The efficacy of two applications of several PRE herbicides for extended control of long-stalked phyllanthus and leafflower were evaluated under container nursery conditions at two climatically different sites in Florida. Prodiamine at 4.5 kg ai/ha provided the longest and most consistent reductions in number, percent coverage (visual) of the medium, and dry weight of both species. Ten weeks of excellent PRE control (percent medium coverage ≤ 10%; number of weeds reduced by ≥ 70%) of both species was obtained at one site after the first and second applications of prodiamine at 2.2 or 4.5 kg ai/ha; two applications were required at the second site for similar control. Rates of the other herbicides were generally too low for excellent control of both species after one application, the exceptions being dithiopyr at 4.5 kg ai/ha and the preformulated combination of isoxaben and oryzalin (1.1 and 3.4 kg ai/ha, respectively). These herbicides provided good (10% < percent medium coverage ≤ 20%; number of weeds reduced by ≥ 70%) to excellent PRE control of long-stalked phyllanthus after the first and second applications at one site. Percent coverage of the medium by either species in untreated containers was 96 to 100%.

Field studies were conducted to determine the effect of soybean cultivar, tillage, and rye mulch on sicklepod growth. Early-season sicklepod height was not affected by tillage or mulch. Sicklepod was tallest when grown with ‘Centennial’ or ‘Biloxi,’ the tallest cultivars, and shortest when grown with a dwarf isoline of ‘Tracy M,’ the shortest cultivar. Soybean competition reduced early-season weed density by 30 to 50%, depending on the cultivar. Centennial and dwarf Tracy M caused a 30% reduction in early-season sicklepod biomass while ‘Sharkey’ and Biloxi reduced sicklepod growth by 40%. By late-season, sicklepod biomass reduction ranged from 18% (Tracy M) to 55% (Biloxi) and was directly related to soybean cultivar height. Mulch or no-tillage independently reduced sicklepod biomass.

The combination of certain herbicides with insecticides can inhibit crop growth. Greenhouse studies were conducted to evaluate interaction effects of herbicides and insecticides with/without protectant, on corn and weed species. ‘Northrup King 9283’ hybrid corn showed greater sensitivity to acetanilide herbicides than ‘Cargill 7567.’ Neither the insecticides terbufos nor isazofos appeared to enhance this sensitivity. Both hybrids were sensitive to the combination of chlorimuron, nicosulfuron, or primisulfuron with terbufos. Cargill 7567 was more tolerant than Northrup King 9283 to the growth inhibiting interaction of sulfonylurea herbicides with terbufos. Imazaquin at 70 g/ha reduced height of Northrup King 9283 corn, but there was no interaction with terbufos. The protectants CGA-154281 and NA reduced corn injury from metolachlor and the combination of nicosulfuron and primisulfuron with terbufos, respectively. Nicosulfuron and primisulfuron treatments combined with metolachlor showed less corn injury than metolachlor alone, but these herbicides increased corn injury when combined with terbufos. The inclusion of terbufos did not enhance primisulfuron activity on barnyardgrass, giant foxtail, or velvetleaf.

HERB, a computer-based expert system for soybean weed management developed at North Carolina State University, was evaluated for managing weeds under Georgia conditions. The project was initiated in two phases: a) training Cooperative Extension county agents followed by evaluation in six Georgia counties and b) revision, licensing, and distribution across the state. Field evaluations indicated that HERB was not highly accurate for predicting final yield loss because of weed species senescence and environmental extremes later in the growing season. HERB generally provided a reasonable prediction for a positive economic return due to treatment approximately 60% of the time. Accuracy was directly dependent upon the accuracy of weed-free yield estimates and extremes in growing conditions. HERB should not be the sole source of weed management information but may be useful to producers and county agents where mixed or low populations of weeds exist. The program was distributed statewide in 1993 after revision, duplication, and training was completed.

The tolerance of canola and wild mustard to postemergence HOE 075032 was investigated in greenhouse and field studies. In the greenhouse, the tolerance of canola to HOE 075032 applied at the 2 Ho 3-leaf stage was approximately twice the tolerance of wild mustard. In the field, HOE 075032 applied at 5 and 10 g ai/ha at the 2 to 3-leaf stage reduced wild mustard plant density and fresh weight by over 95%. Wild mustard contamination in canola seed was reduced from 45 to less than 1%. Application of HOE 075032 at 5 g/ha significantly increased canola yield and fresh weight in each year. Canola yield increases of 25, 139, and 86% were observed for the 5 g/ha treatment in 1991, 1992, and 1993, respectively. HOE 075032 could provide a postemergent alternative to the existing herbicide for wild mustard control in canola.

AAL-toxin, produced by Alternaria alternata, was investigated for its phytotoxic effects on 86 crop and weed species. On susceptible tomato leaf discs, AAL-toxin caused electrolyte leakage and chlorosis at 0.01 μM in 24 h. Plants tested exhibited a range of response. AAL-toxin damaged sensitive plants at 5 μM while other plants showed minimal damage at > 1000 μM. Cotton and the important weeds, Canada thistle, field bindweed, and velvetleaf were largely unaffected. Monocots tested were largely immune.

Experiments were conducted over a 3-yr period to determine the rate and frequency of herbicide application needed to control common bermudagrass growing in a tall fescue turf. In Experiment I, fenoxaprop plus ethofumesate applied at 0.2 + 1.7 kg/ha in late April and repeated at the same rate at 3- to 4-wk intervals for a total of five applications resulted in excellent (≥ 97%) common bermudagrass suppression. The suppression was higher from combination of fenoxaprop and ethofumesate than when fenoxaprop was applied at 0.2 kg/ha in five applications (≤ 67%). In Experiment II, fenoxaprop plus ethofumesate applied at 0.2 +1.7 kg/ha required four applications per year to effectively suppress common bermudagrass (95%) in 1993, but five applications were needed to obtain similar suppression (96%) in 1994. Tifway bermudagrass was not suppressed during 1994 when fenoxaprop plus ethofumesate were applied at 0.2 +1.7 kg/ha in each of five applications (30%). In most instances, fenoxaprop plus ethofumesate applied at 0.2 +1.7 kg/ha caused only slight to moderate (< 30%) injury to tall fescue for 1 to 2 wk after treatment. When injury occurred, it was temporary as the turf fully recovered within 2 to 3 wk after treatment. An exception occurred in early July 1992 when fenoxaprop plus ethofumesate caused 44% injury to tall fescue after the four applications.

Laboratory and greenhouse studies examined effects of atrazine, alachlor, and metolachlor on growth and colonization of grain sorghum roots by Macrophomina phaseolina, causal fungus for charcoal rot disease. In laboratory studies, all three herbicides reduced fungal colony diameter and increased production of microsclerotia. Alachlor and metolachlor reduced germination of fungal microsclerotia. Atrazine did not affect microsclerotia germination, but lessened the effects of alachlor and metolachlor on germination when applied in combination. In greenhouse studies, atrazine reduced numbers of M. phaseolina microsclerotia recovered from soil after 8 wk, and this resulted in reduced colonization of roots by this fungus at harvest. Colonization of grain sorghum roots by M. phaseolina was not affected by alachlor or metolachlor. Grain sorghum growth was reduced by atrazine at all intervals and by alachlor and metolachlor at harvest, despite use of seed safened with cyometrinil.

The tolerance of four established seeded common bermudagrass types to PRE and POST herbicides was evaluated. Pendimethalin at 3.4 kg ai/ha, oryzalin at 3.4 kg ai/ha, and dithiopyr at 0.8 kg ai/ha suppressed the quality of bermudagrass 8 to 16% more than oxadiazon at 4.5 kg ai/ha and prodiamine at 0.8 kg ai/ha. When interactions of PRE herbicide by bermudagrass cultivars occurred, oxadiazon, prodiamine, and pendimethalin suppressed the quality of ‘common’ and ‘Sahara’ 18 to 20% more than ‘Tropica’; oryzalin suppressed the quality of common and Sahara 11 to 18% more than Tropica; and dithiopyr suppressed the quality of common and Sahara 9% more than Tropic and ‘Cheyenne.’ The quality of Cheyenne treated with either oxadiazon, prodiamine, or pendimethalin was generally intermediate to the other cultivars. When POST herbicides by bermudagrass cultivar interactions occurred, MSMA plus metribuzin applied at 2.2 + 0.1 kg ai/ha injured common and Sahara an average of 10 to 12% higher than Tropica during 1993 and 1994. Diclofop applied at 1.1 kg ai/ha and dicamba applied at 0.6 kg ae/ha injured common 9 to 12% higher than Tropica. There was no difference in injury to cultivars when treated with 2,4-D plus mecoprop plus dicamba at 1.1 + 0.6 + 0.1 kg ae/ha. In general, Tropica was affected least by PRE and POST herbicide treatments, while common and Sahara cultivars were affected the most.

Six commercial sweet potato clones were evaluated in field and greenhouse studies for the ethylthio analog of metribuzin (ethyl-metribuzin) tolerance. ‘Southern Delite’ was most tolerant in field studies and ‘Cordner’ the most tolerant in the greenhouse. ‘White Delite’ was the most susceptible clone in the field and greenhouse. Considering the rates used in this study, all the sweet potato clones generally were tolerant to ethyl-metribuzin. When averaged over all clones, sweet potato injury increased as the ethyl-metribuzin rate increased from 1.6 to 3.2 kg/ha but injury decreased as the season progressed and was minimal in late season. Ethyl-metribuzin did not reduce marketable yields at Clayton, NC. At Clinton, NC, ethiozin PRE, POST, or PRE followed by POST at 3.2 kg/ha or PRE at 1.6 kg/ha reduced yield.

Thirteen field experiments were conducted to evaluate quinclorac for cheat control in hard red winter wheat. Cheat control with quinclorac was variable. Quinclorac at 560 and 1120 g a.i./ha applied to tillered wheat controlled cheat 93 to 100% at four sites. In contrast, pooled over four other experiments and four application times, quinclorac at 420 g/ha and 560 g/ha controlled cheat only 20 and 31%, respectively. Quinclorac at 420 g/ha plus chlorsulfuron:metsulfuron (5:1) at 35 g a.i./ha applied PRE increased wheat yield 28% at one of three sites. At two of these sites, averaged over chlorsulfuron:metsulfuron rates of 0, 18, and 35 g a.i./ha, quinclorac at 280 and 420 g/ha applied POST, increased wheat yield 32 to 112%. In two cultivar tolerance experiments, quinclorac treatments did not damage any cultivar. Pooled over cultivars, yields were increased 7 and 10% when quinclorac at 280 and 560 kg/ha was applied, respectively. In a greenhouse experiment, quinclorac plus dicamba or esfenvalerate consistently reduced the leaf area of cheat in a manner suggesting synergistic effects. Of eight adjuvants evaluated in a laboratory experiment, only quinclorac plus the adjuvant BCH 864 01S reduced cheat leaf area more than quinclorac alone.

Trifluralin is used for weed control in wheat but may reduce vegetative growth and yield. Postemergence (POST) herbicides may cause additional plant stress to trifluralin-stressed wheat. Field studies at Groton, SD in 1991 and 1992 and at Highmore, SD in 1992 evaluated the effects of 2,4-D-amine, difenzoquat, metsulfuron, and a combination of fenoxaprop-ethyl + 2,4-D-ester + MCPA-ester on hard red spring wheat cultivars ‘2375,’ ‘Prospect,’ and ‘Butte 86’ seeded in areas treated with preplant incorporated trifluralin either in the spring before seeding (0.56 kg ai/ha) or the previous year (1.12 or 2.24 kg ai/ha). Trifluralin applied alone in the spring, and followed by some POST herbicides, reduced shoot dry weight and grain yield. Trifluralin reduced the yield of Prospect the most and the yield of 2375 the least. Yields of trifluralin-treated wheat were reduced 23% by metsulfuron and 14% by fenoxaprop-ethyl + 2,4-D + MCPA compared to yields of wheat treated with only the respective POST herbicide. Yields were not reduced with any trifluralin-POST herbicide combination when trifluralin was applied a year prior to seeding wheat.

Field experiments conducted in 1992 and 1993 evaluated differential response of 20 soybean cultivars to POST application of AC 263,222 or chlorimuron, as influenced by soil moisture. Natural rainfall was supplemented with overhead sprinkler irrigation to achieve three moisture regimes: excessive (12.5 cm/wk), optimum (5 cm/wk), and low (non-irrigated). Chlorimuron and AC 263,222 injured soybean. Excessive moisture did not increase soybean injury with chlorimuron for any of the cultivars tested compared to optimum moisture; however, 17 of 20 cultivars were injured more by AC 263,222 in combination with excessive moisture than optimum moisture. AC 263,222 reduced the height of five cultivars. Photosynthetic rate of several cultivars was reduced by both AC 263,222 and chlorimuron. Neither herbicide affected the number of nodes per main stem or seed weight; however, pod numbers were reduced for several cultivars with both herbicides. In the low moisture regime, AC 263,222 delayed the maturity of 18 of 20 cultivars with ‘Hutcheson’ maturity delayed 7.1 d. Excessive moisture when combined with AC 263,222 reduced yields for 12 cultivars, compared to five cultivars with chlorimuron. Under optimum moisture conditions, AC 263,222 reduced the yield of 10 cultivars, whereas chlorimuron reduced the yield of 9 cultivars. Low moisture stress only resulted in a yield reduction with 3 cultivars treated with AC 263,222.

Field experiments conducted at three locations in Georgia during 1991 and 1992 evaluated AC 263,222 and imazethapyr rates alone at 18, 36, 54, or 72 g ai/ha and in mixture for a total of 36, 54, or 72 g/ha of herbicide applied early-POST for weed control, peanut injury, and yield. An application of AC 263,222 at 72 g/ha controlled (> 90%) Ipomoea morningglories, sicklepod, smallflower morningglory, and yellow nutsedge in all experiments and coffee senna and Florida beggarweed at Chula in 1991. Bristly starbur was controlled at least 90% with AC 263,222 at 72 g/ha at Tifton in 1991, but less than 62% at Chula in 1991. Imazethapyr applied at 72 g/ha controlled coffee senna, Ipomoea morningglories, and smallflower morningglory at least 85%, but did not control Florida beggarweed or sicklepod and provided inconsistent bristly starbur and yellow nutsedge control. Bristly starbur and yellow nutsedge control was increased with several AC 263,222 plus imazethapyr mixtures. High peanut yields comparable to the standard were indicative of the AC 263,222 rate applied whether alone or in mixture with imazethapyr.

Grass and broadleaf herbicides are available for effective, single-application total postemergence weed control in corn. Field experiments were conducted in 1992 and 1993 on sites with dense natural weed infestations to determine the effects of weed interference prior to herbicide application on corn yield. Nicosulfuron plus bromoxynil was applied at 5-, 10-, 15-, or 20-cm weed canopy heights in plots with or without weed interference. Crop injury was more severe when herbicides were applied to smaller corn. Herbicide applications made to 5-, 10-, or 15-cm tall weeds provided nearly complete weed control. Weed interference did not reduce corn height or grain yield when postemergence applications were made to weeds 10 cm or less in height. Weed interference reduced corn height and grain yield in 1992 when applications were made to 15-cm tall weeds even though weed control was nearly complete. Weed control was incomplete and corn height and grain yield were reduced when applications were delayed until weeds were 20 cm tall.

Acifluorfen, lactofen, chlorimuron, thifensulfuron, imazethapyr, and imazaquin were evaluated for control of Palmer amaranth, common waterhemp, redroot pigweed, and tumble pigweed at three application timings in field and greenhouse experiments. Results from field studies indicated that most herbicides provided greater than 90% control of common waterhemp, redroot pigweed, and tumble pigweed regardless of time of application. Palmer amaranth was the most difficult species to control, and only thifensulfuron and imazethapyr provided greater than 80% control at all application timings. In the greenhouse experiment, herbicides were applied when pigweeds averaged 10 cm, 20 cm, and 30 cm in height. Results were similar to the field experiment, except that common waterhemp was more difficult to control.

The effects of five soil fungi, endemic to the western United States, were evaluated for disease reaction, root dry weights and shoot dry weights on five grass species. The undesired grass, downy brome or medusahead, the perennial forage species, squirreltail or western wheatgrass, and winter wheat were susceptible to take-all. Downy brome, medusahead, squirreltail, and winter wheat were susceptible to crown rot. The desired grasses, squirreltail, western wheatgrass, and winter wheat, were susceptible to barepatch. Crown rot is adapted to dry soils and may be a potential biological control on downy brome and medusahead in the arid environment of the western U.S.

Field studies at three sites in Georgia evaluated broadleaf weed and nutsedge management in peanut with PPI applications of imazethapyr and metolachlor and POST applications of paraquat in mixture with imazethapyr or bentazon. Imazethapyr at 36 g ai/ha applied PPI alone or in mixture with metolachlor at 2750 g ai/ha controlled coffee senna; entireleaf, ivyleaf, pitted, smallflower, and tall morningglories; bristly starbur; and prickly sida better than metolachlor applied PPI. Yellow nutsedge control was generally higher where metolachlor was applied PPI. Postemergence control of the aforementioned species and sicklepod was similar with paraquat plus imazethapyr and paraquat plus bentazon. Peanut yields with paraquat plus imazethapyr and paraquat plus bentazon were similar. With one exception, peanut yields from imazethapyr PPI systems were higher than metolachlor PPI systems when POST herbicides were not used. Inclusion of metolachlor with PPI application of imazethapyr increased yields only at one location.

Growth and development of selected dinitroaniline-resistant (DR) and -susceptible (DS) goosegrass populations were compared in field studies in replacement series, in association with cotton, and under noncompetitive conditions. The DR ‘Florence’ (FR) and DS ‘Orangeburg’ (OS) populations were similar in competitiveness as indicated by relative yields (RY) and relative crowding coefficients (RCC) for vegetative and reproductive biomass production in a replacement series. Relative growth of the FR and DS ‘Anderson’ (AS) populations in replacement series was similar when vegetative biomass was considered, but reproductive biomass of the AS population declined as proportion of FR population increased. RCC values also indicated that the FR population interfered with reproductive development of the AS population. In field studies, the FR population produced greater vegetative biomass than either DS population, while similar reproductive biomass occurred for the FR and OS populations. Inflorescence dry weights were greater for the FR than the AS population under noncompetitive conditions and in cotton, but were greater for the AS population in replacement series studies. The competitiveness of DR and DS goosegrass biotypes appears to be more related to growth characteristics of individual populations than to response to dinitroaniline herbicides.

Greenhouse studies were conducted to determine the response of purple and yellow nutsedge to selective soil placement of 5 cm of soil treated with MON-12037 above and/or below the nutsedge tubers. MON-12037 at 53 g/ai ha applied as a foliar, soil, or foliar + soil application also were evaluated. MON-12037 placement above, below, or above + below the nutsedge tuber decreased shoot number, shoot dry weight, shoot regrowth dry weight, and root-tuber dry weight production in both species, 30 and 60 d after treatment. MON-12037 applied as a foliar, soil, and foliar + soil treatment was effective in reducing purple nutsedge shoot regrowth dry weight to less than 5% of the non-treated control. Yellow nutsedge shoot regrowth dry weight from the foliar + soil and soil-only applications was less than 1% of the non-treated control.