Tuberous Begonia Problems
Symptom	Probable Cause
Buds Drop	Improper Moisture; Temperature Changes
Flowers Spotted; Petals Transparent	Improper Watering
Cottony Tufts On Stems	Mealybugs
Plant Weakens; Leaves Yellow	Whiteflies
Ragged Holes In Leaves	Slugs Or Snails
White Coating On Leaves	Powdery Mildew
Leaves Covered With Gray Mold	Gray Mold

Buds Drop Usually Because of Improper Moisture; Temperature Changes
Bud dropping may be caused by too much or too little water, especially if plants are allowed to completely dry out between waterings. Although tuberous begonias do best when the soil surface dries out slightly between waterings, try not to let them dry out completely. A sudden temperature change from hot to cold or vice-versa also causes buds to drop.

Flowers Spotted; Petals Transparent Caused By Improper Watering
Begonia flowers can be damaged by water spots due to improper watering. Petals show brown spots or transparent blotches where water drops have soaked in. Shield blossoms when misting containerized plants. Outdoors, water tuberous begonias in the garden with a drip system or a hose than drips directly into the soil. Avoid overhead sprinkling.

White Coating On Leaves Caused By Powdery Mildew
Powdery mildews are caused by fungi that live on the surface cells of plants. Infected begonia leaves will be covered with a white or ash-gray powdery mold. Badly infected ones become discolored and distorted, then drop off. Powdery mildews thrive in both very humid or very dry weather. Spray affected plants thoroughly with wettable sulfur once or twice at weekly intervals starting as soon as the whitish coating of the fungus appears. Allow ample spacing between plants and collect and discard all above ground refuse in the fall. Many newer varieties are resistant. For more information see the file on Controlling Fungal Disease

Leaves Covered With Gray Mold Caused By Gray Mold
Gray mold is a fungal disease that often results from poor ventilation, insufficient light or high humidity. Remove faded flowers, a common spawning ground for the disease. Plant begonias in a well-ventilated location in light, rather than deep, shade. If the growing season is especially humid, gray mold may appear despite precautions. In such a case, destroy infected plant parts, and spray buds and blooms with flowable sulfur fungicide every 3 to 5 days. For more information see the file on Controlling Fungal Disease