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Weeds to Watch

November 6, 2003

A new 8 1/2'' x 11'' glossy publication titled "Weeds to Watch" is available. This bulletin will help focus attention on weed species that may pose new threats in corn and soybean fields. It can also be used as an identification guide for the 16 weed species that may be uncommon to your area. Each species is characterized by its current distribution and occurrence. The back of the bulletin contains information about identification, an explanation about why a species is a problem, and management tactics to aid in controlling the weed.

You may ask, "Why is it important to identify new weeds when they first enter a new field?" Preventing a weed from becoming permanently established is the most effective way of avoiding future problems. Prevention relies on the ability to properly identify a weed when it first appears in an area. Misidentifying a new species can result in implementing control tactics with a high probability of failure. Not only does this allow the weed to become firmly established, but misidentification can result in reduced income due to control failures and increased costs.

Most farmers know weeds common to agronomic fields of their local area. They monitor fields for increasing densities of these weeds and adjust their management programs accordingly. However, farmers may have limited knowledge of weeds not common to their immediate area. When a new species moves into a region, farmers may misidentify the plant or assume the presence of the weed is an isolated event and that it will not become permanently established in their fields.

Examples of misidentification include woolly cupgrass being mistaken for giant foxtail and biennial wormwood being identified as common ragweed. The establishment of wild four-o'clock in no-till fields is an example of failure to account for the potential weediness of a species. Failure to properly identify a weed or mistake its potential weediness significantly affects weed management and farm profitability.

Weed shifts occur at increasingly rapid rates due to the simplification of weed management systems. While many of these shifts occur among the prevalent weeds of the area, included in these shifts are weeds recently introduced to an area or plants that previously were poorly adapted to survival in agricultural fields. Responding quickly to invasion by new weeds can result in significant reductions in weed management expenses by preventing establishment of these invaders.

We will attempt to include a copy of this new publication in a future issue of the Bulletin. For those with access to the World Wide Web, the publication can be viewed on the Web version of the Bulletin or at the University of Illinois Weed Science Web site ( Nordby and Aaron Hager

Author: Dawn Nordby

The Pest Management and Crop Development Bulletin
Executive Editor: Kevin Steffey, Extension Entomologist

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