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.

Four cropping systems were evaluated from 1975 to 1977 for the control of yellow nutsedge (Cyperus esculentus L.). Crops grown in 1975 and 1976 included alfalfa (Medicago sativa L. ‘Elcamino WL-600′), barley (Hordeum vulgare L. ‘CM-67′), corn (Zea mays L. ‘Dekalb T214′), and cotton (Gossypium hirsutum L. ‘Acala SJ-2′). Herbicides used included butylate (S-ethyl diisobutylthiocarbamate) in corn, EPTC (S-ethyl dipropylthiocarbamate) in alfalfa, glyphosate [N-(phosphonomethyl)glycine] in fallow plots, and MSMA (monosodium methanearsonate) in cotton. Cotton, which was grown continuously as one of the four cropping systems, was the only crop grown in 1977. Based on weed counts, crop yields, and the consistent decline in the number of tubers, all cropping systems provided substantial control of yellow nutsedge each year. Two years of either alfalfa treated with EPTC or double cropping barley with corn treated with butylate preceeding cotton reduced the number of viable yellow nutsedge tubers by 96%. Two years of chemically fallowing plots with glyphosate following barley and preceeding cotton was 98% effective in reducing viable tubers. Treating continuous cotton with MSMA, although somewhat inferior to the above systems, reduced the number of viable nutsedge tubers by 91% in 3 yr.

Field and greenhouse studies have shown that dinitroaniline herbicides suppress root rot of peas (Pisum sativum L.) caused by the fungus Aphanomyces euteiches Drechs. This investigation was conducted to identify factors which could enhance root rot suppression. In a temperature-soil moisture growth chamber study, dinitroaniline herbicides significantly reduced disease severity symptoms at all temperature and soil moisture regimes except 32 C and 0.75 field capacity. Dinitroaniline herbicides increased pea fresh weight significantly only under those conditions which favored severe disease development. Maximum root rot suppression occurred at 24 C and 1.25 field capacity. In a greenhouse study of the interaction of root rot suppression with pea varieties, dinitroaniline herbicides significantly increased growth of all 12 pea varieties tested including a root rot tolerant wild type of pea. A series of experiments explored the effect of uniformity, time, and depth of dinitroaniline herbicide incorporation on root rot suppression. In greenhouse studies, non-uniform incorporation significantly reduced root rot suppression indicating the need for thorough incorporation to achieve maximum root rot suppression. The combination of trifluralin (α,α,α-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine) + oryzalin (3,5-dinitro-N4,N4 dipropylsulfanilamide) was more effective than either trifluralin or oryzalin alone under non-uniform incorporation conditions but not under uniform incorporation conditions. Field studies showed that herbicide incorporation 2 weeks prior to planting may improve pea yield by 1.12 kg/ha of trifluralin or 0.56 + 0.56 kg/ha of trifluralin + oryzalin but not by 0.56 kg/ha of trifluralin. Herbicide incorporation to 15.2 cm rather than the normal 7.6 cm, increased pea yield at the 1.12 kg/ha rate of trifluralin or oryzalin or at 0.56 + 0.56 kg/ha of trifluralin + oryzalin. At the 0.56 kg/ha rate of trifluralin or oryzalin, herbicide dilution offset any benefit from deeper soil incorporation.