UC Nursery and Floriculture Alliance
University of California
UC Nursery and Floriculture Alliance

Sanitation to Reduce Arthropod Pests

by James A. Bethke

As you can imagine, my colleagues and I have witnessed all manner of cleanliness in ornamental plant production throughout the years. When beginning a new crop cycle or moving production into new facilities, it’s easy to overlook the importance of cleanliness and just start filling benches. And if you have been successful in growing a crop like poinsettias in the same house for years without considering sanitation, you may not think it’s necessary to change your practices. However, not implementing a sanitation program is the most common mistake made by growers and can have dire consequences down the road, especially for those who plan to produce herbs or organic food products. It should be obvious that if you can significantly reduce or exclude pests and damage by starting “clean” (pest and disease free) and maintaining a high level of cleanliness, you will reduce the need for pesticides and have a higher quality product. Although there are other factors that determine quality and crop yield, the level of sanitation will have great impacts.

When I was in college, I had a job sanitizing cleanrooms in a heart valve production company. There were various levels of sanitation and cleaning that were required in this operation, and each level of sanitation was monitored on a daily basis using sophisticated equipment. The highest level of clean was required in the area where the heart valves were assembled. Every day, every square inch of space in the room had to be wiped with concentrated disinfectant and it was also necessary to spray the room with an aerosol disinfectant each time someone left the room. Filtered air flowed into the cleanrooms and out into the area outside the cleanrooms, which required the second level of clean. Obviously, the office spaces did not require as high a level of clean as the lab spaces and areas adjacent to the labs. Clearly, sanitation was a high priority for this operation. The heart valves they produced were of the highest quality and were in great demand.

Fig. 1.  The greenhouse workers at this facility have to follow a high level of sanita??on and strict entry requirements, including double entry doors
 Fig. 1. The greenhouse workers at this facility have to follow a high level of sanitation and strict entry requirements, including double entry doors (anteway), covering clothes that may harbor thrips and other pests, and stepping into a footbath to sanitize footwear. Photo: J. Bethke.

Complacency is the elephant in the room. Complacency is when someone is self-satisfied while at the same time unaware of or ignoring actual threats, and in this industry, it puts plants at risk. Sanitation is the foundation of all pest and disease management programs in commercial floriculture and nursery crops, and you will hear this word in most presentations at horticulture conferences when pest and disease control is discussed. Just as in the heart valve production facility, the level of effort you put into being clean will have an effect on the level of pest management you will eventually have to employ.

Even in ornamental plant production, there are obvious levels of clean required (high level of sanitation and clean, fig. 1). Not every facility will have the same sanitation issues or utilize the same best management practices to address cleanliness. In addition, there is a great variety of production types in ornamental plant production and type of production also affects the level of clean required.  If a crop is going to be on site for a lengthy period of time, the chances of exposure to pests and pest proliferation is high and will require a higher level of sanitation. Regulatory issues also affect the level of clean required. If you are shipping out of the county, state, or country, you will most likely need a much higher level of clean due to phytosanitary requirements; if you are growing a crop that is a host plant for a regulated invasive pest, quarantine measures necessitate that the level of clean be at the highest level.  

Excluding pests is an effective method of maintaining a pest-free greenhouse or production facility, and exclusion screening should be considered, especially if the commodity you are producing is susceptible. For example, years ago it was very difficult to grow impatiens without excluding thrips because they vectored tomato spotted wilt virus (TSWV) and impatiens necrotic spot virus (INSV). Growers can successfully exclude many arthropod pests by screening the pads at the end of the greenhouse where air is drawn in through the fan-and-pad cooling system (fig. 2). Additionally, pests can be excluded from greenhouses by creating a double door entry (anteway) where one door does not oppose the other. Inside the anteway, sticky cards or air curtains can also be used to assist exclusion of arthropod pests.

a1 Bethke fig2
 Fig. 2. One end of this greenhouse is screened to exclude pest entrance through the pad end of a fan-and-pad cooling system. Photo: J. Bethke.

When Plants or Propagated Cuttings Arrive. One of the most important things you can do is to make sure that you are starting with clean plants or propagated material. Inspecting propagated material and maintaining pest-free stock plants for propagation will ensure a clean start and prevent pest populations from spreading (fig. 3). Additionally, if you bring in larger plants for finishing, isolate the introductions until you are sure they are pest free before you introduce them into a clean production area alongside other plants.

 The cleaner you start a production area, the cleaner it will most likely remain. It is very important to remove all old crop residues and weeds, which may be harboring insect pests. If necessary, sterilize the growing environment with a disinfectant prior to new plant introduction because it will likely reduce or eliminate existing or senescing pests, those waiting for the next crop.

a1 Bethke fig3
 Fig. 3. Azalea cutting with chlorotic spots indicating a mealybug infestation. Inspecting mother stock plants and the production area of stock plants that harbored this infestation before taking cuttings could have prevented the spread of this pest. Photo: J. Bethke.

 As an example, we have experienced several cases of excessive numbers of fungus gnats and millipedes attacking crops on raised benches. These pests were reproducing in great numbers in the peat that had been building up under the benches for a long time. Another example is a greenhouse where seeds and propagated material were growing under the benches and harboring mealybugs and the European pepper moth. Needless to say, these problems could have been avoided with good sanitation practices.

Arthropod pests can ride on containers (fig. 4), soil, equipment, new plants and people. Therefore, anything that enters a production area should be cleaned, sterilized or isolated before introducing them into a cleaned environment. Soil and other potting media should be sterilized, and soil that is not used right away should be kept tarped or in enclosed containers to keep it clean. Carts, tractors, trucks, etc. should also be cleaned before entering a clean production area. Workers can be a source of arthropod pests. Are they wearing brightly colored clothing? Have they just come from a pest-infested area? Have your workers just moved older plants with pests and are now entering a house with newly potted plants?

After a clean start to ensure cleanliness, you will need to do a good job of pest monitoring. Early detection of a problem leads to an easier solution and it maintains a clean growing environment to produce a high quality plant. As I mentioned above, the heart valve company monitored each level of clean with sophisticated equipment, but it doesn’t take a lot of sophistication to monitor for pests and diseases.

a1 Bethke fig4
 Fig. 4. Pots and flats should be washed and sterilized prior to use, especially if they are being reused, and plants should be examined for pests when received and prior to potting. Photo: J. Bethke.

Training, Assessments and Record Keeping
In a good sanitation program, commitment is key and employee behavior is worth examining. Have your workers become complacent? Conduct routine self-assessments to eliminate complacency. It pays to periodically scrutinize aspects of your production and production facility because good sanitation requires a conscious effort on the part of every employee. Managers should implement programs to keep sanitation on the forefront of their job and they should remind workers about the importance of sanitation. This can be accomplished by sending out memos, hanging posters, sending texts or emails to employees or holding weekly team meetings. In addition, have you considered a sanitation training program tailored to fit your working environment? I am sure your workers are required to take scheduled training classes. Consider adding a short module about the importance of sanitation.  Periodically reassess progress in sanitation practices at your facility. Keep records of areas that need attention and follow up.

Final Comments
Keeping something clean seems somewhat simplistic, but doesn’t it make sense? I know from experience that a higher quality product can be produced from a clean and well-maintained growing environment. I also know that every grower, no matter how clean they are, can always improve. Hopefully, the information herein will help you take a fresh look at your property and take you to another level of clean.

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