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Disease management is not just chemical usage

Tue, Jun 28th, 2022, created by Jean Williams-Woodward

Greenhouses are transitioning into fall crops with poinsettia and mum cuttings being rooted. Itís a good time to review sanitation, especially in propagation where Botrytis, Rhizoctonia and Pythium can cause significant losses.

In a greenhouse that has a history of Rhizoctonia causing pre- and post-emergence damping off and web blight on cuttings and in plug trays, I was very happy to see that they had implemented small changes that greatly reduced their disease problems. The greenhouse is an older facility that has been in operation for decades. Most of the benches are wooden construction. As a pathologist, I kept harping on sanitation and disinfesting surfaces and propagation trays because Rhizoctonia (and all root pathogens) survive within debris on these surfaces. If we say it enough, hopefully growers listen.

One of the changes they implemented was placing old (clean) plastic plug trays on top of the wooden benches and growing the new cuttings and plugs on top of the trays. Just this simple step using mostly plastic waste raises the new trays in propagation off the wooden benches by an inch. Creating a barrier between the plant roots and the bench keeps the root from potentially contacting fungal spores surviving in debris on and within the benches. They also are preventively drenching with fungicides containing mefenoxam and pyraclostrobin to reduce both Pythium/Phytophthora and Rhizoctonia/Fusarium, respectively. These fungicides have the added benefit of promoting root growth, which is key to reducing root and stem diseases in propagation.

Another step is to disinfest surfaces and used trays between use. This facility is soaking their used trays in a 10% bleach solution for a minimum of 10 minutes because the quick plunge into a bleach or other disinfesting solution that many growers do isn't enough to kill any remaining pathogens on the trays. Using quaternary ammonia or hydrogen dioxide products also are effective. The changes this greenhouse implemented worked.

Bottomline message for growers constantly having disease problems is to work on SANITATION! Small changes, like using the old (clean!) trays to raise the new trays off benches or floors, work to reduce disease incidence, which then reduces diseases in finished flats and containers. Disease management is not just chemical usage.

About the Author:

Jean Williams-Woodward

Associate Professor, University of Georgia

Jean is an Associate Professor and Extension Plant Pathologist at the University of Georgia. Jean provides statewide plant disease diagnosis and management recommendations for ornamental plants in greenhouses, nurseries, and landscapes. She also teaches courses in plant disease diagnosis and ornamental pest management. She brings over 27 years of experience in working with ornamental plant producers and extension outreach providing education programs and on-site plant problem diagnostics.

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