Make note of weed populations at harvest to get a head start on next year's weed control programs.

Watching populations of escaped weeds as the combine rolls through them may cause a crop farmer to cringe. And that's about the only thing left to do if weeds have survived until harvest. Do some scouting before you get on the combine and pay close attention during harvest--a few notes about what weeds escaped and where escapes proliferated can go a long way in planning for next year's weed control.

"You'll be looking at the field closely as you combine," said William Johnson, University of Missouri weed control specialist. "Before harvest, scouting can be your primary focus."

Corn and soybean fields that appeared weed-free all summer can now have "escapes," Johnson added. Weeds frequently seen in August, popping above the soybean leaf canopy, are waterhemp, sunflower and shattercane.

By scouting before harvest, you'll find the weeds are still alive and visible. Living weeds with leaves intact are easier to identify than the dead stalks.

"Soybeans are probably easiest to assess because the escapes grow through the canopy," said MFA staff agronomist Paul Tracy. "But getting a look at weed pressure in all crops can be helpful from August through harvest," he said. Tracy pointed out that most growers won't scout corn fields by foot this time of year so the combine-view survey is particularly helpful.

"And after harvest, you can't really assess what weed pressure was. 'Forensic agronomy' is tough. You have a harder time assessing things compared to if you'd been there before you cut through with the combine."

This year there seems to be more late-season grass growing and setting seed. Grass can be a problem next spring. "Our research shows that early-season grass ties up a large part of the nitrogen before the crop gets it," Johnson said.

There is no practical control now, but prevention can be planned for next season. Knowing the problem areas, farmers can plan for a two-pass system next spring instead of spraying just once.

Tracy stressed that every bit of information a grower can glean from year to year will help with getting the right weed control for future crops. However, he stressed that it is hard to proactively scout for annual weeds.

"The difference with perennial plants, which you can figure will be back in subsequent seasons, and annuals is that annuals tend to be more mobile," said Tracy. "They will move by wind and water and be spread by combine." Tracy said that annuals can go from a problem one year to a negligible presence the next. "They're environmentally triggered, so I'd emphasize taking a close look at harvest and following up with a careful scouting program the next spring. If there's a predominant weed in a field this year, chances are it will be again next year. But we've seen some annuals skip years, laying in wait for the right environmental conditions. For example, two years ago cocklebur pressure was exceptionally high over a wide geographical area. Since then, cockleburs pressure has returned to normal."

Growers with GPS may have a record-keeping advantage over those who have yet to move in that technological direction, but low-tech approaches are still effective.

"Essentially, you will want to draw a map of the field and mark the patches where weeds escaped the early-season control strategies," Johnson said. "Take a closer look at the problem areas to find reasons why the weeds escaped."

Escapes are most often associated with poor stands and reduced leaf canopy. Many factors may cause a thin stand: drowning, poor seed-slot closure, improper planting depth, compaction, disease, nematode, insects, hail and spray boom overlap.

The patches may have historic weed seed buildup--in old farmstead areas or feedlots.

Having the scouting information written in a notebook along with the sketch maps can be good reminders next spring when deciding what weed control to use.

Keeping the past weed control reports can also help identify cases where some weeds are becoming resistant to certain herbicides.

Tracy said that throughout its trade territory, MFA has more than 125 certified crop advisors who can help with assessing weed problems. He added that the University of Missouri has a series of effective guides that help in identifying weeds and plotting their control. They can be obtained from regional extension agronomists.

Check out these guides for additional information. MU publications IPM1006, Introduction to Crop Scouting, $3; IPM1007, Practical Weed Science for the Field Scout: Corn and Soybeans, $3; and MP575 Weed Control Guide for Missouri Field Crops, $7.50, plus shipping, are available by credit card from Extension Publications at 1-800-292-0969. A computer program that contains both weed identification and control strategies for Missouri is available on CD. Information is available at: http://weedsoft.unl.edu.