Mechanical thinning is effective
Three different devices are being compared in WSU trials.
Karen Lewis demonstrates a hand-held thinner being developed at WSU.
Karen Lewis, regional field specialist for Washington State University, discussed mechanical thinning trials during the Wenatchee Tree Fruit Research and Extension Center’s annual field day. She has been testing the Bonner string thinner from the University of Bonn, the Darwin string thinner, and a hand-held string thinner under development at WSU.
Lewis reported that for apples, the Bonner, which has three moveable arms, has been more versatile than the Darwin, which has one spindle. The Bonner can be adapted to different types of canopy. However, all three of the machines she is testing remove bloom and reduce the need for follow-up hand thinning.
In stone fruits, mechanical bloom thinning yields larger fruit than hand-thinning of green fruit alone, and the cost was lower. Bloom thinning with the Darwin costs around $50 to $55 per acre, including the cost of the equipment, she calculates.
Lewis was not able to test the Darwin in commercial cherry orchards this year because of growers’ concern about the extent of winter cold damage, but she was able to do tests with the hand-held thinner, which was adapted from a string trimmer used for weeding. Although the hand-held thinning is non-selective, the operator is able to target specific areas in the trees. Results were mixed, with the hand-held device performing better on some cherry varieties than others. It will be tested with different heads and different numbers of strings in Chile this season.
Other presentations at the field day included: crop load management by Tory Schmidt, Washington Tree Fruit Research Commission; biological replant disease treatments by Dr. Mark Mazzola, U.S. Department of Agriculture, Wenatchee; apple breeding by Drs. Kate Evans and Cameron Peace, WSU; enhancing biological control by Dr. Vince Jones, WSU; and mulching for weed control and water management by David Granatstein, WSU.
Look for full reports in future issues of the Good Fruit Grower.