Tree Fruit IPM Advisory

USU Tree Fruit IPM Pest Advisories provide nearly weekly updates on current insect and disease occurrences, biology, and treatment recommendations for Utah. Updates run from mid-March through September.

To subscribe to this advisory (link to this newsletter sent to your email inbox), click here.

Horticultural Oil/Dormant Oil Demystfied

pdf version

April 14, 2010

In this Issue:

What to Look for/Do Now:

  • Aphid and psylla eggs starting to hatch
  • speckled green fruitworm adults emerging soon to lay eggs
  • lygus bugs becoming active soon
  • Do not prune out old fire blight cankers if the bacteria has started to ooze


Bud Stages

The next six days of warm weather are going to result in rapid bud and insect development.

Davis, Box Elder, Salt Lake, Weber counties:
Apples: green tip - 1/2” green
Apricots: bloom
Cherries: green tip
Peaches: pink - first bloom
Pears: bud burst

Cache County:
Apples: silver tip - green tip
Cherries: swollen bud
Peaches: swollen bud - 1/4” green
Pears: swollen bud

Utah County:
Apples: green tip - 1/2” green
Apricots: first bloom - bloom
Cherries: green tip
Peaches: pink
Pears: bud burst - green cluster

Grand County:
Apples: first pink - open cluster
Apricots: full bloom - petal fall
Cherries: first bloom
Peaches: bloom
Pears: full bloom


Insect and Disease Activity/Info


Codling Moth

On approximately April 20-26 (first pink stage of apple), growers in northern Utah who are using codling moth traps should set traps in their orchard or backyard apple tree.  One trap per 10 acres should suffice to determine biofix (the date that adult moths first start to fly).   Traps should be hung as high as possible, in the direction of the prevailing wind.  Make sure no debris is blocking the openings.  Traps in Carbon and Cache counties will not need to go up until late April.

If you are not trapping, do not worry.  The USU IPM program gets biofix dates in various locations across northern Utah so that we can provide exact starting spray dates for codling moth control.

Rosy Apple Aphid

Rosy apple aphid eggs are hatching now in the warmer areas of northern Utah.  Feeding curls leaves and can sometimes disfigure fruit.  Usually control is not warranted; delayed dormant oil applications will take care of most of the overwintered eggs.  Commercial growers that have not traditionally had success with dormant oil applications could consider a non-pyrethroid insecticide at pink stage of apple, including Actara, Assail, Beleaf, Calypso, or Esteem.

rosy apple aphids
Rosy Apple Aphids



campylomma stings on apple
Campylomma “stings” on apple fruit.

Also known as mullein bug, campylomma is actually a beneficial predator.  Early in the season, however, young nymphs may feed on fruitlets when no prey is available, causing corky bumps.  It overwinters as eggs in woody trees, including apple and pear.  Egg hatch occurs pre-bloom, and adults are fully formed by mid May.  Many adults migrate on to herbaceous hosts.  Over the summer, they feed on thrips, aphids, mites, and psylla.

Scout for nymphs during bloom by vigorously shaking flower clusters into a paper cup, or banging a branch over a cloth tray.  In general, one nymph/tray or cluster for goldens, and 4 nymphs for other varieties warrants a treatment before, during, or after bloom when bees are not foraging.


Lygus Bug


cat-facing on apple cat-facing on peach
oregano lygus bug

Early feeding by lygus bugs on developing apples or stone fruits results in deeply pitted fruit, sometimes referred to as cat-facing injury.  Adult lygus spend the winter in protected areas such as within plant debris or among alfalfa litter, or in cracks and crevices in tree bark.  They start to feed actively when temperatures approach 70°F, between the tight cluster and bloom periods of apple.  They will actively feed throughout the summer on a wide range of hosts including fruits, vegetables, forage crops, and weeds.   Orchards with a heavy weed groundcover or adjacent alfalfa fields are more prone to damage.  Within the orchard, removing weeds such as common mustard can reduce fruit injury.

Lygus bug is difficult to manage, especially for orchards near range or forage land.  Insecticides for control are usually broad-spectrum, and can harm beneficials.  According to Cornell entomologists, the pyrethroids (Asana, Ambush, Baythroid, Danitol, Pounce, Warrior) are most effective, followed by the neonicotinoid group that includes Actara, Calypso, and Assail, plus Avaunt, which are moderately effective.

Predatory Spider Mites 

You may hear us talking (or have read) about not using materials that contain a pyrethroid early in the season.  One of the primary reasons for this is to conserve our native western predatory mite, Typhlodromus occidentalis.  Predatory mites feed on pest mites, including the twospotted spider mites, McDaniel spider mites, rust mites, and blister mites.  The western predatory mite overwinters as mated females in protected sites on trees or in groundcover.  They start activity early (much earlier than spider mites), at the green tip stage of apple, increasing in activity at the tight cluster stage.  They immediately disperse, looking for prey.

Their primary prey at this time of year are the rust mites and blister mites that are also active early.  Keeping these mites in the orchard will help to build up a good population of predatory mites.

Factors that may reduce predatory mite population include:   

  • mortality in winter:  Typhlodromus are sensitive to very cold, dry winters.  
  • amount of prey early in the season
  • application of pyrethroids early in the season


Upcoming Monitoring/Insect Activity

Pest Host Activity/Action
Pear psylla pear Adults active just before bud swell; egg-laying from bud swell to green cluster
Rosy apple aphid apple First egg hatch around first pink
Codling moth pome fruits Hang traps at first pink
European red mite (rare) all First egg hatch around apple full bloom
Campylomma bug apple Egg hatch begins at apple first pink
White apple leafhopper apple Egg hatch begins at apple first pink


Degree Day Accumulations

March 1 - Tuesday, April 13

County Location GDD 50
Box Elder
Perry 46
Tremonton 32
Cache North Logan 27
Providence 39
Smithfield 23
Carbon Price 45
Davis Kaysville 54
Grand Castle Valley 153
Juab Tintic 34
Salt Lake Holladay 73
West Valley City 70
Tooele Erda 59
Tooele 50
Uintah Vernal 46
Utah Alpine 51
American Fork 62
Genola 77
Lincoln Point 53
Payson 65
Provo 83
Santaquin 56
Weber Pleasant View 53


Production Information

Horticultural/Dormant Oil Demystified

At this time of year, we often discuss spraying “dormant oil” and in summer, we talk about “summer oil.”  This dated terminology applied to pest control many years ago.  Dormant oils were never used during the growing season because they were unsafe for plants, and summer oils were only used as a spreader-sticker.  Today, those terms simply refer to the timing of the treatment.  The product that is applied during the dormant period and summer is the same; the only difference is the concentration.  Oils are unique in that they have been used for more than a century and no target pest has developed resistance to them.

Horticultural mineral oil is a term used to describe a class of high quality oils formulated for agricultural use.  They are produced by distilling and refining crude oils.  Other terms are mineral oil,  petroleum oil, spray oil, insecticidal oil, horticultural oil, superior oil, paraffinic oil.  Various other petroleum products are made from crude oils, including gasoline, kerosene, fuel oil, and lubricating oil.

Oil Characteristics

1.  The newest horticultural oils are sometimes considered “narrow range oils” which means that the oil has been through two distillation stages to reduce the temperature range at which the oil boils.  This results in an oil that has high insecticidal properties and low potential for plant injury.  These oils are also sometimes referred to as “superior oil.”

2.  Horticultural oils are made from crude oil that is high in paraffin.  Paraffinic oil occurs in sources in the eastern U.S. and in Texas.  (Oil dug from the western U.S. is high in naphthenes.)  Studies have shown that paraffinic oils have greater insecticidal properties. 

3.  In newer oils, the unsaturated hydrocarbons have been removed.  These compounds that were found in older oils were responsible for plant injury.  The term for oils low in unsaturated hydrocarbons is “unsulfonated residue.”  The safer oils usually have a UR value at 92% to 97%.

4.  The label for oils will provide a variety of information:
     a.  percent oil content:  the oil may be listed as “mineral,”, “petroleum,” or “paraffinic.” 
     b.  minimum UR value:  Make sure it is more than 92% so that injury to plants is reduced.

How Oils Kill Pests

Oils kill pests primarily by smothering, and work best on soft-bodied insects.  Insects require oxygen to live, and oil plugs the insect’s air-exchange apparatus, causing slow suffocation.  Oil works better on eggs just before they hatch because the oxygen requirement is greater.  This is why we suggest spraying oil at the “delayed dormant” timing when fruit tree buds have started to swell.  Oils applied during dormancy or delayed dormancy are more effective at a higher concentration (usually 1.5-2%) and the plants will not be affected.  Oil applied in the summer should be mixed at a lower concentration (1%) to reduce plant injury. 

Oil may also act as a repellent, delaying egg laying (of pear psylla, for example) or preventing scale crawlers from settling.

Oils are targeted at:  aphids, soft scales, pear psylla, immature leafhoppers, whiteflies, mites, and eggs of most insects.

How to Prevent Plant Injury

Oils that are properly applied rarely damage plant tissue.  Oils may injure plants if applied at too high a rate or on hot days.  Trees most susceptible to damage are those suffering from drought stress.  They have a lower tolerance for interruptions in air-exchange supply through stomates or lenticels

Oil should not be applied:

  • on days where temperatures exceed 90 or are below 30 degrees F
  • on dry, windy days

Symptoms of plant damage:

  • dark green to purple discoloration on leaf margins
  • water-soaking around stomates or lenticels
  • swelling or corking of lenticels
  • delay in budbreak
  • leaf drop and death of buds

Other Oils

Vegetable oils are sometimes sold as insecticides, where cottonseed and soybean oils are the most effective.  Neem oil (from seeds of the neem tree, Azadirachta indica) has some insecticidal and fungicidal properties.

Essential oils (rosemary, lavender, thyme, clove, garlic, coriander, peppermint, citronella), are said to include some fumigant and topical toxicity as well as repellent effects.  They are considered minimum-risk pesticides and are exempt from Environmental Protection Agency registration.  As a result, many of the products labeled for control of insect pests have not been subjected to evaluation of efficacy or plant toxicity.  A recent study of several products on greenhouse plants showed that essential oils vary in their effectiveness against certain arthropod pests stated on the label, and are phytotoxic.  The oils controlled spider mites and mealybug but caused significant plant injury, while green peach aphid and thrips were not affected by the oils (Cloyd, et al 2009). 

Cloyd, Raymond, et al.  2009.  Effect of Commercially Available Plant-Derived Essential Oil Products on Arthropod Pests.  Journal of Economic Entomology 102(4):1567-1579.


Bud Phenological Stages


apple green tip apple half-inch green
Green tip 1/2" green


pear bud burst pear green cluster pear first bloom
Bud burst Green cluster First bloom


peach swollen bud peach first pink peach first bloom
Swollen bud Pink First bloom


cherry swollen bud cherry bud burst
Swollen bud Bud burst


apricot first bloom apricot full bloom
First bloom Full bloom


Spray Materials - Commercial Applicators

For dormant and delayed dormant timing

Target Pest Host Chemical Example  Brands Amount
per acre
REI Comments
San Jose scale pome and stone fruits 2% oil alone or with:     varies  good coverage essential
pyriproxyfen Esteem 4-5 oz

12 h

Aphids, including woolly apple aphid apple, cherry, peach 1.5% oil alone or with:        good coverage essential; addition of Lorsban necessary for woolly apple aphid
chlorpyrifos Lorsban  4 pints 4 d
Pear psylla pear 1.5-2% oil with:        good coverage essential

Surround (organic) must be applied up to 3 times before first bloom.
esfenvalerate Asana 3 qts 12 h
lime sulfur   1 pint 48 h
kaolin clay Surround 11 gal 4 hr
permethrin Ambush, Pounce see label 12 hr
lamda-cyhalothrin Warrior 2.5-5 oz 1 day
pyriproxyfen Esteem 5 oz 12 h
Pearleaf blister mite pear 1.5-2% oil with:        
carbaryl Sevin 4 pints 12 h
Peach twig borer peach, nectarine Bt Biobit, Dipel see label  4 h  apply before bloom to target larvae as they leave hibernacula to feed on foliage and before they enter shoots
chlorantraniliprole Altacor 3-4.5 oz 4 h
spinetoram Delegate 3-7 oz 4 h
spinosad Entrust, Success 4.5 oz 4 h
Coryneum blight (shothole) stone fruits fixed copper COCS, Kocide, etc.  varies  1 d   use only fixed copper products.  Do not use after green tip stages.  Be sure tank is always agitated during sprays.
chlorothalonil Bravo, Echo 3-4 pints 12 h
Fire blight apple, pear fixed copper many  varies  1 d  do not apply copper after green tip stage because fruit russetting may result; there are mixed opinions on whether copper has an effect on managing fire blight



Spray Materials - Residential Applicators

Note that these treatments are only recommended if you know you have the particular pest in your trees or had a problem the previous year.

For dormant and delayed dormant timing

Target Pest Host Chemical Example  Brands Comments
San Jose scale, aphids pome and stone fruits 1.5-2% horticultural oil Volk oil, Bonide all seasons spray oil, HiYield Dormant Spray, etc. smothers aphid eggs
Pear psylla pear 1.5-2% horticultural oil Volk oil, Bonide all seasons spray oil, HiYield Dormant Spray, etc. Best to treat before egg-laying and when adults are detected. 
Pearleaf blister mite pear 1.5-2% oil with:   Only a single application is needed
carbaryl Sevin
lime sulfur variety
Peach twig borer peach, nectarine Bacillus thuringiensis Ferti-lome Dipel, Green Light apply before bloom to target larvae as they leave hibernacula to feed on foliage and before they enter shoots
spinosad Ferti-lome, Green Light lawn and garden, Monterey
Coryneum blight (shothole) stone fruits copper sulfate Basic Copper, Microcop copper can be injurious to plant tissues; fixed copper less so.  Do not use after green tip stages.
fixed copper COCS, Kocide, etc.
Fire blight apple, pear fixed copper many do not apply copper after green tip stage because fruit russetting may result


Precautionary Statement:  Utah State University Extension and its employees are not responsible for the use, misuse, or damage caused by application or misapplication of products or information mentioned in this document.  All pesticides are labeled with ingredients, instructions, and risks.  The pesticide applicator is legally responsible for proper use.  USU makes no endorsement of the products listed herein.