A few of us have experienced a number of re-spray cases within this area in the last week or two. The reason behind the weed breaks lack of rain. A few of these corn herbicides need at least inch to an inch of rainfall to activate the chemical in controlling early emerging weeds. One way that I think helped some growers get early activation of their chemical was through rotary hoeing. The crusty ground brought out some rotary hoes and those places where they were used had better weed control.
Early cultivation is also a useful practice to be considered in dry conditions.
Large seeded weeds such as common cocklebur and giant ragweed are difficult to control in one pass herbicide programs and may be the first to appear if escapes develop. Morningglory species and velvetleaf are also larger seeded weeds that are not as easy to control with atrazine premixes. There are several post-emerge options for control of these weeds. A few vines may turn into a lot by harvest. Feeding on the cotyledons of soybean plants can cause serious damage to the plant.