Oxamyl Is an Effective Apple Fruit Thinner when Used Alone or when Combined with Other Thinners

Abstract

In five experiments with `Redchief Delicious' and one with `Braeburn', oxamyl (Vydate 2L) was used alone or combined with other chemicals to thin apples. The thinning response to oxamyl depended on dose. In most cases, oxamyl at 600 mg·L−1 and carbaryl at 900 mg·L−1 thinned trees similarly, but the combination of oxamyl plus carbaryl was no more effective than either chemical alone. The combination of oxamyl plus NAA (2.5 to 5 mL·L−1) was slightly more effective than either material alone. The thinning response to oxamyl and carbaryl was related to the concentration of superior oil added to the spray solution; for both chemicals, adding oil at 5 mg·L−1 or Tween 20 at 1.25 mL·L−1 gave equivalent thinning. Apples on trees sprayed with oxamyl plus oil had a dull finish. Adding Tween 20 at 1.25 mL·L−1 improved the thinning activity of carbaryl (Sevin XLR-Plus) more than oxamyl. Similar thinning occurred whether oxamyl was applied when fruit diameter averaged 4 or 10 mm. On `Braeburn' oxamyl, carbaryl, Accel, and NAA were mild thinners, but all combinations of oxamyl or carbaryl plus Accel or NAA overthinned the trees without improving fruit size. In general, oxamyl at 600 mg·L−1 (2 pints of vydate 2L/100 gal.) and carbaryl thin apple trees similarly, and the efficacy of both chemicals is improved by adding a surfactant.