What Natural Pest Control Actually Works in a Garden?

Different pests need different controls, so the first job is to name what is feeding on the plant. IPM then follows a fixed order.

Chemical control sits near the end because IPM treats it as a method of last resort, used when other tactics fail. IPM does not ban pesticides, though. It asks you to choose one with a clear reason, and to keep a record of the problem, the action and the result so the next season starts with better information.

Chewed leaves with no pest in sight are common, because slugs may come out only at night and some aphids, spider mites and whiteflies hide under the leaves. Turn the leaves over, look under the shaded plants, and go out in the evening with a flashlight if you suspect slugs. A dried slime trail means slugs are active in your garden.

Rule out the weather and watering before you blame an insect. Too much or too little water, too little sun and temperatures outside the plant's range all stress a plant, and the same stress can make real pest damage worse, so a plant may need both fixes.

Once you have a clue in hand, the row that matches it names the pest to suspect and the first thing to try.

If you cannot name the pest, check an app's answer against reliable information or someone with expertise, because identification apps and websites are useful but their results need a second look.

Finding a pest does not mean you have to treat it. Most established plants tolerate aphid feeding and outgrow the damage, and aphids have many natural predators and parasites, so a large colony often declines without your help.

Where you draw the line depends partly on you. One gardener accepts some Japanese beetle damage on roses and another does not, and a blemish on an apple may be fine while a larva inside it is not.

Some pests come with a measured line. For cucumbers and melons that are susceptible to bacterial wilt, Minnesota Extension puts it at half a beetle per seedling and one per plant once they are older. Striped cucumber beetles can carry the bacteria that cause the wilt.

Pumpkins and squash get half a beetle to one beetle per seedling. Once they have two or more true leaves, treatment is worth considering when beetles have defoliated 25 percent of the leaves, and beetles feeding on flowers later do not reduce yield.

Slug damage follows the same pattern. Low to moderate feeding changes how a plant looks but usually not its health, while severe feeding can injure plants, especially seedlings, and older plants tolerate defoliation better than young ones. Act sooner when seedlings are being eaten or when the pest carries a disease, as cucumber beetles do.

Prevention starts with the right plant in the right place, since too little light, too much or too little water, or temperatures outside the plant's range may make pest damage more severe. If the spot is not quite right, you can improve it with soil pH correction, proper watering, more light or air flow, or a raised bed.

For a crop with a known disease problem, look for a resistant variety, and find out which disease a variety resists before you buy it.

A floating row cover is a white, lightweight fabric that lets in light, air and water, and it keeps out insects and also rabbits, deer, birds and groundhogs, but only if you install it soon after planting and hold it tight to the ground. Anchor the edges with soil, pins, boards or stones.

A cover keeps out pollinators as well as pests. Squash, cucumbers and melons need insects for pollination, so the cover comes off when the plants begin to flower, while spring greens and green beans can stay covered until harvest.

Pests that overwinter in the soil can end up under the cover with your crop. Squash vine borers overwinter near their host plants, so skip the cover where cucurbits grew last year. In summer a cover can run 5 to 15°F hotter than the air, so use insect netting for summer crops that need protection, and look under any cover now and then.

Beyond row cover, a few hands-on controls fit particular pests.

Diatomaceous earth is coarse enough to scratch slugs, but it works best dry and has little effect once it absorbs moisture, so it is generally not an effective slug deterrent.

Spiders, lady beetles and parasitic wasps feed on pest insects, and broad-spectrum pesticides can kill them along with the pests. Learn what they look like as both adults and young, because the larval stage of lady beetles and lacewings is the one that most often feeds on aphids.

A crusty, golden-brown aphid is a mummy, the skin of an aphid that a parasitic wasp laid its egg inside, and a round hole in it shows the wasp has emerged. In warm weather the wasps develop quickly, so once mummies appear the aphid population is likely to drop substantially within a week or two.

If aphids persist even with predators around, look for ants. Ants feed on the honeydew and ward off many predators and parasites of aphids, so managing ants is a key part of aphid control.

Buying lady beetles is a weaker bet than protecting the ones already there. Most released convergent lady beetles disperse from a yard within a few days, and University of California research found that one large, heavily infested rose bush needed two releases a week apart of about 1,500 lady beetles each.

Reach for a product only after the earlier steps have not held the pest, and pick the least toxic one that targets it, because broad-spectrum products can kill natural enemies along with the pests. The label must list your plant and the pest, and you follow all of its instructions.

Some of these products work only on a specific set of insects, so the identification step decides which one fits.

Colorado State Extension does not recommend homemade soap sprays, because they are not consistently formulated or tested and dish soaps contain strong detergents that can injure plants, so a commercial insecticidal soap is the better buy. Some plants are sensitive even to labeled soap, so test it on a small area a day or two before you treat a whole plant.

Soaps, neem oil and horticultural oil kill only the aphids present on the day you spray, so a repeat may be needed, and for soap on mites and scale crawlers that can mean every four to seven days. Spray as close to the target as you can to limit drift, and use iron phosphate bait rather than metaldehyde, which is toxic to dogs and wildlife.

Write down the date, the plant, the pest, what you did and what you found at the next check. A few seasons of notes show how the timing and numbers of each pest vary from year to year in your own garden.

Check often while plants are growing fast. For aphids, twice a week is the minimum, since that is early enough to knock them off or prune them out before the leaves curl and shelter them from sprays and predators.

At each check, what you find points to the next step.