Scouting for Mites, Part II
One of the keys to a successful scouting program is being ableto accurately identify the pests and diseases you come in contact with. Thefollowing is a review of the most prevalent greenhouse mites.
Two-spotted Spider Mite (Tetranychus urticae): The two-spotted spider mite is the most commonlyencountered greenhouse mite. Less than a millimeter in size, the two-spottedspider mite normally has two distinct spots on each side of the body beginningat the forward part of the body and ending just beyond half of the body length.The larval stage has six legs, whereas adults have eight. Spider mites canattack virtually every ornamental crop, including most species of foliageplants.
Indications of mite damage include a stippling or mottling,yellowing or bronzing of foliage causing early leaf drop. Where severe infestationsexist, plants may be covered with the characteristic webbing produced by thesemites, thus the term spider mite.
Spider mite infestations occur most often during hot, dryconditions and develop faster on water-stressed plants. Infested plants shouldbe marked and re-inspected with a hand lens several days after treatment toevaluate control.
Two-spotted spider mites commonly migrate via wind and plantmaterial. Weeds can serve as an alternative food source and should beeradicated. Should any of these conditions exist near your greenhouses,appropriate measures should be taken to prevent and/or eliminate them.
Cyclamen Mite (Steneotarsonemus pallidus): This tiny mite hides in protected locations on thehost plant, usually buds and flowers. They are serious pests of a number offlowering and foliage plants, including cyclamen, African violet, ivy,snapdragon, chrysanthemum, begonia and fittonia. The petals of infested budsoften become so curled and distorted that plants are unmarketable.
The injury they cause can resemble thrips feeding damage,phytotoxicity or physiological disorders.
To avoid inappropriate control actions, plants that displaycurled, distorted leaves should be carefully examined, using a hand lens, forthe presence of cyclamen mites.
Lewis Mite (Eotetranychus lewisi): The Lewis mite is a slender, tiny, straw orgreenish-colored mite with several small spots along each side of the body andis smaller than the two-spotted spider mite. Like the two-spotted spider mite,it infests greenhouses and is particularly injurious to poinsettias. Lewis mitefeeding causes leaf stippling and yellowing. Upper leaf surfaces usuallydisplay a mottled or speckled appearance. These mites also produce visiblewebbing, which can completely cover the poinsettia’s flowers and leaves.Infestations must be detected and treated before leaves begin dropping off theplants.
European Red Mite (Panonychus ulm): The European red mite is brownish-red andelliptical in shape with four rows of spines that run down its back. It isabout one-eighth the size of a pinhead. It attacks deciduous shade trees andfruit trees, as well as shrubs, resulting in leaf drop.
European red mites winter as bright red eggs laid inclusters on twigs and branches of small trees. Frequently the twig crevices andscars seem to be covered with red brick dust. They develop from newly hatchednymph to adult in approximately 20 days at 55° F and sometimes as quicklyas four days at 77° F.
Southern Red Mite (Oligonychus ilicis): Southern red mites are typically found onoutdoor-grown woody ornamentals such as azalea, camellia and Japanese Holly.This mite species is most active in cool weather, with the most seriousinfestations usually occurring in fall and spring. The Southern red mite reproducesrapidly then becomes almost inactive in winter and summer. Generally, summerpopulations are controlled predaceous insects and mites.
The female adult has a dark reddish or brown abdomen,pinkish or red cephalothorax and a pale mid-stripe. The male resembles thefemale but is smaller in size, usually darker in color and lacks the pink orred color.
Spruce Spider Mite (Oligonychus ununguis): Spruce spider mites are tiny and almost impossibleto detect with the naked eye. When young, they are yellow-green, turninggrayish-black at maturity. They reproduce rapidly with eggs that arereddish-brown. Spruce spider mites feed on many conifers, including: spruce,pine, cedar and yew. Indications of mite damage include yellow stippling,yellow foliage and dieback. Spruce spider mites are most active in the coolweather of spring and fall, with greatest damage occurring from March to June.Spraying is recommended when 10 or more mites can be tapped from the branch andno beneficials are found.
Control
Each week, the grower and scout should review the scoutinginformation gathered from plant inspections and data from indicator plants.This data will help prioritize a strategy. Looking at trends over a period oftime will help you decide if controls are needed.
When control of a pest population is necessary, there aremany control activities available. The specific method selected should be basedon the type of pest causing the problem and the severity of the loss if thedesired control is not achieved. Control methods fall into four basic groups:
Cultural practices: in general, any activity that promotes plant health and vigor.
Mechanical methods: crop management activities often performed by hand labor in greenhousecrops.
Biological controls: utilizing predators, parasites and pathogens to manage pestpopulations.
Chemical controls: when cultural and mechanical methods cannot provide the desiredcontrol.
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