Washington State University Cooperative Extension

Areawide IPM Update

The Newsletter of Pheromone-based Orchard Pest Management

Vol. 3, No. 5   May 1, 1998

Inside this issue:

Web links:

...Ted Alway's Areawide IPM page

...USDA Yakima Areawide IPM page (with CAMP site descriptions)

...WSU-TFREC Entomology home page

...Index to Areawide IPM Update newsletters

Cooperating agencies: Washington State University, Oregon State University, University of California, U.S. Department of Agriculture, and Chelan County.

Cooperative Extension programs and employment are available to all without discrimination.


Orchard Pest Control with Foliar Oils

O il applications have been a key part of apple and pear pest control programs for most of this century and remain so today. There are few blocks that don't receive oil in the dormant or delayed dormant periods, before trees have leafed out. Oil sprays in the post-bloom period, however, have been rarely used in recent years but interest in their use has picked up, for several reasons. New oils, variously termed summer oils, horticultural mineral oils or foliar oils, have been refined. Many of the products now commercially available offer improved kill of some pests with a reduced risk of phytotoxicity. Growers are seeking "softer" pest control materials that will complement the increased use of minimally disruptive pest control methods, such as codling moth mating disruption. Finally, the pending loss of many of the broad spectrum insecticides that have been central to most orchard pest control programs has left growers and consultants searching for viable alternatives.



There are a number of ongoing investigations into the use of foliar oils for apple and pear pest control, examining both the pest control and horticultural effects.


At the WSU Tree Fruit Research and Extension Center there is a long term study of the use of foliar oils now entering its fourth year. Participating in this study are entomologists Jay Brunner, Elizabeth Beers and John Dunley, plant pathologist Gary Grove, plant physiologist L.E. Schrader, and horticulturist Kathleen Williams. This investigation has settled on the use of two oils developed by Exxon, Orchex 692 and Orchex 796.
Dilute applications of 1% oil solutions by airblast sprayers have been made to apples (Delicious, Golden Delicious and Fuji) and pears (Bartlett and Anjou). Below are brief summaries of some of the research highlights.

Pest Control

Codling moth: Six applications of 1% oil (three each generation) reduced codling moth damage 50 to 75% when compared with non-oil treated blocks. The first application was made at 1% egg hatch, followed at two week intervals by two more sprays in each generation.

Leafroller: Some of the earlier studies that focused on codling moth control also observed a drop in the number of leafroller larvae. Later studies that looked specifically at leafrollers showed little or no effect of the oil on the hatch of leafroller egg masses, larval mortality or colonization by larvae.

White apple leafhopper: Leafhoppers were also observed to be suppressed by the oil applications for codling moth control. Studies showed that there was reasonable contact kill of nymphs coupled with some suppression of oviposition, with higher rates of oil having more activity than the 1%.

Green apple aphid: With a 1% solution, excellent control was obtained with Orchex 692, with suppression (60-75% reduction) from Orchex 796. Little effect was observed on aphid predators.

Mites: Applications of summer oils reduced European red mite levels, but also reduced populations of apple rust mites and predatory mites, raising concerns with the effect of oil on integrated mite management in apples. Despite this, mite flareups following oil use are unlikely.

Apple mildew: Good early season control was achieved with Orchex 682 as 1% and 2% solutions, but control declined with sprays later in the year.

Horticultural effects

After earlier studies showed that 2% oil applications frequently caused unacceptable marking on fruit, their recent studies have used only 1% oil sprays. The 1% oil sprays with Orchex 796 were shown to significantly reduce both photosynthesis and respiration, probably by plugging up the leaf stomata and damaging the leaf chloroplasts. Fruit marking has been a frequent problem on Anjou pears, even with the 1% rate, but 1997 studies showed no significant fruit marking on Anjous or Bartletts or any of the apple cultivars. There was a trend for Delicious and Fuji apples to be slightly more mature and for pear fruit to be more yellow with the use of Orchex 796.

Medford and Hood River

Post bloom applications of oil have been used successfully in the Medford, OR area, together with codling moth mating disruption, since 1995 on over 400 acres of pears associated with the Codling Moth Areawide Management Program. Applications of Orchex 796 oil are made at 200, 400 and 600 D after codling moth biofix in this program, and control of codling moth, pear psylla and spider mites has been equal to or better than that in the nearby conventional blocks used for comparison, and at a lower cost.

Research into the effects of horticultural spray oil on pear tree productivity and fruit quality was initiated in 1996, out of concern with the long-term effects of repeated oil use for pest control. Research blocks are located in both Hood River, OR (with Anjou and Bartlett cultivars) and Medford (with Comice, Bartlett and Bosc). The researchers involved are Philip VanBuskirk, Richard Hilton, Peter Westigard and David Sugar, located at the Southern Oregon Research and Extension Center in Medford, and Helmut Riedl, of the Mid-Columbia Agricultural Research and Extension Center in Hood River. Applications of 1% Orchex 796 spray oil have been made using both hand guns and airblast sprayers, applied at the three times noted above.

Horticultural effects

After two years, it appears that the Anjou and Comice cultivars are the most sensitive to the oil treatments. The oil sprays significantly reduced fruit set and fruit size in Anjous, while Comice had reduced return bloom, in the second year of treatment, as a result of the oil sprays the previous year. Fruit russet was higher on the Bartletts in both locations and on the Hood River Anjous, although it was not enough to downgrade the fruit in any case. Bosc pears in Medford showed no significant differences with oil treatment on fruit size or quality. These results are found in the hand gun portion of the trials, as airblast sprayers were first used only in 1997; the high gallonage of application with the hand guns may overstate the negative effects of the oil. Further study of the effects with airblast application will continue in 1998 and beyond.


Consultant and grower survey results

Some growers have used foliar applications of oil for pest control for many years. Many of these are organic fruit producers, for whom summer oils have been one of the few pest control materials they could choose from. Others have begun the use of foliar oils more recently, with an increasing number of pests as their target. Foliar oils have been used with success on Bartlett pears in much of the California production area but their use in Washington has been much less widespread. In this survey, 22 growers and consultants from Washington state responded with their experiences with the use of foliar oils on apples and pears. Nineteen had used foliar oils on apples and sixteen had experience with oil on pears (beyond its use as just an adjuvant for other insecticides).

Oil types: Most used an oil specifically formulated for foliar application in the post bloom period, such as Orchex 796, Saf-T-Side, Stylet Oil or one of several "summer oils" labeled by an agrochemical distributor. Others used the same oil used in their delayed dormant applications, a Supreme oil such as Volck or Omni. One grower used a fish oil and another used a vegetable oil.

Rates and spray volume: Most growers applied oil as a 1% solution, with others using close to a 2% rate. A few used as little as 0.5% oil in their sprays. Most applications were dilute, applied to the drip point, in volumes of 200 to 400 gallons/acre. Twelve of 22 respondents applied sprays of foliar oil in 100 gpa or less, and many emphasized the critical importance of thorough coverage, whatever the spray volume. The number of applications ranged from 1 to over 6 per season in any one block.

Pest control: An increasing number of pests are being targeted with foliar oil sprays, with timing (and results) varying considerably. The most common pests treated with oil are codling moth, leafminer, pear psylla and spider mites.

Codling moth: 8 of the 22 applied oil for this pest, most commonly applying the first spray at 1% egg hatch and repeating the application at intervals of either 10-14 days or 200 degree-days. Up to three sprays were applied per generation, with several treating only the second generation. Codling moth control was fair to good, with several organic growers being the most pleased. One grower had 2% damaged fruit at harvest with six oil sprays alone, and was quite pleased. Most emphasized the importance of supplementing oil sprays with another control method, like mating disruption, and stated that oil can help maintain low codling moth populations but is relatively ineffective in reducing high populations.

Western tentiform leafminer: 8 of the respondents had used oil for leafminer control, generally targeting the oil spray for peak adult flight/peak egg lay, which corresponded to sprays at pink (1st generation), in June (2nd generation) or August (3rd generation). Most were quite pleased with the control from the oil, frequently getting from 60-70% reduction to up to 99% fewer mines than in nearby untreated blocks. Better control was generally achieved with sprays for the earlier generations, although two were quite pleased with the 50% or better suppression they got with an August spray.

Pear psylla: 14 had used oil specifically for pear psylla control, beyond its use as an adjuvant for insecticides such as abamectin. In general, from 1 to 3 oil applications were made for psylla control, aimed at the smaller instars. Control was considered fair to good, providing suppression by reducing populations 50 to 75% with 1-2 applications. Nonetheless, most growers supplemented the oils with other materials to get adequate psylla control. Those who had good to excellent control with oil relied upon 3 or more sprays.

Mites: Most of the oil used on mites was meant for European red mite control, with oil being applied in the summer to kill eggs. The reports indicate that most results were good to very good with foliar oil sprays, reducing populations 50% or more with a single application and with minimal effect on predatory mites. Control of McDaniel or two-spotted spider mites was less consistent and effective. Rust mite control on pears was reported by a few, with generally good results.

Other pests: Green apple aphids were controlled to a moderate extent in three reports, and one other consultant reported excellent control of large colonies with a single oil application during hot weather. White apple leafhopper control was reported as poor to fair with oil, with no more than a 50% reduction in nymphs with a single spray, although control was somewhat better when the first generation was targeted. There were several reports of good leafroller control, when repeated oil sprays were timed for the beginning of egg lay. Improved kill of large larvae was also reported when Bt was applied with oil. Two growers used foliar oil sprays for apple mildew control, and were pleased with the results when it was used tight cluster through petal fall as one part of a mildew control program.

Natural enemy effects:
Many users saw little effect of oil use on the natural enemies (predators and parasites) found in their orchards. Aphid predators, both adults and larvae, appeared untouched and parasitism rates of leafminers were unchanged by oil applications. Several noted reductions in apple rust mites and, in one case, predatory mites, which could have an impact upon integrated mite control with repeated applications.

Phytotoxicity: This is the major downside of foliar oil use. Marking of fruit or foliage, or both, was observed by many users at one time or another, although damage was not necessarily economic. Phytotoxicity from oil was prevented or minimized by avoiding the more susceptible cultivars (e.g. Anjou pear), ensuring good spray tank agitation, applying oil in good drying conditions but not when trees are stressed or temperatures are hot (>85F), and avoiding applications with or close in timing to incompatible materials, such as Captan, Thiodan, calcium chloride and sulfur compounds. Few problems were seen with only one or two oil sprays, but with more applications per season concerns arose with marking and fruit finish. Several growers and consultants worried about the long-term, chronic effects of oil use on fruit trees and possible effects on tree vigor, spur health, fruit size and return bloom; two consultants observed reduced spur vigor and enlarged lenticels on young pear wood with summer oil use over several years.



The use of foliar oil sprays for pest control is slowly increasing in the Northwest. They are relatively cheap and, with the better refined oils available today, have less risk of fruit marking than did some oils used in years past. Their use may assume added importance in future years if we lose the use of many of the key insecticides we currently rely on. They can provide suppression of many orchard pests, and control of a few, and they may best be used as one tool to include in a multi-faceted pest management program that includes mating disruption, insect growth regulators and other new pesticide chemistries and pest control methods. Hopefully, ongoing research with foliar oils in the Northwest will help answer concerns with phytotoxicity and chronic effects from oil use, and better define how they can fit into an effective orchard IPM program. Until then, many growers and consultants will continue to share the opinion of one grower who responded, "They are better than nothing!"

Ted Alway, Editor
Phone: (509) 664-5540
Fax: (509) 664-5561
e-mail: alway@coopext.cahe.wsu.edu

Partial Funding provided by: Washington State Tree Fruit Research Commission, U.S. Department of Agriculture-Agricultural Research Service.

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