Healthy, vigorous plants are the best defense against pests and disease.

Recent research has shown that plants produce an array of compounds that are stored in different parts of the plant. When a chewing insect shows up, some plants can combine phenols, alkaloids and terpenes and send those compounds to the leaves being eaten. To the insect, the taste or smell can be enough to make it move on.

Some plant species can even release these compounds through their pores, called stomata, or through their roots to help protect themselves from predators. Some plants in the nightshade family secrete sugary nectar from their pores to attract ants. In return, the ants protect their food source by eating flea beetle larvae and other insects competing for the plant.

Nature has plenty of ways to protect itself. But when soil is depleted, a garden is new or summer heat stress weakens a plant’s natural defenses, gardeners may need to step in to help ward off pest insects.

One of the most popular ways to manage pest insects is by using biological controls, including beneficial insects, bacteria, fungi and nematodes. These methods are becoming more common as gardeners and farmers look for ways to reduce pest pressure without relying solely on chemical sprays.

BENEFICIAL INSECTS

Ladybugs are among the best-known beneficial insects. An adult ladybug can eat about 50 aphids a day, and young ladybug larvae can eat even more as they prepare to pupate and become adults.

Parasitic wasps are another useful garden ally. These tiny wasps have stingers that can’t puncture human skin, but they can help control pest insects. When a parasitic wasp lands on a host insect, it inserts an egg into the insect’s abdomen. As the egg develops, the young wasp feeds inside the host. Once it hatches, it emerges and continues the cycle by finding more pest insects.

BACTERIA-BASED CONTROLS

One of the most widely used biological controls is Bacillus thuringiensis (Bt). Gardeners have used Bt products, such as DiPel, for decades.

Bt is a naturally occurring bacterium that is considered nontoxic to people when used according to label directions. It’s sold as a dried product that can be mixed and applied to plants. When certain caterpillars, beetles or mosquito larvae eat it, Bt forms crystals inside the insect’s digestive system, killing the pest from the inside.

FUNGI THAT TARGETS INSECTS

Entomopathogenic fungi are less familiar to many gardeners, but they can be highly effective. The word comes from Latin roots: “entomo” means insect, “patho” means disease and “genic” means producing.

There are more than 700 species of entomopathogenic fungi, but Beauveria bassiana is one of the most used. It’s found in products such as Mycotrol and BotaniGard. It’s considered safe for people, bees and other pollinators when used correctly, but it can be harmful to aphids, whiteflies, thrips, corn borers, alfalfa weevils and certain beetles.

When dormant, the fungus forms a thick-walled spore that can be stored under refrigeration and shipped. Once mixed with water, preferably irrigation or distilled water, it can be sprayed onto infested crops.

Unlike Bt, the fungus does not need to be eaten. It only needs to land on the body of a pest insect. From there, it attaches to the host and releases enzymes that break down the insect’s exoskeleton. Once inside, fungal growth spreads through the insect, killing it within days through nutrient depletion and toxic activity.

In some insects, the fungus affects the muscular system, causing paralysis or dysfunction before death. That is why these infected pests are sometimes called “zombie insects.” After the host dies, the fungus can produce new spores that spread to other insects.

These fungi are most effective when temperatures are between 70 and 90 degrees and humidity is high enough for the spores to germinate. Because ultraviolet rays can damage them, apply fungal products near sunset, when pest insects are still present but sunlight is fading. They can be especially useful in heavily infested areas, where crowded and stressed pest populations are more vulnerable.

HELPFUL NEMATODES

Entomopathogenic nematodes (EPNs) are another biological control gaining popularity. These soil-dwelling organisms are effective against thrips, leaf miners, whiteflies, fungus gnats in houseplants and grubs, cutworms and webworms in lawns and turf.

EPNs are considered safe for people, mammals and many other non-target organisms when used properly. They can be applied with a watering can or hand sprayer, but they should be used quickly after mixing so they don’t drown in the water.

Like fungal controls, nematodes are best applied near sunset. For top-notch results, keep the soil moist for two to four weeks after application. Once nematodes find a host insect, they release symbiotic bacteria that kill the host within two to three days. The nematodes then feed and reproduce inside the host, increasing their population.

Researchers are also studying whether these nematodes can be used beyond horticulture to help manage fleas, cockroaches, body lice, yellow jackets and house flies.

JULY GARDEN TIPS

Hot, dry July weather is not ideal for starting seeds outdoors or transplanting young plants into the garden. For now, focus on enjoying the harvest. Depending on late-summer rains, the end of August can be a good time for another round of planting.

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