Pests are a major concern for newbies and experienced gardeners alike. In most cases, however, they’re actually easy to control if you stick to the following principles of Integrated Pest Management (IPM).
Acceptable pest levels
The first principle dictates that you should only take action if the pests have gotten so bad that they cross a threshold, since removing too many pests might allow populations to develop a resistance.
For the average gardener, this just means that a few damaged leaves aren’t worth losing sleep over.
Preventative cultural practices and monitoring
Often the pests themselves aren’t the problem, but rather the plant’s poor health. Too much (or too little) sun, moisture, or fertilizer can weaken a plant enough that it actually attracts pests, since many are attracted to the yellow color of a dying plant’s leaves.
Weeds or plants growing too closely together forces plants to compete for sunlight, water and nutrients. Once targeted by pests, a weakened plant finds it harder to fend for itself.
To figure out why pests are a problem, first research the plant and learn about its needs. Are you meeting them?
Then let the plant itself tell you what’s wrong. Brown and crispy leaves indicate that the plant is likely getting too much sun; while deep-green and stretched-out leaves can mean that the plant is getting too little. Mushrooms or moss around the base of the plant could indicate that poor drainage or overwatering is the issue.
To identify the pest causing all the trouble, look at the damage being done. The pests’ feeding method will help you identify and get rid of them. Parched, stippled leaves and a dusty residue indicate a spider mite infestation. Sticky ‘honeydew’ secretions are caused by aphids or scale insects.
Aphids can leave “honeydew” secretions on plants, attracting even more pests.
Leaves that look as if they have been chewed between the veins are often the victims of beetles, while caterpillars and grasshoppers can eat entire leaves (or plants) without a trace.
Usually you can see the pests themselves if you look closely enough, especially the larger ones. Some pests, such as cutworms or armyworms, may emerge at night to do their feeding.
Unless the infestation is out of control, removing pests by hand is the most effective solution. Very small insects or mites can often be removed with nothing more than a damp rag. Barnacle-like scale insects can be removed by scraping them off with your fingernail or a pocketknife.
Pick off caterpillars by hand and drop them in a bucket of soapy water; they’ll die quickly that way and you won’t have caterpillar gunk on your shoe when you’re done.
Very hungry caterpillars cause significant damage to foliage.
Sometimes it just makes sense to remove the whole leaves and stems that are affected by pests. If an infestation is particularly bad, removing all infested stems and leaves will allow the plant to grow back without the pests in tow.
Biological controls are better than synthetic ones, but even they are to be avoided if at all possible. Read the directions thoroughly and treat these substances with the same caution with which you would regard chemical pesticides. They are also still harmful to so-called “good bugs,” so only use them once you’re sure that physical removal isn’t working.
Here are a few common types of biological controls:
- Horticultural soaps are a relatively easy way to rid plants of aphids, thrips, whiteflies, scale and mealybug, but these products should not be applied to the ground, as they are also toxic to beneficial creatures like earthworms.
- Neem oil is especially useful because it first repels pests, then poisons those like beetles, lacewings, aphids, caterpillars and grasshoppers.
- Bacillus thuringiensis (BT) is a bacterium that can be used to treat for caterpillars, fungus gnats and potato beetles, depending on the strain used.
- Diatomaceous earth consists of the tiny exoskeletons of marine organisms, and can be applied to the soil to slice through the waxy coatings of insects, as well as the flesh of snails and slugs. The downsides are that you must wear a mask to prevent inhalation while applying, and that you may have to re-apply after rains.
- Pyrethrins are made up of a dried flower, and can kill a wide variety of pests, both by contact and by ingestion. Once again, whichever product you use, follow label directions and practice caution.
A potato beetle infestation may call for drastic measures.
Responsible use of synthetic pesticides
Under IPM guidelines, chemicals are the last resort. Orthene, a common pesticide, represents the typical limitations of synthetics in the garden: It kills a very wide variety of pests, but is also toxic to beneficial insects and birds. It should not be used on anything you intend to eat, since it may poison you as well.
Malathion, for the moment, is registered as safe to use on edibles, but since it is still toxic to animals like birds and fish, you should use with caution.
Pyrethroids are a manmade version of pyrethrins and are considered safer than other synthetic pesticides. Follow label directions when using any natural or chemical controls, and keep out of reach of children and pets.
Left unchecked, grasshoppers are capable of eating entire leaves.
If the steps outlined above seem daunting, just remember that you can usually solve the problem without even resorting to biological or chemical controls. Often, all it takes is improving the plant’s situation with the right amount of water, fertilizer or sunlight.
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