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NEW thinning strategies D r. Duane Greene at the University of Massachusetts is exploring new thinning strategies that can be used with existing thinning products. NAA (naphthalene acetic acid), one of the oldest thin- ning materials around, is usually used postbloom, when fruitlets are about ten millimeters in diameter, but Greene said it can be used at petal fall at higher rates—perhaps twice the dose. Greene defines petal fall as immediately after the bees are out of the orchard and you can get a sprayer in. Amid-Thin, or NAD (naphthaleneacetamide), is also an old compound. It is widely used in the West but not the eastern United States. This also can be used at petal fall, though it is more often used when the fruitlets are ten mil- limeters in diameter. The product can cause pygmy fruit, but this is less of a problem at the earlier timing. Combinations Greene said combinations of thinners allow growers to use lower rates and yet get better thinning responses. He has been testing MaxCel (benzyladenine) with NAA. The Clarke said this compound is of academic interest, but a long way from being a commercial product. Tests show that it can be a strong thinner in apples, with a wide win- dow of application from 10- to 20-mm fruitlet size. “If there’s an opportunity for a rescue thinner, this and metamitron would be serious contenders,” he said. ACC also shows promise in combination with MaxCel, but its combination can cause small fruit, but the size effect seems to vary by cul- tivar, and is more likely with Fuji and Red Deli- cious, he said. He has also been testing a product called Sysstem- CAL, a calcium and copper foliar fertilizer, with NAA. Sysstem-CAL, a product sold around the world, is a phosphite-based product that aids penetration of some compounds. Greene had heard anecdotal information that it enhanced the activity of thinners so he did experi- ments with McIntosh last year at both petal fall and ten- millimeter timings. It was not effective at petal fall, but the later timing did provide some thinning. A combination of MaxCel (100 parts per million) and Sysstem-CAL (two quarts per acre) reduced fruit set to 30 percent of the control. A combination of Sysstem and NAA down side is that it causes significant leaf drop. Up to 30 percent of the leaves can be lost. In tests, it has been effective as a postbloom thinner of peaches, which would be of great interest to growers in major peach producing regions, Clarke said. “A post- bloom peach thinner is the Holy Grail in some ways, but what makes it unacceptable is the amount of leaf drop.” (7.5 ppm) was less effec- tive, reducing fruit set to 70 percent of control. “This compound appears to work primarily with MaxCel but not NAA to enhance thinning,” Greene concluded. “Any time we had Sysstem-CAL and MaxCel together, we got rather good thinning.” The MaxCel and Sysstem-CAL combination also resulted in larger fruit (235 grams in weight versus 156 grams for the control), which Greene said was probably due to enhanced penetration of the MaxCel because the gain was beyond what would be expected just from thinning the crop. Fruit in the NAA and Sysstem-CAL treatment was the same size as the control treatment fruit. The MaxCel and Sysstem-CAL treatment had no other extraordinary effects on the fruit. —G. Warner The product has also given variable results, depending on the variety of peach. Greene concluded that while there are no silver bullets for thinning, there are options, and U.S. apple growers are fortunate that they still can use carbaryl for a little longer while alternatives are explored. • www.goodfruit.com GOOD FRUIT GROWER JUNE 2011 29 MELISSA HANSEN