Eliminating Weed With Cultural and Chemical Practices

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Choosing the row width and associated equipment to manage a crop might seem an easy choice. However, it is not. Historically, farmers have managed soybean and corn production on 36 inch rows. However, reducing rows to 20-30 inch width can dramatically increase yield. Such a change will result in new or modified planters as well as harvest equipment. Whether or not making such a change is economically feasible will depend upon the age of the operator and future plans to continue production. However, there is more to increased yield to gain from switching to narrow rows.

Consider the images below taken the day of corn harvest. The two images on the left are corn planted into 30 inch rows. The two on the right are corn planted on 36 inch rows  Note that the narrow rows have fewer and smaller weeds in the row middles than the 36 inch rows. Fewer weeds existing in narrow rows is a typical response due greater number of corn plants per acre and greater light interception by this corn to utilize nutrients within the narrow rows than one would realize if planted in wider rows. In this case, the narrower rows actually decreases the number of weeds. Fewer weeds results in less seed production and fewer weeds for future germination. Thus, this simple cultural method of weed control should be considered as added value when examining the potential change to more narrow rows.

Three images showing progressively more weeds as row width increases

While this method does in fact aid in reducing the number of weeds competing with a crop for water and nutrients, it is not always sufficient as a practice used alone. Consider the three images below. The image to the far left shows the weeds in early June within a corn production system that was planted into a clean, weed free field followed by only glyphosate and a pre-emergence product at planting. The middle image is the same field with glyphosate applied as an additional application made with drop nozzles when corn had about 6 leaves. The far right image shows the reduced weed population when a pre-emergence product (in this case, Zidua) is added to the glyphosate. Again, the point is that adding additional practices and management to reduce successful weed development not only increases the probability of increased yield for that year, but also reduces the seed bank to eliminate future weeds.

Three images of corn showing greater weed population with no herbicides compared to use of proper herbicide use

While reducing row width and following sound weed management strategies do indeed show to increase yield, one critical point to recall is that not all weeds are equal when it comes to germination and seed survival. Suppression of seed development will prohibit future weeds but realize that some weeds can germinate even after remaining in the soil several years to decades! As such, to greatly reduce the seed bank, one must be diligent and not allow weeds to produce new seeds. To be blunt, this is simply not always possible due to management and climatic factors that may delay timely application. Simply realize that all efforts do indeed aid in the long term management.