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Common Pests

 

Behavior and Control

 

It is unlikely that any plant goes unscathed by some pest during the Oklahoma growing season. Many are so predictable that measures to prevent them are justified, such as controlling the two-spotted spider mite on tomatoes. How to recognize these pests and how to select appropriate measures to control them is often difficult. Therefore, it may be helpful to review some of the common insect/spider pests and their control in a condensed and hopefully useful form.

 

This is a long document. Listed below are the pests discussed; click on one of your interest to go to that section.

 

 

Aphids

 

Almost all plants have an aphid unique to that plant and they are major problems. Like physicians, there are a few general practitioners, but most are specialists. These insects come in all colors, typically about 1/8th inch long. They are classified as piercing sucking insects, which describes their feeding behavior. They pierce the plant parts and suck out the sap.

 

This type of feeding occurs with aphids, lacebugs, whiteflies and some scales. They consume sugar-rich sap and excrete sweet sticky liquid called honeydew. Other insects, notably ants, feed on the liquid. Ants go so far as to protect the aphids, similar to a farmer tending his cows. Often, a fungus called sooty mold grows in the honeydew, turning the leaves black.

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Aphids appear early in the spring on some of the cool season vegetable crops, and infest ornamentals soon after. They may be hard to see depending on your eyesight, a hand lens is helpful, but a clue will be sticky sap on yellowed leaves and stems. They can multiply rapidly; the females do not need to mate with a male and in summer give birth to live females. A generation may be completed in 2 weeks. Wings seem to be optional; they grow them when needed to migrate to new feeding territory. At the end of summer, they lay eggs and produce males.

 

Control of all of the piercing and sucking insects (aphids, lacebugs, whiteflies and crawler scales) are similar. Firstly, a strong jet of water will remove many of the pests. Environmentally friendly insecticides such as insecticidal soap and horticultural oils, such as Neem, are effective.  Neem oil both smothers the insects and suppresses feeding in this group. When using these insecticides complete coverage of leaves and stems is important.

 

 

Control of these pests in nature is by “good” insects, such as ladybugs and lacewings, which feed on them. Standard chemical insecticides such as malathion, bifenthrin and others are effective in killing this group of pests, but also kill the good insects, causing loss of natural control.

 

Remember to always read and follow the labeled direction of all these insecticides and do NOT use an insecticide for vegetables unless labeled specifically for that vegetable.

 

Lacebugs

 

The lace bug is another piercing sucking insect. They are 3/16 of an inch or less in size and have clear lace-like wings. They, like the aphids, also tend to be species specific. In Tulsa, the most common plant to be involved with lacebugs is the azalea.

 

Infested plants develop mottled yellowing of the leaves similar to damage of other insects. Distinctive and diagnostic of lacebugs are spots of ink-black poop (frass) on the leaf backs. If these spots are not present, lacebug involvement is unlikely. Some azaleas have genetic resistance to lacebugs. Others tend to get yearly infestations.

 

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Lacebug control is the same as with aphids, using insecticidal soaps and oils. Another product particularly useful in susceptible azaleas is a systemic insecticide imidacloprid. It is applied once yearly as a drench, absorbed by the plant, and transmitted to the lacebug as they feed. This insecticide has low toxicity. In small doses it is given orally to pets to control fleas. It is effective for all of the piercing sucking insects mentioned in this review.

 

Whiteflies

 

Whiteflies are tiny, at about 1/16th of an inch. They are both indoor and outdoor pests, but are serious pests in greenhouses. Whiteflies have profound economic importance in agriculture. In addition to direct damage to food crops, they also spread a number of microbial diseases. Feeding is by piercing and sucking leaves. They also cause leaf yellowing and produce sticky honeydew. When present in large numbers, they may all fly at once producing a small white cloud of insects. Control of these insect pests is the same as outlined in aphids.

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Scales

 

Scales are similar to the above insects, having piercing sucking feeding behavior, and specialize in certain plants, but similarity stops at that point.

 

Scales are one of the most damaging insects to ornamental plants. They come in two types, hard and soft, depending on the type of shell they carry. They hatch in the spring, the young crawl about the plant and are appropriately called “crawlers”. The females, after mating, develop a shell and attach to a stem or leaf. After attachment, they are resistant to insecticide sprays.  The males develop wings, never eat, and after mating, die.

 

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If one can pinpoint the time the crawlers are active, standard insect sprays, many of which are labeled for scales, are effective. A problem with this is that each scale variety has its particular time of crawler production; all varieties do not hatch at the same time.  This is so important to scale control, nurserymen will apply sticky tape to plants and inspect daily for crawlers in order to identify the best time to spray.

 

Another helpful technique is to spray oil dormant oil on deciduous plants in the late winter. This kills many of the overwintering scale and the source of eggs in the spring. Horticultural oil, such as Neem and standard insecticides help control the adult soft scale varieties during the growing season, but not the armored variety. Lastly, the systemic insecticide imidacloprid, either as a drench or spray, can be helpful. Keep in mind, that scales, like the other insects, have a number of good insect predators that should be protected, if possible. Selecting scale resistant varieties of plants is the ultimate prevention.

 

Spider Mites

 

Spider mites are not insects; they are spiders, which has implications in their control. There are many mite varieties and some specialize in particular plants. Some of the mites prefer cool weather, but our chief mite, the two spotted mite, loves heat. They love tomatoes and marigolds, but will infest other plants. The two spotted mite appears in late June and is present through September.

 

These pests are so small they are difficult to see with the unaided eye. They usually cause yellowing and distortion of leaves and many will produce webs, a clue that you are dealing with spiders. One way to identify them is the white paper test. Hold a white sheet of paper under the plant and tap the plant sharply. Look for dots, usually red, on the paper that move.

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Successful control depends on early recognition. Jets of water from the hose, insecticidal soaps and horticultural oils are very useful for early infestations, but must be used regularly. With dense populations of mites, these measures will not control them. Most General chemical insecticides, especially Carbaryl (Sevin) will actually increase the numbers of mites through a complicated mechanism of killing off good predator insects and also changing some chemistry in the plants, making them more favorable for the mites. Some of these insecticides are labeled for mites, but are best used for insect control, not spider mites.

 

It is best to treat early and attempt to prevent large numbers from developing. In tomatoes, if extensive involvement develops, it may be best to simply pull up the old tomato plants and start over, aiming for fall fruit production.

 

Fall Web Worms

 

Two types of webbed worms are found in Oklahoma, the eastern tent caterpillar and fall webworms. Tent caterpillars make webbed nests in spring while fall webworms produce webs summer and fall. Tent caterpillars have their webs centrally, at the junction of the tree limbs with the trunk, while the fall webworms have webs at the tips of the limbs. Fall webworms prefer pecans and other nut trees but will invade many varieties. They will not kill the tree but, in pecan trees, may reduce nut production.

 

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Treatment of these caterpillars is either to do nothing, mechanical removal or insecticides. A safe biological insecticide, a bacterium, called Bacillus thuringiensis (Bt) is effective. It may be used around pets, children and fish ponds. They are also susceptible to other standard insecticides containing acephate, carbaryl and others. A significant problem in large trees, however, is delivering the insecticide into the web, causing most people to take the do nothing approaches.

 

Boxelder and Red Shouldered Bugs

 

These are two similar species which are closely related in appearance and behavior. People either know them very well or have never heard of them. They dwell, reproduce and feed on boxelder, chinaberry, golden raintree and other trees. They do very little damage to the trees. The main problem is that their numbers may be overwhelming outside your home, and if they find a small access, may end up inside your home. In the home, if you mash one, you have a permanent stain.

       

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These insects may be sprayed with any number of standard chemical insecticides labeled for them. However, unless they are sprayed while very young, they are somewhat resistant to insecticides. In the home, they are best vacuumed up and sent to the trash. Recurrent problems with home invasion should prompt one to look for cracks around windows, doors and soffits which can be caulked to eliminate access. If worse comes to worse, consider removing the offending tree.

 

Bagworms

 

Bagworms are pests that are aptly named for the bags they form. They love to chew on our Junipers, Arborvitae, Spruce and Pines. They also damage some deciduous trees, but in our area, the eastern red cedar (a juniper) is a favorite.  The insect eggs start out the growing cycle by hatching from a spindle-shaped bag, consisting of silk and old plant parts formed during the previous summer. The tiny caterpillars then begin to feed and grow. The males eventually develop into a moth; the females remain a caterpillar and start to build a bag around themselves. Eventually the female attaches the bag to a twig, mating occurs; she closes the bag and lays eggs. These hatch the following year and the cycle begins anew.

 

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Once the bag closes insecticides are not useful. Insecticides must be applied while the worms are small and are feeding on the plant. In our area, this is late May to early June. General insecticides such as malathion and bifenthrin are effective, but also kill the good insects, such as parasitic waslps.  The best choice is a safe biological insecticide, Bacillus thuringiensis (Bt). As mentioned above it is safe for children and pets and has little impact on the good insects (FYI, Bt is useful for almost every caterpillar in the garden and landscape and may be used on vegetables). After the bag is sealed, the only recourse is to pick off the bags by hand.

 

White Grubs

 

White grubs are the larvae of many species of Scarab beetles—May or June beetles, masked chafers and Japanese beetles—all of which are similar. In summer they are found in the upper soil. They are “C” shaped and ¾ to 1 ¼ inch in length.  We have a predominance of May and June beetles. They all differ in life cycles ranging from 1-3 years. Adults emerge from the soil at different times, but most appear in May or June.

 

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After mating, females enter the soil and deposit eggs.  Larvae hatch three to four weeks later and begin feeding on dead organic matter, later moving to the roots of  grasses and other plants and may inflict significant damage. White grubs are rarely a problem in Bermudagrass but typically damage cool season grasses like bluegrass and fescue.

 

Aboveground symptoms of white grub damage are browning and dying of the grass in localized spots or in large irregularly shaped areas. Major damage may occur in September and October when grubs mature. 

 

To diagnose the problem use a spade to turn over a square foot of sod at the junction of brown and green grass. Various criteria for treatment have been suggested, based on the numbers of grubs found per square foot, but generally if there are 5 or more grubs per square foot and if there is damage, you should treat. An interesting note is that these beetles are more likely to be near an outdoor light. The adults lay eggs at night and are drawn to the light like a moth to a flame.

 

The presence of moles on your property is not a reason to treat the grubs. It has been shown that moles eat mainly earthworms, not grubs, and killing the grubs will not eliminate moles.

 

There are two chemical control strategies targeting species of white grubs: preventative and curative or rescue treatments.  Both strategies can make use of systemic products that make the host plant toxic prior to and during egg hatch.  Preventative applications typically are applied in late May and can provide season-long control of newly hatched white grubs.  Larvae feed on roots of protected plants and consume a lethal dose of the insecticide.  Insecticides used for preventative white grub control include imidacloprid and others in this class.  Preventative products are rapidly absorbed by turfgrass roots and tend to be most effective against young larvae. They are not recommended unless there is a history of white grub infestations in the area. 

 

Curative/rescue treatments are applied in locations where white grubs are known to occur from pest records for the site, monitoring efforts, or visible damage.  Curative/rescue applications are made any time white grub populations are high and/or damage is present, but are most common in late summer/early fall for infestations missed earlier in the season or in spring when large multi-year white grubs are active.  Insecticides used for curative/rescue treatments include Carbaryl (Sevin) and others. Always read and follow labeled directions of the product.

Many of the recommended insecticides are available only to licensed applicators.

 

Snails and Slugs

 

Slugs are snails without shells, they come out at night and eat on many of our plants, but when they find our hostas, it seems to be the equivalent of our tailgate party. They are also very much at home in the vegetable garden.

 

It is easy to tell if you have slugs, both by the damage to the plants and especially the slime trails they leave on structures. In order to travel, they secrete a mucous material which later hardens and becomes shiny, documenting their passage.

 

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There are several strategies for control. One is to remove all trash under and around plants. This produces a quandary, in that most of us would like to add mulch to all plants, including hostas. However, if slugs are a problem, it is best to remove their home. Other measures, including beer in saucers, are not very effective. Laying out a board in the garden, under which they may hide during the day, has some merit. Checked daily, the slugs may be collected and destroyed. Since they feed only at night, a little time in the garden after dark, with a flash light, is productive.

 

Lastly, there are two types of commercial slug killers. One, metaldehyde, is a poison in a granular form, which is spread around the plant. This is poisonous to animals and must be used with caution. Another more expensive product is iron sulphate. This natural compound is found in your garden soil and is safe for all animals. It, too, is in a granular form to be spread around the plants at risk.

  Control of Garden Pests

 The single best control measure is to purchase plants resistant to their common pests. It is not always possible, but always consider this when selecting new plants.

 

Many of the pests and their eggs over-winter in trash left from the previous growing season. Weed beds near the garden are also a refuge for pests. Sanitation, with careful clean-up at season’s end and elimination of weeds can be very effective in pest control.

 

A jet of water will remove many of these pests. Depending on the situation, many of the pests may also be removed by hand.

 

Barriers are useful. Paper barriers around some vegetables will prevent cutworm, row covers over other vegetables block out flying insects.

 

Go to our page on insecticides for additional information as to strategy and specific insecticides.