Spider Mites
You'll first suspect spider mites when your plants start showing up with little yellow speckle marks, right on the leaf surface. (Also see thrips.) When you turn the leaf over, tiny, oval shaped mites are seen scurrying around, about pin-head in size. Their eggs, best seen with a magnifier, will be scattered around at random (perfectly round, all the same size, color ranging from clear to tan). With larger infestations, a fine webbing can be seen covering the plant tops (crawling with mites), and leaves will be browning and dying. Spider mites seem about the most common pest to show up in a greenhouse or indoors. They're best controlled with spider mite predators (see right), similar sized mites that eat them. A few gardeners report success with pirate bugs or ladybugs.

Spider mites take about 2 weeks per generation at 70 F. (from egg to adult). At low temperatures below about 50'F. they become dormant, and at higher temperatures above 86 F., their life cycle is speeded up to about double. They prefer lower humidity levels, so raising the humidity helps control them.

The most common mite species by far is the "two-spot" spider mite. They're usually yellow/tan/ greenish in color, and have two dark spots on their shoulders, one on each side. How large these spots get depends on the age of the mite; they get larger as the mite gets older. These two spots are also varied according to how much chlorophyll is in. the plant being reared; some crops produce mites colored much darker than others.

Strangely, spider mites have the ability to go dormant in winter, and then return when it warms up again. Triggered mostly by the daylight getting shorter in the fall, some or most of the mites turn red in color, stop feeding and egg laying, and then crawl off to protected nooks and crannies to hide through the winter. A warm, heated greenhouse can counteract these impulses to hibernate, but some probably will anyway, so it's easy to 'see why spider mites tend to keep coming back - season after season. Spider mites can also float along with wind currents, or be carried by pets or clothing. The common two-spot spider mite is found throughout the world, it's so widespread.

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Whiteflies
Suspect whitef1ies when you start seeing small (1/12"), pure white "moths" that are mostly resting on the plant leaves. When disturbed, all rush out in the air, hesitate a while, then fly back into the foliage. Looking closer, the plants might appear shiny with honeydew. With a magnifier, small clear- white "scales" (the pupa) are seen on the lower, underneath sides of the plants. All stages suck on plant juices, and heavily infested plants will yellow and grow poorly.

There are at least 2 whitefly species now causing distress for gardeners, greenhouse whitefly and sweet-potato whitefly. What finally kills plants off with a heavy whitefly infestation isn't usually whiteflies themselves, but a black sooty mold that grows on accumulated honeydew. By the time plants get to this stage, there'll be clouds of whiteflies, and no mistaking this pest. If you're at that point, rinse the shiny coating off the plants with a strong water or soapy' water spray, so the mold can't grow on it.

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Aphids
What you notice first with aphids is leaves that are curled, puckered, and discolored. Looking closer, dense colonies of tiny (1/32"-1/8"), soft bodied, pear shaped insects are seen, especially on tender growing tips and underneath sides. Young aphids look like miniature adults, and the whole family will be found feeding together. Even when disturbed, aphids move quite slowly, compared to most other insects.

Coming in almost very color, aphids can be green, yellow, pink, brown, or black, or any shade in between, for that matter. To make a final diagnosis of aphids, with a magnifier, find the pair of tiny "dual exhaust pipes" coming out of their rear end, called "cornicles" - aphids are the only insects that have these. Aphids all feed by sucking on plant juices, which is damaging enough, but their most serious damage is the plant diseases they carry - that's what causes the leaf distortions so often seen with aphids. They produce shiny honeydew, too, and when enough of this builds up a choking mold starts growing that can quickly kill plants. (Keep this mold hosed off.) Combine these problems along with aphids unusual breeding abilities - they're born already pregnant (in fact, there are miniature embryos inside of other embryos!), they're all female, and they reach adulthood in one week - and you see why aphids can be such a rapidly devastating pest. There are lots of aphid species, too, with enough variety that just about every plant has at least one species that really likes it.

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Thrips
Tiny, slender thrips feed by scraping and rasping at tender leaf surfaces. First symptoms are usually leaves that appear finely speckled with yellow spots. Later, a silvery- metallic looking sheen may cover leaf surfaces (not with all thrips, though), and black specks (thrips fecal material) may be scattered about. Only after close inspection is the real pest found. About 1/10" 1ong, thrips can move quite quickly for their size. To the bare eye, many gardeners report thrips as a small "worm" with legs. Both . larvae and adults look similar, except adu1ts have wings and can fly. In small numbers, thrips may not do much damage. However, with larger populations, they can be quite damaging.

There are hundreds of varieties of thrips, coming in many colors, but they all feed and damage plants similarly. For control purposes, the main difference is where they pupate as youngsters. Most pest thrips move down into the soil (they'11 also use rockwool or other synthetic media) to pupate, as part of their lifecycle, where they can be controlled by predator nematodes. This is the easiest stage to kill. It does take 2 or 3 applications before good control is seen, however, because only the immature thrips are killed, and not the adults. These adults can be controlled with Safers Soap, if necessary, and after 2 months regular applications of predator nematodes alone usually gives good control. A few other thrips species pupate directly inside leaf tissue.(notably the species greenhouse thrips), where the nematodes are not as effective. You can tell if thrips are using the leaf to pupate, because when they are, the hatching thrip causes a small eruption on the leaf surface - it looks something like a tiny pimple, or a little volcano complete with crater. Unhatched eggs look like a little dab of Elmers glue.

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Fungus Gnats
When you see small, dingy-gray flies flying around aimlessly, or seeming to come out of the soil, you've probably got fungus gnats. Adults look very similar in size and appearance to fruit flies, and don't feed on plants in any way. Their larvae, a smal1 worm that lives in the top inch or two of the soil, feeds mostly on organic debris, fungus, algae, etc. While they're doing this, however, they can nibble on the roots of young seedlings, too. Plants usually outgrow them rapidly, though, so they're often more of a nuisance than a real pest.

Fungus gnats can be told apart from whiteflies, a much more serious pest, because fungus gnats are a dingy gray instead of pure white, and they don't spend much time resting on the leaves like whiteflies do

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Mealybugs
Another insect that sucks on plant juices, mealybugs cause damage similar to aphids - leaves will be distorted, plants are weakened, covered with shiny honeydew, and finally a sooty mold grows, killing the plant. However, when a search is made for the cause, they don't look much like insects. Clusters of mealybugs look more like some kind of cottony mass instead of pests. It's only on close examination that they're seen to be individual, soft bodied, very slow moving insects.

Coated with a fluffy, waxy coating, mealybugs tend to gather quietly together in groups, often at a crotch or joint in the plant. But don't let this innocent looking crew fool you. Even though mealybugs breed somewhat slower than other insects (each generation takes about a month), they can build up to quite damaging populations. Fortunately, we have mealybug destroyers that like to feed on them. Green lacewings feed on mealybugs too, but need to be released regularly. And be sure to keep that honeydew rinsed off the plants as much as possible, with a water or soapy water spray, to keep mold from growing. Between these measures, you should get good control.

Scales
Related to mealybugs, scales don't look much like insects, either - they look more like little "oyster shells" attached to the stems and leaves. Active only as babies, they soon lose their legs, grow a hard outer shel1, and settle in for a quiet life of sucking on plant juices. Often, the first symptom noticed is shiny honeydew covering the leaves. (Not all scales produce this.) Looking closer, especially on the undersides of leaves and stems, the scales are visible, singly or in clusters. Shaped circular to slightly oval, they readily scrape off with a fingernail. Plants may be stunted, yellowed, and distorted, damage similar to that of other sap-sucking insects.

There are many varieties of scales, both hard and soft, coming in many colors, but all feed and damage similarly. Mealybug destroyers also feed on scales when mealybugs run low, and green lacewings feed on the crawler stage, giving some control. Scale control with natural predators has been variable, and we continue to search for improved controls. Many gardeners resort to spraying or dabbing alcohol, light oil, soapy sprays, or mixtures of the above for scale control. Test a small area for toxicity from any of these products first

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