Spider mites are extremely common pests in the urban landscape and can inflict serious damage to trees, shrubs, and flowers. Both evergreen and deciduous plants can be attacked. Spider mites are actually not insects but are more closely related to ticks and spiders.
Spider mites can produce silk, but they do not exactly resemble a spider's web. They produce very fine webbing when infestations are high (see picture). They are also extremely small, about the size of the period at the end of this sentence.
Spider mites have a simple, oval-shaped body with no wings or antennae. Under optimum conditions, spider mites can complete their development from egg to adult in less than one week. Therefore, populations can build up rapidly and cause extensive plant damage in a short time.
Their needle-like mouthparts damage plants by removing sap from individual plant cells. The pattern of damage is what we call stippling. Prolonged, heavy infestations cause yellowing or bronzing of the foliage (see picture) and premature leaf drop similar to drought stress. Severely infested plants may be stunted or even killed.
There are several species of mites that live on plants. Some are warm-season and some are cool-season. This article will address the spruce spider mite.
Spruces are common landscape plants and many people will experience spruce spider mite damage on their trees. Even though the name refers specifically to spruces, these mites can feed on more than 40 species of conifers including spruce (especially Alberta spruce), pine, juniper, fir, arborvitae, hemlock, taxus, and false cypress.
Spruce spider mite is considered a cool-season mite being most active in the early spring and late fall. It overwinters in the egg stage attached to the base of needles or on bark. Damaging populations may be reached in April and May, before warm summer temperatures slow their activity. Damage inflicted by mites often go unnoticed until the heat and dryness of June and July. Damage will generally occur at the base of the plant first and then proceed up.
When assessing whether or not you have spider mites, it's important to pay attention to plants that have a history of mite problems as they often re-infest the same plants year after year. Examine the undersides of leaves or needles. You will need very good eyesight or a magnifying lens to see the culprits.
An efficient way to sample vegetation for mites is to hold a white piece of paper under a branch and tap the foliage sharply. If mites are present, they will be dislodged and appear on the paper as slow-moving dark specks.
Your goal in controlling these pests is to not annihilate the entire species. Your goal is to keep them at low enough numbers that they do not cause damage.
The best (and least toxic) way to combat spider mites is to spray your tree with a hard stream of water weekly. It sounds crazy - and you may be called crazy - however, the hard stream of water will dislodge many of the mites. This prevents populations from building up.
Spider mites can be difficult to control because they require the use of specific pesticides called miticides. However, the improper use of general purpose insecticides will actually cause spruce spider mite populations to ramp up as you kill the beneficial insects keeping them in check.
There are only two over-the-counter pesticides that have any efficacy against spruce spider mites. They are both marginal products and don't do a very good job unless you have excellent spray coverage. Those products are horticultural oils and insecticidal soaps. Both are contact-kill pesticides meaning the spray must hit the mite to kill it.
Oils can be tricky. Never, ever use it off-label (as with any pesticide) and never use more than the label recommends. Watch out for temperature restrictions as well as the product can be phytotoxic when temperatures are high and ineffective when temperatures are low.
For more information, call the Pulaski County Extension office at 679-6361 and request the publication ENTFACT-438 Spider Mites on Landscape Plants. Become a fan of Pulaski County Horticulture on Facebook, follow me @hortagentbeth on Twitter and kyplants on Instagram.
The Lake Cumberland Master Gardeners have pine straw mulch for sale at the Pulaski County Extension office. It is sold in bales for $7 per bale (over 50, $6 per bale). It can be purchased during office hours 8am to 4:30pm Monday - Friday.
Become a fan of Pulaski County Horticulture on Facebook and follow @hortagentbeth on Twitter and kyplants on Instagram.
Come to the Pulaski Co Extension office on June 20 at 6pm and Stump the Extension Agent. This program will focus on weeds - bring in any that you don't know or are having a hard time controlling. This is a free program.
All changes to or cancellations of Extension programs will be posted to social media.
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