Postemergent herbicide use in corn and soybeans is booming.

Recent surveys show 80% of soybean growers and nearly 70% of corn producers are applying post products. There are good reasons.

"With a postemergence treatment you can match the herbicides to the weeds," points out University of Wisconsin weed scientist Chris Boerboom. "And there are a number of good, solid programs available."

Soybean Digest asked a farmer, a custom applicator and a crop consultant, all experienced in postemergence weed control, how they make post products more productive.

Alan Madison, no-till grower from Walnut, IL, starts with a burndown on both corn and soybeans. He also applies a pre-emergent grass killer for corn at half or full rate. He follows that with various postemergent programs, each geared to meet the specific needs of specific fields.

"We have three basic post programs for corn," Madison says. "They are based on the weed history of the field and also are calculated to be different in their application timing. The timing differences spread our workload.

"For example, on fields with primarily broadleaf pressure, we apply Shotgun or Marksman at the spike to the three-leaf stage. (He adds a little atrazine to the Shotgun for residual.) Or, we might wait until the five- to six-leaf stage and apply Buctril plus atrazine."

On fields with moderate grass and broadleaf pressure, Madison applies Basis Gold and Clarity at the five-leaf stage.

For fields with heavy broadleaf and grass pressure, including shattercane, he goes slightly later with Liberty ATZ or Roundup Ultra on Liberty Link or Roundup Ready (RR) hybrids.

Madison also spreads the post spraying times on soybeans. He plants conventional, STS and RR varieties.

Generally, he applies Galaxy as his post product for conventional beans and Synchrony-Poast Plus on STS varieties.

"We apply the Galaxy program first and the Synchrony and Roundup programs later," he reports.

Madison has an 800-gallon sprayer equipped with a flush and rinse tank. It has a 60' hydraulic-fold boom.

"I really like the convenience of both the hydraulic fold and the rinse system," he notes. "It reduces the time for moving from field to field and for changing products. As a part of our spray scheduling, we try to minimize the times the sprayer needs to be thoroughly rinsed (in preparation for spraying another herbicide)."

For controlling drift, Madison generally uses a moderate 30-40 psi pressure, lowers the boom when conditions call for it, and does not spray when wind is excessive.

To make certain he sprays the right product in the right field, Madison draws maps of every field, along with the herbicides to be used, and carries the maps when spraying.

Marquis, Inc., an ag supplier at Buda, IL, has seen sizable growth in its custom application business. Much of that is for post products.

"There are several things that we, working with our customers, can do to optimize the postemergence programs," notes Tom Marquis.

The first step is to plan ahead.

"We like to sit down with a customer over the winter, map out his farm field by field and decide which herbicides to apply in each field," he says. "Those maps are then used when we spray. It greatly reduces the chances that the wrong product will be applied.

"We can still make last-minute adjustments if needed, but generally we're able to stay with the original plan."

Marquis strongly recommends soil-applied residual herbicides, especially for corn, which can be hurt by early weed competition.

"A soil-applied herbicide also provides more flexibility in the timing of the postemergent products," Marquis points out.

"Without that early protection, weeds can get out of control if postemergence applications are delayed by wet ground or windy conditions."

Marquis suggests that, if possible, customers call one or two days ahead to schedule post spraying.

"That is the ideal," he notes. "When we can schedule ahead, we can be more efficient and better serve farmers."

Crop consultant Joe Nester, Bryan, OH, provides weed management advice on 25,000 acres of corn and soybeans. It's largely no-till and requires post herbicides.

"Some postemergent herbicides, especially when applied to no-till corn, can reduce yields," Nester notes. "That's usually because the corn is sprayed too late, and not because of the herbicide.

"The label on Accent, for example, says it can be applied on corn up to 20" tall. However, no-till corn, or any corn that is stressed, has slow early growth. Consequently, I prefer to determine spray timing by stage of growth rather than by plant height. We recommend spraying Accent before the six-leaf stage."

On soybeans, Nester recommends, in nearly all cases, that grass control be by post treatment.

"We suggest that beans be sprayed about six weeks after planting. That's prior to canopy and before there's a detrimental effect on yield."