Premier Press

Winter 2001 vol. 8/no. 1

Keeping your greenhouses free of insects, diseases, algae and weeds is a good way to prevent them from becoming a problem. Before placing crops in your greenhouses, you should implement good sanitation practices.

Sanitizing Structures & Equipment:
Disease organisms and algae are always present in a greenhouse. Many fungal and bacterial disease organisms produce resting structures that can survive for several years. These pathogens are present in dust and in used media on benches, floors, walkways, irrigation devices, re-used pots, labels, etc. Algae can be present on floors, benches, some irrigation devices, evaporative cooling pads, glazing and in irrigation water.

To sanitize the greenhouse, start by removing plant and media debris from floors, walkways and benches. Sweep and discard media that falls on the floor near a mixing machine, flat filler or potting bench, as it can easily be contaminated with pathogens from the floor.

Next, disinfect benches, irrigation devices, carts, floors, walkways, glazing and evaporative cooling pads with quaternary ammonium chloride salts (Q-salts) or bleach. If the irrigation water is a significant source of algae, such as pond water, treat it with bromine, chlorination, an ozone generator or hydrogen dioxide (Zero-tol). These treatments should also keep mist and drip lines free of algae. If not, increase the rate of hydrogen peroxide or chlorine; allow the material to remain in the water system for 24 hours, then flush the lines.

Re-using pots:
It is best not to re-use pots, but it inevitably happens. Start by removing all growing medium from pots, flats, tags, etc. Then soak them in Q-salts solution for 10 minutes or a 10% bleach solution for 30 minutes. Rinse the pots with water. This should kill most pathogens, but it does not necessarily kill weed seed. The growing medium needs to be removed, as it can tie-up the active ingredient in both chemicals, making them ineffective. Keep in mind the activity of a bleach solution is reduced by 50% every 4 hours and should be recharged every 2 hours.

Weeds:
Remove all weeds inside the greenhouse as well as any weeds outside near the vents, doors or fans. Weeds can harbor fungal, bacterial and viral diseases as well as insects that transmit these diseases. Remove dead weeds as they might have seed heads or resting spores from fungal and bacterial pathogens. Place the weeds in garbage bags, so insects or weed seed do not disseminate in the greenhouse. If there are a large number of weeds under the bench, they can be sprayed with postemergent herbicides such as Clethodim, Diquat, Glufosinate, Glyphosate or Pelargonic Acid. It is best to apply them when there are no plants in the houses. Check the label for rates and for any greenhouse application restrictions.

Source: Gaston, M.L., et.al. 2000. Tips on Managing Floriculture Crop Problems. O.F.A. Services, Inc. Ohio