All other treatments were single pigweed plants spaced at the given intervals. All other treatments were single pigweed plants spaced at the given intervals. Effect of Time of Germination Weeds that emerge early in the season are likely to reduce corn yields more than those that emerge later. However, if allowed to grow for several additional weeks, these weeds can cause severe crop loss. Once crop and weed plants reach a certain size, the available water, nutrients and light do not meet the needs of both, and competition begins.
Broadleaf weeds compete effectively with corn for nutrients.
In fact, shallowly placed fertilizer may stimulate early weed growth at the expense of crop growth and subsequent yields. Research has shown that pigweed can use nutrients from the soil more effectively than corn. The effect of weed competition in corn also varies with the stage of crop growth. However, during the next 5-week period or so, competition can be devastating. In fact, it has about the same effect as season-long competition.