Fruit Crops

Pesticides and Tarnished Plant Bug Parasitoid in Strawberries

Success in implementing biological control programs sometimes requires integrating the use of natural enemies with pesticide use. Although natural enemies are generally more susceptible to pesticides than pests are, choosing physiologically selective pesticides, selective application techniques or selective timing of treatments can help minimize the impacts on the natural enemies. Many different insecticides, acaricides and fungicides are applied to strawberries on the central coast in California. Most insecticide applications are directed at nymphs of the western tarnished plant bug (Lygus hesperus). The first releases of the mymarid egg parasitoid Anaphes iole for inundative control of the plant bug are made before these sprays, but because of an extended egg laying period by the plant bug, additional releases of the wasp are necessary after plant bug treatments have begun (or insecticide treatments for other insect pests) - making compatibility between insecticide use and A. iole a critical factor.

Survival of adult wasps to foliar residues of 6 insecticides, 2 acaricides and 6 fungicides was determined at 4-6 different times after pesticide application. As would be expected, fungicides were the least toxic, acaricides more so, and insecticides were the most toxic. Among insecticides, fenpropathrin, bifenthrin and carbaryl caused the greatest mortality (> 75%), while naled, methomyl, and malathion caused the least mortality. 

Integration of A. iole with insecticides is most likely with naled, with an estimated mortality by day 13 after application of <1%, followed by methomyl, with mortality of <25% on day 13. Higher release rates of the wasp may be necessary after applications of malathion (53% mortality on day 13), and integration with fenpropathrin, bifenthrin or carbaryl is not realistic, with estimated mortalities >75%. Wasp releases should be compatible with acarcide or fungicide use, except for sulfur. Replacement of sulfur by myclobutanil for powdery mildew control would greatly minimize impacts on A. iole.

Source:

Udayagiri, S., A. P. Norton and S. C. Welter. 2000. Integrating pesticide effects with inundative biological control: interpretation of pesticide toxicity curves for Anaphes iole in strawberries. Entomologia Experimentalis et Applicata 95(1):87-95.

Fruit Injury Affects Green Mold Biocontrol on Citrus

AspireŽ, a formulation of the yeast Candida oleophila (Ecogen), is registered for postharvest application to citrus for the control of green mold (Penicillium digitatum). It competes with the pathogen for nutrients and space at wound sites. Once established, the yeast grows quickly to prevent the pathogen from germinating, growing and infecting the fruit. A major factor affecting efficacy is how quickly and well the yeast colonizes injuries to the fruit surface, including minor injuries involving only oil vesicles.

The yeast was able to colonize puncture-related injuries (that either encompassed oil glands or individually ruptured glands) within 1-2 days at 21° and 30°C, but no colonization occurred at 13°C. Ruptured oil glands were colonized more effectively if treated several hours after injury rather than immediately, probably because peel oil was toxic to the yeast but not to green mold spores. C. oleophila colonized punctures more uniformly than individually damaged oil glands, and provided more effective control of green mold originating at punctures than at oil gland injuries. Incubating treated fruit at 30°C for 2 days before storage at 21°C enhanced the control of green mold, and control was significantly improved by the addition of Aspire in one of two trials.

Source:

Brown,  G. E., C. Davis, and M. Chambers. 2000. Control of citrus green mold with Aspire is impacted by the type of injury. Postharvest Biology & Technology 18(1):57-65.


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