Eric P. Prostko1, Timothy L. Grey1, and Jerry W. Davis2. (1) Crop & Soil Sciences, The University of Georgia, 104 Research Way, Tifton, GA 31793, (2) Experimental Statistics, The University of Georgia, 1109 Experiment Street, Griffin, GA 30223
Imazamox is the only imidazolinone herbicide registered for use on Clearfield® sunflowers. Imazamox does not effectively control sicklepod (Senna obtusifolia L.). Imazapic is a peanut herbicide that growers would prefer to use on Clearfield® sunflowers because of it’s effectiveness on sicklepod. The objective of this research was to evaluate the tolerance of three Clearfield® sunflower hybrids to postemergence applications of imazapic. Field trials were established in 2007 and 2008 at the UGA Ponder Research Farm located near Tifton, GA. All treatments were arranged in a split-plot design with four replications. Whole plots were sunflower hybrids (Dekalb DKF3880CL, Mycogen 8N386CL, Mycogen 8H419CL) and sub-plots were herbicides (non-treated control;imazamox @ 0.031 lb ai/A + Activator 90 @ 0.25% v/v + 28% UAN @ 2.5% v/v; imazapic @ 0.063 or 0.125 lb ai/A + Activator 90 @ 0.25% v/v). The sunflower hybrids were planted on April 2, 2007 and April 1, 2008. The herbicide treatments were applied on May 1, 2007 and May 2, 2008. At the time of application, the sunflowers were 5-8" tall with 6-10 leaves. The entire plot area was maintained weed-free throughout the season. Plant height and above-ground biomass data were collected 7 and 30 days after treatment (DAT) by measuring and harvesting five plants from each plot. Seed-head numbers were counted from one row meter in each plot. Seed-head weights were collected by harvesting five heads from each plot at maturity. All data were subjected to ANOVA and differences among sunflower hybrid and herbicide least squares means were determined by pairwise t-tests at the 5% level of significance. Imazapic had no effect on sunflower biomass, height, seed-head production, or seed-head weight. Imazapic @ 0.125 lb ai/A caused significant sunflower whorl chlorosis early in the season but this injury was transitory.