Bacterial leaf spot of begonia, another Xanthomonas

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.

Bacterial leaf spot of begonia is caused by Xanthomonas campestris pv. begoniae. Symptoms include water soaked lesions of the foliage, which are especially visible from the underside of the foliage. Severely affected leaves may fall off the plant. This bacterium can also become systemic, meaning it colonizes the vascular tissues of the plant, causing wilting symptoms.

When I mention Xanthomonas most growers automatically think of geraniums. The good news is that this is a different “kind” or pathovar of Xanthomonas. Bacterial leaf spot on begonia is caused by a Xanthomonas that can only infect plants in the genus Begonia. There are many different types of begonias, most of which can be affected, there are however differences in susceptibility among them. There are few specific cultivars available that are reported to be resistant.

The disease is frequently spread via contaminated plant material. Within the greenhouse, spread occurs when irrigation water splashes from an infected plant to the foliage of nearby hosts. Research has shown that the bacterium can be released from roots of systemically infected plants into ebb-and-flood irrigation systems. Theoretically, this allows for movement of the bacterium to healthy plants, but this is not typically a significant means of dissemination.

Disease management begins with healthy plant material. Inspect incoming begonias for signs of disease. Plants with any suspicious symptoms should be tested at a diagnostic lab. Please note that diagnostic test kits for X. campestris pv. pelargonii (bacterial wilt of geranium) cannot be used to detect X. campestris pv. begoniae. Diseased plant material should be removed and destroyed. Avoid handling plant material when the foliage is wet. Overhead irrigation should be carefully timed to minimize the amount of time that the foliage will remain wet. Applications of copper based fungicides can be used to reduce disease spread. Plants that are systemically infected can not be successfully treated.

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