Washington's famous apple industry brought in $1.4 billion in 2006, but a disease is cutting into those profits.
Lenticel breakdown disorder, known as LB, creates brown spots and indentations most commonly on the 'Gala' variety of apple, but these signs don't show up until after apples are harvested, stored, and processed. Time and materials are spent on fruit that can't be sold, and if a shipment goes out before symptoms are detected, the reputation of the grower is jeopardized.
Researchers at the U.S. Department of Agriculture, led by Eric A. Curry, are looking for ways to reduce the incidence and/or severity of LB in 'Gala' apples. The study, published in the October-December 2008 issue of HortTechnology, compared several coatings sprayed on apples in three commercial orchards with a history of LB.
The coatings were EpiShield™ made from waxy plant extracts, PrimaFresh®, a concentrate of vegetable oils, and Natural Shine™, a concentrate of natural carnauba wax.
In 2005-06, selected trees in Chelan, Washington, were sprayed one day before harvest. The same formulas were sprayed on a set of trees in Malaga, Washington, in 2006-07 either 1 week before harvest or once a week for 3 weeks before harvest. In 2007 in Linares, Chile, the same formulas were sprayed on trees either 1 week before harvest or once a week for the 4 weeks before the harvest.
Harvested apples were stored and evaluated for quality after 90 and 180 days. A subset of the apples underwent a simulated packing process in which apples were soap-washed, cool-water rinsed, waxed, polished, and warm-air dried. After 3 days of storage, these apples were assessed based on the number of LB pits.
During storage, Chelan apples showed severe symptoms of LB regardless of treatment, suggesting insufficient time before harvest for the coatings to work. Typically the symptoms get worse with storage, but the study found the presence of LB to be strongest at 90 days, with little difference between 90 and 180 days.
Malaga apples also showed the most LB at 90 days. However, three treatments before harvest did reduce LB between 41% and 65% compared to untreated apples. At harvest, the fruit quality seemed unaffected, but some ripening effects increased with storage time. Apples treated three times were the least firm of all of the groups.
Of the Linares apples receiving a single application, only the EpiShield apples had fewer LB symptoms. When all four treatments were applied, apples had less LB—between 48% and 61% compared to the untreated apples. "Generally, multiple applications were more effective than single treatments for reducing incidence of LB," the study reports.
The researchers point out that further study is needed to better understand the optimum time and number of applications in relation to climate in order to make the most of LB-reducing treatments.
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