Pest Elimination

By Bob Randall, Ph.D.

Make It Difficult For Pests To Find Food Or A Place To Breed.

We make it easy for a beneficial to find a pest, and we make it hard for a pest to find its food.

Separate Pest Prone Plants

Probably the easiest way to keep a pest from bothering a plant is to separate the pest prone plants as widely as possible. Diseases and insects spread quickly enough without making their work easy by planting pest prone plants next to each other. Bugs that move by crawling, flying, or blowing should have to work to find the next plant. By separating from each other peaches, tomatoes, or mustard, there is much less infestation. As well, pests will be more widely dispersed in the yard, so they will be more easily found by beneficials and controlled. Beneficials will therefore be more likely to breed.

Rotate Crops

Another way to make it difficult for the pest to find the plant is to rotate crops. Don't plant the same things again and again in the same place. Diseases and soil pests including nematode round worms tend to stay in the soil. If you plant the same thing or its relative in the same place every season or every year, the pest has no trouble finding its target. Thus, when you plant something, rotate the planting to an unrelated family of plants with different pests. Onions, garlic, corn, and grasses will starve out nematodes (root pests) so it is good to plant tomatoes in a place where these other crops grew. Move groups of plants about and keep a record of your rotation. For some diseases, a four year rotation cycle is preferred. As well, if you recycle dead plants, put them well away from next year's related crops.

Covers and Nets for Flying and Jumping Pests

To prevent flying pests from finding their targets, use a cover or net. Insect row covers are available in many thicknesses and sizes at many places. The lightest have the least heat buildup and are the most fragile. The widest selection is PEACEFUL. One type they sell will last for years. Most local garden stores sell something in this line.

Row covers are effective in keeping stink bugs and birds off tomatoes, grapes and other fruit, and they keep flea beetles, slugs, snails, and loopers off the cabbage, mustard and other brassicas. Bird nets in standard sizes are available at most local garden stores. Other sizes are available by mail (PEACEFUL, GARDENSA). These keep birds off tomatoes, peaches and other fruit, but you may need a big net and a long pole to put it over and take it off. Use plastic ties or clothes pins to eliminate holes, or weight net down with rocks. Nets are not easy to use and are less effective ways to prevent bird damage than is fiberglass window screen stapled pockets on fruit combined with birdbaths to alleviate thirst in birds, and small fruit plants year round to keep them away from big fruit.

Walls for Crawling Pests

To prevent crawling insects from reaching plants, it is often easiest to put materials around the plant that the pest can't crawl over. Some like to use diatomaceous earth (GARDENSA) but I have not been impressed. It seems to become ineffective in damp conditions and it is a lung hazard if put in the air.

For Trees

Tree tanglefoot (WOLFES) put on a piece of wide masking tape around a tree, will keep crawlers off trees, and prevent sowbug damage on young bark and aphid problems from ants. Tansy has been reported to keep cabbage and kale free of aphids, so it may well keep aphids off other plants.

A barrier of at least 20 ft from power lines, tall trees, buildings and other squirrel transit ways to the low growing food trees they bother, will reduce squirrel problems considerably.

A piece of sheet metal at least two feet high placed several feet up a tree trunk and around it, can stop squirrels from getting into the tree.

White interior latex paint diluted 50% stops most borers on peach and plum.

For slugs and snails

Circle the cabbage, etc. with copper barrier (PEACEFUL). This was easily the most effective barrier in a national test. In cool weather, for a few plants cut the end out of a gallon nursery pot, and cover the top with row cover or fiberglass screening secured with twist tie, wire or string. Place it securely over the plant until it is large enough to deal with pests.

For early spring crawling pests

Cut out the bottom of plastic milk jugs and place around squash, tomatoes, etc.

For cutworms

Save the rolls inside toilet paper and place around new transplants in Spring.

For rabbits, rats, deer, raccoons

The only effective permanent solution is appropriate fencing. Rabbits can pass through a chain link fence at full speed.

For fruit damages by ground dwelling pests

A number of pests locate their target when fruit touches the ground. By trellising tomatoes, grapes, brambles, and even strawberries, rots and sow bugs are kept away. Similarly, cantaloupes can be kept pest free by almost anything that keeps the underside dry: pine needles, a plastic planting pack, rocks, etc.

If all else fails, surround your plants with other plants the pests prefers

Finally, it is possible to solve some pest problems with a living barrier. Vine borers can probably be trapped by planting acorn squash in a circle around other squash earlier than the main crop. They apparently bore into the acorn stems and can then be disposed of before they breed and their offspring destroy the rest. Similarly, cherry tomatoes are easier for fruit eating birds to carry, so some gardeners plant cherry tomatoes to protect the main crop.

When steps 1 - 3 fail, try trapping

Controls take too much labor and cost too much to be used when they are not necessary. More importantly, by intervening in the predator-prey cycle of nature, you reduce the food supply for the beneficials you want to encourage. Thus, only control when damage will be excessive. How bad is "excessive?" If a valuable plant will die or a large crop will be destroyed, then I generally take action. If there is just a little damage and no reason to think that the pest will devastate things, then I usually let the pest stay where it is. Recently, some tent caterpillars invaded my cherry plum. I didn't do anything. The worms ate most of the leaves on one large branch, and wasps ate quite a few worms! I encouraged the beneficials. Then the worms passed on to the next stage of their life cycle and new leaves returned to the branch. Nothing seems to have been harmed, I probably have more worm eating wasps, I did no work and spent nothing.

In any event, before resorting to poison, try hand picking or traps.

Hand Picking

Where it is effective, the best control is hand picking. Go out at night with a flashlight or in early morning and put the slugs or snails in a pail of soapy water or just stomp them. Leaf footed stink bugs can be grabbed (without squeezing!!), thrown to the ground and quickly stepped on.

Similarly, you can hand kill peach borers apparently by poking a hot coat hanger wire into the holes.

There are now commercial vacuums for farm pests. Lets hope good ones for the garden get here soon.

Traps

You can buy slug and snail motels and bait them with nutritional yeast and water. You can also put a pot over a damp place such as a wet newspaper in the summer shade and raise one side slightly so snails crawl under.

There are now a variety of traps for catching peach borers, whitefly, etc.

As A Last Resort, Use Pest Control Products Which Are Safe For the Gardener, Consumer, Beneficials, & The Environment.

There are perhaps four million people in the Houston area. Most of them are spraying and dusting various "pests" without any significant pesticide training at all. Half of the public water supplies in the U.S. already show some level of toxic contamination. If the water table is polluted, the land obviously is also. We therefore need to put an end to pesticide contamination of the Houston environment before we all suffer. Avoid highly toxic pesticides (including organics like nicotine sulfate), avoid long lasting ones, or ones that will kill a lot of beneficials.

Spraying: What You Need

Except with the most harmless sprays, use rubber gloves, hat, glasses or goggles, respirator if appropriate or mask, shoes, and old clothing covering all skin. Buy measuring spoons and measuring cups so the proportions mixed agree with the label. For powders, buy something to mix it with water such as a natural dish soap. Mix 1/2 tsp. per gallon.

Unless you have a very large garden or are doing fruit trees, you will probably need to spray about a quart or less at a time. Cheap plastic spray bottles sold in garden stores are often not very durable, so you should look for spraying devices that will hold up after repeated sprayings. If you have fruit trees to spray or a lot of vegetables, a plastic pump sprayer is best. Sprayers should be semi-transparent so you can see what is in it. It is useful to have a valve for releasing pressure. 1.5 gal is most convenient for the garden, but 2 or more can work.

Caring for the Sprayer

Never operate a sprayer when the parts are damaged. Before filling, make sure powders do not have lumps and that the sprayer has no dirt in it. A leaking container of pesticide is a bad thing and could be dangerous. When you are through spraying, to prevent a sprayer clogged with dry pesticide, always clean out the sprayer quickly. Put in water, mix, and pour out on to the nearest fireants. Then put in fresh water, pressurize, and spray until a clean hard stream comes out.

How to Spray

Spray when there is little chance of rain so it will last; spray at sundown so as not to kill bees; spray when there is little wind so it will land where you want it and not on you; and avoid getting it on your skin by using long clothing, glasses, and hat which are only used for spraying. Read the directions and warnings every season until you know them. Use a mask or respirator if the stuff is very toxic. With chemical pesticides, bathe with soap and water as soon as possible after using. Store pest controls away from children and high summer temperatures.

Buying "Organic" Sprays

We use to be pleased that we could buy any products which had low toxicity. Now however, more and more companies are marketing products which they call "organic". Not all organic sprays are equal. Last year, for example, a mass-marketed insecticidal soap was contaminated with a chemical herbicide and it did wide damage. Wetable powders are generally better since they don't require wetting agents, and use less fossil fuels in transport. Look for products that have detailed listing of ingredients and suspect supply sources that also sell hard poisons.

What to Spray

What to spray is determined by the nature of the problem and its severity. Wherever possible, try to use controls which kill just the pest and nothing else, or at least won't kill the pest's predators. For example, BT products such as Dipel, Bioworm, and Thuricide kill only caterpillars because they are a disease of caterpillars.

Many soft-bodied pests such as aphids, white flies and mites can be discouraged by water sprays, but insecticidal soap and dormant oils are even more effective. These products are quite safe for humans, but they do wipe out a wide range of insects including beneficials, so they should be used with caution.

Insecticidal soap is available everywhere. Natural dishwashing liquids formulated with coconut oil derivative laurate work equally well at 1-2% dilution (1-2 tsp. per pint), but watch out for plant damage with high concentrations.

Horticultural (dormant) oils are also available in most gardening centers, but people preferring renewable resources to petroleum can do very well with soy oil from a supermarket. Try 5 tablespoons per gallon mixed with a half teaspoon of liquid dish soap. This will kill eggs as well, and if applied every 2 weeks in hot damp weather, may stop leaf fungus. Be sure to test this on part of the plant several days before you try it full scale since homemade sprays could hurt your plants.

Hard-bodied insects, bugs, and beetles are attacked by more poisonous organic substances such as sabadilla dust, rotenone, and rotenone-pyrethrum. All come from plant products and do not last long in the environment, but rotenone is fairly toxic, so sabadilla is the product of choice.

Sabadilla (Red Devil) is the safest, most durable, and probably most effective. It is made from a tropical lily, and kills both at contact and in the stomach. It has low toxicity for mammals, but can cause eye and respiratory irritation, so mask and goggles are necessary in using. Sabadilla deteriorates quickly upon exposure to light, so is safe within days of use.

Pyrethrum is by itself is a very mild insecticide. It is made from an African chrysanthemum and paralyzes most insects, but kills few without another poison. It degrades quickly and poses little problem to our water systems. It sometimes causes problems to people with asthma or ragweed allergies. Thus, organic mixes include rotenone, while others include the synthetic piperonyl butoxides and cyclonenes. The toxicity of the mix thus depends on what it is formulated with.

Rotenone comes from the Asian derris root or the South American cube root. It is a highly toxic slow-acting stomach and contact poison to most insects and fish. It is toxic to mammals flip including people, can irritate the respiratory tract, and deteriorates rapidly on plants with no harmful residues after a week. Users should wear a mask. At this time, there appears to be no reason to use this product and many organic gardeners no longer use it.

All three of these are broad spectrum contact pesticides. They kill nearly any insect or even fish they contact in sufficient amount. They are thus best used rarely.

Weevils-especially the vexsome plum curculio - is so far resistant to all organic efforts. Peaches and plums are some of the most delicious fruits and are some of the most reliable, as long as you keep the plum curculio off when the fruit is tiny. 5% Rotenone sprayed weekly can do it, but this is generally bad for beneficials. It is possible that sabadilla, neem, or beneficial nematodes will work, but no one is doing real research on this problem.

Other than curculio, there is only one insect pest that I have trouble with. The squash vine borer destroys squashes between late May and late August every year. There are a number of ways to deal with this, but there are no simple, cheap, effective controls other than the synthetic carbaryl products like Sevin. Although many people use this, I don't. It is known to harm developing fetuses in mammals including humans. From my perspective, anything that dangerous could have other problems as well.