ARS | Publication request: Eugenol bloom thinner on peach

Submitted to: Annual Cumberland Shenandoah Fruit Workers Conference
Publication Type: Proceedings
Publication Acceptance Date: February 8, 2010
Publication Date: March 23, 2010
Citation: Miller, S.S., Tworkoski, T., Hott, C.F. 2010. Eugenol bloom thinner on peach. Annual Cumberland Shenandoah Fruit Workers Conference.

Technical Abstract: Peaches must be thinned to obtain annual crops of marketable size fruit. Traditionally, peach thinning has been accomplished by hand in the absence of reliable chemical thinners. Peach thinning is a labor intensive, expensive cultural practice. Previous studies in our lab have demonstrated that eugenol, an essential oil, at rates ranging between 2 percent and 8 percent (v/v), will thin peach trees at bloom time. The current study examined the effect of eugenol applied at five rates (0, 0.5, 1, 2, and 3 percent v/v) on mature 'John Boy' peach trees at the 90 to 100 percent full bloom stage. All sprays were applied with an airblast sprayer in full dilute water carrier volume based on the calculated tree-row-volume. Response to eugenol was rate dependent. Eugenol at 1, 2, and 3 percent significantly reduced total fruit numbers (r(2) = 0.698) and crop load (r(2) = 0.626) [fruit/cm(2) trunk cross-sectional area (TCSA)]. A 1 percent eugenol spray reduced fruit number per tree by 52 percent compared to the non-thinned (0 percent eugenol) control trees. Fruit diameter was increased on trees bloom thinned at the 1, 2, and 3 percent rate of eugenol. At the 2 percent and 3 percent rate, eugenol reduced fruit numbers by 91 percent and 94 percent respectively, thus, nearly defruiting the trees. A frost on the morning of spray application reduced the overall crop load on all trees. A crop load of 2.26 fruit/cm(2) TCSA on the control trees was about four-fold less than normally expected on the trees used in this study. Fruit on control trees averaged 7.85 cm diameter, well above marketable peach fruit size, and was not different from the mean fruit diameter for all other treatments. Because of the reduced crop load resulting from frost damage, gross returns (based on prevailing market prices and fruit size distribution) minus thinning costs were greater for control trees than for trees sprayed with 1, 2, or 3 percent eugenol. The current trial confirms the effectiveness of eugenol as a bloom thinner and further illustrates the potential problem growers could face in applying a bloom thinner to peach trees before the threat of frost has passed.