For example, Table 2 indi- cates that giant foxtail seeded and beginning growth 3 or more weeks after corn did not significantly affect corn yields. However, late-emerging weeds can still produce many seeds to add to the soil's weed seed reservoir. Thus, full-season weed control should be the goal. However, you must be able to get into the fields within a few weeks after planting with a postemergence material that will give good control. And relatively few selective herbicides have been available for controlling grass weeds postemergence in corn.
Many farmers prefer to have good weed control beginning when the crop is planted.
This has long been an effective method for con- trolling annual grass weeds. However, the trend is away from this practice and toward conservation tillage methods that reduce soil erosion. In many areas, the moldboard plow has been replaced by the chisel plow, field cultivator, large disk and even zero-till. Some annual grass weeds, such as fall panicum, may tend to increase when tillage is reduced. Fortunately, an increasing arsenal of herbicides is helping make conservation tillage practical, with chemical con- trols replacing much of the tillage.