A combine can be a moving observation deck for weed scouting. This year's infestation is a clue for next year's spray plan.

Nobody knows your fields better than you do. But as you climb aboard the combine this fall, you may want to watch for any unpleasant surprises that have happened during the growing season.

"The combine cab gives you a good view of any weeds that may have escaped your weed control program," said Kevin Bradley, state extension weed scientist, University of Missouri. "Note the identity, location and density of weed escapes. Keeping track of this information now will help you plan ahead and make decisions about next year's approach to weed control."

Lyndon Brush, MFA staff agronomist, agrees with the wisdom of scouting weeds from the combine. "Weeds that are in the field at harvest time have already done their damage for this year," said Brush. "But by noting what kind of weeds are there, how big they are and how widespread in the field, you can make better plans for next year. Ask yourself: why is this weed more prevalent than anything else out there, and what do I need to do to get rid of it?"

Most years, it's easy to spot corn and bean fields with scattered weeds poking up above the crop canopy. Usually, these will be some of the more familiar troublemakers: sunflower, shattercane, common waterhemp, cocklebur.

"However, if you see a dense stand of a weed that you are unsure of and haven't seen in that field before, it's a good idea to get a positive identification," said Bradley. "This is the best way to prevent the spread of a new weed that could cause real problems in the future. Remember: many growers had no idea what common waterhemp was just 10 or 15 years ago."

Proper identification of weeds is the first step in deciding what to do about them.

"Patches of perennial weeds may need a fall herbicide application," said Bradley. "Horse nettle, for example, is easier to control in the fall."

"As you find weed escapes, it's important to try to figure out why there are weeds in that particular area of the field," said Brush. "Look for patterns to explain why there are more weeds in parts of a field."

For example, if you find widely scattered common waterhemp throughout the field, it's likely due to late-germinating flushes of the weed, or poor herbicide activity overall. On the other hand, if you have excellent weed control in most of the field and find only a patch or two of waterhemp, then you might want to do some more checking. It could be poor spray patterns, holes in the crop canopy, history of weed infestations in this location-or the possibility of herbicide resistance.

"Another thing to keep in mind is the density of the weed patches you see from the combine," added Bradley. "Some weed escapes you'll see at harvest are mature and have already produced viable seed for next year."

For instance, most pigweed relatives (waterhemp, red-root pigweed, Palmer amaranth) can produce thousands of seeds per plant. "Therefore, a dense patch of common waterhemp you see at harvest this year will almost certainly mean a larger and thicker stand of waterhemp in this area next year," said Bradley.

When you're on a combine, shelling 12 rows-or even eight rows-of corn, you already have plenty to occupy your attention, without rubber-necking for weed escapes. But with a little planning, scouting for weeds through the combine windshield need not occupy much time and thought.

"A simple way to do this is to mark the location and identity of weed patches on a map of the field being harvested," said Bradley. "With outline field maps or FSA aerial photos on a clipboard, it doesn't take much time to note the location, kind and density of weed escapes right on the map."

Even better is a yield monitor with a GPS (global positioning satellite) receiver. Many yield monitors have software that lets you mark the locations of weed escapes in the field and then print out maps that show the exact locations of weed escapes.

"A yield monitor can help you estimate yield cuts due to weed pressure, too," said Brush. "Did yield dip in that weedy patch? How much?

"Could there be something else that explains the lower yields: poor stands, insect damage?" Brush added. "You may want to note areas of unexplained yield loss and investigate further, whether or not weeds are the first suspect. For example, if the yield drop is due to insect damage, pests like grubs and wireworms will still be there in 2 years, when you rotate back to corn."

Knowing and keeping track of the information you gather through the combine windshield will let you make decisions about what to do in these areas next year, agreed Kevin Bradley.

"You may want to consider selecting a different herbicide program, crop rotation or tillage regimen for these fields next year," he said. "At the very least, you'll be better prepared to monitor these areas more closely during the next season."