Effect of Retain on Reducing Pistillate Flower Abortion in Serr Walnut

Retain, a commercially available ethylene inhibitor developed by Valent BioSciences, has been widely tested on stone fruit for improving post harvest shelf life. This season, a simple test of its effect on Serr PFA was conducted in Kings County. A nine-year old block of Serr walnuts south of a Chandler orchard was selected. Ten fruiting shoots in each of twenty trees 120 to 150 feet south of the Chandler orchard were then tagged. The selected shoots each had two female walnut flowers in an early stage of pollen receptivity. Five of the shoots on each tree were treated with the equivalent of 11.7 ounces per acre of Retain. The other five shoots per tree were left untreated. On May 5, 2003, the number of fruit set per shoot were recorded and analyzed as a randomized complete block. The shoots within each tree were treated as subsamples and the trees were evaluated as replications. Visual and statistical results showed a consistent improvement in fruit set from the Retain application. Overall, Retain® treatment resulted in 89.0 percent set of the potential 200 flowers. Only 21.5 percent set was recorded in the untreated shoots. Counts taken in August confirmed similar percent nut retention for each treatment. This was highly significant statistically. Unfortunately, no water-only control was included in these non-funded tests.