Spider Mites on Ornamental Plants
By Linda Lindquist, CMG

If you are seeing spots before your eyes….it just might be due to spider mites. These pesky critters pierce the outer leaf surface of over 180 known host plants in order to feed on the sap. Mostly, they will live on the underside of leaves, so inspecting your plants often is important. The leaf will collapse and turn yellow at the spot(s) where they are feeding. If there is a particularly heavy infestation, photosynthesis is reduced, this causes the leaves to yellow or bronze, fall off and eventually the plant will die.

Mites live in soil and weeds, especially chickweed, poke weed, violets, wild mustard and blackberry. They will move to more tasty ornamentals at the first chance, especially when weather turns warmer.

It may be easier to see the impact of these insects rather than the insect themselves. Inspect your plants every week to avoid letting the infestation get too heavy. Look for webbing where the leaf attaches to the stem, on the stems and along the edges of the leaves. Look for stippling on the upper side of the leaf. It may look like the leaf has been pierced by many tiny needles.

You may have to use a magnifying glass to see these creatures. They are small – just .5 to .7mm long - about the size of the period at the end of this sentence. You can try holding a piece of white paper under the leaves and strike the foliage sharply. The mites will fall onto the paper. Draw circles around the black specks – mites will crawl out of the circles, dust & dirt won’t move!

If chemical control is needed for heavy infestations, avoid broad-spectrum chemicals which will kill beneficial insects and natural mite predators as well. Look for products labeled as miticide. These will only kill the adults and nymphs (not eggs) so re-spraying at 5 day intervals will be needed. Horticultural oils and insecticidal soaps may also be used, but the product must come in direct contact with the mites and eggs. These have no residual activity, so reapplication is required.

Whatever you use, be sure to spray the underside of the leaves where mites accumulate and always read the label directions for proper use and safety precautions.

If the problem isn’t too bad, mites can be dislodged by using a high pressure spray of water on the undersides of leaves about every three days. Mites have natural predators: lady beetles, predatory thrips, and predatory mites which can be encouraged by keeping plants healthy and not overusing chemical controls.

Sources: UFL.edu/woodypest/mites; clemson.edu; UTextension.edu publication #SP290-D, PB595