Cultural controls

Plant health can be thought of as a holistic enterprise. What helps with one part often helps with another. For instance, cultural controls can help a lot with both managing bacterial diseases and reducing insect pressure.

Janna Beckerman, Ph.D., a member of Envu’s Green Solutions Team, says one of the first steps growers should take is reducing their fertilizer amounts. Studies have shown that using more than the recommended amount of fertilizer does not increase plant growth. Instead, the excess fertilizer contributes to a pythium problem and powers up algae, which creates a breeding ground for fungus gnats and shoreflies.

The lush growth of fertilized plants is desirable, but it makes plants more susceptible to infections and infestations.

“We think of fertilizer as a vitamin for plants, but it’s not,” she says. “It’s a steroid.”

Another cultural control that Beckerman says can help growers is spacing. Growers tend to want to pack as many plants as possible into tight spots. But Beckerman says that for what growers gain by cramming more plants per square foot, they might end up losing in the cost of pesticides and fungicides.

Without proper spacing, you won’t have the airflow you need between plants to keep them healthy. Humidity will increase, leading to more problems with botrytis, downy mildews and leaf spots. More space between plants is also helpful in making insecticide applications more effective.

“It will improve their pesticide applications, no matter what they’re trying to control,” she says.

Don’t forget about weed control

Weed management plays an important part in plant health as well, Beckerman says. If a nursery or greenhouse grower uses a preventative herbicide that gives them eight or nine months of control, it allows them to focus their efforts on the more pressing disease and insect problems that may be happening.

“By getting control of those weeds, you’ve prevented a place for a lot of insect pests to hide,” she says.

Many of these pests, like shoreflies and fungus gnats, are vectors for plant diseases. As if growers needed another reason to hate these nuisance insect pests, they can spread soilborne diseases like Thielaviopsis, Fusarium, Pythium spp. and black root rot. Thrips are another well-known culprit.

Western flower thrips are vectors of many plant diseases, the most important of which for greenhouse producers are two plant viruses in the genus Tospovirus: impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).

Future issues

As a technical specialist for Envu, Beckerman spends a lot of time talking to nursery and greenhouse growers about the problems they’re having. So, she has a good grasp on the typical problem pests and the typical solutions she recommends to solve them. But there are certain pests that don’t have a great solution yet, or the existing solution for that pest problem potentially could cause another problem.

One of the biggest needs she sees in the industry is better control for flea beetles. There is room for improvement for that pest in particular.

Matt McClellan is editor of Nursery Management magazine. Contact him at mmcclellan@gie.net.