Weeds on Your Field Edges

Weeds growing on the edges of fields may be causing more problems than you think. Dr. Susan Weaver, weed scientist at Agriculture and Agrifood Canada at Harrow, has compared weeds in the middle and the edges of fields, and has noticed some very different behaviour.

Weeds that grow between the last crop row and the edge of the field produce many more seeds than weeds growing in the midst of a crop. Dr. Weaver looked at 4 weeds in corn and soybean fields and found large differences in seed production. Foxtails, velvetleaf, ragweed and Eastern black nightshade all produce large numbers of seeds, but seed production increases by 10 to 150 fold when weeds grow without competition on the edges of the field.

There is a difference in weed seed production in different crops. Weed seed production in corn is often much less than in soybeans, due to the strong competition from corn for moisture and sunlight. For example, foxtail escapes in corn produced 1000 seeds/plant, while escapes in soybeans produced 3000 seeds/plant. But foxtails on the edges of these fields averaged 10,000 seeds/plant!

Some weeds produce more seeds than others. Ragweed seed production in corn was 3000 seeds/plant, while those towering escapes in soybeans produced 8000 seeds/plant. But let a ragweed flourish on the edge of the field, and each plant may produce 50,000 seeds/plant. Eastern black nightshade usually does not compete well with crops, but on the field edges it took the prize, producing 300,000 seeds/plant!

This information may change your thinking about managing your field edges. Weed escapes on field edges are now well established, but mowing before seeds are dispersed can be an effective tool to reduce weed pressure. Establishing grass strips around field edges, especially near windbreaks will allow you to prevent weeds from germinating and to eliminate weeds by mowing. At least leave enough room for a mower beside your last row.

This knowledge of weed behaviour can be useful for your Integrated Weed Management (IWM) programs. By scouting for weed escapes and using border sprays around field edges where weed pressure is greater, growers may be able to improve weed control and reduce the need for herbicide use. But for now, Dr. Weaver suggests taking a look at the weeds around your fields, and getting rid of those seed producing problems.

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