New angles covered in greenhouse IPM program
Deborah Sweeton, IPM practitioner and co-owner of Techni-Growers Greenhouse, Warwick, welcomes visitors, as Orange County IPM coordinator Teresa Rusinek looks on. Photo: M. Haining Cowles.
Management of two insect pests and of three aspects of diseases were tackled in the comprehensive greenhouse IPM effort that took place in 1996.
Insect Management. One of the major components of the 1996 greenhouse IPM effort was a study of three IPM methods for control of western flower thrips, an insect that was the primary concern mentioned by New York greenhouse owners in a 1995 survey.
Thrips is difficult to manage because it has developed resistance to insecticides, has a short life cycle (which leads to rapid population growth), and has mysterious feeding habits. Furthermore, thrips can carry a viral disease complex (impatiens necrotic spot virus/tomato spotted wilt virus) that has caused crop losses in New York greenhouses as high as $20,000 in one year.
The first of the three methods studied in 1996 involved new packaging - a slow-release sachet - of a predatory mite (Amblyseius cucumeris). These mites succeeded in suppressing the thrips population for three weeks at a retail store participating in the IPM demonstration. After three weeks, thrips-infested plants were brought into the store from the owner's growing area, and the mites were no longer able to keep up. The grower was nevertheless satisfied with the level of control achieved by the mites and plans to expand the area of mite releases to include her growing area.
Sticky traps were a not-so-new method that was examined from a new angle. Blue sticky traps have been used for some time to catch thrips because blue has been considered the best color for attracting them. But a 1992 study (reported in an Illinois publication) has indicated that hot pink sticky traps will catch twice as many thrips as blue ones. This finding was tested in the fall and winter of 1996 in four New York greenhouses. Preliminary results confirm that hot pink is more attractive to thrips than blue. The traps will be compared again this spring, when greenhouse light levels will differ from those of the fall and early winter.
The third method of thrips management tried in 1996 was the biological control Beauveria bassiana. This fungus, along with a neem-based biopesticide, was applied twice to impatiens in a commercial greenhouse. (Neem is a natural substance originating from trees in India. It has many medicinal and pest management uses.) Thrips levels dropped by approximately 63 percent and stayed at or near that lowered level for at least a month following the applications.
Fungus gnats are another persistent insect pest of greenhouses. Various life stages cause significant root system injury, carry plant diseases, or are a nuisance to greenhouse workers and customers. Three biological control agents, a predatory mite, a biopesticide, and nematodes (microscopic roundworms) are commercially available and have been shown to be effective for fungus gnat management. Various combinations of these methods were tested on a greenhouse poinsettia crop in 1996. Better season-long control was achieved with the biological methods than with the standard chemical sprays. The mites reduced the fungus gnat population from a high level to a moderate one in two weeks, while the population rose sharply two weeks after a chemical application and stayed high for three weeks.
An early-season release of the mites (Hypoaspis miles) coupled with a late-season application of the biopesticide (a Bt-based material called Gnatrol) seemed to be the most effective combination for season-long control of fungus gnats. A fact sheet on fungus gnat biological control was written to accompany this project and should prove useful to all New York greenhouse growers.
"I've been practicing IPM for four years now. One difference it makes is that I use fewer chemicals. I probably use 50 percent less than I used before. I wait for the weekly monitoring reports, and I don't treat for insects if the pest count is too low to warrant it. This year we've been extremely clean. There were only two thrips on all of our sticky cards yesterday."
-John Russell, Owner, Brookside Florist and Greenhouse, Newburgh
Disease Management. Techniques for early detection of diseases in greenhouses are badly needed. Detection of root system problems is a top priority. Stopping problems before they affect the visible portions of plants is obviously preferable to stopping them after that. Root system health is a complex aspect of successful greenhouse production. Not only are workable techniques needed for disease detection, but the interrelationships of several factors that contribute to root diseases need to be better understood. These factors include soil pH, soluble salts, nitrogen, and the link between Pythium root rot and fungus gnat larval feeding. Which factors contribute the most? Are some of them innocuous? For example, is Pythium root rot anything to worry about when there is no accompanying damage from fungus gnats or soluble salts?
Work done in the 1996 season did not answer all the questions, but much was learned:
- monitoring of soil pH and salt levels will enable growers to correct cultural practices before disease problems develop, with the side benefit of reducing fungicide use
- excessive nitrogen in fertilizers is a key factor in the development of Pythium root rot
- "rapid detection kits," donated to the project by Agdia, Inc., of Elkhart, Indiana, confirm the presence of plants infected with the impatiens necrotic spot virus (INSV) much faster than outside laboratory tests, enabling growers to remove the plants immediately and stop the spread of the virus
- fava beans are effective indicator plants, warning growers of the presence of INSV-infected thrips before the thrips reach the crops to be sold