I know its February and weed control for the upcoming field season is probably the last thing on your mind. It is not uncommon to already have your plant food and seed inputs planned and purchased by now. Even though integrated pest management is reactionary by nature, planned pest management is often a very good idea.

Over the past several years, weed control systems have changed appreciably. Now is the perfect time to address those changes and prepare for the field season. Let’s discuss a few key components of a planned progressive weed control program.
Fall weed-control strategies have increased over the past decade. Many of these programs use residual products designed to keep weed pressure low through spring planting. We noticed a large downturn in fall herbicide use in 2010. The main reason given for less fall herbicide use was that the early harvest combined with dry weather allowed some much needed fall tillage to be done. Environmental conditions in 2008 and 2009 were not conducive to tillage.

As a result, many fields were severely rutted. Additionally, terrace work, grass waterway construction/maintenance, and drainage improvement projects, which were put on hold for several years, were finally initiated. All the ground work kept fall weeds in check. Don’t be lulled into a false sense of weed control security, as we often experience a weed flush following tillage. I expect to see that flush in full force this spring.

Be prepared to use an aggressive burndown program. In many cases, that burndown should include a full-rate residual product. If a residual is not used in the burndown, I recommend a planned residual as a preemerge or early post-emergent application.
Even with a residual herbicide, plan on an additional post application of glyphosate on tolerant crops once the weeds reach a height of 4 to 6 inches. Where resistance is an issue (almost everywhere in Missouri), the glyphosate needs to be applied with an appropriate tank-mix partner.

I am a big supporter of agronomy programs designed to slow weed, insect and disease resistance. I have discussed resistance as the key message in this column many times in my tenure. For obvious reasons, glyphosate resistance has received the most attention. However, as of 2010, the Weed Science Society of America lists 348 herbicide resistant weed biotypes present in over 50 countries. The United States alone accounts for 123 of those biotypes. To fine-tune those numbers, they represent 194 weed species and have been documented in over 400,000 fields.

Weeds developing resistance to glyphosate is part of a long list that includes resistance to seven other herbicide modes of action. In Missouri, 12 weed species have developed resistance to herbicides since 1992. They include common cocklebur, barnyardgrass, common sunflower, horseweed/marestail, common ragweed, Palmer amaranth, giant ragweed, annual bluegrass and most impressively, common waterhemp, which has developed resistance to four different herbicide families.

The society lists the following general principals of weed resistance management as:
•    Apply integrated pest management practices. Use multiple herbicide modes-of-action with overlapping weed spectrums in rotation, sequences or mixtures.
•    Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the field.
•    Scout fields after herbicide application to ensure control.
•    Monitor site and clean equipment between sites.
For annual cropping situations they also suggest you consider the following:
•    Start with a clean field and control weeds early using a burndown treatment or tillage in combination with a preemergence residual herbicide as appropriate.
•    Use cultural practices such as cultivation and crop rotation where appropriate.
•    Use agronomic principles that enhance crop competitiveness.
Weed control strategies are constantly evolving. Even when the most aggressive herbicide programs are required, the return on investment is very positive, especially with today’s commodity values. Don’t let the season sneak up on you. Take time during a cold February day to visit with your local MFA Certified Crop Adviser. They can help develop a custom weed control program for each of your fields.
Dr. Paul Tracy is director of agronomy for MFA Incorporated.