Greenhouse growers in northern New England are getting a lot more scientific about how they grow their plants — and how they control the pests that want to damage them.

Back in 1996, when officials in Maine, New Hampshire and Vermont started offering annual workshops on integrated pest management, only about 25 percent of the participants were using biological controls in their greenhouses. Now, according to Margaret Skinner of the University of Vermont Entomology Research Lab and one of the organizers of the Tri-State Greenhouse IPM Workshops, the number is 75 to 85 percent.

That does not mean all of those greenhouses are using only biological controls in their greenhouses. The theory behind integrated pest management is that growers keep a high vigilance for any problems in their operation, and when they see problems, they act early with the least harmful method of controlling that problem.

Many of the greenhouses that use biological controls are conventional greenhouses that will also use chemical pesticides, said Matthew Krause of Bioworks, a national supplier of biocontrols and one of the major presenters at this year’s workshops, held in early January.

In fact, he said, 95 percent of the company’s sales are to conventional greenhouses.

The biological controls include bacteria, fungi, nematodes, viruses and protozoa, and can protect plants in a variety of ways, not just by killing the pests. Some of them will take up space in the soil so the pests can’t come in. Some will create a shield the pests can’t penetrate. Some will attract pests away from the plant.

Krause said the biological controls are just one part of making a good greenhouse.

You can make a good start to controlling diseases, he said, by planting disease-resistant varieties of plants and practicing good cleanliness in the greenhouse.

That is a piece of advice that is directly transferable to the home garden. Do not allow old plant material to remain near your garden plants, because the old material will harbor disease.

Krause also stressed that it is important to act when the pests first show up on the plants, because biological controls work as a preventative measure rather than a cure.

“You have to get it on in the right amount, and get it on early,” he said. 

And it is not necessary that the biological controls get rid of 100 percent of the pests.

“Plants can still tolerate a lot of disease if they are not stressed in other ways,” Krause said.

While all of these organic controls are living things, for the most part they are going to disappear from the greenhouse or garden, and the owner will have to reapply them again when the problem reappears.

“The EPA does not want an organism that is going to stay there forever,” he said. “They want it to help the plant recover and then go away.”

Nancy and Bruce Stedman of Little River Flower Farm in Buxton discussed how they use lady beetles and Aphidius wasps to control aphids at their operation.

Nancy Stedman said she buys about 5,000 of the beetles and releases them about a third at a time. The beetles eat the aphids in the greenhouse, but she has found that she also has a lot of them where she is growing the flowers outside, because they apparently escape.

The Aphidius wasps, like the lady beetles, attack the aphids, but arrive with some growing barley and are released in the greenhouse.

Shawn O’Donnell of Olivia’s Garden, a hydroponic vegetable grower in New Gloucester, said they use a lot of biological controls, including the Aphidius wasps. And they have been able to go pesticide-free.

NOTE FOR SUMMER

This comment from Krause was interesting: The plant that almost all scientists working on biological controls use in their tests is the cucumber.

“The cucumber is a plant that gets every disease you can think of,” he said. “And don’t use Straight 8 cucumbers (when planting at home). It gets all the diseases.”

During a break in the program, Kevin Kearns of the Morrison Center in Scarborough and I were discussing cucumbers, and he said it took three plantings last year before he got any viable cucumber plants in mid-June.

He likes to make small raised beds using old automobile tires, which provide extra heat and give the cucumbers a boost.

Tom Atwell has been writing the Maine Gardener column since 2004. He is a freelance writer gardening in Cape Elizabeth and can be contacted at 767-2297 or at:

tomatwell@me.com