Xanthamonas bacteria survive on previously infected begonia leaves. Once any signs of a begonia disease appear on a plant, the owner should remove the affected begonia and quarantine it from other plants. The most common reason begonia leaves rot is too frequent watering. They're most likely to... Foliar Nematodes. Spotted leaves must be carefully removed and burned. You can also use biological control as begonia botrytis treatment. The first signs of begonia leaf spot may often be present on the underside of the plants’ foliage. Fortunately for begonias with botrytis, there are chemical controls that can be used to help infected plants. Use a fungicide that is appropriate for begonias every week or so. Treating Begonia Bacterial Leaf Spot The best way to maintain a healthy planting of begonias is to monitor and check the overall health of the flowers before planting them into the garden. Maintain low humidity by spacing plants and venting to improve air circulation. Control by surface or bottom watering, keep the humidity below 80 to 85 percent, space plants, and practice strict santiation. Propagate cuttings from healthy plants, and use sterilized soil or media with a pH of 5.5 to 5.8, a temperature of 72°F... Isolate new cutting or plug shipments for an observation period to be sure they are not diseased. Bacter ial leaf spot on the upper surfa ce of a beg onia leaf. Severely affected leaves may … Water. Lower surface of begonia leaf infected with bacter ial leaf spot. Note the yellow “Halos” around the lesions. Alternate fungicides to prevent fungi from building up resistance. Other factors that affect begonia leaves' health are temperature and humidity. Managing Bacterial Leaf Spot. Temperature and Humidity. Figu re 1. Bacterial leaf spot of begonia is caused by Xanthomonas axonopodis pv.begonia (formerly known as X. campestris pv.begonia) Symptoms include water-soaked foliar lesions and wilting.Foliar lesions are especially visible from the underside of the foliage. … Closely examine the leaves of the begonia plants. Water Spots on Begonia Leaves Bacterial Leaf Spot. Begonias in the early stages of leaf-spot disease develop yellow-margined, water-soaked spots. Any knives used for cutting an infected begonia should be disinfected with 70 percent rubbing alcohol before it is used on another plant. Why Do Begonia Leaves Fall Off Real Suddenly & Rot?