Trifluralin soil behavior: Persistence, movement and weed control

Abstract

Trifluralin (α,α,α‐trifluoro‐2, 4‐dinitro‐N, N‐dipropyl‐p‐toluidine) was applied in 1976 to Egam loam and Beason clay soils on the same field plots that were utilized in a 1973 study. The rates and methods of herbicide application, herbicide formulation and soil incorporation and plot size were also the same. Soybean (Glycine max L.) was seeded in both years with the same crop row‐width. Average herbicide residues, expressed as per cent of 0 day residues in 1976, were initially up to 7% higher in 1976 than in 1973, in both soils. The residues dissipated to about the same level, however, in both years starting 70 days after herbicide application, could be largely explained on the basis of rainfall distribution patterns in the two years. Less than 4% herbicide remained in 1976, 126 days after its application. The herbicide persistence was generally higher at higher herbicide rates in each soil, and could be described by first‐order kinetics.

The herbicide moved downward below the depth of herbicide incorporation to 12 in. soil depth, and generally persisted longer than in the surface soil. Upward herbicide movement was not discerned in 1976.

Initial control of both grass and broadleaf weeds was better than the one in 1973, being consistent with initially higher herbicide residues in 1976. Good correlation coefficients were obtained relating the weed count and herbicide‐residues in July of each year.

Soybean yield in Egam soil was 3 to 4 times that of control.

Key words:

• herbicide persistence
• herbicide residues
• pesticides
• herbicide carryover
• herbicide degradation
• soil residue analysis
• weed control