Scouting Notes - July 2008

Control thrips in spring. Spring is when thrips populations in greenhouses really start to explode, said Michigan State University entomologist David Smitley. A combination of factors is responsible. Overwintering thrips begin to reproduce under higher temperatures and longer days. An ample supply of pollen allows thrips to reproduce faster. Most importantly, the low number of thrips present on greenhouse crops since February have completed a second generation, multiplying from 100 thrips into 30,000 thrips.

Smitley said the best way to avoid thrips problems is to carefully watch scouting reports and begin a management program when thrips numbers begin to increase on yellow sticky cards increase beyond the tolerance level (for most growers the threshold is from 10 to 100 per card).

Spray with labeled chemicals every five days for four applications. Using a product from a different chemical class every six weeks may help slow the development of thrips resistance.

For more: David Smitley, Michigan State University, Department of Entomology, (517) 355-3385; smitley@msu.edu

Gladiolus rust detected again in Florida. On March 10, an inspector with Florida Department of Agriculture and Consumer Services, Division of Plant Industry submitted a gladiolus leaf sample suspected to be infected with gladiolus rust from a commercial gladiolus production farm in Hendry County, Florida. A DPI pathologist confirmed the sample was positive for gladiolus rust (Uromyces transversalis). USDA-APHIS, Plant Protection and Quarantine confirmed the diagnosis on March 14.

This is first detection of the rust in Florida this year. It was found in 2006 and 2007 at the same operation. Following the initial find, further survey of the site revealed more infected plants. DPI and APHIS-PPQ are conducting a comprehensive survey to determine spread of the rust.

For more: Anwar Rizvi, APHIS, Plant Protection and Quarantine, (301) 734-4313; anwar.s.rizvi@aphis.usda.gov; www.pestalert.org.

Beetles take a bite out of loosestrife. Purple loosestrife (Lythrum salicaria) is especially a problem in the Midwest where it clogs wetlands and waterways. In the early 1990s, researchers at the University Minnesota were among the first to release two types of loosestrife beetles (Galerucella calmariensis and Galerucella pusilla) that feed on the plant’s foliage. Five years after the initial release of the beetles, the scientists found a dramatic reduction in loosestrife stands.

The successful trial paved the way for beetles to be released across 13 Midwest and Northeast states. The beetles not only stunt loosestrife, but also cause a delay in the time of the invasive weed’s flowering by stripping away its canopy reducing the time for loosestrife to produce seeds and spread.

To date, more than 8 million beetles have been released in Minnesota. From 1989 to 2003, annual expenditures for herbicide management of loosestrife in Minnesota has decreased tenfold mostly due to the success of the beetle program.

For more: Jeanie Katovich, University of Minnesota, Department of Agronomy and Plant Genetics, (612) 625-5230; katov002@umn.edu. Weed Science Society of America, (202) 746-4686; www.wssa.net.

More thrips overwinter in Maryland. As an overall study of the possible impact thrips may be having on vegetable and fruit quality, Maryland cooperative extension IPM vegetable specialist Gerald Brust, has been conducting a two-year survey to determine their numbers and species. Over the last two winters he has taken weed samples from vegetable fields looking to see if any thrips were overwintering and if so what species they were.

For most samples no thrips were found. In five of the 12 sample sites, thrips were found in December through January on winter annuals. Western flower thrips were found to overwinter in Maryland, Delaware and Virginia, although only in low numbers. Chickweed was found to harbor 70 percent of all thrips with wild mustards and henbit being the next best winter hosts.

For more: Gerald Brust, Maryland Cooperative Extension, Lower Eastern Shore Research and Education Center, Salisbury, Md., (410) 742-1178; http://extension.umd.edu/agriculture/IPM/mdIPM/network/pestNet.

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July 2008