Chemical Thinning of Peaches

In the past, the only method of thinning peaches was either by hand or mechanically with rope thinners. Wilthin is a desiccant that is labeled for blossom thinning of peaches and nectarines to reduce fruit set. Wilthin should be applied at a rate of 3 to 6 quarts per acre. Application should be made using an airblast sprayer only. Apply as a dilute spray to achieve adequate wetting of target flowers. This requires 100 to 250 gallons per acre of spray volume, depending on tree size. Low volume concentrated sprays are NOT recommended. The 4 to 5 quart rate is usually optimum, but results may vary depending on variety, tree size, and bloom uniformity.

Thinning response to Wilthin is linear with rate, and the desired amount of at-bloom thinning should take into account other factors that will affect fruit set and quality. Optimum timing is when trees are at 70 to 80 percent of full bloom. Thinning occurs mainly on flowers that are open but not yet fertilized. Apply only after adequate pollination and fertilization of the early bloom has occurred. Direct the air blast spray pattern to the primary fruiting zone of the tree. Shut off the lower nozzles on the spray boom to avoid overthinning of weaker blooms on the lower and inside portions of trees.

It is not recommended that Wilthin be sprayed with any other materials except for Regulaid. The use of other spray adjuvants is NOT recommended. The use of spray oils, or other nutrient, sulfur, or fungicide sprays, in the prebloom stages should be according to the manufacturer's label but not closer than 14 days before Wilthin application. Do not apply if the foliage is wet, or if rain is expected within 2 hours. Minor leaf burn may occur on expanded foliage exposed to Wilthin spray.

Only one application of Wilthin may be made during the bloom period. Subsequent hand thinning may be necessary to adjust proper fruit load, depending on the variety and bloom density of the trees. Wilthin application will not harm bees.