HORTICULTURAL OILS CAN CONTROL MANY ORCHARD, NURSERY PESTS

                         Roanoke Times
                 Copyright (c) 1995, Landmark Communications, Inc.

DATE: WEDNESDAY, April 14, 1993                   TAG: 9304140133
SECTION: CURRENT                    PAGE: NRV10   EDITION: NEW RIVER VALLEY 
SOURCE: 
DATELINE:                                 LENGTH: Medium
HORTICULTURAL OILS CAN CONTROL MANY ORCHARD, NURSERY PESTS
Horticultural oils provide homeowners with an excellent means of controlling some important landscape pests. They have been used successfully by fruit tree owners for years and are now finding uses in greenhouse and nursery enterprises.
Horticultural oils can provide good control of aphids, scale mites, psylla, mealybugs and plant bugs. They are particularly useful for knocking back pest populations before the grower releases beneficial organisms, because they do not have a toxic residue.
How they work
Horticultural oils have various modes of action against insect pests. They can suffocate insects by plugging their spiracles, or breathing openings. They also can act as a poison by interacting with fatty acids in the insect body and disrupting metabolism. Insect eggs are susceptible to the same suffocating and poisoning effects.
Finally, oils can repel insects for up to a week after application. In a study conducted by Hiram Larew with USAID, plants treated with oil had 95 percent fewer greenhouse whitefly eggs deposited on them than untreated plants.
Using horticultural oils
Horticultural oils are typically applied in a 2 percent solution. For small operations, that works out to about five tablespoons per gallon of water. Some researchers have reported that mixtures with 1 percent oil and 1 percent insecticidal soap can be more effective than either soap or oil alone.
Oil also has been said to enhance the effect of Bacillus thuringiensis (commonly called Bt, it's sold under such brand names as Thuricide and Dipel) possibly by acting as a buffer against chemical breakdown of the Bt toxin and by inhibiting Bt degradation by ultraviolet light.
The timing of the spray can be adjusted for the pest of greatest concern to the grower. Oil sprays have their greatest effect on European red mite eggs just before they hatch, at about the pink stage of apple bud development. Oil sprays should not be applied to buds once pink is showing because of the risk of phytotoxicity, or harming the very plant you're trying to protect.
If the bark has many European mite eggs, the timing for mites may be followed. These eggs are tiny reddish spheres best seen with a hand lens. Look in growth scars and crevices on fruit spurs, although in heavy populations, eggs may cover the underside of large branches, giving them a reddish appearance.
In most backyard situations, the timing for aphids may be more appropriate. If an insecticide is mixed with the oil, apply the spray when there is about\ inch of green showing in buds. This is when the eggs of rosy apple aphid hatch; after hatching, the nymphs crawl into the opening buds where they cannot be reached by sprays.
If no insecticide is to be added and the grower is relying solely on the suffocating effect of the oil, a better timing would be at the silver tip stage of bud development.
Precautions
Successful application of horticultural oils require strong agitation of the oil and water emulsion before and during spraying. Failure to agitate sufficiently will allow the oil and water to separate, and you could end up spraying the majority of the plants with water and a few with damaging doses of straight oil.

by Bhavesh Jinadra by CNB