Attractive Varieties

• Some cutlivars of petunias---including "Calypso," "Super Blue Magic" and "Summer Madnessare"---are more vulnerable to western flower thrips, according to University of Massachusetts Amherst Extension.
  
  

Viruses

• Two main types of viruses carried by the western flower thrip are impatiens necrotic spot virus and tomato spotted wilt virus. As they grow and feed, larvae infected with the viruses spread the disease to petunias and other garden plants. For gardeners trying to detect the presence of INSV or TSWV, petunias are an indicator because they show damage quickly after infection, according to UMass Amherst Extension.
  
  

Damage

• Thrips cause growing flowers to appear deformed, often with a silver-streaked appearance, according to the Penn State University Extension website. Petunias infected with INSV or TSWV develop white feeding scars, which are followed by the development of a brown rim on leaves and a circular lesion.
  
  

Control

• Petunias should be inspected often for signs of thrip damage. Sticky traps may be used to trap adult thrips. Removal of weeds and plant debris from under growing petunias, as well as elimination of flowers in which INSV or TSWV infection is suspected, helps control thrips.