How to Prevent Garden Pests and Diseases

Some type of pest is bound to "bug" your garden, no matter how much effort you put into prevention. You may notice yellow patches in the lawn, holes in leaves, or stunted plant growth. The more you water and fertilize, the more you may play host to pests. Or it may be that insects and diseases are making a neglected area even worse. Alas, pests are everywhere, but help is here with organic remedies that are easy on the environment, as well as safety guidelines if you have to resort to chemical methods.

Many of the bugs in your garden are a nuisance, but some,
such as ladybugs, can be good for your plants. See more
pictures of garden ideas.

Disease is another problem you may encounter. Plants with enough space are likely to be healthy, but in an overcrowded garden, airflow stagnates, just as it does in an overcrowded room. Without free air circulation, foliage dampened by dew, rain, or sprinkling will stay wet longer and be more susceptible to fungus and other diseases.

In this article, learn about inviting beneficial garden guests, keeping pests away, pesticide safety, washing container plants, eliminating garden disease, and common garden pests.

Some of the critters in your garden are actually good for your plants. Go to the next page to learn about beneficial garden inhabitants.

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Good for the Garden

Some bugs and amphibians are actually good for your garden. Add toad houses to the garden to attract toads for natural pest control. Just as fairy-tale toads can be turned into handsome princes with just a kiss, ordinary toads become plant protectors just by hopping into the garden. They may not be pretty, but toads eat plenty of bugs, so you'll be glad to see them. To encourage toads to come to live in your garden, try the following:

  • Put several broken clay pots in the garden for toads to hide under.

  • Water when the ground gets dry to keep the environment pleasant for amphibians.

  • Avoid spraying toxic chemicals on the garden.

  • Watch out for toads when tilling, hoeing, or shoveling.

Beneficial insects, such as ladybugs, can help your plants fight off pests.

You can also attract beneficial insects that will prey on plant-eating pest insects. Distributing some flowering plants amid the garden helps attract "good bugs" such as ladybugs, spiders, lacewings, and tiny parasitic wasps. The flowers provide shelter plus nectar and pollen, an alternative food source. Once beneficial insects are at home in your garden, keep them there. Remember, they can be killed as quickly as plant pests by broad-spectrum pesticides, which kill all insects indiscriminately. It's best to avoid pesticides or use targeted pesticides such as Bt (a bacterial disease of caterpillars that won't harm other insects) to protect beneficial insects.

Not all plants and animals are welcome in your garden. On the next page, learn about keeping pests away from your plants.

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Keeping Out Pests

When pests strike at your garden, you need to strike back. Use organic repellents to chase away rodents and deer. Sprays made out of hot peppers, coyote or bobcat urine, rotten eggs, bonemeal, or bloodmeal (even castor oil) can make your garden unappetizing to herbivores. Reapply the repellents frequently, especially after rain.

Soap and human hair can also be used to deter deer. Soap can be stuffed in a mesh bag and dangled from branches at the nose height of deer -- about three feet. Replenish the soap supply frequently so it won't dissolve away or lose its smell. Human hair stuffed in mesh bags will make deer wonder if you are hiding in the garden.

Floating row covers can keep flying insects away.
Floating row covers can keep flying insects away.

Grow French or American marigolds to kill any nematodes in the garden soil. Nematodes -- microscopic wormlike pests that can damage tomatoes, potatoes, and other crops -- are killed by chemicals that are released by marigold roots and decaying foliage. You can plant marigolds in and around other nematode-susceptible plants. Or just till marigolds into the soil and let them decay before planting potatoes or tomatoes.

Floating row covers will keep pests off vegetables. When draped over plants, these lightweight fabrics allow sun, rain, and fresh air to penetrate but keep flying insects out. Secure them to the ground with rocks, bricks, or long metal staples. They can:

  • Eliminate maggots (fly larvae) that tunnel into the roots of radishes, turnips, carrots, and onions. They keep egg-laying flies away. If there are no eggs, there are no maggots.

  • Keep potato beetles from eating the foliage off potato leaves and vines. Pin the row cover edges down tightly so the beetles can't crawl under.

  • Protect cucumbers, squash, and pumpkins from cucumber beetles, which carry a wilt disease capable of killing entire vines. Since flowers of these vines need insect pollination for fruit set, the covers must be lifted for several hours at least every other day for honeybees to do their work.

Use barriers of copper strips or diatomaceous earth to keep slugs away. Slugs eat tender plants down to the ground. They come out from under rocks, logs, or mulch when it's rainy or cool and dark. Diatomaceous earth is a gritty substance that pierces the skin of soft-bodied slugs. Sprinkle it on the soil, encircling plants plagued by slugs. Use the horticultural grade, not the kind sold in swimming pool stores. Copper strips, set around the edge of the garden, prevent slug trespass by creating an unpleasant reaction when touched by slimy slugs. Set strips on edge an inch deep and several inches high.

Spray aphids off plants with a strong stream of water from the hose. Aphids, small sap-sucking insects with soft bodies, cling to succulent young stems and buds but are easily dislodged. This works best on roses and mature or woody plants that won't be damaged by the force of the water. Repeat every few days or when you see new aphids.

Using these disease-resistant cultivars should help to keep your garden healthy:

  • Apples: Freedom, Jonafree, Liberty, MacFree

  • Beans: Buttercrisp, Florence, Jade

  • Cucumbers: Fancipack, Homemade Pickles, Park's All-Season Burpless Hybrid, Salad Bush, Sweet Success, Tasty King

  • Peas: Green Arrow, Maestro, Sugar Pop, Super Sugar Snap

  • Roses: Carefree Delight, David Austin English Roses, The Fairy, Meidiland roses, Red Fairy, rugosa roses, Town and Country Roses

  • Strawberries: Allstar, Cavendish, Delite, Guardian, Lateglow, Redchief, Scott, Surecrop

  • Tomatoes: Beefmaster, Better Boy, Big Beef, Celebrity, Enchantment, LaRossa, Mountain Delight, Roma, Sunmaster, Sweet Million, Viva Italia

  • Zinnias: Cherry Pinwheel, Crystal White, Orange Pinwheel, Rose Pinwheel, Salmon Pinwheel, Star Gold, Star Orange, Star White

Sometimes pesticides are the best tool to keep your plants healthy. Keep reading to learn about pesticide safety.

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Pesticide Safety

Follow your pesticide's directions and clean up thoroughly when you're done.
Follow your pesticide's directions
and clean up thoroughly
when you're done.

Pesticides are a good tool in the battle against garden pests. These days, chemical pesticides come and go. Yes, they kill plant pests, but they often have unforeseen consequences. Several formulations have been taken off the market due to their ill effects. For example, DDT was pulled from the market because it was spreading through the environment, causing death among bug and fish-eating birds, including the American eagle (it made their eggshells too fragile for survival of the young).

Unfortunately, there are times when a particular pest, such as fire ants, requires strong measures. Use every caution when you resort to pesticide. Follow the directions on the package, wear protective clothing (and wash it afterward), and take a shower or at least wash your hands and face as soon as possible. Keep in mind that insects and microorganisms sometimes evolve rapidly and become immune to chemical remedies whose damaging effects remain in the environment nonetheless.

Mild soap can help you keep container plants pest-free. Keep reading to learn about washing container plants to eliminate pests.

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Washing Container Plants

Potted plants get pests too. Any time yours are suffering from insect damage, you can try the Ivory soap trick.This is an old-time remedy you can use before bringing potted plants indoors after their summer outside. Follow these steps:

  • Fill a bucket halfway with lukewarm water.

  • Get a bar of Ivory soap (which is not a detergent and is milder than most other soaps), lather it up in the water with your hands (just for a minute), and then remove it. The water should not be bubbly, just a little cloudy.

    Dunk small potted plants, soil and all, in soapy water to eliminate pests.
    Dunk small potted plants, soil and all, in soapy water to eliminate pests.

  • For small potted plants, dunk the whole pot with its soil and plant under the soapy water for a minute. Then remove it and set it where it can drain. For larger plants, take both the soap mixture and the plant outdoors on a warm day or to the bathtub. Splash and wet every leaf and stem of the plant, and let soapy water go into the potting soil as well. (Do not let potting medium or leaves go down the drain!) Set the plant where it can drain.

  • If the plant is infested with a difficult pest, cut off damaged leaves, prune for shape, and repeat the process every few days to make sure you get rid of the last few critters.

When disease strikes your garden, you must act quickly to protect your plants. Go to the next page to learn about eliminating garden disease.

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Eliminating Garden Disease

Growing healthy plants is the first step toward a great garden. To achieve this, it's important to prevent diseases through careful plant selection, planting, and care. Choose disease-resistant cultivars whenever possible. They are bred to resist infection-an ideal way to avoid diseases. Growing disease-resistant vegetables prevents chemical tainting of your food. Planting disease-resistant varieties of popular flowers such as roses saves you time, trouble, and expense. There are varying levels of protection available:

Find cultivars that are resistant to diseases that are common in your area.
Find cultivars that are resistant to diseases that are common in your area.

  • Some cultivars have multiple disease resistances for maximum protection. The Big Beef tomato, for instance, resists various types of wilts, tobacco mosaic virus, nematodes, and gray leaf spot. Little is left that can harm it.

  • Some cultivars resist only one disease. But if that disease is a problem in your area, then these plants will be worth their weight in gold.

  • Other plants are disease tolerant, meaning they may still get the disease but should grow well despite it.

When it comes to garden pests, you need to know your enemy. On the next page, you'll find symptoms and control methods for common garden pests.

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Common Garden Pests

Here are some common garden pest problems and suggestions about how to deal with them. A reputable garden center sells pesticides, repellents, and fungicides, keeping up with current regulations and usage. Each entry below names the pest, describes the damage, and suggests one or more controls.

Keep harmful insects away from your plants if you want a good harvest.

AnthracnoseThis tree blight of dogwood, ash, willows, and others causes leaves to develop brown spots, giving them a scorched look.Remove badly diseased branches. Prune for good air circulation.
Tiny green, gray, reddish, or brown pear-shape insects suck juices out of plant leaves and stems. You can see them clustering around the tips.Spray them off with a forceful jet of water, use insecticidal soap or rotenone, or bring in ladybugs to eat the aphids.
Beetles, variousYou can sometimes find beetles burrowing into flowers or leaves. They chew away foliage, leaving it very ragged.
Pick them off by hand or spray with rotenone. Look for beetle egg cases on the undersides of leaves and destroy them.
Caterpillars, variousLacy holes and big bites appear in leaves. Sometimes you can catch criminal caterpillars in the act.Kill them by hand or spray with Bacillus thuringiensis or pyrethrin.
Chinch bugsRound or irregular yellow patches appear in the lawn in hot, dry weather. This can mean chinch bugs, which are barely visible insects that suck juices from grass blades.Use an insecticide labeled for this problem and repeat at three-week intervals.
CutwormsCertain grubs and caterpillars live underground and chew through entire young plants, nipping them off at the base.
Destroy any cutworms you find by searching underground near the damage. Make protective collars for plants out of cardboard tubes two inches tall, setting each one around a plant, halfway into the soil.
GrubsPatches of dead turf and garden plants that vanish without a trace are signs that you may be dealing with grubs, the larvae of beetles.Control adult beetles by hand picking. If the problem is severe, use a recommended insecticide in late spring or early summer.
Lace bugsLeaves of azaleas and other plants become speckled and lose vigor. Lacebugs, with telltale small black specks, are the culprits.Spray the undersides of leaves with the appropriate remedy, after you have taken an afflicted leaf to the Agricultural Extension agent or garden center expert for confirmation of the diagnosis.
Leaf hoppers
Leaves are peppered with small round holes and begin to curl. Small, triangular hopping insects are the cause.Spray off light infestations with a garden hose before you turn to stronger remedies.
Leaf minersThere are white, curling trails inside the layers of a leaf. You can sometimes see a dark spot where the leaf miner is doing its damage.Remove all damaged leaves. Throw them in the trash, not the compost pile.
MealybugsA type of white, fuzzy scale insect, mealybugs make sticky clumps on leaves, buds, and stems and seriously weaken plants.Wash them off with Ivory soap and water solution, paint them with alcohol, or use pyrethrin to get rid of them.
MolesIf you have tunnels under your grass, it could be moles. They are carnivores that eat grubs and earthworms they find underground.Control insects that they feed on, or trap and remove the moles. Voles sometimes use similar tunnels.
ScaleLike mealybugs, scale insects cluster on stems. Some forms are dark and have a shell about an eighth of an inch long. Juvenile forms can move but adults stay in one place, sucking plant juice and spreading disease.
Wipe branches with alcohol or soapy water, and spray them in early spring with dormant oil.
Slugs and snailsSlimy trails are one clue left by these mollusks, and irregular holes in leaves and stems are another.Handpick and destroy, or use newer types of slug bait that are earth-friendly. A classic remedy is to trap them in shallow tubs filled with beer, set with the tops at soil level near the damaged plants. Or place a cabbage leaf near the damage, then look under it a day or two layer and find the critters hiding there.
Spider mitesFoggy little webs are nearly invisible, but the damage caused by spider mites can be extensive, killing leaves and plants.Spray with water often, for they prefer dry, dusty conditions. If the problem is extensive, use a miticide at three-day intervals.
SpittlebugsIn a mass of tiny white bubbles on plant stems, spittlebugs are hiding.They are not much of a problem, so unless they are pervasive, just spray them off with the hose from time to time.
WhitefliesSmall white insects shaped like houseflies but less than a quarter-inch long make their home on the undersides of leaves, laying eggs and sucking plant juices.
Wash plants off, use yellow sticky traps, improve air circulation, or destroy afflicted plants before the pests spread.

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