P&PDL Picture of the Week for
March 10, 2008

Roberto Lopez, Department of Horticulture & Landscape Architecture, Purdue University
Cliff Sadof, Department of Entomology, Purdue University
Gail Ruhl, Department of Botany & Plant Pathology, Purdue University

Western Flower Thrips

Thrips feed on leaves, buds and flowers. Their damage is often observed before the thrips are observed. Discolored or distorted plant tissue or black specks around stippled leaf surfaces are clues that thrips are present. Populations of thrips should be closely monitored as they can be vectors of viruses, such as Impatiens Necrotic Ringspot Virus (INSV). Use sticky cards placed 1-2 “ above the plant surface and inspect at least weekly for early detection of adults. Leaves need to be inspected for the presence of wingless immatures. Please see E-110 (pdf file) for advice on monitoring and controlling this pest.

Fungus gnats

Propagation houses, dead plants and constantly moist media are ideal environments for fungus gnat development. If they are not already in your greenhouse, they may arrive in bagged soil media. Sticky cards, placed 1-2” above the plant surface, are useful for monitoring adult fungus gnat populations. Potato slices, cubes or disks placed on the growing media surfaces helpful for monitoring fungus gnat adult and larval populations, respectively. After 48 hours look closely at the potato slices to see if fungus gnat larvae are present. Larvae are easy to spot because they have a black head that stands out against the white potato. Remember to place potato slices, disks or cubes in pots scattered throughout the bench, cooler or greenhouse since infestations can be localized. Please see E-111 (pdf file) for advice on monitoring and controlling this pest.

Click image to enlarge

Thrips feeding damage on Zinnia - Roberto Lopez

Thrips damage on New Guinea Impatiens - Roberto Lopez

Symptoms of INSV (vectored by thrips) on Double Impatiens - Gail Ruhl

Fungus gnat adults on Echinacea foliage - Roberto Lopez

Fungus gnat larvae feeding damage - Roberto Lopez

Potato wedge used to attract fungus gnat larvae - Roberto Lopez

Excessively moist media promotes fungus gnat infestations and root rots - Roberto Lopez

Purdue Plant & Pest Diagnostic Lab Purdue Cooperative Extension Service