Factors affecting the phytotoxicity, soil movement, and soil persistence of norflurazon

Abstract

Norflurazon {4-chloro-5-(methylamino)-2-((alpha),(alpha),(alpha)-trifluoro-m-tolyl)-3(2H)-pyridazinone} decreased the total chlorophyll content and the chlorophyll a/b ratio of nine plant species. Grain sorghum {Sorghum bicolor (L.) Moench.}, wheat (Triticum aestivum L.), and sicklepod (Cassia obtusifolia L.) were the most susceptible plants, while corn (Zea mays L.), oats (Avena sativa L.), peanuts (Arachis hypogaea L.), soybeans {Glycine max (L.) Merr.} and sunflower (Helianthus annuus L.) were intermediate in susceptibility, and cotton (Gossypium hirsutum L.) was the most tolerant plant. When applied to the soil preplant incorporated, approximately twice as much norflurazon was required to reduce chlorophyll content of test plants by 50% as was required when applied preemergence. The soil properties most closely correlated with norflurazon activity were organic matter content and type of clay, but not clay content. The movement of norflurazon in dry soil after the addition of 16 cm of water to the soil surface was limited. However, norflurazon was readily leached if applied to wet soil with a low adsorption capacity and if additional water was added to the soil surface. Persistence of norflurazon was longer at 5 C, or in air-dry soil than in soil at 25 and 37 C, or in soil at 60, 80, and 100% field capacity. Norflurazon was more persistent in soil with pH 8.6 than in soil with pH 5.8 and 2.8, and in clay soil than in sand. Bioassays were less accurate than a gas-liquid chromatograph (GLC) for determining the concentration of norflurazon in soil, and the spectrophotometer was no better than visual estimations for determining the low concentration of norflurazon in soil. None of the chemicals tested as crop safeners showed protection against norflurazon. A synergism was observed when norflurazon was applied with CMAA {4-chloro-5-(N-methyl,N-amino)amino-2-(3-trifluoromethylphenyl-3(2H)-pyridazinone}, fluometuron {1,1-dimethyl-3-((alpha),(alpha),(alpha)-trifluoro-m-tolyl)urea}, or fluridone {1-methyl-3-phenyl-5-{3-(trifluoromethyl)phenyl}-4(1H)-pyridinone}. An inhibition of seed germination was observed when ABA (abscisic acid), DAFU {N,N-(diallyl)-N'-(3-trifluoromethylphenyl)urea}, or DHOP (3,6-dihydroxypyridazine) was coated onto seeds.