Sanitation Recommendations for Management of Insect and Mite Pests of Greenhouse Vegetables

Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 290/621
Publication Date: 01/94
Order#: 94-029
Last Reviewed: 02/97
Written by: G.M. Ferguson - Greenhouse Crop Advisor/OMAFRA; J.L. Shipp - Agriculture and AgriFood Canada

Table of Contents

  1. Introduction
  2. Sanitation During Seedling Production
  3. Sanitation During Crop Production
  4. Sanitation at the End of Crop Production


Sanitation is an important cultural strategy for protection of greenhouse crops from arthropod (insect and mite) pests. Sanitation for greenhouse crops requires the destruction or removal of not only infested materials, and also potential sources of infestation. Effective sanitation practices reduce and delay the onset of pest (insect, mite, weed) problems, and eventually can eliminate or minimize pest problems. It is easier and less expensive to exclude pests than to control them after they appear. To be effective, sanitation should always be practised. It should be carried out in the greenhouse and adjoining structures (boiler rooms, etc.), in the immediate external environment of the greenhouse, and during every stage of crop production. Proper greenhouse sanitation is a continual, year-round process.

Sanitation During Seedling Production

Sanitation at this stage should include the following practices:

Pest Monitoring

Use yellow sticky cards, measuring 8 x 13 cm (approximately one for every 50 - 100 m2 of greenhouse area), for early detection of whiteflies, fungus gnats, thrips and aphids. Traps should be placed along walkways, close to doorways and air intakes, and be inspected at least weekly (Figure 1).

Pest monitoring using yellow sticky cards.

Figure 1.
Pest monitoring using yellow sticky cards.

Additionally, inspect seedlings weekly for detection of spider mites and aphids. The presence of spider mites is determined by visually examining the plants and observing the presence of the mite and its characteristic damage. Feeding by the two-spotted spider mite produces a yellow speckling of the leaves. The non-winged forms of aphids are usually present in a crop before winged aphids are caught on yellow sticky cards. Hence, the importance of visual inspection for detection of this pest. Aphids may be observed on leaf undersides or on growing points where they shed small, white skins and excrete shiny, sticky honeydew droplets. Take appropriate action as soon as pests have been detected and accurately identified.

Weed Control

Remove all weeds from inside and immediately outside the greenhouse. Weeds can be important sources for insects and mites on a year-round basis.

Hanging Baskets

Never place hanging baskets of ornamentals over vegetable seedlings and transplants, as these will serve as an alternate source of pests.

Sanitation During Corp Production

At this stage, practices recommended during the seedling stage should be continued. Additional recommendations are:

  • Promptly remove all plant debris from walkways and drains and do not leave any trash piles inside or close to the greenhouse (Figure 2).
  • Maintain good drainage to eliminate puddles and wet surfaces, as these provide ideal breeding sites for flies such as fungus gnats and shoreflies.
  • Never have other crops (e.g., ornamentals, grape vines, fig trees) in the greenhouse, as these serve as alternative refuges for insects, mites and other pests.
  • Where feasible, consider insect screens to exclude pests (Figure 3). Screening is an effective and simple method of excluding larger pests such as moths, beetles, bees and bugs from the greenhouse.
  • Maintain at least a 10-metre strip of mowed lawn around the greenhouse. (If herbicides are used outside, beware of drift near ventilators and intake fans.) Bedding plants and home vegetable gardens are excellent habitats for insect and mite pests, and are therefore considered to be weeds when placed close enough to the greenhouse to serve as a source of infestation.

Good sanitation inside and outside the greenhouse: (a) clean walkways; (b) no plants or refuse around the outside.). Such piles serve as sources for further infestations.

Figure 2. Good sanitation inside and outside the greenhouse: (a) clean walkways; (b) no plants or refuse around the outside.). Such piles serve as sources for further infestations.

Insect screening on a side vent.

Figure 3. Insect screening on a side vent.

Sanitation at the End of Corp Production

Crop Disposal

If the crop is infested with insect and mite pests, begin pest treatment as soon as possible after the last harvest, and before its removal. This minimizes opportunities for pests to disperse and hide in the ground under plastic sheeting or in the cracks and crevices in the greenhouse structure. Effective crop treatment may be chemical or non-chemical.

Chemical Treatment

Application of effective pesticides before and after crop removal usually results in destruction of a major portion of insect and mite pest populations. Consult your OMAFRA Pest Management Advisor for recommendations. As with the use of any pesticide, follow proper procedures for application and adequately ventilate the greenhouse before re-entering.

Non-chemical Treatment

High ambient temperatures of at least 40EC and a relative humidity of l ess than 50% for a minimum of three to four days will effectively control insect and mite pests. After removal of the crop, this treatment may be repeated. Using the environment for pest control is most easily and economically carried out in the summer months after the spring crop.

Pest Monitoring

After treatment and removal of the crop, one should monitor for any remaining flying pests, such as thrips, whiteflies and aphids, by using yellow sticky cards. Check these cards regularly and if any pests are detected, further remedial action should be taken (see your OMAFRA Pest Management Advisor).

Growth Media Sterilization

Sterilization of growth media will reduce pest carryover, particularly of spider mite and thrips. Between August and September, diapausing mites move downwards from the crop and can hide in rockwool slabs, under ground plastics, in crop debris, etc., where they are sheltered until favourable conditions resume. Thrips pupate on the ground and can survive in refuges similar to those mentioned for spider mites.

Soil Steaming

For efficient soil steaming, the soil should have a good tilth and be neither too wet nor too dry. Use a soil thermometer to ensure that the soil is heated to over 80EC (180EF) for 30 minutes. If this temperature or time is exceeded, problems of waterlogging, high salts and ammonia burn may be encountered.

Soil Fumigation

Methyl bromide is the most commonly used soil fumigant. Fumigation should be carried out in moist, warm soil (at least 15 °C) that has a good tilth (to depth of 15 cm). After fumigation, the soil should be thoroughly aired for three to seven days as the fumes are very toxic to plants and mammals. Methyl bromide treatments should not take place prior to crops that are harvested for their leaves (e.g., lettuce), because bromides accumulate preferentially in the leaves and stalks of plants.

With soil, steaming is advantageous over fumigation because, in addition to destroying most pests, it leaves no toxic after-effects. Moreover, planting can be done as soon as the soil cools and is leached.

Rockwool Steaming

The time required for steaming depends on the wetness of the rockwool and temperature used. Steaming at 90 °C for 30 minutes should be adequate. Generally, the wetter it is, the longer the steaming period, and for this reason the substrate should be as dry as possible before steaming.

Rockwool without the polyethylene bags and stacked on pallets can be steam sterilized in two hours. Rockwool wrapped in polyethylene require 5 hours of steaming. The rockwool should not be stacked higher than 1.5 m (5 ft.). To stabilize the stacked slabs, the placement of each row should alternate, with each row at right angles to the next. In addition, a 2.5 cm (1") space should be left between individual slabs to allow for better steam penetration.

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