Greenhouse studies were conducted to identify a chemical that would temporarily suppress net photosynthesis (Pn) of peach leaves. Antitranspirants and photosynthetic inhibitors were tested on leaves of greenhouse-grown peach trees [Prunus persica (L.) Batsch]. Leaf dips of 8% Vapor Gard (poly-1-p-methen-8-9 diyl), 10−3m ABA, 10−3m diuron, and 10−3m terbacil reduced Pn by more than 50% within 1 day after treatment, without causing excessive visual phytotoxicity. Since terbacil strongly reduced Pn with minimal phytotoxicity, it was applied as limb treatments to bearing ‘Madison’ peach trees in the field. Treatments were single applications at 1000 or 2000 ppm, double applications a week apart at 1000 ppm, or 2000 ppm at week 1 followed by 1000 ppm at week 2. Fruit drop was 73% to 90% on terbacil-treated limbs compared to 20% natural drop on nonthinned controls. All terbacil treatments increased the size of remaining fruit over that of the nonthinned checks. The 1000 ppm treatment resulted in fruit size similar to the hand-thinned check, but higher concentrations caused smaller fruit than the hand-thinned control.
Chemical names used: abscisic acid (ABA); N’-(3,4-dichlorophenyl)-N,N-dimethylurea (diuron); 5-chloro-3-(1,1-dimethylethyl)-6-methyl-2,4(1H,3H)-pyrimidinedione (terbacil).
Winchester Fruit Research Laboratory, Winchester, Va.
Received for publication 23 Feb. 1984. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.