ORNAMENTALSAND
TURF
ORNAMENTALS
The information and recommendations in this newsletter are applicable to North Carolina and may not apply in other areas.
Mites are tiny arthropods that insert their minute, scissor-like mouthparts into needles, leaves and petals, inject saliva, and suck out the contents of the plant cells. Three families of mites are particularly damaging to ornamental plants: spider mites, threadlegged mites and eriophyid mites. Spider mites include the warm weather mites (twospotted spider mite, tumid spider mite) and the cool weather mites (spruce spider mite, southern red mite, boxwood mite). Spider mites often spin a silk webbing over the plants they infest. They cause a tiny, pale spot each place they feed. I am now receiving samples of junipers and hollies that have spruce spider mite and southern red mite injury, but no mites, only eggs. These mites tend to die out in hot weather. Perhaps because of the unusually cool spring, several samples with broad mites have been submitted. With threadlegged mites and eriophyoid mites, the saliva injected as they feed acts as a plant growth regulator or even as a herbicide. Threadlegged mites are represented by the cyclamen mite and broad mite. Eriophyoid mites tend to be rust mites, erineum mites and gall mites. They are very specific as to the kinds of plants each species infests (hemlock rust mite and other rust mites, juniper tip dwarf mite, maple bladder gall mite, maple erineum mite and other erineum mites, maple spindle gall mite). Once the weather becomes very hot, broad mites and eriophyoid mites will probably die away but it will take plants a long time to outgrow the injury caused by broad mite feeding.
The most common spider mite pest of conifers in North Carolina is the spruce spider mite. Predaceous mites and small lady beetles feed on spider mites and parasitic fungi infect these mites, especially in humid weather. The spruce spider mite does most of its damage in spring and fall. But often, the foliage does not turn yellowish-brown until June or July when the mites have died out (only the eggs survive the summer in the Piedmont and Coastal Plain of North Carolina). Spruce spider mite eggs are round, or slightly flattened and have a diagnostic stipe (thread) projecting up from the center. Spruce spider mites are relatively inactive in very cold weather and tend to die out in hot weather. Because the spruce spider mite tends to feed on older growth, thorough coverage is necessary to get the pesticide inside the plant where the mites are feeding. This mite is not particularly resistant to miticides. Kelthane is the old standby for spider mite control. If Kelthane is unavailable, then Cygon will do the job and it has the advantage of being systemic. The horticultural oils are also effective for spider mites and they also control armored scale insects such as juniper scale. There is some additional information on spruce spider mite control in Ornamentals and Turf Insect Note No. 77.
Hot, dry weather apparently inhibits the parasitic fungi and speeds up the life cycle of the spider mites. Daylilies, roses, butterfly bush, hollyhock, some cultivars of euonymus, marigolds and bedding plants are often infested by twospotted spider mites during the summer. Because spider mites flair up in dry weather, their control is somewhat difficult because plants that are wilted are much more susceptible to pesticide injury than turgid plants. Also, plants are much more likely to be burned if pesticides are applied during mid-day. Watering plants thoroughly before spraying and spraying in early morning or late afternoon so that the pesticide residue is dry before the bright, noonday sun hits it helps to lessen the chances of plant injury. Because spider mites are tiny and relatively fragile, they can be dislodged from ornamental plants by hosing the plants down with an ordinary garden hose. Many of the dislodged mites will drown. There is a problem with this method of spider mite control; if the plant is tender, the stream of water may bruise or break it. Insecticidal soaps and horticultural oils are fairly effective for spider mite control. There is some additional information on twospotted spider mite control in Ornamentals and Turf Insect Note No. 25.
Broad mites infest a variety of ornamental plants (African violets, ageratum, azaleas, begonias, gerberas, gloxinias, lantana, marigolds, snapdragons, verbena, zinnia, etc.). Broad mites are so small that they are virtually invisible on the host plants even with a good hand lens. Also the mites tend to crowd into the crevices and buds and feed on the growing tips. Their toxic saliva causes the twisted, hardened and distorted growth in the terminal of the plant. The effects of their feeding may persist long after the mites have been eradicated. The current miticide recommendations are Talstar, Thiodan, Avid and Pentac for control of cyclamen mites and broad mites. Kelthane also works well for mites. Of these pesticides, only Avid is translaminar to any real degree. Ornamentals and Turf Insect Note No. 28 explains more about the biology and control of broad mites.
The juniper tip dwarf mite is a microscopic animal that feeds by
piercing the needles or buds of junipers with microscopic
scissors-like mouthparts and injecting its saliva. They then feed
on the contents of the cells. Some juniper varieties are sensitive
to eriophyoid mite saliva and respond in several ways. A few
junipers are apparently sensitive enough that the buds die after
enough mites have fed in them. Other junipers develop
strange-looking growth that looks almost like herbicide injury. Oddly
enough, eriophyoid mites are sensitive to the pesticide Sevin.
Research by entomologists with the Pennsylvania Department of
Agriculture has shown that Cygon is also very good for tip dwarf
mite control. An advantage to using Cygon is that Cygon also will
control spruce spider mites and scale insects as well. Joust
(Morestan) will also give very good control of these mites.
Web page last updated on June 23, 1997 by Stephen J. Toth, Jr..
