Chapter 21

Integrated Pest Management for Greenhouse Crops

Cultural Pest Control Tactics

Cultural pest control tactics involves altering a pest’s habitat—in this case, the crop production environment—so that it is less favorable to a pest. Pests may be thwarted by making simple changes to planting procedures, such as adjusting planting schedules, rotating crops, fallow periods, or planting resistant crops. Some of these techniques are further explained below.

Managing the Greenhouse Environment

Environmental factors such as light, air temperature, plant temperature, relative humidity, air circulation, media composition, pH and electrical conductivity, as well as the nutritional status of the crop, impact both the health of the plants and the pests that attack them. The use of environmental controls to manage diseases is complex because of the simultaneous effect on crop production.

Resistant Cultivars and Alternative Crops

Prior to planting, learn whether a species or cultivar is less susceptible to pest infestations. Some species or cultivars can tolerate a certain level of infestation without any damage. Maintaining good records that describe susceptibilities across multiple cultivars may allow the grower to make more informed pest management decisions.

Weed Control

The goal of weed control is to eliminate all possible sources of pest contamination in and around the greenhouse. Weeds inside and near the outside of the greenhouse can harbor pests. It is best to pull the weeds inside the greenhouse rather than spray them, because insects may survive the spray and migrate onto the greenhouse crops. Bag all the weeds and dispose of them outside of the greenhouse. If using chemical weed control for the greenhouse, select only those herbicides that are labeled for greenhouse use.

Sanitation

Sanitation is the first step in any pest control program. If a source of infection or infestation persists due to poor hygiene, pest control programs will be expensive and frustrating. Practice proper sanitation in the greenhouse and adjoining structures (boiler rooms, etc.) in the immediate vicinity of the greenhouse and during every stage of crop production. A good sanitation program will include adopting proper greenhouse hygiene measures and the use of disinfectants and cleaners for greenhouse surfaces.

Greenhouse Hygiene

Proper greenhouse hygiene is a continual, year-round process. A good hygiene program will include a number of approaches. For instance, the use footbaths between greenhouse compartments, particularly between propagation and stock plant areas will minimize the transmission of diseases. Remove dead and dying plants, leaves, and flowers as detected. Do not leave diseased plants under benches.

Disinfectants and Cleaners of Greenhouse Surfaces

Disinfectants and cleaners play an important role in the prevention and control of fungal and viral pathogens and algae within the greenhouse. They should routinely be used as a pre-crop clean-up and during the cropping cycle to sanitize greenhouse structural surfaces and equipment. Disinfectants are oxidizing agents that are fast-acting, broad spectrum and considered low-toxicity biocides. Disinfectants can be categorized into the following types; sodium hypochlorite, quarternary ammonium compounds or hydrogen peroxide based.

Soil Pasteurization

Greenhouse media containing field soil (unless guaranteed sterile or pasteurized by the manufacturer) and cut flower soil-based ground beds typically contain weed seeds, insects, bacteria and fungi that may be harmful to the plants being grown. Pasteurization of media containing soil is important to eliminate these harmful organisms. Ideally, this is accomplished without injuring beneficial soil organisms. 

Steam

Steam is the most common heat source for pasteurization. The most common use of steam for soil pasteurization is in ground beds used for some cut flower crops.

Chemical Fumigants

Chemical fumigants such as Basamid Granular and Vapam Liquid can be used to pasteurize soil for pre-planting treatments for potting or in greenhouse beds or benches.

Fallow Periods

Insects and mites can be an ongoing problem in a greenhouse because there is often a constant supply of plant material. This plant material provides food for the pest and for their offspring. Removal of all plant material for a sufficient period of time results in starvation of the pest.

Watering Practices

Overwatering can lead to plant disease problems, poor soil aeration, wet soil beneath benches, standing water and more. Algae, fungi and other organic material will grow in these moist areas, and lead to problems with fungus gnats and shore flies.

Pruning and Rouging

Discarding infested or diseased plants sometimes is more cost effective than using a chemical control. An effective way to manage some pests on plants is pruning.

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