Crop Vigor and Weed Pressure

The middle of the main season can be a pivotal stage in crop-weed relations. Weed growth may begin to overcome steps taken earlier to control it, including herbicide application and cultivation. Also, pre-harvest intervals or plant-back restrictions, concerns over potential crop damage, and other factors may limit the use of additional chemical or mechanical tactics like applied before crops emerged and closed rows. Further, weed seed produced mid-late season can increase weed control challenges in following years. Under these circumstances, vigorous crops able to slow weed growth for even a short time can be beneficial. Creating shade and utilizing water and nutrients are two ways vigorous crops can tip the crop-weed competition in the grower’s favor. The vigor and “out-grow/out-compete the weeds” factor may be most important for crops for which cultivation and herbicide options are relatively limited. The two pictures below partially illustrate the crop vigor-developing weed pressure relationship as it stands in a potato planting before the potato vines fall, the canopy opens, and vines eventually decline or senesce. A large, vigorous crop canopy as a product of the variety and good growing conditions and supportive management is its own type of weed suppression.

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