Dormant Sprays, Pear Fruit Sawfly – IPM Pest Advisories

In this Issue

Dormant Oil Sprays – with images of targeted insects and diseases
Pear Fruit Sawfly – controlled with insecticide before bloom

Dormant Oil Spray

If you live in northern Utah, you may not be thinking of fruit tree care when you look out the window and see all the snow! But warmer weather is coming and tree buds will be popping soon–at one of the latest times in about two decades.

Horticultural oil is a great option to target many insect pests (see images below) because other insects like beneficials or pollinators, are not active. The term we use is “dormant oil,” but the timing of application is after trees break dormancy. This timing matches up with the increasing activity of the overwintering insect stages. If applied too early, the oil will not work as well on these insects.

In the warmest areas of Utah, the dormant oil may already have been applied. But in northern Utah, the time to spray will be in at some point in April (more information below).

Dormant Copper Spray

Copper is another material that can be used at the same time as oil. Copper should only be applied if the following pest problems were present last year: fire blight (apple, pear), coryneum blight (peach, nectarine, apricot), and peach leaf curl (peach).

Some Insects and Diseases Affected by the Dormant Spray

Click on an image for caption information.

Aphids overwinter as eggs near buds. Use oil alone or with an insecticide.

San Jose scale nymphs — San Jose scale overwinters as a mix of nymphs and adults. Use oil alone or with an pyrethroid or pyriproxyfen (Esteem, for commercial use).

Peach twig borer overwinters as larvae in peach/nectarine tree crevices. Use oil alone or mix with an insecticide.

All the tiny specks on this bud are eriophyid mites. Blister mites, peach silver mites, and rust mites are all eriophyid mites. They overwinter in bud scales.

Brown mites overwinter as eggs in protected sites on trees (unlike spider mites, which overwinter on the ground).

Pear psylla eggs are laid near buds in early spring. If this was a problem last year, apply oil twice, spaced about 7 days apart.

For fire blight, apply copper to apple/pear between swollen bud and green tip stages. It is OK to mix with 2% oil for the insect treatment.

Peach leaf curl is only prevented by applying copper in spring, when green leaf tips emerge. Infections occur during cool, wet springs. The foliage becomes distorted, discolored, and swollen.

Dormant Spray Instructions

Do I Need to Spray?

If your trees were newly planted last fall, or if they have never been affected in the past by the pests shown in the image gallery above, you can forego a dormant spray.

When do I Spray?

There are two factors to consider for determining when to spray: the bud stage of your fruit trees (pictures of fruit bud stages), and weather conditions.

Bud Stages

The window for application extends from bud swell to when leaves just start emerging, usually a period of several weeks.

The last point at which you can safely apply the dormant spray for each crop is:

apple: half-inch green (ideally, application is made at green tip stage)
apricot: just before first bloom
cherry: white bud
pear: green cluster
peach/nectarine: pink stage (when the pink shows through the flower bud)
plum: green cluster

Weather Conditions

Only apply oil and/or copper if temperatures remain above freezing (ideally above 40°F) for 24 hours after application.
Ideally, spray on a clear, non-windy day in the 50° to 70°F temperature range.
Do not apply if rain is predicted within 24 hours. This will help give the spray time to work.

How do I Spray?

Commercial growers

Oil should be applied at a rate of 2%, which is 2 gallons per 100 gallons of water.
(Optional) Mix oil with an insecticide such as Warrior or Asana to help improve knockdown of overwintering pests.
Copper can be mixed with the oil/insecticide.
Thoroughly cover all cracks and crevices of the tree bark and buds.

Backyard growers

Oil should be applied at a rate of 2%, which is 5 Tbs in 1 gallon of water.
If you are not growing organically, and aphids or scale have been a serious problem and oil alone has not worked in past years, consider mixing the oil with the appropriate rate of an insecticide, such as Spectracide Triazicide, GardenTech Sevin, or Malathion.
The oil can be mixed with copper, for example if apple or pear trees have had fire blight in the past.
Make sure to thoroughly cover all cracks and crevices of the bark and buds.

More details about oil and copper

Oil is sold as a concentrate, so it must be mixed at the proper rate with water before application.
There are plant-based oils and petroleum-based oils. For the dormant oil application, the petroleum-based oils work the best, although canola-based oil is another option.
- Petroleum-based oils – There are many brands, and they all work the same. Examples include All Seasons Horticultural Oil, Monterey Horticultural Oil, Gordon’s Dormant Oil Spray, Ortho Volk Spray Oil, Hi Yield Dormant Oil, etc.
- Plant-based oils – One example is Natria Multi-Insect Control, and there are many others. Neem oil is not as effective at the dormant timing.
Copper products can be found at any local garden center. Monterey Liqui-Cop is one example (copper diammonia diacetate complex); however, copper products that have the ingredient, copper octanoate (Gardens Alive Soap Shield; Bonide Liquid Copper Fungicide; Natural Guard Copper Spray; Espoma Copper Soap) contain a lower concentration of copper so they are safer for the environment.

Pear Fruit Sawfly

Pear fruit sawfly (Hoplocampa brevis) occurs primarily in Utah County and southern Salt Lake County. The adult is a small, fly-like wasp that is reddish-yellow in color. Females lay eggs inside flowers, and the hatched larva feeds within the developing pear for approximately six weeks from early to mid-spring. After this time, the insect goes into a dormant stage until the following spring.

Symptoms of pear fruits with larval feeding include:

deformed and swollen shape
blemished skin
round hole located near the calyx, accompanied by black decay and wet frass
premature fruit drop

To distinguish pear fruit sawfly from codling moth, keep these factors in mind:

Pear fruit sawfly larva exiting a fruit.

symptoms of pear fruit sawfly will appear several weeks before codling moth
sawfly frass is wetter and darker
sawfly larvae are smaller, darker in color, and have 7 pairs of prolegs (as opposed to codling moth’s 5)

The population size of this insect fluctuates from year to year depending upon the previous year’s damage level, whether adult flight is synchronized with pear bloom, the level of fruit set, and overwintering conditions.

If the crop load is high, damage from pear sawfly will be “absorbed” by crop thinning, and therefore, intervention may not be necessary. If the crop load is light, the injury could cause a greater negative impact.

Treatment

Utah pear growers have found success with a single spray applied just before bloom (targeting adults before they lay eggs inside flowers).
They reported that the use of horticultural oil (2% rate) mixed with a broad-spectrum insecticide (such as carbaryl, a pyrethroid, or diazinon) labeled for pear, have reduced losses.
Do not spray too early, or the treatment will miss the arrival of the adults.