Weather is the wild card in postemergence weed control and no one knows it better than Rock Katschnig. Mother Nature turned on the spigot over his Prophetstown, IL, soybean fields and left him staring at a forest of giant ragweed.

"I had fields three days away from calling a helicopter for rescue treatment," he recalls. "When we finally got in, I raised the boom as high as possible and got nearly perfect kill without any chemical injury in the Roundup Ready fields. But it took a custom applicator with a high-clearance sprayer to get over my non-GMO beans. That field stayed wet and the rescue was so late, I took a 5- to 10-bu yield hit. The cost wasn't very friendly either."

Today's herbicide programs are more dedicated to post products than ever before. And while they're designed to give you versatility, too much reliance without proper planning can narrow the window for optimum control.

"Application timing has become the foremost issue as farmers increase post programs and try to cover more acres in general," says Bill Johnson, University of Missouri weed specialist. "Throw a weather problem in and that window tightens even further."

The good news is that the opening isn't glued shut, and finding ways to widen it a crack can pay off.

Speed counts. Katschnig, who devotes all of his 1,500 acres of no-till soybeans to the Roundup Ready program, hasn't found the need for a high-clearance sprayer - yet. But he has moved to a sprayer with 60' hydraulic booms, foam markers and a 1,000-gallon tank.

Think bigger equipment, reduced spray volumes, higher speeds - anything to quicken your spraying pace. "Everything that needs to be planted in a day needs to be sprayed in a day," says Ford Baldwin, University of Arkansas weed specialist. "Everything you plant in a week's time should be able to be sprayed in the same time - including weather delays."

Custom applicators offer a way to increase manpower and equipment without actually adding to the payroll or machinery inventory. What you sacrifice is timing, especially if weather sets in.

"We've had farmers waiting seven to 10 days after contacting a custom applicator," says Johnson. "To be safe, don't put the entire burden on custom applicators. Scout those fields in a timely manner so you know where weed problems are most likely and then work out a plan of attack with your custom applicator ahead of time."

"A soil-applied residual on at least half your acres will help get you and the custom applicator out of a time crunch," says Phil Needham, manager of Opti-Crop, the crop consulting arm of Miles Farm Supply, Owensboro, KY. "Our research in 15" soybeans shows a 7-bu/acre yield penalty if growers wait until weeds are 8-10" tall, compared to 5-6". In 1998, wet weather got us to that 10" stage all too quickly."

Laying down a soil-applied herbicide spreads risk and helps timeliness. "I worry more about losing ability to control weeds than about competition," says Baldwin.

Granted, it makes for a costly program if you've also paid the tech fee for herbicide-resistant genetics. "But it makes sense to put a pre-emergence treatment down, particularly on those fields with a history of higher weed pressure," says Orvin Bontrager, an agronomist at Servi-Tech, Inc., Aurora, NE. "We're recommending it - usually as a banded treatment - in fields where we've had a harder time controlling velvetleaf or waterhemp when Roundup is not properly timed."

Trying to kill weeds after they've gotten too large is job security for weed scientists, points out Baldwin.

Timing with Roundup is often thought to be less critical compared to other herbicides, but Baldwin says it depends on the weed species.

"Morningglory, coffeebean, teaweed and barnyardgrass need to be sprayed within the first 14 days, even under ideal conditions," he says. "Let them get large and a little drought stressed and you can't kill them at any rate. Go ahead and say you should have used a soil-applied with the Roundup, but timing is still everything.

"Our research shows excellent results on most all weed species using two applications of Roundup with the first applied at 10-14 days after emergence and the second, seven-10 days later," adds Baldwin. "Done timely, we can do it below label, with two 1 pint/acre applications. That's as good as it gets down here, cost-wise and control-wise. But a lot of farmers have trouble pulling that off on large acreages."

Some growers in the Midwest can wait longer and hold out for one pass with Roundup. "But they get themselves into trouble by waiting just a little too long," says Marshal McGlamery, University of Illinois weed specialist. "Any kind of weather and they're in a bind."

So you missed the timing on that first application. Raising the postemergence herbicide rate can compensate and buy you a little more time.

"But our work shows timing is far more critical than rate," adds Baldwin. "I'd rather have1 pint/acre applied timely than I would 1 quart/acre applied a week too late."

Plan your attack. It may seem like a small thing, but sometimes where you plant fields can give you a break - especially if you're spraying Roundup. Roundup works well applied by air, but isn't an option on most farms because of close intercropping. Drift concerns also lessen somewhat if you group Roundup Ready fields.

For some growers the answer is simply to devote more time to weed control programs that work for the specific weed species in their fields, rather than trying to adopt the latest technology.

"We're mostly rowed beans here," says Bontrager. "We're seeing some Roundup users come back with mechanical cultivation."