Sanitation: the first line of defense

Sanitation is the “first line of defense” in any plant protection program and can reduce potential problems with insect and mite pests and diseases. The effectiveness of pesticides (in this case, insecticides and miticides) or biological control (e.g. parasitoids and predators) is contingent on implementing a stringent sanitation program. Sanitation is one of the easiest and least expensive practices to implement because sanitation can be performed during normal operating hours. Sanitation involves the following: 1) removing weeds, 2) reducing algae and 3) removing plant debris from both within and outside the greenhouse facility. Although this sounds simple enough, the fact is that many greenhouse operations do not have in place a stringent sanitation program. Therefore, this article discusses sanitation in relation to minimizing problems with insect and mite pests.

Photos: Raymond Cloyd

Cleaning up

Weeds inside and outside the greenhouse provide refuge for insect and mite pests, such as aphids, leafminers, thrips, spider mites and whiteflies, allowing these pests to survive and disperse onto the main crop. Weeds that can serve as a refuge for insects include sowthistle, Sonchus spp. (aphids and whiteflies); oxalis, Oxalis spp. (thrips); and dandelion, Taraxacum officinale (whiteflies). In addition, many weeds serve as reservoirs for pathogens, such as viruses that can be acquired by insects and then transmitted to the main crop during feeding. Weeds that serve as reservoirs for viruses, specifically the tospoviruses, Impatiens Necrotic Spot and Tomato Spotted Wilt virus include: chickweed (Stellaria media), lambsquarters (Chenopodium spp.), nightshade (Solanum spp.), oxalis (Oxalis spp.), shepherd’s purse (Capsella bursa-pastoris), pigweed (Amaranthus spp.) and bindweed (Convolvulus spp.). One method of reducing problems with weeds is to install underneath benches, landscape or fabric barriers, which are geotextile, non-biodegradable materials that will prevent weeds from emerging from the soil underneath benches and also diminish algae growth. There are herbicides (weed-killers) registered for use in and around greenhouses, although caution must be exercised when using herbicides inside greenhouses. A pre-emergent herbicide can be applied prior to weed emergence whereas a post-emergent herbicide can be applied after weeds emerge. However, be sure to avoid any inadvertent plant injury (phytotoxicity) when using herbicides, especially those that have systemic (when applied as a spray) and post-emergent activity, by making applications when greenhouses are empty. Always read the label directions before mixing and loading. Large weeds [>15.2 cm or 6.0 inches in height] should be physically removed by hand, taking care to remove both the aboveground portion and the roots. Weed-free zones or areas around the outside perimeter of greenhouses [3.0 to 9.1 m or 10 to 30 feet] can reduce the migration of insects, such as winged adults of the western flower thrips (Frankliniella occidentalis), through openings, which decreases the potential incidence for disease transmission.

Algae provide an ideal breeding substrate for fungus gnats and shore flies; subsequently algae must be reduced or “eliminated” from benches and floors. The practices of not over-watering and over-fertilizing plants, and using well-drained growing media will definitely help to avoid problems with algae. Furthermore, reducing algae may be accomplished by using commercially available disinfectants such as those containing the following active ingredients: hydrogen peroxide, hydrogen dioxide and quaternary ammonium chloride salts. Another practice is routinely pressure-washing growing medium from benches and walkways, which will alleviate algae building-up and avoid having to deal with insect pests.

Photos: raymond cloyd

Plant debris, such as leaves and flowers, and growing medium debris provide refuge for certain insect and/or mite pests. Insects and even mites can migrate to fresh plant material as plant debris desiccates. For example, reports have shown that plant material and growing medium debris placed into unsealed refuse containers can be a source of insect pests. As plant material desiccates, adults can migrate onto the main crop. Therefore, always place debris into refuse containers with tight-sealing lids. Also, any leftover growing medium provides sites for fungus gnat (Bradysia spp.) adults to lay eggs and western flower thrips (Frankliniella occidentalis) to pupate. Use a broom or shop-vacuum to remove plant or growing medium debris. Moreover, old stock plants or those remaining at the end of the growing season should be removed because they can be a potential source of insect and mite pests. Old stock plants can also serve as reservoirs for the viruses transmitted by insects such as the western flower thrips (Frankliniella occidentalis). Another important sanitation practice is to immediately remove any plants heavily-infested with insect or mite pests from the greenhouse.

Photo: Raymond Cloyd

In conclusion, sanitation is the “first line of defense” in any plant protection program. Consequently, in order to be successful when using pesticides or biological control, implement a stringent sanitation program that includes weed removal, reducing algae and discarding plant material and growing medium debris, which will help avoid problems with insect and mite pests.