CHEMICAL CONTROLS: INSECTICIDES (Vegetable Gardening)

The surest way to control most of the insects and similar creatures that threaten your vegetable crop is by using a chemical insecticide. A word here about terminology: In horticultural language the terms “pesticide” and “insecticide” are not interchangeable. A pesticide is any form of chemical control used in the garden; an insecticide is a specific type of pesticide used to control a specific situation — to kill insects. A herbicide is a different kind of pesticide with a different application — it’s used to help control garden weeds. These distinctions are important, because using the wrong one will cause havoc in your garden. For instance, if you use a herbicide instead of an insecticide you’ll lose your entire crop for the season. It’s also important to keep separate equipment for use with each kind of pesticide.
Insecticides are chemical products that are sprayed or dusted on the affected crops. The type you spray on is bought in concentrated form, then diluted for use with a hand sprayer or a spray attachment fitted to the end of your garden hose. Dust-on insecticides are powders that you pump on to the plants. Spraying is preferable because it gives more thorough coverage, and it’s easier to treat the undersides as well as the tops of leaves and plants with a spray. You can also apply insecticides directly to the soil to kill insects under the soil surface — this technique is known as applying a “soil drench.”
Used correctly and responsibly, insecticides are not harmful to humans or other animals. They are toxic, but the toxicity levels are low, and their residual or carryover effect is short — the longest any of the insecticides commonly used in the home garden will remain on the plant is about 14 days. Malathion, for instance, has the same toxicity level as Scotch whiskey and breaks down faster. As to any long-lasting hazards that may be involved — nobody knows if hazards exist or what they might be; we don’t know what the long-lasting hazards of any product might be. The choice of an organic or a synthetic pesticide is a matter of personal opinion. If you know all the options you’ll be able to make your own choice.


Commonly used insecticides

The insecticides listed below for use in your home vegetable garden will provide effective control of garden insects with minimum hazard. Remember, though, that most insecticides are poisons and must be handled as such.


Diazinon.

This is an organic phosphate, and it’s an effective insecticide for general use. Diazinon is a contact poison. Its toxicity is low, and it’s a good control for underground insects that attack the roots of cabbage family plants, onions, and radishes. You can get it as a wettable powder or in liquid form.

Malathion.

This is also a phosphate insecticide; it kills sucking insects like aphids. Its effects are not as long-lasting as those of some other insecticides, but it’s effective and safe in use. It’s available as a dust, a wettable powder, or a liquid.

Sevin.

This is also known as carbaryl and is another safe material for use in home gardens. It’s an effective control for many leaf-eating caterpillars and leafhoppers, and is available as a wettable powder or a dust.

Bacillus thuringiensis.

This is an organic insecticide. It’s a bacterium that is considered harmless to all but insects, and you can buy it under the brand names of Dipel, Thuricide, or Bactur. It controls cabbage worms and other caterpillars and is available in wettable powder or liquid forms. This is the choice of many gardeners who prefer not to use chemical insecticides.

Cause and cure:

Be sure you’ve got them right.Because an insecticide can’t distinguish between friend and foe, it’s your responsibility to make sure you’re eliminating the pest, not the friendly insect that’s out there working for you. Let’s say, for instance, that aphids are attacking your cabbage plants, and you use carbaryl (Sevin) to try to get rid of them because you know carbaryl is a relatively safe insecticide with a short residual effect. You’ve overlooked the fact that carbaryl has to enter the insect’s stomach in order to kill it, and since the aphid’s mouth is inside the cabbage plant, none of the insecticide is going to enter the insect through the mouth and reach its stomach. Ladybugs, however, love aphids and are most helpful in keeping down their numbers. So when the ladybug eats the aphid, the carbaryl on the aphid’s body enters the ladybug’s stomach and kills it. Despite the best intentions in the world, you’ve killed off the useful insect and left the pest unharmed. In fact you’ve done the pest a favor by killing off its enemy — a ladybug can put away hundreds of aphids in a day.
Carbaryl can also be toxic to bees, and bees are important to your garden because they pollinate most fruiting vegetable crops. To avoid killing the bees, spray in the late evening when the flowers are closed. This way you kill the destructive pests but protect the bees.
If you use an insecticide you must always be aware also of how long its residual effect is going to last. A residue of insecticide left on the plant when it’s harvested is poisonous. The residual effect of an insecticide that you use in your vegetable garden is likely to be fairly short, but the effect may vary from one type of crop to another. And because the effect is not long-lasting, you can’t spray as a preventive measure; you have no way of knowing which pests . are going to attack your plants before they’re actually on the scene.

How to use an insecticide

Because research is constantly being done to determine the safety of insecticides and improve their effectiveness, it’s difficult to give long-term recommendations about their use. Basic rules, however, always apply: Read the directions and precautions on the label and follow them meticulously, and never make the solution stronger than the label says because you think it’ll work better that way. If the product would be more effective in a stronger solution the label would say so. You need to use common sense when working with an insecticide. If there are just a few, visible insects on your plants, it may be a lot easier to remove them by hand than to go through the full routine of applying a chemical remedy. Also, weather conditions limit when you can use a product that has to be sprayed or dusted on the plants — you can’t do it on a windy day because you can’t control the direction of the application. The wind can take your insecticide over into your neighbor’s garden; so you’ll both fail to correct your own pest problem, and you’ll make your neighbor mad. As the one who’s using the pesticide, you are responsible for it.
You’ll also defeat your own purpose by using an insecticide if rain is expected within 12 to 24 hours. The insecticide must dry on the plant in order to be effective. Whether you use a spray or a dust, make sure that you reach all parts of the plants—you’re aiming for a light covering on both the tops and the undersides of all the leaves. Don’t give the pests a place to hide; proper coverage is essential if the insecticide is to do its job.
The products we suggest are commonly used in the home vegetable garden as we write this. But before you go out to buy one, check with your local Cooperative Extension Service to make sure that these recommendations are still current.
If you do decide to use a pesticide to control insects in your vegetable garden, here are some important points to remember:
• Read the whole label; observe all the precautions and follow all the directions exactly.
• Check the time period that must elapse between application of the insecticide and harvesting the plant, and observe it strictly. Note all restrictions carefully — often products must be applied at a certain stage in the plant’s development.
• Wear rubber gloves while handling insecticide concentrates; don’t smoke while you’re handling them, and take care not to breathe the spray or dust.
• Sprays usually have to be mixed before each use. Follow the directions, and use only the exact proportions indicated on the label. If it’s not used exactly as indicated, an insecticide may be harmful to people, animals, or plants.
• Use equipment that you keep specifically for use with insecticides. Don’t use equipment that has been used for herbicides.
• Do not apply an insecticide near fish ponds, dug wells, or cisterns; do not leave puddles of pesticides on solid surfaces.
• Use a spray or dust-type insecticide only when the air is still. Wind will carry the product away from your garden and, possibly, be a nuisance to someone else. Don’t spray or dust within 12 to 24 hours of an expected rain — the insecticide must dry on the plants to be effective; rain will wash it off.
• After using an insecticide, wash your clothes and all exposed parts of the body thoroughly with soap and water.
• Store unused material (undiluted) in its original container out of the reach of children, irresponsible adults, or animals — preferably in a locked cabinet or storage area.
• Dispose of the empty container carefully. Do not leave it where children or animals can get to it or where it might be recycled for another use.
• Wash all treated vegetables carefully before eating them.

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