Summer Spider Mites

Spider Mites, of which there many different species in the Greater Main Line region, are tiny insects that can cause serious damage to a wide range of trees and shrubs. Because they are microscopic in size and “hide” on the underside of leaves, they are very difficult to detect. Indeed, it is their unsightly damage, stippling and discoloration on the leaves, curling leaf edges, premature defoliation and dieback, that ultimately cause a homeowner to call and ask, “What’s wrong with my plant?”.

So what exactly is going on? Spider Mites are in a group of insects referred to as “piercing and sucking insects.” As the name indicates, the spider mites use their mouthparts to “pierce” the underside of the leaf tissue and then “suck” the chlorophyll out of the leaf as food. The missing chlorophyll causes unsightly yellow, light brown, or white/translucent appearance. If the Spider Mite population is large enough, chlorophyll production is severely impacted, weakening or causing dieback in the tree or shrub.

This summer, Spider Mites have been particularly bad due to the extreme temperature and prolonged drought. They absolutely love hot, dry conditions (85°+) and reproduce even quicker and in greater numbers in these ideal conditions. (From Penn State’s Agricultural Extension: “…females lay eggs and the first generation begins. The eggs hatch between 7-20 days depending on temperature - hotter temperature, faster egg hatch. There can be 10-15 generations each year, again depending on temperature.” Considering each generation can consist of several hundred eggs, your tree or shrub could easily be hosting 1,000+ Spider Mites in the short summer season.

I have treated Spider Mites on a wider range of plants and trees this year than ever before, including Oak trees, Redbud trees, Spruce trees, fruit trees, Skip Laurels, Boxwood, Roses, and many others.

What to Look Out For:

• Discoloration and stippling on foliage (small yellow, brown or translucent spots).

• Completely yellow or brown leaves and premature defoliation on deciduous trees.

• On the underside of foliage, small black or reddish spider mites may be visible to the naked eye (resembles a black pepper flake). Also, thin, silken web, similar to that of a regular spider.

• Brown or yellow-speckled needles on Spruce trees and other evergreens. Widespread brown patches, especially on Alberta spruce.

Pictured above: Spider Mites on Boxwood

Pictured Above: Spider Mites on a Swamp White Oak

Pictured Above Left: Spider Mites on a Skip Laurel, Pictured Above Right: Spider Mites (and Anthracnose!) on a White Oak.

Champion Tree Control:

Miticide treatment is either a foliar-applied or trunk-injected product depending on the size and type of tree or shrub. It is best to apply miticide in the spring to kill the eggs that have overwintered and prevent any damage to your trees and shrubs. That being said, if an infestation is not known until later in the summer, we do provide control throughout the hot, dry months of June, July, August and September as well.

Note: although the Spider Mites will die on contact from a foliar-spray, the foliage will not recover until the following season.

I always recommend customers keep their plants and trees (YES, even mature trees!) well irrigated, especially if they are located near the home, driveway, walkway, or are in any other spot that is particularly hot and dry. Our prolonged summer drought has severely weakened our trees and shrubs, leaving them particularly vulnerable to secondary stressors such as Spider Mites. By keeping your trees and shrubs well-irrigated, you are fortifying them against various insects, diseases, severe weather (such as strong winds), mechanical injury (such as repeated lawn mower damage to above ground roots) and more. If you suspect a Spider Mite infestation or do not know what is wrong with your tree or shrub, please give us a call.

Water, water, water!