J. S. Russin

Delayed Maturity Associated with Southern Green Stink Bug (Heteroptera: Pentatomidae) Injury at Various Soybean Phenological Stages

Abstract Delayed maturity in soybean, Glycine max (L.) Merr., occurred in response to infestation by southern green stink bug, Nezara viridula (L.), in 4 yr of field studies. Maturity delays followed stink bug infestation that occurred only during the pod set and filling stages (R3–R5.5), and infestations at R3–4 and R5 resulted in delayed maturity more consistently than did infestation at R5.5. Infestation levels of six stink bugs per 0.3 m of row for 7–14 d generally were required to delay soybean maturity. The greatest impact on seed yield and quality parameters followed stink bug infestations that occurred during R3–R5.5, which corresponded closely with the periods of infestation that resulted in delayed maturity. If both delayed maturity and yield reduction are considered, the pod elongation through late pod filling stages were most critical for protecting soybeans from southern green stink bugs.

Control of Italian Ryegrass (Lolium multiflorum) in Winter Wheat

Field studies were established in 1999 and 2000 to evaluate Italian ryegrass, wheat, and double-crop soybean response to fall and spring postemergence applications of flucarbazone, sulfosulfuron, clodinafop, diclofop, and tralkoxydim applied alone and in combination with thifensulfuron + tribenuron to winter wheat. Fall-applied herbicides caused 5% or less wheat injury. Spring-applied herbicides caused 3 to 45% wheat injury, and the greatest injury occurred with the combination of flucarbazone with thifensulfuron + tribenuron in the spring of 2001. Spring-applied sulfosulfuron, tralkoxydim, diclofop, and clodinafop caused 3 to 6% and 16 to 26% wheat injury in 2000 and 2001, respectively. Herbicide injury to wheat did not reduce wheat grain yield compared with the hand-weeded treatment. Italian ryegrass competition in the nontreated plots reduced wheat yield by as much as 33% compared with herbicide-treated plots. Italian ryegrass control was 89 to 99% from clodinafop and diclofop and 78 to 97% from flucarbazone, with no differences because of application timing in either year of the study. Italian ryegrass control from sulfosulfuron and tralkoxydim was greater from the spring of 2000 applications (94 to 99%) compared with the fall of 1999 applications (65 to 88%). However, in 2001, application timing (fall vs. spring) for sulfosulfuron and tralkoxydim did not affect Italian ryegrass control. Thifensulfuron + tribenuron combined with tralkoxydim reduced control of Italian ryegrass control compared with tralkoxydim alone in both years of the study. Italian ryegrass control was not reduced when thifensulfuron + tribenuron was combined with sulfosulfuron, flucarbazone, diclofop, or clodinafop. Italian ryegrass was controlled effectively by the acetyl-CoA carboxylase–inhibiting herbicides diclofop, clodinafop, and tralkoxydim. However, control of Italian ryegrass with the acetolactate synthase–inhibiting herbicides flucarbazone and sulfosulfuron was inconsistent. Double-crop soybean after wheat did not have foliar symptoms or yield loss from fall- or spring-applied herbicides. Nomenclature: Clodinafop; diclofop; flucarbazone; sulfosulfuron; thifensulfuron; tralkoxydim; tribenuron; Italian ryegrass, Lolium multiflorum Lam., Marshall #3 LOLMU; soybean, Glycine max (L.) Merr, ‘BT369CR’; wheat, Triticum aestivum L., ‘Pioneer 25R26’. Additional index words: Application timing, herbicide carryover, tank mixtures. Abbreviations: ALS, acetolactate synthase (EC 4.1.3.18); DAT, days after treatment; POST, postemergence.