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Diseases & Pests

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From Where I Stand

From Where I Stand

Pest of the Month: Spruce Spider Mites Disease of the Month: Landscape Sanitation

by Heather Prince

Pest of the Month: Spruce Spider Mites

As temperatures cool, spruce spider mites become active on various evergreens including spruce, pine, and juniper. These tiny mites suck the plant fluids causing a brown stippling on needles and also spin a fine silk along twigs. From a distance, needles appear to be turning bronze. To determine the presence of spider mites, try the paper test. Hold a sheet of blank white paper beneath the branch. Give the branch a sharp blow, allowing material to fall onto the paper. Grab your hand lens and see what has dropped off the tree. The mites are about the size of a grain of pepper and should be green or red. Green mites are herbivores and are eating the plant. Red mites are carnivores and are eating the green ones among other things. Take a look at the numbers of each to determine if treatment is necessary. If you have a high number of red mites, they may do the job for you. If there is an abundance of green mites, it may make sense to treat them. Spruce Spider Mites

Treatment: Disease Practice of the Month: Sanitation in the Landscape

Although there are differing schools of thought on fall clean up of plant material, if you or your client has been dealing with fungal problems or pest issues, sanitation may make sense. There are many foliage diseases that overwinter on fallen leaf litter such as apple scab, cytospora on spruce needles, tar spot on maple, etc. Cleaning up diseased plant material considerably helps stave off further infection the next year. If you are dealing with pine diseases, clean up the pinecones this fall. Diplodia tip blight overwinters on cones and by disposing of them, you significantly reduce the infection the following spring. Some pests can be controlled by pruning off the egg masses. With viburnum leaf beetle, eggs are laid on the top 6 to 8 inches of the twigs. A fall pruning may sacrifice some berries, but you take the bug away from the plant, ensuring less pesticide use the following year.

When controlling for spruce spider mite, a miticide is best. Some chemical miticides include acequinocyl, bifenthrin, fenazaquin, or spiromesifen. Mites can also be controlled with insecticidal soap or summer oil. Miticides will kill both herbivorous and predatory mites, so you may want to consider letting nature take its course if you want to encourage an existing population of predatory mites.

University of Illinois Extension Service https://web.extension.illinois.edu/state/ horticulture/index.php 217-333-0519

Additional resources:

The Morton Arboretum http://www.mortonarb.org/Plant Clinic: http://www.mortonarb.org/trees-plants/ tree-and-plant-advice/ 630-719-2424 Chicago Botanic Garden Plant Information Service: https://www.chicagobotanic.org/ plantinfoservice 847-835-0972

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