Good Fruit Grower

April 1

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Thinning OPTIONS Several chemicals are available for both bloom and postbloom thinning. by Richard Lehnert G rowers have several chemicals available for thinning fruit at different times. Materials available for blossom thinning include lime sulfur and oil and ammonium thiosulfate (ATS). Both are harsh materials that achieve their effect by burning pistils, suppressing photosynthesis, and, perhaps, preventing pollination. ATS is usually applied after king bloom, said Phil Schwallier, Michigan State University district horticultural agent. Schwallier does not favor lime sulfur, which, in research, he says, ���has not really given larger fruit but just reduced yield.��� If the goal is to remove fruit and prevent biennial bearing, it does that. In developing recommendations, Schwallier used two sprays of lime sulfur and oil during full bloom at a rate of 2 pounds of lime sulfur and 2.5 gallons of oil in 100 gallons of spray. He used three gallons of ATS in 100 gallons of water, with 100 gallons applied per acre, and sprayed twice. Some of the advantages of blossom thinning are that fruit drop early, which should maximize fruit size and return bloom. And, for this year, it gives that additional step in reducing a heavy crop. Remember, it is an insecticide and is toxic to bees. A third workhorse is MaxCel, which is rated as a moderate thinner that is gentle on the apples. It improves fruit size. It is dose-dependent, and the standard rate is 100 parts per million, or 64 ounces in 100 gallons of spray. It is labeled up to twice that, and the dose should be adjusted upward on hard-to-thin varieties. MaxCel and NAA lose effectiveness as thinners once fruits reach 17 to 18 millimeters, Schwallier said. Fruits in general become unresponsive when they are 24 mm in size. Schwallier likes the MaxCel plus carbaryl thinning program somewhat better than the NAA plus carbaryl program. ���In all our studies,��� he said, ���fruit thinned with MaxCel is always larger, because MaxCel increases cell size.��� The late option for thinning is to use ethephon (Ethrel) with or without carbaryl, together with an acidifying buffer and, possibly, a quart of spray oil. Golden Delicious and Rome are very sensitive to C O L U M B I A B A S I N ethephon. Schwallier rates ethephon, applied at 1 pint to 1 quart per acre, as a dangerous option, ���the elephant gun,��� but perhaps the only choice left except hand thinning if there are too many fruitlets and they are 20 millimeters or larger. New thinners are being tested, and these also appear to be late season, rescue options. Schwallier and other researchers (Dr. Jim Schupp in Pennsylvania and Dr. Steven McArtney in New Carolina), are testing three experimental apple thinners���ACC, ABA, and metamitron. ��� N U R S E R Y OuR V ARIETIES ARE Proven& Profitable Main thinning window The window for thinning is usually three or four weeks long, from petal fall to when fruitlets reach 20 millimeters in size. Studies have shown that the most effective part of the thinning window is when fruit are 10 to 12 millimeters in diameter, and there are several ���workhorse thinners��� used at that time. One is naphthaleneacetic acid (NAA, sold as Fruitone) and, new this year, PoMaxa. Among thinners, it is the most potent and active. It is dose-dependent, being applied at rates from 2.5 to 20 parts per million. It can stunt fruit and foliage, and is not recommended on Red Delicious or Fuji, where pygmy fruit often results. It should not be applied with Promalin or with MaxCel (benzyladenine, or BA). Naphthaleneacetamide (Amid-Thin) is less aggressive than NAA, but is not used on Red Delicious because seedless pygmy fruit can result and will persist. It is often used as a petal fall spray at rates from 25 to 50 ppm. A second workhorse thinner is carbaryl (the insecticide Sevin). It is mild to moderate in its thinning ability, but relatively safe and gentle, Schwallier said. It tends to promote large fruit size, he said. It can be used throughout the thinning window, but is generally used later. It is not dose-dependent, so whenever carbaryl is used, he recommends it be applied at a one quart per acre rate, in 100 gallons of spray per acre. Successful orchards start with productive future tree varieties. Columbia Basin Nursery offers a number of polular and proven tree varieties. If you will be planting soon, start your successful future now with a call to Columbia Basin Nursery. Call today for a complete listing and availability. PEARS APPLES CHERRIES Bartlett Columbia Red D���Anjou Comice Concorde�� D���Anjou Forelle Golden Russet�� Bosc Hailey Red��� Bartlett Noble Russet�� Bosc Red Clapp Banning Red Fuji Blondee�� Brookfield�� Gala Buckeye�� Gala Honeycrisp Jonastar�� Jonagold Midnight�� Red Spur Morren���s��Jonagored Supra��� Pacific�� Gala Ultima��� Gala Bing BlackPearl�� Chelan��� Early Robin�� Lapins Rainier Regina��� Santina��� Skeena��� Sweetheart Tieton�� Van Sour Cherry Montmorency We offer over 100 Varieties of Apples, Apricots, Cherries, Nectarines, Peaches, Pears and Prunes & Plums. 800/333-8589 GOOD FRUIT GROWER April 1, 2013 11

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