Growth and development of young apple fruits following applications of ethephon plus carbaryl for thinning

In three experiments, apple trees (Malus xdomestica Borkh.) were sprayed, when fruits were 20 to 30 mm in diameter, with a combination of ethephon (800 mg · L^-1) and carbaryl (600 mg · L^-1) to induce abscission of all fruits on the tree. Two days after treatment (DAT), most treated fruits stopped or slowed increasing in diameter, fruit water potential was less negative, and starch accumulation was less than for nontreated fruits. Cellulase activity appeared in the abscission zone by 4 DAT. Fruit growth cessation following treatment was probably due to inadequate assimilate supplied to the fruit, but assimilate flow slowed before cellulase activity was apparent in the abscission zone. Chemical names used: 2-chloroethyl phosphonic acid (ethephon); 1-naphthyl (N-) methylcarbamate (carbaryl).