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.

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Fall Chores, Spotted Wing Drosophila

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September 21, 2011

In this Issue:

What to Look for/Do Now:

  • Make sure trees get thoroughly irrigated toward late season because root growth will continue until the ground freezes.
  • Remove overly weak and very diseased trees this fall.
  • Prune out dead and diseased limbs on other trees, and rake leaves, debris, and fallen fruit.
  • Evaluate your incidence of pest damage this season and plan to make changes if necessary for next year.

Current Insect and Disease Activity


Spotted Wing Drosophila


Cory Stanley, USU Coordinator for the Cooperative Agriculture Pest Survey program, reported that low numbers (1-5 flies) of spotted wing drosophila (Drosophila suzukii) were recently found in Utah monitoring traps at the USU research farm in Kaysville and in a peach orchard in Fruit Heights.

Stanley monitors for SWD in 50 fruit-growing locations throughout Utah, and these are the first captures for 2011. The fly was first trapped in Utah in 2010, also in Kaysville. Stanley's traps are specially designed cup and lid arrangement baited with either cider vinegar or a sugar-yeast solution. A variety of trap designs will work for the orchardist or backyard grower, including Solo cups with holes and lids, or store-bought traps.  A grower will not know whether a treatment program is necessary unless monitoring traps indicate that the flies are present.  The Utah Plant Pest Diagnostic Lab can help with identification.

SWD maggots will feed in a wide variety of fruit: cherry, blackberry, raspberry, strawberry, grapes, blueberry, and peaches. Cherries and small berries are the prime hosts, but all overripe fruit is fair game. It is important to take precautions to prevent spread and new infestations by picking fruit before it is overripe, removing fruit from trees after harvest, and removing or mowing/shredding fallen fruit.

Below are links to more information about monitoring and treatment for spotted wing drosophila, and images of damage to fruit:

    • USU Extension fact sheet
    • USU Extension video about trapping and identification.
    • Oregon State has a wonderful website, including some very detailed spray recommendations for a variety of fruits.

Please contact Cory if you have any questions or concerns.


Blister Mites and other Eriophyid Mites


Blister mites and other eriophyid mites should be treated now, and no later than just before leaf drop. Treatment options include:

    • 1.5-2% oil, thoroughly covering the bottoms of the leaves
    • Sevin (carbaryl), alone or with 1% oil
    • lime-sulfur (can mix with oil, but not on drought-stressed trees)

Appleleaf and pearleaf blister mites have been feeding within blisters on apple, pear, and crabapple leaves since spring. The blisters are barely visible at first, and by late summer, they become obvious necrotic (dead) spots, almost looking like a fungal leaf spot (but the lesions are raised bumps). Sometimes they will feed on pear fruit in early spring. As the fruit develops, the feeding damage appears as depressed, circular brown spots.

At this time of year, blister mites will start migrating from the leaves to bud scales where they will spend the winter. Treating them while they are exposed is the perfect time to knock their population down. Next spring, they will migrate back out of the blisters to the leaves, and can be treated with oil at that time as well.

Other eriophyid mites include peach silver mite, cherry rust mite, and apple rust mite. Peach silver mite causes  peach leaves to have a metallic sheen, while damage from the other mites looks similar to spider mite damage. These other species of mites also migrate from the leaves to bud scales and will be susceptible to an oil treatment now.

These mites, as well as the blister mites, actually have a beneficial value. In spring, when spider mites are not active, they serve as a food sources for predatory mites. A healthy population of predatory mites leads to good biological control of spider mites later in the season.

Pear Psylla


The end of pear harvest is a good time to treat for pear psylla before the adults migrate to overwintering sites in leaf litter, on tree bark, or even outside the orchard. Lime-sulfur alone or with oil is the best treatment option.

To determine whether a postharvest treatment is necessary, examine one upper canopy terminal shoot of at least 20 trees in your orchard for the presence of nymphs (usually sitting in a drop of honeydew). If activity is seen on at least 5 shoots, a treatment is warranted.

Fire Blight


This fall, examine your trees for fire blight cankers that have not yet been pruned out. If you are diligent about removing as much fire blight as possible this fall and winter, you are reducing the amount of inoculum in your trees and lessening the chances of an outbreak for next season.

Infected shoots will be easy to spot because the leaves will remain attached to the dead shoots, and the tips of the shoots will be curled downward. Prune them 8-10 inches below the dead/damaged tissue, and during dormant season pruning, it is not necessary to sterilize your pruners between cuts.


Coryneum Blight


A copper spray on peach/nectarine and apricots should be applied at 50% leaf drop for prevention of new coryneum infections. This spray will knock off much of the remaining leaves, so that most of the targeted infection sites--leaf scars--will get treated. Options include:

    • fixed coppers or copper sulfate (Kocide, C-O-C-S, Bonide, Lily Miller Microcop, etc.)
    • chlorothalonil

With the wet springs northern Utah has had for the past 3 years, coryneum blight (also known as shothole) infections on fruit, foliage, and twigs are on the rise.  In fall, new infections target fresh leaf scars, where the fungus enters the buds to spend the winter. In spring, those buds will be dead, with a slight oozing, ready to infect the newly emerging leaves and fruit.

Trees or orchards with severe infections will need at least three years of diligent fall, spring, and growing season treatments to suppress the disease incidence. During dormant season pruning, inspect trees thoroughly for sunken cankers and remove and destroy those stems and twigs. In spring, spray trees at shuck split (when the papery covering over fruit splits away) with chlorothalonil, Pristine, or captan.  If necessary, apply captan or Pristine during the growing season during wet periods.

Powdery Mildew on Cherry


A late season treatment of lime-sulfur just prior to leaf fall can help reduce overwintering inoculum of Podosphaera. (If you applied oil soon after harvest for powdery mildew, you should not need the lime-sulfur spray.)  Powdery mildew can reduce photosynthetic ability, reduce yields, and when it has infected fruit stems, prevent fruit from shaking off.

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.