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Prepare now, sweat less later

Guide: Greenhouse sanitation for growers

For many greenhouse growers, November is a month of preparation. Growers are planning plant shipments, making orders, replacing plastic, pouring concrete and performing other routine maintenance. Growers who plan and prepare ahead of time when moving into the 2016 growing season will be better able to focus on the task of the day and face fewer challenges. Michigan State University Extension recommends growers perform the following pre-season tasks to ensure a smooth growing season:

1. Power wash empty greenhouse
Growers should consider power washing the concrete pathways, walls, benches and other equipment in their greenhouse. It will remove dirt, algae and other sources of pathogens.

2. Replace plastic
Growers should routinely replace the plastic covering the greenhouse because, as it ages, a decreasing amount of light will reach the plants. New, clean plastic will also reduce sources of pathogens.

3. Use sanitizing agents on walls, benches, equipment and floors
Numerous sanitizing agents are available to clean walls, equipment and other surfaces in the greenhouse. Sanitation for Disease and Pest Management from Purdue University provides examples of some of the chemicals growers can use to sanitize the greenhouse.

4. Remove weeds
Weeds in the greenhouse are a source of insects, pathogens and viral diseases. Growers should manually remove weeds that escaped weed mats or are under the benches. Using herbicides in the greenhouse is risky business as they may volatize and damage crops months after their use. There is one preemergent selective liquid herbicide that is labeled for greenhouse floor use (Marengo, produced by OHP).

5. Clean irrigation equipment
Irrigation equipment is the lifeline of a plant grower and it is important to sanitize it for next season. Growers using drip irrigation should clean the lines according to the manufacturer’s recommendations. Some growers fill the irrigation line with sulfuric acid for 24 hours and then flush the lines with water. Be sure to flush the lines adequately prior to the arrival of your first propagules.

6. Remove and replace weed mats
Each grower has a schedule with which they replace their weed mats in the greenhouse. If you had an outbreak of any serious pathogen, like Pythium, Phytophthora, Thielaviopsis or tobacco mosaic virus, during last growing season, be sure to replace all weed mats in affected areas.

7. Treat soil under existing weed mats for thrips pupae (if problematic in the past)
The extent to which the soil serves as a reservoir for overwintering thrips for future seasons is not known. However, if growers have struggled with thrips in their greenhouse or had issues with thrips-transmitted viruses, such as tomato spotted wilt virus or impatiens necrotic spot virus, then growers may want to consider treating the soil under the black weed mats to kill any overwintering pupae. Growers should use a grub rate of either imidacloprid or Chlorpyrifos, or a tank-mix of both together. For growers using biological control, the residues on mats and the soil surface could be harmful to predators and parasitoids if exposed.

8. Sterilize pots, if applicable
If you are reusing pots from last season, be sure to sterilize the pots in a bleach solution and adequately rinse them. Plug trays should never be reused as they could widely spread diseases from past seasons to a high percentage of newly-planted propagules. Once clean, be sure to store the pots in an area where they will remain clean. Some growers choose to shrink-wrap the pallets of pots.

9. Dispose of refuse appropriately
While performing all routine maintenance tasks, an abundance of trash is often generated. Dispose of old pesticides appropriately, recycle all plastics and place any weeds or diseased, leftover plant material in garbage bags and discard. Do not place diseased plant material in a compost pile.

10. Check maintenance of heaters and boilers
To prevent an emergency during the growing season, perform routine maintenance on your heaters and boilers. When doing so, look for cracked heat exchangers and vents that may have fallen off or are not securely venting to outside of the greenhouse. Doing so will prevent ethylene exposure to your plants which can cause abnormal, twisted growth and the abscission of flowers.

For more information:
Michigan State University Extension
888-MSUE4MI (888-678-3464)
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