The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: My tomato and squash plants are covered with white flies. What is the best method of eliminating this infestation.
Answer: Did you follow a spray schedule (an application every 5-7 days) or was there only one application made? Generally, multiple applications are required. Also, thorough coverage of the foliage (the upper and lower surfaces of the leaves) is essential. Always read and follow all label directions before using pesticides.