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Weeds on the Horizon

May 3, 2002
This past winter, at Extension meetings throughout the state, we conducted a survey titled "The Illinois Invasive Weeds Survey." This survey was designed to determine what weeds are thought to be the most prevalent throughout the state and to give us a head start on what may be some of the emerging weed problems in the future. It has been a number of years since a survey of this nature has been conducted in Illinois, and it is very interesting to look back and compare the results from past years.

The first question of the survey asked the participants to rank the top six weed species that they encountered most frequently in their cornfields and soybean fields. This question generated a list of 76 different species in corn and 68 different species in soybeans. Not surprisingly, waterhemp, giant foxtail, and giant ragweed were among the top three weeds that were ranked as the number one most common in both corn and soybeans. These results are very different compared with results from a survey conducted in 1995 that ranked velvetleaf, common cocklebur, and giant ragweed as the most common weeds in corn and velvetleaf, common lambsquarters, common cocklebur, and giant ragweed as the most common weeds in soybeans. Table 1 lists the weeds that growers, retailers, consultants, and Extension educators ranked as the top six broadleaf weeds in corn and soybeans. This table also provides percentages of how many times that weed appeared as the number one most common weed on the survey. In this survey, annual grasses as a group were ranked number one in corn and number two in soybeans. More than 50% of the annual grass weeds were accounted for by foxtail species, followed by fall panicum, shattercane, and woolly cupgrass (Table 2).

The next question asked the participants to rank the top three weed escapes that they most frequently encounter in their cornfields and soybean fields, and whether they were escapes due to "late emergence" or "hard to control." The top three escapes in corn were ragweed, waterhemp, and giant foxtail; in soybeans, waterhemp topped the list, followed by giant ragweed, with velvetleaf and common lambsquarters tying for third (Table 3).

The next question asked what herbicide-resistant weed species are being encountered in their fields. This topic will be covered in the next issue of the Bulletin in an article reviewing herbicide resistance. The final question asked what weed species are becoming more frequent or invasive in fields, ditches, and wooded areas. The top three weeds that are becoming more invasive in fields are waterhemp, giant ragweed, and common pokeweed. Even though waterhemp and giant ragweed ranked extremely high in the previous questions, many growers are just beginning to see these weeds move into their fields. Giant ragweed, common pokeweed, and poison hemlock were ranked the top three weeds in ditches, and in wooded areas common pokeweed, multiflora rose, and giant ragweed topped the list. Knowing which weeds are becoming more prevalent in these areas should give us an idea of what the problem weeds of the future will be.--Christy Sprague and Aaron Hager

Author: Aaron Hager Christy Sprague

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

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