Grapes:
Drosophilds and Sour Rot: As the sugars start to increase in early verities like Chardonnay, be aware of Spotted Wing Drosophila combined with native fruit fly species. These populations increase at this time of year and help spread sour rot. Sour rot will only be present when you also have injured fruit. Fruit splits and various insects can help cause that initial injury. It is thought that the spotted wing drosophila (SWD), because of its saw-like ovipositor, can help cause this initial injury, helping to make the fruit more attractive to native drosophilid species. After injury the fruit serves as a food source for ethanol-producing yeasts and acetic acid producing bacteria, the causal agents of sour rot. This in turn attracts more fruit flies to lay more eggs and spread the decay. Good canopy management for air circulation is useful to reduce sour rot incidence. However, this must be combined with insecticides and antimicrobials. A treatment regime that consists of weekly applications of an insecticide (Mustang Maxx (or other pyrethroid), Malathion, Delegate/Entrust, + Oxidate 2.0 has been found to be helpful. Other sterilants can also be used. Since it is important to rotate insecticide classes when treating this often, growers should use no pyrethroid or other insecticide class more that 2 times in a row. These treatments should be started before the onset of visible sour rot and fruit fly presence. [Read more…]
