8 tips for controlling Xanthomonas on begonia

Photos: A.R. Chase

Begonias were first reported infected with X. axonopodis pv. begonia (Xab, =X. campestris pv. begoniae) in 1928 from Denmark. In 1938 it was well established in Europe and in 1939 the disease was reported in the United States. Since that time, Xanthomonas leaf spot and blight has been reported from nearly every region growing these plants with occasional outbreaks. All begonias are susceptible to Xab to one degree or another.

Suggested control strategies

1. Keep each shipment of begonia cuttings or plugs labeled and separated from the rest of your crop until you are sure they are free of Xanthomonas. Leave a gap of space between groups of cultivars if possible.
2. Examine carefully at least once a week for symptoms. Dump any with symptoms immediately.
3. Do not place cuttings in a dip tank unless you want to spread bacteria throughout the shipment.
4. Keep leaves as dry as possible.
5. Never water overhead at night or late in the day.
6. Use the optimal rate of fertilizer. While higher rates might reduce susceptibility to Xanthomonas they are likely to damage the crop and perhaps make them more susceptible to another pathogen like Pythium, Fusarium, Myrothecium or Botrytis.
7. Test bactericides for safety prior to broad scale use.
8. Spray no more often than once a week. Spraying twice a week will be counter-productive = MORE disease.

Dr. A.R. Chase is president of Chase Agricultural Consulting. She has more than 35 years’ experience in research, diagnostics and practical consulting in plant pathology. She has been retired from the University of Florida – Mid Florida Research and Education Center in Apopka since 1994, but remains on staff as a Professor Emeritus. This information has been excerpted from the December 2017 issue of Chase Digest, published by Chase Agricultural Consulting.