Soft red winter wheat has waxed and waned in popularity as prices, disease and weather abuse its fortune. University of Missouri agronomist Shawn Conely says, with proper scouting and management, wheat can be part of dependable and profitable crop rotation in the Midwest.

Maybe it is the wheat plant's general tenacity. Or perhaps it is because the crop's price sometimes makes wheat a dodgy investment. It could be mere tradition, but there is something that makes wheat management less than a priority for many Midwest growers. And that's something Shawn Conely would like to change. As the extension wheat specialist for the University of Missouri, Conley encourages growers to manage wheat a little more like other cash crops, giving it the weed control, pest control and fertility it needs.

"We can look back on a survey that's a few years old now--from 1998," said Conely. "It said only 2 percent of wheat in Missouri was scouted by a professional crop scout. The data may be old, but that mindset for scouting wheat is probably still out there."

Yet pushing wheat production requires an understanding of what is happening in a field both spring and fall, and how a wheat stand weathered dormancy--things difficult to know via the 25-mile-per-hour windshield survey. Consequently, Conley says that growers should be in the field scouting wheat several times in a growing year.

Autumnal concerns
Growers tend to push the Hessian fly-free planting date when corn and soybeans come out in a timely manner. Planting dates also get pushed if wet weather is forecast and likely to force wheat planting deeper into fall.

"Miss that planting window, and instead of 1 week early, sometimes the grower is 3 weeks late," Conley said. "[In some circumstances] it might be acceptable to push the fly-free date, but we have to manage differently."

Earlier planting often leads to increased, more vigorous fall growth, a target for increased aphid feeding. Late planting allows less time for root and tiller development.

Regardless of planting date, growers should make tiller counts prior to dormancy. A good tiller count informs producers of the relative yield potential for the stand. Low tiller counts prior to dormancy signal the need to make a late-winter nitrogen application prior to green up.

"We are looking for two to three tillers on those plants going into winter dormancy. If you have that, you're setting yourself up for a good wheat year," Conley said.

The green up application (usually applied before the ground is fully thawed) triggers the wheat plant to form additional tillers, which makes for more grain heads and the potential for better yield.

"Basically, anything less than 70 tillers per square foot at green up calls for a nitrogen application right away," said Conley.

But early scouting is critical: "The window for encouraging tillers is the first couple of weeks just after green up (jointing is too late). The time of year depends on weather. This year we had green up 10 days or 2 weeks early."

Scouting wheat in dormancy is important, said Conley, because it keeps the grower apprised of what the crop will need when it breaks dormancy.

That allows a grower to get nitrogen on while the ground is still hard to stimulate tiller formation.

Total nitrogen recommendation for a wheat crop is usually about 100 pounds, depending on yield goal and previous crop. A targeted fall/spring split application with a third in autumn and two-thirds in spring is common.

Aphids like warm falls
Another good reason for fall scouting is the damage aphids can wreak as they feed on plants and introduce diseases. In recent years, warmer-than-normal fall temperatures in the Midwest have boosted aphid feeding and associated diseases--especially barley yellow dwarf virus (BYDV). Several types of aphids are vectors for BYDV, and because it is widespread, growers are probably familiar with the symptoms: red, purple or yellow discoloration of the leaf, typically beginning near the tip, spreading down the leaf.

Aphids that spread the virus are attracted to green plants, so in autumn, when other plants are harvested or in senescence, aphids see a wheat field as one large smorgasbord.

"An aphid injures wheat not just in its mechanical feeding, but it also can transmit a virus," said Conley. "It's the fall transmission that is really most detrimental to the crop. Studies show anywhere from 40 to 70 percent yield loss if you have a high infestation rate."

Barley yellow dwarf virus has been a focus for Conley for the last couple of years. Such focus is due partially to recent years' warm autumns, which kept aphids feeding longer in the season, and partly because the economic threshold for fall-time aphid infestations needs refined.

"If we have an early killing frost and temperatures stay cool, the weather does a good job of knocking the aphids down and keeping them out of the system," said Conley. Last fall, aphids fed into winter months spurring producers in regions of Missouri's Bootheel and Arkansas to apply insecticide into December. Such extended feeding resulted in evidence of fall transmission of BYDV in stands this spring. But Conley said that high aphid numbers alone might be misleading.

Conley has worked with Laura Sweets and Wayne Bailey (MU plant pathologist and entomologist, respectively) to crack the intricacies of the aphid/disease complex in wheat.

An interesting lead, if only loosely correlative so far, is how the presence of beneficial insects in fall might affect aphid counts.

Even with extended warm weather last fall and some evidence of wheat contracting the virus through fall aphid feeding, Conley said that wheat damage from barley BYDV is lighter than he expected. The reason may be related to Asian soybean aphid numbers and the number of predators they encourage. "One of the things we've got to do when we scout is keep track of beneficial insects. If there is a good side to soybean aphids, it's that they've boosted the number of beneficials like lady beetles. That actually helps with wheat aphids. When the soybean aphid is finished feeding and moving into its winter refuge, the lady beetles need something to eat."

It works the other way, too. In a year with low populations of soybean aphids, the number of beneficial insects may be reduced, and that should figure into decisions about insecticide treatments.

Finding the threshold
So many variables make for inconsistent economic thresholds. Conely said that the economic threshold recommendation for aphids in fall wheat varies from state to state. Because plants infected in early growth stages stand to suffer the most damage from BYDV, thresholds for fall growth wheat are lower than springtime infestations. But they range from just a few aphids per foot of row in intensively managed wheat to old-school thresholds of 25 or 50 aphids per foot of row. Finding the right threshold is complicated not only by the presence of beneficials, but also by weather.

If an economic level of aphids is detected but a killing frost is in the forecast, most growers will look to save a rescue treatment and let Mother Nature do the mercenary work.

Conley said a systemic seed treatment can provide some protection against aphids, especially for early planted wheat. But again, it's a matter of timing and cost. For wheat planted later, an early killing frost may negate the need.

Still, there is little doubt that in some instances a rescue is needed.

"In the 2001/02 growing season, a grower sent a sample in to the diagnostic lab at MU to perform a virus assay that would detect the strains of viruses infecting his wheat. We looked at it and found two different strains, which can indicate fall infestation. Because that grower had a yield monitor, we were able to look at overall yield reduction.

It looked like about 50 percent reduction on the field edges where the aphids would have moved in and a lesser amount of damage in the middle of the field, but probably 30 percent reduction in yield overall."

That discovery spawned an experiment in which Conley and company are looking at fall versus spring virus infection and damage. The results will help formulate a new economic threshold for fall infestations. Conley said it will be out by this fall.

As for spring aphid infestation and spread of BYDV, Conley said there can be significant damage. In the research that is underway, Conley noted a peak of 15 aphids per plant last spring. That sizeable of an infestation, even as late in the season as jointing, translated to a 18 percent yield loss.

Hidden weeds
Winter annuals grow under the same conditions as winter wheat, noted Conely. And a thriving stand of winter annuals can be lurking just below the canopy of a wheat field.

"With Roundup Ready rotations and no-till, we're seeing a buildup of these winter annual weeds. But there's not a lot of good data about how weeds like henbit and chickweed affect wheat yield," said Conley.

"We are looking at some initial data and trying to get some numbers down. Of course it depends on weed density, but we've found up to a 38 percent yield loss associated with some of these winter annuals."

Such heavy damage derives from a scenario in which wheat is planted and emerges just prior to the winter annuals. The winter annuals come in but don't look like an economic threat. However, they have significant fall growth, remaining just below the wheat canopy.

"It may look like a great wheat crop, but you might have some of these winter annual weeds moving into the system and causing great problems," said Conley.

Wheat has long been a major crop in the Midwest. In rotation with corn and soybeans, it spreads weather risks and provides cash flow midseason. Timely scouting along with tighter weed and pest control might just make that cash flow a little larger.