Issue link: https://read.dmtmag.com/i/629538
14 FEBRUARY 1, 2016 GOOD FRUIT GROWER www.goodfruit.com Growth regulators can prevent drop and enhance storability of pears if used correctly. by Geraldine Warner S everal plant growth regulators are available to control prehar- vest drop, extend the harvest window and improve storabil- ity of pears, but the products do not have exactly the same effect, reports Dr. Yan Wang, postharvest physiologist at Oregon State University. Postharvest drop is a significant con- cern both in summer and winter pear varieties. It results from the expressions of genes and activities of enzymes asso- ciated with cell wall degradation in the abscission zone, Wang explained during Washington State University's Fruit School on Apple and Pear Horticulture in November. Expression of the genes is triggered when auxin drops below a certain threshold in the abscission zone, which then becomes sensitive to the rip- ening hormone ethylene. Three growth regulators are commer- cially available for controlling drop by maintaining the balance between auxin and ethylene: —NAA (naphthaleneacetic acid), sold under the brand name K-Salt Fruit Fix, which is a synthetic auxin. —AVG (aminoethoxyvinylglycine), sold as ReTain, which inhibits ethylene biosynthesis. —1-MCP (1-methylcyclopropene), sold as Harvista, which inhibits the action of ethylene. NAA Research has shown that NAA is more effective in controlling drop than either AVG or MCP, but that a combination of NAA and AVG works best, Wang reported. He stressed that this might not be the case for apples, as pears produce much less ethylene while they are on the tree. However, if not applied at the right time or concentration, auxin-type plant growth regulators can increase ethylene production in the fruit and reduce its storability. In a trial, pears were treated three weeks before the anticipated harvest date with the label rate of 33 parts per million of NAA. The treatment had no effect on the amount of ethylene in pears kept for four weeks in storage at 30°F. However, NAA applied two weeks before antici- pated harvest increased ethylene in the stored pears. NAA applied at 15 ppm (less than half the label rate) two weeks before harvest had no effect on the fruit ethylene level, but the same rate applied one week before harvest increased ethylene production in the fruit, reducing its storability. Wang said to avoid this negative effect of NAA, growers should apply a reduced rate of 20 ppm on Bosc or d'Anjou pears and 15 ppm for Bartletts and avoid apply- ing NAA within two weeks of harvest. An NAA application will become effective within two to three days and will control drop for at least two weeks. Applying AVG with the NAA helps to further reduce fruit drop and counteracts the negative effect of NAA on fruit stora- bility, Wang said. Extending harvest ReTain and Harvista can also be used to delay maturity and extend the harvest window. Ideally, Bartlett pears should be harvested at between 19 and 17 pounds pressure, d'Anjou at 15 to 13 pounds, Bosc at 15 to 13 pounds and Comice at 13 to 11 pounds. However, it is sometimes a challenge for growers to harvest pears at the right maturity if fruit is maturing quickly, as it did in 2015, or if they are short of labor. In a trial, Wang applied ReTain to Bartlett pears one week before antici- pated harvest when the fruit firmness was 21 to 20 pounds. ReTain did not affect fruit maturation until the fruit softened to 19 pounds. It then slowed maturation of the fruit while the pressure was between 19 and 17 pounds, extending the harvest window by about five days. It was less effective if applied two or more weeks before harvest. Research at the University of California, Davis, showed that Harvista could also delay maturity of Bartlett pears, but results were inconsistent in fruit of different harvest maturity and from year to year. Postharvest Wang has also studied the effect of growth regulators on fruit disorders in Bartlett and Starkrimson that result How to use PEAR growth regulators Horticulture SLIMLINE MANUFACTURING LTD. Turbomist technology allows all growers the ability to reduce drift substantially and save 25% to 40% of their annual spray fuel bill, at the same time. Check out these savings at www.turbomist.com 1 800 495 6145 SLIMLINE MANUFACTURING LTD. CALL ONE OF OUR DEALERS TODAY! Order NOW for SPRING DELIVERY