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Beating Botrytis: How to Keep This Devastating Disease Out of the Greenhouse

Identification Saves Heartache

Like any disease, early detection is the key to treatment. For this, there are two main areas to keep a close eye on throughout the winter. First, any cut, scrape, or bruise is susceptible to botrytis. This makes freshly cut plants especially susceptible. Second, the first signs of the disease appear up on the lower portions of the plant wherever there are tender tissues such as flowers, fruits, or seedlings. Botrytis can be identified by the onset of grayish-colored soft spots. Fruits and plants will then quickly shrivel and rot while developing black, stone-like sclerotia under the rotted areas.

Prevention Is Key

There are more than 50 different species of botrytis, also known as gray or brown mold, which can destroy an entire season’s worth of work in one fell swoop. This aggressive plant-killer attacks nearly all crops, including ornamentals, vegetables, and fruits. With botrytis, no plant is safe but there are steps you can take to prevent this onset of this disease.

Free moisture (water) remaining on plant surfaces for several hours is prime conditions for botrytis. This occurs when watering occurs late in the day, allowing plant leaves to remain wet for extended period of times. Although temperatures between 60 and 70F are most favorable for this disease, Botrytis can rapidly establish at nearly any temperature when water remains on the leaves for long durations and the relative humidity is high.

That brings us to the next important preventative tip: controlling humidity levels [video]. This is imperative to prevention of botrytis. For this, an environmental control apparatus helps measure and optimize the relative humidity levels in your greenhouse. Anything greater than 85% relative humidity is prime conditions for botrytis to fester and thrive.

Air circulation helps to prevent this from occurring. Small clip fans or angled wall fans are both useful options. But, again, perhaps the most important way to avoid this onset of this fungal disease is to avoid leaving free water on plant surfaces. This can be done by avoiding overhead irrigation on cloudy days or late in the day when evaporation is limited.

Four other preventative tips:

• Prune or stake plants to improve air circulation

• Disinfect pruning equipment with one part bleach to four parts water after each cut

• Never compost infected leaves or stems and do thorough clean up after fall season

• Use copper or sulfur based organic fungicides

Effective Treatment

It won’t take long for this disease to ravage your crops. Just a matter of days is all it takes to destroy an entire season of work. With immediate action, you can salvage your harvests. The most important step is to first identify any areas that indicate the botrytis. Remove these sections, and if possible, bag the section before cutting it to prevent the spores from spreading into the air and onto surrounding plants. The cut should be made 2 to 4 inches below the infected areas as to ensure all infected areas are removed from the environment. Then treat the remaining areas with the organic fungicides.

This is a malicious disease than can have devastating effects on your crops and your livelihood. Prevention is key to the health of your plants. A final suggestion is to completely clean out your greenhouse and disinfect it with a 5-10% bleach solution or a food-grade hydrogen peroxide solution after each season. This will kill any remaining spores and reduce the likelihood of disease for the next season. For growers, a “better safe than sorry” approach to botrytis is always the best approach.

How about you? What are your best tips for treating botrytis and other cool-season diseases in the greenhouse during the winter? Share below in the comments!