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Karen Delahaut, Outreach Specialist, UW-Madison
There are two methods of control utilized in an IPM program as the first line of defense against pest problems: cultural and mechanical controls.
Cultural control is a non-chemical, preventative action that creates a pest-free growing area and provides the appropriate environmental conditions that promote proper plant health. The use of resistant cultivars whenever possible, crop rotation, sanitation, and the adjustment of plant care activities are the most common cultural controls.
Greenhouse crops are grown for their appearance and aesthetic attributes. Sometimes the consumer desires specific cultivars that are more susceptible to pest problems because of the attributes they possess. If you find your customers a little less demanding, you should consider growing and selling resistant cultivars whenever possible. Remember that resistance is not immunity and some insect feeding or infection may occur but it will not be enough to damage or stress the plant. Do your own comparative studies to determine the performance of the various species or cultivars of plants you typically grow.
Irrigation timing and frequency is important to prevent edema, a physiological problem that produces blister-like lesions on plants that are watered too frequently. Conversely, marginal necrosis results when plants are grown under hot, dry conditions. The amount of water isn’t the only consideration in a cultural control program. The quality of water is just as important. Hardness, pH, and salinity can produce adverse symptoms that mimic insect damage or plant diseases in plants.
Proper temperature and light levels are also important. Excess heat and light can cause sunburn while necrosis can result from too much heat alone. Because these symptoms can resemble the symptoms of virus infection, you must be sure that lighting or temperature is the cause or have your plants tested for viruses.
Sanitation is another form of cultural control. Refer to the article in the July 2003 issue of the Green Side Up for more information on sanitation in the greenhouse.
Besides cultural control, mechanical or physical control excludes pests by preventing them from coming into contact with the host plants and by modifying the growing environment. Fine mesh screens should be placed over windows, vents, and fans to exclude insects. Sticky barriers can be placed along benches to prevent climbing insects like ants from reaching the crop. Adjustments in light intensity, duration, and wavelength based on the particular plant’s needs will reduce stress on the plant. Similarly, temperature and humidity modification will also provide the plant with the conditions it needs to grow, thrive, and fight off pests. Additional measures you can take include the use of double doors at the greenhouse entrances and positive pressure ventilation if this is an option. Both will further exclude pathogens and insects from entering the greenhouse.
Your first line of defense should be all available cultural and physical control methods that will prevent pest problems from occurring. Although this may result in a financial output initially, it will save you money in the long run by reducing your pesticide applications.
