'Coming clean'

It is that time when people are making their New Year’s resolutions. Perhaps you want to lose those extra five pounds, spend more time with family, or finally talk to that special someone at the gym? When it comes to greenhouse production, many of us should move greenhouse cleanliness and sanitation to the top of the list.

Not only are regularly sanitized greenhouses aesthetically pleasing, but they experience fewer issues with diseases and pests that can reduce crop productivity and profitability. For this reason you should evaluate your greenhouse sanitation practices and insure that you are setting yourself for success in 2014. The following list discusses important aspects of greenhouse sanitation.
 

1. Learn about diseases, pests, and weeds of greenhouse crops

In order to understand how to fix or prevent a problem, one must be able to determine if a problem exists. Anyone working in the greenhouse should be able to recognize pests and pathogens and understand what they can do to minimize issues. In addition, workers should understand the important sources of diseases and pests in the greenhouse. Training in basic disease and pest identification and management is offered by your local or state extension services and courses are often offered at local and regional grower meetings. There is also an abundance of information on the Internet. However, beware! Always use a trusted source (such as factsheets published by reputable universities) when searching the Internet for information.
 

2. Check your floors

The greenhouse floor can be a huge source of pests and pathogens. Once you understand this you will start to notice easily addressable items that can minimize pathogen and pest issues. Many disease causing pathogens can live in soil or residue for long periods of time. Such soil-borne or residue-borne pathogens can be spread to new plantings through water splash or contact with the infested soil or media.

How can you minimize issues related to contaminated floors? Do what you can to minimize the chance of plantings coming into contact with soil or residue on the greenhouse floor. For example, never place hoses or sprinkler heads on greenhouse floors. Instead, use a hose rolling system or hose rack mounted to a wall to store watering equipment (Figure 1). If you have a floor with exposed soil, create a barrier by using plastic sheeting or landscape cloths (Figure 2). Ensure that these cloths are changed regularly.

An inch or two or gravel provides an excellent barrier, and of course, concrete trumps all. If you do have concrete floors sweep them regularly and wash them with water and a labeled product (Table 1). No, those floor sweepings cannot be reused! Lastly, use raised benches whenever possible. Metal benches are more expensive, but last longer and are easier to clean than wood benches.
 

3. Clean those benches

Raised benches help minimize pathogen spread from the floor, but they can also be sources of pathogens and pests. Benches are like dishes, they need to be scrubbed using some sort of cleansing agent to be clean. Most of us would make a sour face if we were at a restaurant and found out that the dishware was rinsed lightly with cold water. You should feel the same way about your benches. Clean your benches often. All debris should be removed with water and a stiff bristled brush. Next, use a product labeled for cleaning benches (Table 1). Products have advantages and disadvantages, so choose wisely. In general, metal benches are easier to clean than wood benches as wood is porous and most chemicals cannot penetrate into these areas.

 

4. Manage weeds

Not only is a greenhouse full of weeds ugly and unprofessional in appearance, but it also serves as a hotel for insect pests and plant pathogens (Figure 3). Ensure that weeds are removed frequently within the greenhouse and in the areas bordering the greenhouse. Hand-weeding is very effective in most cases and avoids issues with having to apply chemicals. However, some weeds are difficult to control by this method alone and herbicides may be required. Check with your local extension service to see what herbicides are recommended for your crop(s) and region.
 

5. Thoroughly wash tools

If benches are similar to plates, then tools are similar to silverware. Tools should be washed after every use. Many of the compounds listed in Table 1 are excellent for sanitizing tools. Store tools off of the ground away from soil and residue.
 

6. Wipe your feet, close the door, and take out the trash

Workers can easily introduce pests and pathogens into greenhouses on their work boots or simply by leaving the entrance door open for extended periods of time. Provide your workers with a wash station with tools and brushes outside of the greenhouse to help with cleaning. Special mats containing disinfectants can also be used. Trash bins should be located outside of the greenhouse whenever possible. At a minimum, empty trash bins at the end of each work day.
 

7. Save the worst for last

If you are working in several greenhouses during the day, end your day in the problematic greenhouse. This will limit the potential for pest and pathogen spread by worker movement between greenhouses.
 

8. Make it a routine

Every time new plants are about to be moved into a greenhouse, take the time to thoroughly clean the entire structure. Use power washers on walls to remove mildew and algal buildup. If possible, close vents and allow the greenhouse to run hot (around 110°F) for several hours to kill pathogens and pests.

Clean evaporative cooling vents, sanitize all tools and benches, and clean out any water tanks.

Staying on top of greenhouse sanitation does require additional effort and time, but in the end you will save time and money by avoiding costly chemical applications and crop losses. Once you get on the clean greenhouse wagon make sure not to fall off! It is easy to become complacent and fall back on poor habits. Keeping your greenhouse clean make take a little extra time and requires attention to detail, but will result in a productive operation and healthy plants.

Nathan Kleczewski is an Extension Specialist in Plant Pathologyat the University of Delaware Department of Plant and Soil Sciences and Cooperative Extension.