Not long ago, I kept track of all the time I spent on the telephone during a year talking to county agents, farmers and pesticide purveyors about current weed science issues.  I was surprised to learn from that self-inflicted obsessive exercise that I spent nearly 160 hours, or one entire month of work, with a phone plastered to the right side of my head.

Perhaps this helps explain my ever increasing blurred vision and forgetfulness? Pop Warner, high school and D3 college football probably didn’t help that either.

The general topic of many of those phone conversations was about what growers can do to improve the performance of their weed management programs.  Usually, this is also the main topic of most e-mails that I answer and on-farm visits that I make.  As I think back over the last 13 years or so, especially since herbicide-resistant Palmer amaranth reared its ugly head, there are two problems that I consistently observe that cause me (and you) the most headaches.

The first of these is failing to start weed-free at planting.  Growers who do not start weed-free at planting are, more often than not, going to lose their weed control battles and/or will spend tons of extra money trying to catch up.  In order to start weed-free at planting, some combination of cover crops, tillage and herbicides needs to be used.  If temperatures remain above-average this winter, weed emergence will be earlier than usual.  Thus, regular field scouting prior to planting is imperative.  

When tillage is used to control large pigweed plants prior to planting, it is very common to observe preemergence herbicide failures.  Preemergence herbicides are designed to be absorbed by young shoots and roots that are developing from seeds not shoots growing from lateral buds on older plants.  I cannot think of a single residual preemergence herbicide that would provide any level of control of a Palmer amaranth plant pictured with this article.   One way to avoid this particular problem would be to include a residual herbicide in your early preplant burndown, especially if planting will be delayed. 

The second most-common problem I have observed with weed control programs has to do with the timing of in-crop postemergence (POST) herbicide applications.  Hopefully, you have heard me say on more than one occasion that POST herbicide applications for Palmer amaranth need to be applied before the tallest plants in the field exceed 3 to 4 inches in height.

You will note in Figure 2 below that if you delay applications for the average, it is very likely that a large portion of plants in that population will be larger than the average.  This difference in size between the average and tallest plants could help explain some of the postemergence herbicide inconsistencies that are often observed in the field.   Over time, weeds have evolved to adapt to man’s influences.  Weeds are not cultivated crops that have been manipulated by man to germinate, emerge and grow as uniformly as possible.

I will be the first to admit that getting good weed control can be very challenging.  Unfavorable and uncontrollable environmental conditions are a weed scientist’s worst nightmare. However, starting clean and spraying earlier are two strategies growers can implement to significantly improve their weed control chances.

As always, good weed hunting!