Mites are tiny arachnoid insects, barely perceptible to the eye. They appear as web like entities on the leaves. A technique employed to detect them is to place a blank paper under the leaf and tap the leaf a few times. They will drop off appearing on the white paper. The signs of infestation are stippled and yellow leaves.

Mites can be washed off with a garden hose and that is the recommended first defense. Application of insecticidal soap is effective if additional control is necessary. Further plant-based remedies are discussed in this fact sheet from the University of California Integrated Pest Management Program.

Begonias are susceptible to a host of diseases. If your plant's symptoms are different from those described for mites, you can find additional information on begonia diseases from Penn State Extension. Another excellent resource is the Cornell Insect Diagnostic Lab where you can send a sample for diagnosis.

Please let us know if we can offer further help. Good luck with your begonia!

Courtesy of NYBG Plant Information