Disease management strategies for celery in the greenhouse

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Damping-off (caused by Pythium spp., Phytophthora spp. and Rhizoctonia sp.) affects all vegetable seedlings and is also common among flowering bedding plants. Damping-off results in collapse of the plant at the soil surface. To prevent damping-off, avoid over-watering because some fungi that cause damping-off prefer wet conditions.

Good sanitation is the key and ensures that root rot problems from one crop are not carried over to another crop. Root rot pathogens survive in the greenhouse in soil particles or plant parts clinging to containers, benches, walkways and equipment. If root rot occurs, remove and destroy the diseased plants. Also, remove healthy-appearing plants that are immediately adjacent to the dead plants because the disease may have already spread to them although they are not yet showing symptoms. Plug sheets containing diseased transplants should not be reused.

Botrytis gray mold can infect all vegetable transplants causing an irregular brown spotting or “blight” of leaves and stem cankers. This is the same Botrytis that infects a wide range of floriculture crops producing gray masses of powdery spores. In vegetable transplants, Botrytis is a threat when plants grow and form a canopy of leaves keeping the relative humidity high which favors disease. Since the fungus that causes gray mold depends on water to germinate on the plant surface, increasing air circulation through fans and reducing the relative humidity by venting or heating (depending on outside temperatures) will help prevent condensation of water on plant surfaces and thereby reduce the occurrence of gray mold. Watering early in the day will help ensure that the plants dry by evening, reducing the occurrence of disease.

Bacterial disease can infect celery resulting in blighting. Not all spotting on the foliage is caused by fungi. It is important to distinguish between spots caused by fungi and bacteria because disease management differs. Bacterial disease causes small, dark-brown spots surrounded by a yellow “halo” on the leaves. A diagnosis from an extension agent or other knowledgeable professional is often warranted to separate symptoms of bacterial diseases from symptoms caused by fungi or other causes.

Celery seedlings with bacterial disease should be immediately removed from the greenhouse and destroyed. In addition, seedlings immediately adjacent to those showing symptoms should also be removed and destroyed. Although epidemics may seem to appear overnight, chances are it began in just a few plants and progressed unnoticed for a couple of weeks. Plug sheets containing infected transplants should not be reused. Removing infected transplants from the greenhouse is the most critical component of managing bacterial diseases once they’ve been introduced.

Bacteria move readily in a film of water and can spread through splash droplets. It is important, therefore, to water plants early enough in the day to ensure that the foliage dries completely by evening. Good ventilation, circulation, and low relative humidity are also important in helping to maintain dry foliage. Clipping, pruning, or any other type of injury provides a means for the bacteria to enter the plant and should be avoided.

Dr. Hausbeck’s work is funded in part by MSU‘s AgBioResearch.

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