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Title: PERSISTENCE OF DIBLUBENZURON ON SOYBEAN LEAVES

Author
item Southwick Jr, Lloyd
item WILLRICH, MELISSA - LOUISIANA STATE UNIV
item Fouss, James
item BOETHEL, DAVID - LOUISIANA STATE UNIV

Submitted to: Journal of Entomological Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/10/2004
Publication Date: 10/1/2004
Citation: Southwick Jr, L.M., Willrich, M.M., Fouss, J.L., Boethel, D.J. 2004. Persistence of diblubenzuron on soybean leaves. Journal of Entomological Science. J. Entomol. Sci. 39:398-406.

Interpretive Summary: Diflubenzuron is an insecticide that provides long-term control of velvetbean caterpillar on soybean plants. Research in Louisiana in 1999 and 2000 demonstrated control for 35 and 21 days after application, respectively, and in a study in 1986 control for 54 days was observed. We have extracted diflubenzuron residues from treated soybean leaves and have found that the initial residue on the leaves disappeared within two days to a level only 15% of the leaf coverage immediately after application. This low-level residue remained with only a slow disappearance for another 54 days until the leaves began falling from the plants at the end of the growing season. This persistent residue of diflubenzuron on soybean leaves is consistent with the extended efficacy against velvetbean caterpillar observed with this insecticide on soybean.

Technical Abstract: Diflubenzuron [Dimilin, N-[{(4-chlorophenyl)amino}carbonyl]-2-6-difluorobenzamide] is an insect growth regulator that is highly effective and provides residual control (up to 54 days) against velvetbean caterpillar (Anticarsia gemmatalis Hübner) on soybean [Glycine max (L.) Merrill] in Louisiana. We conducted a study to quantify the field persistence of diflubenzuron residues on soybean leaves when applied at 0.035 kg/ha, a rate used in preventive programs for velvetbean caterpillar. Day of application (day 0) concentration of the insecticide on the leaves was 206 ± 41 ng/cm2. The initial leaf residue decreased with a half life of 3.3 days. The residue for the remainder of the study (from day 7 to day 56) varied between 32.6 ng/cm2 at 14 days after treatment (DAT) and 15.6 ng/cm2 at 42 DAT, but this slow decrease in persistent residual diflubenzuron beyond 7 DAT was not a statistically significant trend. This persistent low level residue on the soybean leaves is consistent with the extended diflubenzuron efficacy toward velvetbean caterpillar that has been documented in Louisiana.