Sunday, May 22, 2011

They Mite..... If You Let Them!

This past week I did a program on growing fruit in the Lowcountry. I basically did a ten minute presentation, which was WAY too short to do anything of substance, then the other two on the panel did the same. After that it was almost an hour of "Stump the Chump" style questions. The one gentleman was a small fruit farmer from the Edisto area and the other was the host of the TV show "Making it Grow", Rowland Alston. I only bring that up because you would figure that he would get the majority of the questions, being a big star and all.....Nope, probably 70% of the questions were directed at me and Citrus.
There was one question however that the three of us kind of teamed up on, and that was about Spider Mites.
Spider mites belong to the family, Tetranychidae. They are classed as a type of arachnid, which are relatives of insects that also includes, spiders, ticks, and scorpions.
These microscopic creatures are pests to over 180 species of plants including many fruit trees, vines, berries, vegetables,and ornamental plants.
Spider mites are less than 1 millimeter in size and vary in color. They are difficult to see with the naked eye.
Under a very good microscope, they look like this:
Creepy little things, aren't they?
Spider Mites, as you can see, have a simple, oval‑shaped body and no wings or antennae. All species pass through an egg stage, a six‑legged larval stage, and two eight‑legged nymph stage before transforming into an eight‑legged adult. Immature stages resemble the adults except in size. They reproduce rapidly in hot weather and commonly become numerous in June through September. An adult female may live for several weeks and lay many dozens of eggs during her lifetime.
The damage they do is caused as they feed, bruising the cells with their small, whiplike mouthparts and ingesting the sap. Injury can lead to leaf loss and even plant death. Damaged areas typically appear marked with many small, light flecks, giving the plant a somewhat speckled appearance.
Photo courtesy of Clemson University

They can also cause a bronzing effect of the leaves,similar to this:

One last sign that you might have Spider Mites is the webbing on heavily infested plants:

If you are unsure whether you have Mites or not, there is an easy test. Place a white piece of paper or paper plate under your plant and give it a decent shake. If you see tiny little specks wandering around, you have them. The size of the Spider Mite "specks" on the paper is about the same size as the period at the end of this sentence.
How do you control them? Irrigation and moisture management can be important cultural controls for spider mites. Adequate irrigation is important because water stressed plants are most likely to be damaged. Keeping the plants in a high humidity environment encourages pathogenic fungi that attack the mites.
Various insects and predatory mites also feed on spider mites and can provide some level of natural control. One group of small, dark-colored lady beetles known as the "Spider Mite Destroyers" (Stethorus species) are specialized predators of Spider Mites.
Courtesy of UC Davis

Then you have the Minute pirate bugs (family Anthocoridae)
Courtesy Bug

Big-Eyed bugs (Geocoris species)

and Predatory Thrips
Courtesy Bug

Which can all be important natural enemies.
Chemical control of spider mites generally involves pesticides that are specifically developed for spider mite control (miticides or acaricides). Few insecticides are effective for spider mites and many even aggravate problems because they kill the beneficial insects. Plus, most miticides do not affect eggs, so a repeat application approximately every 10 to 14 days is usually needed for control. Then to top it all off, spider mites can become resistant to certain pesticides.
Some control can be obtained with horticultural oils, like Neem oil, and insecticidal soaps. These materials have no residual activity and must come in direct contact with the mites. House plants can be tricky. There is no biological control. You can use the oils and soaps, but one easier method is to periodically hose small plants in the sink or shower.
Some of the mites that you may encounter are:
The Twospotted Spider Mite (Tetranychus urticae)
This is the most common and destructive mite on deciduous ornamentals. It has an extremely wide host range and will feed on many varieties of trees, shrubs, flowers, weeds, fruits, greenhouse and field crops. Immature mites and adults are yellowish to greenish with two dark spots on either side of the body.
European Red Mite (Panonychus ulmi)
This mite attacks deciduous trees and shrubs and is especially common on flowering fruit trees such as Apple and Crabapple, Cherry, Pear, Plum, Hawthorn, and Serviceberry.
Southern Red Mite (Oligonychus ilicis)
This is the most common and destructive spider mite on broad‑leaved evergreens, especially Japanese and American hollies, Azaleas, Viburnum, and Roses.
This is just a brief discussion of these pests, there are many more out there and much more that can be said about them. Your best defense is to just keep a good eye out. When scouting for Spider Mites, pay particular attention to plants having a history of mite problems. Spider Mites often re‑infest the same plants year after year. The good news, plants will often recover after the Mites have left as long as there was not too much death!
Happy Growing!

No comments:

Post a Comment