You have to marvel at the weeds on this list. Despite all the efforts to eradicate these pests, they continue to come back, year after year. To make matters worse, they’ve adapted to modern farming practices and in some cases have developed resistance to modern crop protection products. Most growers have firsthand experience with most of these weeds, listed in no particular order.
1 Common waterhemp (and its relative Palmer amaranth) is ideally suited for row-crop production. A single plant can produce more than a million seeds, has an extended germination and emergence events, and has developed resistance to several herbicide classes.
2 Giant ragweed can compete with the best crops. Its growth cycle fits with conservation tillage and it has developed resistance to several herbicides.
3 Common lambsquarters has adapted to conservation tillage practices, is resistant to some herbicides, and has early germination and emergence.
4 Velvetleaf is still a problem for farmers. It germinates deeper in the soil and has an extended seed life.
5 Giant foxtail is probably one of the most widely spread and economicaly important weeds in the Midwest. Although it isn’t difficult to control, it is tough to manage.
6 Woolly cupgrass is more competitive and difficult to control than giant foxtail.
7 Burcucumber is not difficult to control but is impossible to manage due to extended germination and emergence timing.
8 Annual morning glory species can be difficult to manage in row crops.
9 Horseweed/marestail is a significant problem in conservation tillage and no-till systems. It has developed resistance to many herbicides, including glyphosate.
10 Common sunflower with its early emergence, rapid growth, and resistance to several herbicides is an important weed where populations exist.
Sources: Micheal Owen, Iowa State University, and Aaron Hager, University of Illinois