied POST and all application methods of AC 263,222 at 72 g/ha had better yields than the pendimethalin control.

Pesticide leaching experiments using widely spaced sampling sites may not adequately characterize chemical leaching behavior such as nonuniform flow between sampling points. We conducted this study to determine the three-dimensional variability of atrazine and chloride movement within a small volume of soil (2,700 cm1) under field conditions. A 1-m2area of Williamson silt loam (coarse-silty, mixed, mesic, Typic Fragiochrept) was sprayed uniformly with atrazine (1.1 kg ai/ha) and chloride (80 kg/ha). We used the Leaching Estimation and Chemistry Model (LEACHM) to simulate chemical movement. After 6.5 cm of rainfall during a 29-d period, we sampled 36 squares (5 by 5 cm) in the central 30- by 30-cm portion of the treated area at six depth increments (0 to 2, 2 to 5, 5 to 10, 10 to 15, 15 to 21, and 21 to 30 cm) and determined atrazine and Cl−concentrations. We recovered 26% of the applied atrazine and 138% of the applied chloride. Low atrazine recovery may have been due to leaching beyond 30 cm and/or degradation while excess chloride recovery is attributed to high background concentrations. Coefficients of variation (CVs) for atrazine significantly increased with depth and ranged from 26 to 353%, while CVs for Cl−were independent of depth and ranged from 32 to 66%. Derived atrazine concentration isograms illustrated highly nonuniform herbicide transport. Although LEACHM overestimated atrazine movement in the upper 15 cm, it was fairly accurate in the lower 15 cm. The overall trend in Cl−flow was adequately predicted, even though the predicted Cl−concentrations were underestimated. LEACHM could not accurately predict nonuniform flow or the variability in solute concentrations between points. However, its prediction of the atrazine center of mass (about 4.7 cm) agreed well with the derived isograms. These findings demonstrate that localized nonideal solute transport may be missed in larger sampling schemes and in simulation models.

A seedling bioassay was used to determine the response of triallate-resistant (R) and -susceptible (S) wild oat populations to difenzoquat and EPTC. The bioassay, based on seedling shoot length at 10 d after treatment, provided a reliable and rapid means of determining if wild oat populations were resistant to difenzoquat. Using a bioassay concentration of 15 ppm difenzoquat, it was possible to identify populations that were resistant to the recommended foliar-applied rate (0.85 kg ai/ha). Expected herbicide dosages that reduced shoot length by 50% (ED50) derived from nonlinear regression analysis indicated three and two levels of response to difenzoquat among eight S and seven R populations, respectively, indicating within population variability in their response to difenzoquat. Of the populations tested, none was resistant to EPTC. On the contrary, some R populations had lower ED50 values than did S populations, suggesting an increased sensitivity to EPTC.

Spurred anoda is an increasing weed problem in Colorado pinto bean production. This research was designed to evaluate reduced rates of bentazon and imazethapyr applied at various times for spurred anoda control and profitability. In 1993, spurred anoda control with early applications of either bentazon or imazethapyr was superior to late applications. Bentazon provided better spurred anoda control than imazethapyr in June. Spurred anoda control in 1993 was better than in 1994 due to late-emerging weeds and herbicide treatments not providing residual control. In 1994, bentazon controlled spurred anoda better than imazethapyr 1 and 3 wk after late POST, but no treatment provided commercially acceptable full-season control. The number of treatments with gross margins greater than the untreated check increased as pinto bean prices increased, but ranking of gross margin did not change due to pinto bean prices.

Field studies conducted in 1991 to 1993 evaluated the efficacy of clomazone applied at various timings for weed control in soybean. Clomazone applied 45, 30, 15, or 0 days prior to planting (DPP) provided season-long control of velvetleaf and giant foxtail. In 1991 and 1992 clomazone alone 30 and 45 DPP failed to control redroot pigweed. Clomazone alone 45 DPP failed to control common lambsquarters. In 1991 and 1992 clomazone at 0.84 kg/ha plus metribuzin applied 45 DPP failed to control redroot pigweed. The addition of metribuzin plus chlorimuron to the above clomazone treatments resolved these weed control deficiencies. Weed control in 1993 was nearly complete across all clomazone treatments. In 1993 clomazone treatments which included metribuzin or metribuzin plus chlorimuron applied PPI or PRE reduced yield. Herbicide injury is the likely cause of this reduction because most treatments in 1993 provided 99% control of all weed species.

Angora goats have been suggested as biological control agents for leafy spurge, especially in environmentally sensitive or limited access areas. Dietary preferences and dietary nutritive content of herded Angora goats were evaluated over a two-year period in North Dakota. Relative preferences of forages were evaluated by comparing botanical composition of diets as determined by microhistological analysis of fecal samples to forage availability in the field. Leafy spurge and shrubs comprised the largest percentage of goat diets throughout each grazing season. Goats preferred leafy spurge and shrubs at all times and avoided most cool-season grass species. The nutritional requirements of Angora goats nursing kids were met throughout the grazing season. Use of Angora goats is another tool available to land managers to manage leafy spurge infestations in the Northern Plains.

‘Lemberger’ wine grape response to fall application of selected herbicides applied at simulated drift rates was studied in 1992 and 1993. Chlorsulfuron, thifensulfuron, 2,4-D, glyphosate, bromoxynil, and 2,4-D plus glyphosate were applied at 1/100, 1/33, 1/10, and 1/3 of a selected maximum rate for use in wheat or fallow. All herbicides, except bromoxynil and thifensufluron, caused symptoms on grapevines at the highest rate during the spring following fall application. The most severe symptoms were caused by 2,4-D and 2,4-D plus glyphosate, whereas the least symptoms were caused by chlorsulfuron and glyphosate. The severity of symptoms increased and shoot growth, leaf area, internode length, and dry cane weight decreased as the rates of 2,4-D and 2,4-D plus glyphosate increased. Chlorsulfuron and glyphosate reduced the growth of grapevines only when applied at the highest rate during the fall. The data show that exposure of wine grapes to 2,4-D or 2,4-D plus glyphosate during the fall can adversely affect the growth of grapevines the following spring.

An experiment was conducted at four locations in North Carolina during 1994 and 1995 to evaluate weed control, cotton yield, fiber quality, and net returns in no-tillage bromoxynil-tolerant cotton. The experiment focused on using bromoxynil or pyrithiobac sodium applied early POST over-the-top as alternatives to fluometuron plus MSMA applied early POST directed. Fluometuron plus MSMA was more effective than bromoxynil or pyrithiobac sodium on tall morningglory, large crabgrass, goosegrass, and broadleaf signalgrass. Bromoxynil and fluometuron plus MSMA were similarly effective on common lambsquarters, common ragweed, and eclipta and more effective than pyrithiobac sodium. Pyrithiobac sodium and fluometuron plus MSMA were similarly effective on smooth pigweed and Palmer amaranth and more effective than bromoxynil. Prickly sida control by bromoxynil and pyrithiobac sodium was equal to or greater than control by fluometuron plus MSMA. All early POST herbicides controlled pitted morningglory similarly. Regardless of the early POST herbicides used, fluometuron applied PRE and cyanazine plus MSMA applied late POST directed increased control of most weeds and increased cotton yield and net returns. Bromoxynil and pyrithiobac sodium effectively substituted for fluometuron plus MSMA only in systems that included fluometuron applied PRE and cyanazine plus MSMA applied late POST directed. Effects of herbicide systems on cotton fiber quality were minor.

Seven postemergence (POST) herbicides were evaluated alone and in various mixtures for Palmer amaranth control in peanut from 1992 through 1994. AC 263,222 at rates as low as 0.04 kg/ha controlled ≥ 95% Palmer amaranth. Imazethapyr at rates of 0.05 to 0.07 kg/ha controlled ≥ 90% Palmer amaranth in 2 of 3 yr. Acifluorfen alone or in combination with bentazon or 2,4-DB and lactofen alone controlled > 90% Palmer amaranth in 2 of 3 yr. Bentazon or pyridate failed to provide adequate control (≤ 60%), while 2,4-DB provided good control (80%) in only 1 of 3 yr.

Farmers need information on herbicide technology and crop performance to assess the profitability of new herbicide-resistant crop technologies. First-generation imazethapyr-resistant corn hybrids evaluated at the University of Wisconsin yielded less than other commercial hybrids. To determine if this resistance trait affected yield or agronomic traits, 10 near-isogenic pairs of imazethapyr-resistant and -susceptible corn hybrids were compared. Whether treated with imazethapyr or not, imazethapyr-resistant hybrids yielded the same when averaged across hybrids, although yield varied among a few individual hybrids within single experiments. Seven of the imazethaypr-resistant hybrids yielded the same, two yield more, and one yielded less than their susceptible near-isogenic counterpart during eight site-years. Grain moisture was not affected, but imazethapyr-resistant hybrids had fewer broken stalks than did susceptible hybrids. The imazethapyr resistance trait does not appear to affect yield potential, but the backcrossing procedure may have caused early resistant hybrids to lag behind in yield compared to other new hybrids.