Alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide] at 3.4 and 6.7 kg/ha controlled weeds present in sweet potatoes (Ipomoea batatas L. ‘Jewel’, ‘Centennial’, ‘Caromex’) at two locations in North Carolina. Yield was not reduced from slight early season injury observed with the herbicide treatments. Most sweet potato root samples contained less than the detectable limit of 0.05 ppmw of alachlor. At one location, samples of the cultivars Jewel and Centennial that received 6.7 kg/ha contained 0.06 and 0.05 ppmw, respectively. Averaged over locations, residue levels in soil samples from plots treated at 6.7 kg/ha decreased from 1.55 ppmw initially to less than 0.05 ppmw by 16 weeks after application.

Two Nicotiana tabacum L. cultivars, ‘North Carolina 88’ and ‘Coker 319′, were grown in a charcoal-filtered greenhouse and treated with three different herbicides according to the herbicide labels. Labeled rates (X) for diphenamid (N,N-dimethyl-2,2-diphenylacetamide), isopropalin (2,6-dinitro-N,N-dipropylcumidine), and pebulate (S-propyl butylethylthiocarbamate) were 9.2 kg/ha, 2.3 kg/ha, and 6.2 kg/ha, respectively. Three weeks after treatment with 1/2X, X, or 2X rates of herbicide, half of the plants were fumigated with 15 μl/liter ozone for 2.5 h for four consecutive days. North Carolina 88 and Coker 319 grew equally well and were equally sensitive to ozone injury. Ozone reduced plant height and levels of reducing sugars and total nonstructural carbohydrates of both cultivars. Isopropalin, at X and 2X, reduced the ozone sensitivity and growth of both cultivars, while the X rate of pebulate reduced the ozone sensitivity of North Carolina 88. The chemical composition of the plants was not correlated with the sensitivity of the tobacco plants to ozone-induced injury. The major factors governing fleck intensity, growth, and chemical compositions were ozone and herbicide treatments.

Herbicides were evaluated alone, in combinations, or as sequential treatments on direct-seeded tomato each year from 1982 through 1984. Diphenamid at 4.5 kg ai/ha or napropamide at 1.1 to 2.2 kg ai/ha alone are registered but frequently do not control weeds adequately, particularly when yellow nutsedge and/or Florida pusley is common. Combinations or sequential treatments are necessary to overcome these weed problems in cropping systems. Metolachlor at 0.8 to 3.4 kg ai/ha injured direct-seeded tomato in proportion to the rate applied. Pendimethalin at 0.6 kg ai/ha also injured tomatoes. Fluazifop at 0.3 to 0.6 kg ae/ha and sethoxydim at 0.2 to 0.5 kg ai/ha effectively controlled annual grasses without injuring tomato seedlings. These herbicides would reduce competition and would increase harvesting efficiency where grass weeds are a problem.

Studies determined the effect of common lambsquarters, goosegrass, and a mixture of these on ‘Beauregard’ and ‘Jewel’ sweetpotato transplant production with or without polyethylene bed covers. Effects of herbicides on Beauregard in propagation beds were also studied. Black and infrared transmissible (IRT) plastic covers gave near 100% control of goosegrass and common lambsquarters, resulting in the greatest number and weight of Jewel transplants per plot. Common lambsquarters reduced transplant number and weight per plot with Jewel under clear plastic covers when compared with black and IRT plastic covers. Beauregard transplant number was not affected by row cover treatment. However, with data combined over all covers, Beauregard transplant weight per plot was lowest for treatments with weeds compared to weed-free plots. With the exception of DCPA, no significant (10% or greater) injury to Beauregard was observed with diphenamid, napropamide, chloramben, or chloramben plus fluazifop.

Tolerance of direct-seeded pepper under clear plastic mulch to herbicides applied pre- and post-emergence was investigated in 1991 and 1992. Weed control of herbicides applied preemergence was also studied. Paprika cultivar ‘Buketen’ and canning cultivars ‘Piquillo de Lodosa’ and ‘Pico de Mendavia’ were seeded in the field in Zaragoza, Spain, in a loamy soil. Percent emergence, plant mortality after the postemergence treatment, dry weight of plants, and fruit weight were recorded. Pepper was tolerant to diphenamid and napropamide applied preemergence but these herbicides did not control broadleaf weeds. Clomazone, when applied preemergence resulted in chlorotic seedlings and at 2 kg ai/ha reduced the final stand, but was selective when applied at the 6 to 8-leaf stage of the crop. Pepper was tolerant to diethatyl-ethyl when applied preemergence. However, diethatyl-ethyl applied postemergence caused severe phytotoxicity symptoms, and when mixed with diphenamid, fruit ripeness in 1992 was delayed. Weed control during the crop emergence period was better when diethatyl-ethyl was used mixed with diphenamid or napropamide.

Field experiments were conducted at two locations in Virginia to evaluate the following herbicides: alachlor, diphenamid, diuron, metolachlor, napropamide, norflurazon, oryzalin, oxyfluorfen, paraquat, pendimethalin, and simazine. One experiment involved newly-transplanted apple trees; the others, three in apple and one in peach trees, involved one-year-old trees. Treatments were applied in the spring (mid-April to early-May). Control of annual weed species was excellent with several treatments. A broader spectrum of weeds was controlled in several instances when the preemergence herbicides were used in combinations. Perennial species, particularly broadleaf species and johnsongrass, were released when annual species were suppressed by the herbicides. A rye cover crop in nontreated plots suppressed the growth of weeds. New shoot growth of newly-transplanted apple trees was increased with 3 of 20 herbicide treatments and scion circumference was increased with 11 of 20 herbicide treatments compared to the nontreated control. Growth of one-year-old apple trees was not affected. Scion circumference of one-year-old peach trees was increased with 25 of 33 herbicide treatments.

Field studies were conducted in 1978 and 1979 on broadleaf signalgrass [Brachiaria platyphylla (Griseb.) Nash] management in peanuts [Arachis hypogaea (L.) ‘Florigiant′]. In both years, preplant incorporated applications of benefin (N-butyl-N-ethyl-α,α,α-trifluoro-2,6-dinitro-p-toluidine), alachlor [2-chloro-2′,6′-diethyl-N-(methoxymethyl)acetanilide], and metolachlor [2-chloro-N-(2-ethyl-6-methylphenyl)-N-(2-methoxy-1-methylethyl)acetamide] provided better than 75% initial control of broadleaf signalgrass. Preemergence applications of alachlor and metolachlor provided 90% or better initial control. Vernolate (S-propyl dipropylthiocarbamate) and diphenamid (N,N-dimethyl-2,2-diphenylacetamide) provided less than 45% initial control. An at-cracking application of dinoseb (2-sec-butyl-4,6-dinitrophenol) plus naptalam (N-1-naphthylphthalamic acid) plus either alachlor or metolachlor increased control over that provided by at-planting herbicides alone and maximum yields were obtained. No at-planting herbicide alone provided better than 60% control at harvest and consequently yields were lower. In three of four experiments, sequential applications of at-planting and at-cracking herbicides provided better than 75% control at harvest. In the fourth experiment, only benefin and metolachlor followed by at-cracking applications provided better than 70% control at harvest.

Six herbicides were evaluated at two rates on sweet potatoes [Ipomoea batatas (L.) Lam. ‘Georgia Red’, ‘Georgia Jet’] with and without cultivation from 1972 through 1976. Cultivation with a ground-driven rotary hoe about 2 weeks later improved the control of late-season broadleaf weeds such as Florida beggarweed [Desmodium tortuosum (Sw.) DC] and showy crotalaria (Crotalaria spectabilis Roth.). Cultivation improved weed control where vernolate (S-propyl dipropylthiocarbamate), DCPA (dimethyl tetrachloroterephthalate), and napropamide [2-(α-naphthoxy)-N,N-diethylpropionamide] were applied. The improved weed control in cultivated treatments resulted in increased sweet potato yields in 1972 and 1973, which also were the years with the highest weed populations.

Black nightshade was selectively controlled along with other annual weeds in direct-seeded tomatoes by BAY SMY 1500 applied preemergence. BAY SMY 1500 was also found selective for transplanted tomatoes when applied prior to transplanting or soon after planting prior to black nightshade emergence. Black nightshade control and crop selectivity were obtained with BAY SMY 1500 at 0.75 and 1.25 kg ai ha-1 applied on sandy loam and clay loam soils, respectively.

Studies were conducted to determine the response of ‘Jewel’ sweetpotato in propagation beds to DCPA and napropamide. Napropamide at 2.2 and 4.4 kg ha–1 caused slight injury, and reduced plant number and weight when compared with the untreated control. Napropamide at 1.1 kg ha–1 combined with chloramben at 3.3 kg ha–1 was not injurious; plant production was equal to the untreated control, diphenamid at 4.4 kg ha–1, and chloramben at 3.3 kg ha–1. DCPA at 8.3 and 10.0 kg ha–1 caused unacceptable injury and reduced plant number and weight.