Fruit Crops

UV Light and Yeast Combine to Control Postharvest Storage Rots

A relatively recent concept in postharvest disease control is the use of hormetic doses (a stimulatory, sublethal amount) of ultraviolet light to elicit resistance to plant pathogens. Previous research has shown that hormetic UV treatment significantly reduces the severity and incidence of storage rots of harvested produce. Light treatments in combination with biocontrol agents might further reduce disease levels in stored produce.

The nonantibiotic-producing yeast Debaryomyces hansenii was used in experiments on preventing storage rots on peaches, tangerines, tomatoes and sweet potato roots. The fruit was first exposed to low doses of UV light (average 1.26 mW cm2) and then, after allowing 48 or 72 hours for induced resistance to the disease to develop, was dipped in a yeast suspension for one minute and allowed to air dry.

The combination of D. hansenii with UV irradiation was the most effective treatment in reducing storage rot of artificially inoculated fruits and of decay of naturally infected peaches. UV light alone only reduced brown rot of peach from 100% to 55%, but the combination light-biocontrol treatment reduced brown rot of peach to levels comparable to that achieved with fungicides (12%).

The yeast alone was only about as effective as the UV light alone, indicating a possible synergistic effect. More research is needed before these treatments could be commercialized.


Stevens, C., V. A. Khan, J. Y. Lu, C. L. Wilson, P. L. Pusey, E. C. K. Igwegbe, K. Kabwe, Y. Mafolo, J. Liu, E. Chalutz and S. Droby. 1997. Integration of ultraviolet light with yeast treatment for control of postharvest storage rots of fruits and vegetables. Biol. Control 10: 98-103.

Implementing Mite Biological Control in an Apple Orchard

Biological control of mites on fruit crops requires a great deal of patience, and careful selection of insecticides and fungicides that are applied in the orchard. In general, predator mites are not as resistant to the standard pesticides that growers use as are the pest spider mites.

Last year, there was a bumper crop of predator mites in Michigan orchards, with Amblyseius fallacis and Zetzellia mali the most common species. One reason for higher numbers of predators in recent years is the use of Provado insecticide for leafminer control instead of other chemicals that would wipe out the good mites. This makes biological control of mites just a little easier.

Some steps to take to successfully establish biological control in your orchard are:

Another option to improve chances of success is by "seeding" orchards with predators. In preliminary trials, 10-inch shoots were taken from an orchard with high Z. mali populations and placed in several orchards with a history of mite outbreaks and no predators. There were nearly two Z. mali per leaf in the seeded areas and none in the unseeded areas. Because Z. mali is more of a general feeder than A. fallacis, it can survive on very low levels of mites, whereas A. fallacis, which feed mainly on other mites, often does not appear in high numbers until the pest mites are over threshold.


Thornton, G. 1998. Protect mite predators when selecting pesticides. Crop Advisory Team Alert Sept. 29, 1998 Vol. 13, No. 18., page 2-3.

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