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Allsup: Timing key for pest issues

Spruce spider mite

Spruce spider mite

Integrated Pest Management (IPM) is a phrase tossed around abundantly in the industry. IPM means that a grower or gardener utilizes a combination of cultural, mechanical, biological and chemical methods to address pest issues.

Let's say I had an infestation of spruce spider mite on one of my landscape trees. Spruce spider mites feed on the chlorophyll of needled evergreens and are most active in the spring. When under heavy attack, spruce needles become brown and unsightly.

My cultural method may be to ensure I do not stress my tree. Some of the major stresses are incorrect planting, root disturbances, Illinois climate and soil pH. My mechanical method may be implementing a hard water spray to wash off the pests or removing debris from under the tree. My biological method would be scouting for beneficial mites by taking a piece of white paper to the tree and shaking the limb vigorously. The mites will fall onto the paper; when smashed, the spruce mites will make a green streak and the beneficial insects will make a yellow-orange streak. My chemical method would be to spray an insecticidal soap or a miticide to knock down some of the population at the correct time.

Horticulturists have a way of determining when it is the right time to spray chemicals, by timing the pest management with ornamental plant development. I spray my spruce for mites when the saucer magnolias are in bloom. We track the temperature to determine when the magnolia blooms and when the spider mites will be at their most susceptible stage. Other times of the year, a chemical spray may be mostly ineffective.

Saucer magnolias bloom in March or April, and may even provide a show for our Easter holiday. Their bloom is short lived; if it freezes, they turn brown. If it is too hot, they shatter and fall to the ground. However, saucer magnolias are a great indication for the best timing of chemical applications for Zimmerman pine moth, eastern tent caterpillar, spruce gall adelgid, and pine sawfly.

Overwintering larvae of Zimmerman pine moth begin feeding on bark and then the cambium, ultimately girdling branches of Scotch, white and Austrian pine. Eastern tent caterpillars hatch around bud break and feed on cherries, plums, crabapples and serviceberries in communal tents in the branch angles of trees. Spruce gall adelgid eggs hatch and soon the tree forms a gall in response to feeding damage so timing is crucial for this unsightly insect. Pine sawfly larvae hatch and eat needles and at times defoliate most of the trees.

Kelly Allsup is the University of Illinois Extension horticulture educator in Livingston, McLean and Woodford counties.

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