CGA-154281 and temperature effects on metolachlor absorption and metabolism were studied in corn seedlings grown in untreated soil or soil treated with metolachlor, CGA-154281, or both. Seedlings were grown under a cool (21/13 C, 16-h day) or warm (30/21 C, 16-h day) temperature regime and exposed to 14C-metolachlor for 10 min at either 21 or 30 C. Corn grown under the cool temperature regime absorbed slightly more 14C-metolachlor than corn grown under the warm temperature regime. Corn held at 21 C during a 10-min 14C-metolachlor exposure period metabolized metolachlor more slowly than corn held at 30 C. Decreased corn tolerance to metolachlor observed at lower temperatures may be due in part to slower metolachlor metabolism. Corn grown in the presence of metolachlor plus CGA-154281 metabolized 14C-metolachlor to the glutathione conjugate twice as fast as corn grown in the presence of metolachlor alone. The increase in metabolism rate was due to a fivefold increase in glutathione-S-transferase (GST, EC 2.5.1.18) activity and not to an increase in glutathione (GSH) content. Results are consistent with the hypothesis that CGA-154281 protects corn from metolachlor injury by enhancing GST activity, which accelerates metolachlor detoxification via GSH conjugation.

Leaching of EPTC (S-ethyl dipropylthiocarbamate) plus R-25788 (N,N-diallyl-2,2-dichloroacetamide) through columns of four soils resulted in the separation of R-25788. Separation of R-25788 from EPTC was greater in coarser than in finer textured soils. When soil columns were placed under drying conditions for 6 days after leaching, R-25788 moved upward in the columns faster than EPTC.

The susceptibility of corn (Zea mays L. ‘Pioneer 3334A’) at different stages of growth to EPTC (S-ethyl dipropylthiocarbamate) plus a herbicide-protectant, R-25788 (N,N-diallyl-2,2-dichloroacetamide), was studied in the greenhouse. Corn was treated with either 25 ppm or 12.5 ppm EPTC containing R-25788 at planting and at 2, 4, 6, and 8 weeks thereafter. The herbicide was soil-applied and immediately incorporated by watering. Phytotoxicity and plant height were observed periodically for 56 days after herbicide treatment. Within 21 days after treatment with 25 ppm EPTC containing R-25788, injury and plant height reduction occurred in corn treated at planting, or at 2 and 4 weeks but not at 6 or 8 weeks after planting. At 56 days, however, corn treated at planting or 2 weeks after planting had outgrown all injury symptoms and was as tall as the controls (>84%). Corn treated at 4 weeks after planting, however, still remained injured and was 45% as tall as its respective control. Corn treated at 6 to 8 weeks showed no injury during the entire period of observations. The data indicates that corn is most susceptible to EPTC plus R-25788 at 4 weeks after planting. The results of this greenhouse study are discussed in relation to corn injury as observed in the field.

A field trial was conducted in 1988 and 1989 to confirm the efficacy of naphthalic anhydride (NA) for providing full-season protection of corn from imazethapyr applied at various times and rates. NA applied as a 1% by weight dust to corn seed caused 6% injury 2 weeks after treatment (WAT) in 1989; however, plants recovered within 6 WAT and grain yield was not affected. Imazethapyr applied to corn untreated with NA resulted in greater than 30% injury for all treatments in both years except PRE in 1988. NA reduced phytotoxicity from all imazethapyr applications in 1989 and from PPI, early POST, and 4- to 5-leaf stage (mid-POST) applications in 1988. Despite the safening effect, corn injury was still observed 6 WAT in NA-treated corn for all imazethapyr applications in both years except early POST in 1988. Higher yields were produced from NA-treated than untreated corn with imazethapyr applied PPI in both years, PRE in 1989, early POST in both years, and mid-POST in 1988. Safened corn treated PPI and early POST yielded the same as the safened corn in the control in both years. Imazethapyr applied at the 8- to 10-leaf stage caused total yield loss regardless of NA treatment. Drought conditions may have caused the lower corn injury and yield loss from imazethapyr observed in 1988 compared to 1989.

Use of R-25788 (N,N-diallyl-2,2-dichloroacetamide) eliminated early-season corn (Zea mays L. '501D′) injury, stand loss, and yield reduction caused by EPTC (S-ethyl dipropylthiocarbamate) at 3.4, 6.7, and 13.4 kg/ha. R-25788 also eliminated early-season corn injury from butylate (S-ethyl diisobutylthiocarbamate) at 9.0 kg/ha. R-25788 did not consistently prevent corn yield reduction from 2,4-D [(2,4-dichlorophenoxy)acetic acid] or EPTC + 2,4-D. R-25788 had no effect on weed control from any of the herbicides evaluated nor any effect by itself on corn injury or corn yield. No corn injury or yield reductions occurred from vernolate (S-propyl dipropylthiocarbamate) at rates up to 6.7 kg/ha or alachlor [2-chloro-2′, 6′-diethyl-N-(methoxymethyl)acetanilide] at rates up to 13.4 kg/ha. Early-season corn injury frequently did not result in reduced corn yield.

Flurazole [phenylmethyl 2-chloro-4-(trifluoromethyl)-5-thiazolecarboxylate] and acetochlor [2-chloro-N-(ethoxymethyl)-N-(2-ethyl-6-methylphenyl)acetamide] were examined in the laboratory and greenhouse for effects on grain sorghum [Sorghum bicolor (L.) Moench ‘G-522 DR’]. Flurazole did not protect against acetochlor-induced inhibition of primary root growth when sorghum was grown in distilled water, but some safening occurred after 8 days when nutrients were available. Flurazole did not protect primary roots completely. In the presence of nutrients, however, flurazole stimulated growth of the mesocotyl roots and protected the second adventitious root system.

Field studies were conducted in 1989 and 1990 to determine if corn seed treated with naphthalic anhydride (NA) at 0.5% (w/w) would result in a reduction in corn injury caused by clomazone applied preplant incorporated (PPI) or preemergence (PRE) at 0.56 and 0.70 kg a.i. ha–1. NA significantly reduced corn injury, especially where clomazone was incorporated. Plant population, height, ear number, and grain yield also were higher in plots where NA was used. In most instances, corn injury was less and plant population, height, ear number, and grain yield were higher in plots where clomazone was applied PRE compared with PPI.

Laboratory studies demonstrated that naptalam safens cucumber against the phytotoxic effects of chloramben. In petri dish studies, cucumber seedlings grown from seeds exposed to chloramben plus naptalam had greater shoot growth, root growth, and dry weight than seedlings grown from seeds exposed to chloramben alone. Naptalam also partially reversed the reduction in dry weight of various plant parts caused by exposure of roots of hydroponically grown seedlings to chloramben. More radioactivity from root-applied 14C-chloramben remained in cucumber roots and less was translocated to shoots with a 14C-chloramben plus naptalam treatment than with a 14C-chloramben alone treatment. Naptalam appeared to influence chloramben metabolism. In various plant parts, concentrations of chloramben and its metabolites differed between the two treatments.

The effects of the antidote CGA-154281, available soil water (ASW), and soil temperature on corn injury from preemergence applications of metolachlor were evaluated in field and growth chamber studies. In field studies, metolachlor at rates of 5.6, 8.4, and 11.2 kg ha–1 caused corn injury when there was sufficient ASW before corn emergence to activate the herbicide. Injury was prevented when CGA-154281 was applied with metolachlor (30:1, metolachlor:CGA-154281 by wt). The effects of surface-soil ASW, soil temperature, and CGA-154281 on corn tolerance to metolachlor were further evaluated in growth chamber studies. Corn injury from metolachlor was more severe when the surface soil was wet for 5 days immediately after herbicide treatment than when the surface-soil was dry. Corn injury from metolachlor also was greater when corn was grown under cool temperatures (21/13 C, day/night) than when grown under warm temperatures (30/21 C, day/night). CGA-154281 conferred protection against metolachlor injury regardless of surface soil ASW or growth temperature.