Essential concepts for managing Xanthomonas in Begonia — Part 3

How to approach phytosanitary control in a begonia crop with Xanthomonas.

A crop of Rieger begonia infected with Xanthomonas axonopodis pv. begonia. Photo by Heidi Lindberg, MSU Extension.
A crop of Rieger begonia infected with Xanthomonas axonopodis pv. begonia. Photo by Heidi Lindberg, MSU Extension.

In Part 1, we covered what Xanthomonas is, how it infects plants, its potential impact on a crop and its diagnosis. In Part 2, we covered cultural practices to reduce disease pressure and chemical treatment options. Unfortunately, disposing infected and possibly-infected plants requires some tough decisions by the greenhouse growers or owners. In this final article in the series, Michigan State University Extension answers some commonly asked questions about how growers should approach plant disposal in order to minimize losses in the crop.

Once a grower receives a positive diagnosis for Xanthomonas, how should they proceed?

Since there is no cure for begonias infected with Xanthomonas, all symptomatic plants should be discarded as soon as possible. Scout the crop for symptomatic plants and dispose of those that are within splashing distance of infected plants. Remember that there is a time lag between when plants are infected and when they develop visible symptoms. As a result, treat plants that are within splashing distance of symptomatic plants as infected and discard them.

How should growers approach scouting the crop and determining what to rogue out?

When considering how to dispose of plant material, take note of the location of symptomatic plants and the prevalence of the infection. In situations where a low percentage of the crop is symptomatic, scouting and rogueing may be practical. However, in cases where a larger portion of the crop is infected, consider destroying entire portions of the crop.

How should growers dispose of infected plant material?

Dispose of infected plant material when foliage is dry to prevent further spread to nearby begonias. Limit the number of people handling the infected plants. Wear disposable gloves and disposable coats or bleach-able aprons. Do not compost the diseased plant material or reuse pots that contained infected plants.

How should growers document their losses?

Have a diagnostic report showing a confirmation of the pathogen. Take photos of the symptoms on the infected plants as well as the scope and quantity of crop losses. Using a smartphone or tablet to record a walking video with a timestamp is an excellent means to document the losses.

How do growers sanitize the greenhouse after having Xanthomonas-infected begonias?

All infected plant material must first be removed from the greenhouse; this includes plant debris remaining on and under benches, aisles and trays. Additionally, soil and other debris should be washed off surfaces prior to sanitizing. Surfaces in the production facility should be cleaned with quaternary ammonia or other commercially available sanitizing agents.

To read more about greenhouse sanitation, refer to the Purdue Bulletin, “Sanitation for Greenhouse Disease and Pest Management.” Porous surfaces such as black weed mats can be hard to clean and sanitize; we recommend you replace the black weed mat after a disease problem.

Additional resources

For additional information and insight from plant disease experts, start here:

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