Washington State University Cooperative Extension
The Newsletter of Pheromone-based Orchard Pest Management
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.
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
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
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.
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.
|Vol. 3, No. 5 || || May 1, 1998|
Inside this issue:
Alway's Areawide IPM page
Areawide IPM page (with CAMP site descriptions)
...WSU-TFREC Entomology home
...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
Orchard Pest Control with Foliar Oils
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
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.
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.
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
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
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
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
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
Partial Funding provided by: Washington State Tree Fruit Research Commission,
U.S. Department of Agriculture-Agricultural Research Service.
Cooperative Extension, Chelan County
400 Washington St.
Wenatchee, WA 98801
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