How to Keep Your Greenhouse Crop Free of Disease

How to Keep Your Greenhouse Crop Free of Disease


A good sanitation program is the most important tool you have to keep viruses out of the greenhouse. Photos credit: Pleasant View Gardens

One of the most dangerous disease problems we deal with at Pleasant View Gardens is viruses. Viruses can easily spread throughout a greenhouse by insects, pollen, seed, plant contact, and by mechanical transmission, which includes cutting and/or pinching. New viruses are found every year in the horticulture industry, but most are insignificant and infrequently found in production.


Scout Your Plants Regularly

Our biggest problems today are Impatiens Necrotic Spot Virus and/or Tomato Spotted Wilt Virus (INSV/TSWV) and Tobacco Mosaic Virus (TMV). Scouting for symptoms is an important part of any virus management strategy but especially for INSV/TSWV. At Pleasant View Gardens, we have a dedicated person to scout all the greenhouses for both insects and disease symptoms every week. We also believe in educating our employees on what to look out for and encourage them to call anything unusual to the attention of their crew leaders.


Scouting for virus symptoms is an important part of any virus management strategy but especially for Impatiens Necrotic Spot Virus (symptoms pictured on begonia), Tomato Spotted Wilt Virus, and Tobacco Mosaic Virus (TMV).

Watch for These Signs, Then Take Action

Symptoms to watch for commonly include ring spots, yellow mottling, necrotic spots, interveinal chlorosis, and mosaic patterns on leaves, stunting, distortion, and plant death. Any unusual leaf spots, necrosis, or plant growth could be considered a possible virus symptom, especially if no other causes seem likely. The only way to be sure a suspected plant has a virus is to test.

We test a sample both in-house and at Agdia, an independent diagnostic testing laboratory. Here we can test for the seven viruses most commonly found based on past testing results. Agdia can test for most of the plant viruses that exist, but we typically test for up to 15 of the most common viruses found in our operation, as well as in the horticulture industry. We try to be on the front line of new and emerging problems and review the viruses we test for every year, adding any we feel are significant to our testing screen. Pleasant View was one of the first greenhouse operations to test for Alternanthera Mosaic Virus, and helped the industry to determine the host range for this virus.


Perform weekly randomized virus tests and record the information for each sample, so you can trace any positives found back to the exact trays infected.

What to Do About Symptomless Viruses

As if looking for all those symptoms wasn’t hard enough, some viruses are symptomless, which means a good sanitation program becomes the most important tool we have to keep viruses out of our greenhouse. We have a multi-pronged approach to sanitation at Pleasant View Gardens. We require all employees and visitors to wear disposable gloves when entering the greenhouse. The biggest benefit to this is that it makes sanitation top of every employee’s mind.

We also have alcohol gel hand sanitizer units throughout the greenhouses and at all entrances. The rule is if you pass one, use it. A big part of our sanitation program is the required clean-up after one crop leaves an area and before another can be put down there. Not only do we sweep and wash the area, we will also clean with a sanitation agent. At the end of the season, we sweep, wash, and then pressure wash all areas, followed by a sanitizing spray and a horticultural oil spray. We make sure to include sanitizing equipment such as drip lines or booms, as well.

For our general pinching and sticking crews, we have rules based on the crop’s susceptibility to viruses as to how often an employee’s gloves need to be changed and tools sanitized. This information is included in all new employee handbooks and is reviewed during their orientation.

Start With Clean Stock

A big part of our sanitation program is making sure our incoming material is clean. Our stock greenhouses in Costa Rica perform randomized virus testing weekly, and we are notified of any positives immediately. We also receive information as to which stock greenhouse each group of cuttings comes from, so if there is a virus-positive, we know exactly which plants could be affected. We make sure to put this information on the tray those cuttings are stuck in so we can track individual trays.

We also perform weekly randomized virus tests. We test a percentage of all the plants produced each week, making sure to record location information for each sample, so we can trace any positives found back to the exact trays infected. In the past five years, we have tested more than 280,000 plants, and while the number of virus-positive incidents is less than 1%, each incident is time-consuming and costly. At Pleasant View Gardens, we feel scouting, testing, and our sanitation program are all essential to producing a disease-free crop and helping us avoid those hassles.