Most people think of beneficial insects when it comes to biocontrol, but there are a number of other natural organisms that can control pests and diseases on plants as well. They include nematodes, fungi, bacteria, and viruses. Get familiar with the various categories of biocontrols and how they work.
Pathogens: A pathogen can be a bacteria, virus, fungus, or any disease-causing agent. The most common entomopathogenic (insect-killing) fungal agent used in greenhouse biocontrol is Beauveria bassiana, which kills insects such as whiteflies, thrips, aphids, and a number of other common greenhouse pests. B. bassiana kills by penetrating the outer cuticle of the insect, growing through its body and eventually covering it with a layer of mold. It can be applied using standard spray equipment, but the fungus must make direct contact with the insect in order to work.
Parasites: Several types of nematodes are quite effective at controlling pests in the soil, such as cutworms, armyworms, weevils, fungus gnats, fleas, and thrips. Steinernema spp. and Heterorhabditis spp. are the two nematodes generally used for biocontrol. They have a symbiotic (mutually beneficial) relationship with bacteria that kills many types of insects. When the juvenile nematode attaches to the insect, the bacteria infect and kill the pest, usually within one or two days. Once the insect dies, the nematode feeds on its body, becomes an adult, and the cycle continues. It is important to know what pest you are targeting, because the nematodes are host specific.
Parasitoids: While parasites can live in a host for years without doing much harm, parasitoids will kill a host insect outright. There are a number of parasitoid wasps and flies useful in greenhouse biocontrol. Some target whiteflies, others aphids, soft scales, mealybugs, caterpillars, or leafminers. They are species specific, but in general, kill by laying eggs inside the pests’ bodies upon which the hatching larvae feed.
Predators: Predators come in many forms: beetles, mites, midges, flies, and more. They eat whiteflies, thrips, mealybugs, scale, spider mites, and other pests. Adults, larvae, or both may consume the pest, depending upon the species. Lacewings (Chrysoperia spp.) are one of the most common predators used in biocontrol programs, because they feed on a broad range of greenhouse pests.
Biofungicides: These are naturally occurring microbes used alone or in combination to kill fungi such as Pythium, Rhizoctonia, Fusarium, and Thielaviopsis. Depending on the microbe and the targeted organism, they can be applied to the soil, to the foliage or both. They should be used as a preventative, not as a cure when disease has already taken hold. There are a number of biofungicides available; one of the most well-known is Trichoderma harzianum. This particular microbe protects roots from infection by forming a protective barrier around them and excreting an enzyme that damages the cell wall of the harmful pathogen.