Bugs-From Beneficial To Beastly!
From Beneficial To Beastly
By: Bastiaan M. Drees, PhD and John A. Jackman, PhD
These creatures can be unsightly on their own, but they can really make plants look ratty by chewing leaves, stems and roots or by sucking juices out of buds, fruit or other plant parts. Pest management becomes a concern from the minute you till the garden soil until you harvest your crops.No matter how much you fantasize in the spring about your beautiful garden, the reality is this: when you plant your garden, you are really planting an smorgasbord for pests. Each type of vegetable you plant is a potential food source for a plethora of insect and arthropod pests.
Diagnosing pest problems is the first and most critical step in conducting a sound pest management program in your garden. For help in identifying pests and selecting the best treatment, obtain the publication, Managing Insect and Mite Pests of Vegetable Gardens (B-1300, Tex. Agric. Ext. Serv., Nov. 1998) from your local County Extension Agent or visit the web site, http://insects.tamu.edu. You can also visit http://vegipm.tamu.edu to access images of garden vegetables for identification and to query a database about control options for home vegetable pests. A Field Guide to Common Texas Insects (Gulf Publishers) can also help you identify these and other insects and learn about their biologies. Also, some nurseries and garden centers are good places to get advice and a diagnosis of plant pest problems.
In typical Dave Letterman style, the top ten “creepy-crawly-critters” invading your garden will probably include:
- 10. Many beneficial insects
- Those that eat other insect and mite pests. Lady beetle larvae, ambush bugs and assassin bugs, damsel flies, minute pirate bugs, preying mantids, parasitic flies and wasps are occasionally misidentified as pests and occasionally are “controlled” using pesticides needlessly. Dont just pull out the insecticide at the first sight of a bug! Know your good bugs from the bad.
- 9. Soil dwelling (non-insect/arthropod) pests
- Pests that often require unique approaches to their management. Sowbugs and pillbugs are crustaceans often dwelling in or under leaf litter, landscape timbers or mulch. These, along with some species of snails and slugs (Gastropoda) emerge at night or on cloudy days to consume leaf tissue on a variety of plants, particularly your tender leaves. Removal or disturbance of harborage areas is a key to eliminating these pests.
- 8. Grubs
- The immature stages of certain beetles. Underground, the C-shaped larvae of June bugs/beetles will eat the roots off of just about any vegetable plant when numerous, and the Southern corn rootworm produces larvae that attack young corn roots, causing early death, stunting or goosenecking which describes a corn plant that has fallen over because it lacked brace roots, trying to grow up straight again.
- 7. Red imported fire ants Sterile female worker ants build and defend their nests or mounds in and around the garden and search the garden for suitable prey (caterpillars and other slow-moving critters) and plants on which they can feed (potato tubers, okra buds and developing fruit). They sting repeatedly and can cause medical problems or generally be a nuisance to anyone trying to work in the garden.
- 6. Grasshoppers
- Both in the wingless immature (nymphal) and winged adult stages. A number of species will be attracted to the green leaves in your garden-particularly when the vegetation in bar ditches and meadows dries up in late spring. They will feed on just about any vegetable and immigrating adults quickly replace those you might kill with a pesticide!
- 5. Bugs
- In both immature (nymphal) and adult stages can suck the juices out of a variety of vegetable plants. The most notorious members of this group (Hemiptera) are the stink bugs which include the Southern green stink bug which causes deformed or discolored tomatoes and beans. Harlequin bugs are stink bugs that attack cole crops (cabbage, broccoli, etc.). Other close relatives include the squash bug, which can outright kill squash vines and attack developing fruit, and leaf-footed bugs on southern peas and tomatoes. If you grow okra or herbs, watch out for tiny, black, hopping critters called garden fleahoppers that cause leaves to become speckled.
- 4. Leaf beetles
- Both adults and larvae can injure a variety of plants, but they are generally fairly specific to a particular vegetable crop. Adults and red larvae (grubs) of the Colorado potato beetles attack mainly potatoes, whereas those of the yellow-margined leaf beetle go for turnips and greens in the coastal region of Texas. A number of flea beetle species produce small holes in a variety of crops like potatoes and tomatoes.
- 3. Spider mites
- Non-insect arthropods that are more related to ticks and chiggers than to insects, and often are not controlled with insecticides. The clear, round eggs laid by females are also resistant to most pesticides and allow populations to build up rapidly-particularly on water-stressed plants.
- 2. Aphids
- Several species on a number of different crops, particularly on cabbage (cabbage aphid), tomatoes (green peach aphid) and other crops (cotton aphid or melon aphid). These insects reproduce like nesting dolls, with females (stem mothers) giving live birth to other reproducing females throughout the season without mating! This process is called parthenogenesis. These are really nasty when they infest leafy vegetables or plant parts you intend to eat. If they leave these plant parts alone, you might just want to observe them for signs of natural enemies like parasitic wasps which turn aphid bodies into brown, blown-up aphid mummies when parasitizing them. Also, be on the lookout for the immature stages of green lacewings (called aphid lions) or maggots of flower flies (Syrphidae). With luck and patience, these natural enemies could clean up an aphid population.
- 1. Worms (caterpillars)
The immature (larval) stages of moths and butterflies. Some of these can get pretty big and may only be good-looking in the eyes of an entomologist! These pests include cutworms, armyworms, cabbage loopers, tomato and tobacco hornworms (3 to 4 inches long, full grown!) and many others. Probably THE UGLIEST, damaging and hardest to control is the squash vine borer that tunnels through squash and melon vines. Some caterpillars of butterflies like the parsleyworm or black swallowtail on dill, parsley and fennel may be desirable, while others like the European cabbage worm on cole crops damage these plants just as easily and completely as cabbage loopers.
After reading this list, you might ask yourself: Why even bother? Well, that is just part of the fun and challenge of gardening. Surely, you are not going to let the tiny brains in these pests out-smart you. You can, in most cases, win the battle by finding the most cost-effective, environmentally sound method to prevent or suppress them when they get out-of-hand. Some of the more friendly methods and control alternatives are discussed below:
Use good horticultural practices. Selecting pest-resistant or -tolerant plants best adapted to your growing area whenever available is a good first step to prevent pest problems. But in addition, prepare the soil, plant properly (proper spacing and depth), apply proper amounts of water and fertilizer. Vigorously growing, healthy plants are less prone to pest problems.
Keep weeds and trash out of the garden well before planting seeds or transplants. Often cutworms and white grubs are present on weeds, and when removed just before planting vegetables, these immature feeding stages of pests merely move on to your valuable plants. Landscape timbers, rock borders and piles of dead leaves can serve as condominiums to a host of soil dwellers! Remove or disturb these and other harborage areas in which pests may hide during the day. If you see a lot of white grubs when tilling the soil in the spring while preparing your garden, consider using some type of soil treatment using an insecticide or biological control agent (some parasitic nematodes have reportedly provided some control of white grubs and other soil-inhabiting pests).
Barriers to baits
Use barriers, cages, traps and baits. Containers like milk jugs with the bottom removed can be placed around tomato transplants to discourage access to these young plants by cutworms, pillbugs and slugs. Cages provide structures for vine crops like melons and tomatoes and prevent them from laying on the ground where they are vulnerable to attack from numerous insects and other pests-and are impossible to spray on the undersurface of leaves. Floating row covers are available to help keep pests out of the garden, but they are not much to look at and often trap insects inside. Even copper strip barriers are available for keeping slugs and snails out of small containerized garden planting boxes. On the other hand slug and snail pit-fall traps baited with beer are a lot of fun to try!
Eliminate red imported fire ants from around the garden using appropriate methods. Most bait-formulated fire ant insecticides can not be used inside the garden, but when applied around the garden, they eliminate ants nesting in and outside of small gardens. An even better idea is to control ants in your entire lawn and to get your neighbors involved in a community-wide fire ant management program as described in brochures available from your County Extension Agent (see L-5070, The Two-Step Method: Do-it-yourself Fire Ant Control for Homes and Neighborhoods, Nov. 1998) or found on the web site, http://fireant.tamu.edu. To do a really good job of ant control, control efforts should really be started (or continued) in the fall!
Use high-pressure water sprays. For aphid and mite populations just beginning to build up on the plant, try spraying them with water! A few companies sell hose-end attachments that produce a fine, high-pressure spray that will dislodge many arthropods pests – particularly spider mites, given that you can direct the spray to the under surface of the leaves.
Try insecticidal soaps and horticultural oils. For small soft-bodied arthropods like aphids, spider mites and small caterpillars or larvae, commercially available insecticidal soap or horticultural oil products will kill whatever you hit with the solution. Soap solutions dissolve and remove the waxy layer from the outer surface (exoskeleton) of these creatures which is critical for water-retention. Without this waxy layer, the creature desiccates or suffocates if the soap gets into the breathing pores (spiracles).
Horticultural oils (paraffinic waxes) also suffocate insects while not generally injuring the plants foliage. Homemade concoctions of soaps or vegetable oils occasionally work well, but they do not come with instructions or precautionary statements. Soap sprays have little to no residual effects, so they pose a minimal threat to parasites and predators that arrive after treatment.
Use available biological controls. Biological control agents or natural enemies (parasites, predators and diseases of insect and mite pests) are becoming more available to release into the garden to try suppressing specific insect and mite pests. These are not generally available in retail outlets.
One of the more promising groups of biological controls are the predaceous mite species (they are hard to see, but they do not fly off the plants you put them on and they do not eat each other). A number of species and strains are available and when released early (before spider mites become a problem) and regularly (in concentrations suggested by the insectary), populations of spider mites might be suppressed. Results of field releases are not guaranteed by the producer(s) of these organisms because weather conditions, pesticide residues and other factors beyond the control of the manufacturer might cause these treatments to fail. However, this is a great way to learn about ecology and involve the kids in the gardening experience!
Be aware of microbial insecticides. Some bacteria, fungi and other microorganisms are formulated and sold as bio-pesticides. They should be respected as pesticides (which they are) and used according to the directions provided on the products label. The spores and (endo)toxins of the bacterium, Bacillus thuringiensis, or BT, is the most readily available and commonly used. This strain (var. kurstaki) is target-specific to only young (small, early stage or instar) caterpillars that ingest treated plant surfaces. Treatments do not affect natural enemies like parasitic wasps, green lacewing larvae and lady beetles. However, if you intend to raise caterpillars of butterflies, be careful not to contaminate their host plants with the spray! Other strains of this species are now available (generally by catalog order only) that are effective for controlling other insect groups. The variety, san diego, is specific for controlling immature stages of beetles such as the Colorado potato beetle.
Have fun experimenting with new approaches. There are a number of barriers, traps and practices that are fun to try. Some recipes are available for making home-made insecticides. However, these may not be safe, scientifically tested or very effective. Use these at your own risk. Garlic water and hot pepper wax sprays are now available as repellents.
There are dozens of insecticide/miticide products on the market. Most are effective when used correctly. Spraying to insure under-the-leaf coverage is critical to getting good control. Study available information to find out which is the least toxic to the user and environment, which crops are permitted to be sprayed and how long to wait after spraying before harvesting your crop. Avoid mixing more product than can be used at one time. Some products require the user to wear special protective clothing during mixing and application. Keep equipment and protective clothing clean and in good working order; do not use insecticide-contaminated articles for any other purpose; wash clothing you wear during application separately from others.
A visit to any community garden will allow you to observe that there is an infinite number of approaches to managing garden pests. Some peoples gardens are continually covered with the white dust from weekly insecticide treatments, while other folks do better at raising insects than vegetables!
The bottom line is to have fun, enjoy the fauna and ecology of Texas, and be aware that there are places to go for help if you need it. Part of vegetable gardening is educating yourself to make the most appropriate selections for managing the pests that arrive and thrive, and to learn how to use pesticides (organic or synthetic) responsibly and safely. If you do choose to use an insecticide, please set a good example for your children or grandchildren and use them judiciously and correctly.