In trials, benzyladenine has resulted in larger fruit.
Ammonium thiosulfate (ATS) has been the best treatment overall for thinning pears in trials conducted by the Washington Tree Fruit Research Commission.
Crocker's Fish Oil and lime sulfur, which has been the best bloom thinner in apple trials, performed so poorly in pears that it is no longer being tested, Dr. Ines Hanrahan reported at the North Central Washington Pear Day in January.
Hanrahan, project manager with the Washington Tree Fruit Research Commission, said that the commission has conducted 19 chemical thinning trials in pears since 2003. For bloom thinning, it has tested ATS, urea, Crocker's Fish Oil and lime sulfur, and lime sulfur alone. For postbloom thinning, it has tested BA (benzyladenine) and NAA (naphthaleneacetic acid).
Hanrahan said the products were tested in two different types of trials. In one set of trials, Research Commission staff tested treatment combinations on small areas using a Proptech tower sprayer. In the other trials, growers applied the products using their own equipment to find out how the treatment worked in real-life conditions.
In a Bosc orchard in Tonasket, Washington,where ATS (ammonium thiosulfate), BA, and urea were tested, BA was the only product that reduced the number of fruitlets, she said. However, both ATS and BA increased fruit weight.
In a Bartlett orchard near Yakima, Washington, where ATS and BA were tested, ATS reduced the number of flowers, and both treatments increased fruit weight. There was no difference in russet, fruit firmness, or soluble solids between any of the treatments at that site.
In a Bartlett orchard at Monitor, Washington, ATS, BA, lime sulfur, and urea were tested. None of the treatments had much of a thinning effect, though BA did increase fruit size, Hanrahan reported.
Overall, ATS was the most consistent bloom thinner. It reduced the crop load in about a third of the 19 trials and increased fruit size in about 20 percent of the trials. BA, which has not been tested so extensively, reduced crop load a third of the time and resulted in larger fruit each time it was tested. Hanrahan said this would be tested further.
Urea has not worked in Washington conditions.