Warm winter poses unique crop threats

03/06/2012 @ 12:58pm

It's been a warm winter in much of where the nation's corn, soybean and wheat crops are grown. And, it's been dry...a lot of farmers are heading into spring with a lot less soil moisture than a year ago.

In addition to the risks those conditions alone pose to potential crop output this year, other risks, like increased pest pressures, could eat into yield potential.

Warmer winter temperatures alone don't exclusively mean more bugs. A lot depends on how much snow cover there's been throughout winter, as well as the intended crops and when they'll be planted this spring, according to Ohio State University Extension field crop entomologist Ron Hammond.

"The area where warmer temperatures can, and probably will, impact field crop insects concerns when the pests might show up and require scouting," Hammond says, adding much depends on the number of heat units accumulated. "The time for scouting will probably come earlier in the season. We would recommend sampling to determine the actual need for treatment. Then, there are the many insects that migrate from southern areas, so their development is affected by weather conditions further south, e.g., black cutworm, true armyworm, potato leafhopper.  Whether they migrate earlier or not into Ohio will depend on the weather conditions later this spring."

Overwintering insects

Then, there are the insects that can overwinter in the Corn Belt. The warmer winter weather could have 1 of 2 distinct outcomes. First, if the pest -- like the corn flea beetle, for example -- start to actively feed before the crop's planted or mature enough to offer enough of a feedstock, it could mean an early demise. If the crop is off and running, though, potential crop damage could be worse than normal.

"A few years ago, we saw soybean aphids hatch earlier on buckthorn, their overwintering host, because of warmer temperatures, but suffer significant mortality because of a late spring freeze," Hammond says. "There is one crop pest that we specifically tie into winter temperatures, corn flea beetles and their ability to vector Stewart’s bacterial wilt. Because of the warmer temperatures during December, January and February, more corn flea beetles are expected, and thus, the potential for greater Stewart’s bacterial wilt."

Dry soils & pest damage

Now, add in drier-than-normal soils. If some insect pests get an early start on account of the warm winter and spring, any shortage of soil moisture could worsen potential damage, says Iowa State University Extension agronomist Mark Licht.  

"If we go into planting dry, what does that do to insect pressures? Corn rootworm pressure tends to be more damaging when it's dry. Any damage is potentially higher when it's dry," he says. "With corn aphids and soybean aphids, if we stay dry into July and August, they can be more damaging because they're sucking moisture out of the plant."

Wheat worries

If you're a wheat farmer, you've got an altogether different set of issues on your hands because of the warm, dry weather this winter. First and foremost, the warm air may fool the hard red winter wheat crop in the Plains into popping out of dormancy early, making it susceptible to late-season frost damage.

"This is a scenario somewhat reminiscent of 2007, which was a year with severe spring freeze injury. Hopefully we will avoid that this year," Shroyer said. "The wheat has begun to grow as a result of several days with temperatures in the 60s and nighttime temperatures above freezing. It would be much better if temperatures were colder."

If, however, the mercury doesn't slide too much between now and spring, the wheat crop's slipping winterhardiness won't be a problem. But, that will mean insect pressures will.

"Army cutworms are sometimes a problem in wheat fields during March. Other early-spring insects to watch include winter grain mites and greenbugs. Early-season disease concerns include powdery mildew and tan spot," says Kansas State University Extension crop production specialist. "Producers should watch their wheat crops for insects and diseases, and make every effort to get on their topdress nitrogen soon, before the crop reaches the jointing stage -- if they haven't already done so."

What to do?

So, what can be done at this point about any of these issues? Unfortunately, not much. It's still way too early to consider changing your planting intentions because of the weather, Licht says. Once you start thinking in those terms, all you're doing is robbing yourself of yield potential.

"Farmers are asking a lot of questions. There's not a lot that we can do right now. I get asked if they should plant with a reduced seeding rate or change maturity group. At least from that standpoint, we really don't recommend changing it," Licht says. "We find our higher yields come from longer maturity groups and higher seeding rates. We're automatically reducing yields in doing that."

The only adjustment that could help, Licht says, is making sure you're planting at the right depth for the seed to get to subsoil moisture that may be lower than normal.

"If we go into a dry spring, evaporation can really take a lot from our planting. If we plant at a 2-inch soil depth, we can do more to guarantee better emergence. That's about the area where we don't want to go much deeper from a germination standpoint."

If you're one of those wheat farmers fearing damage from the early warm-up, you can graze your wheat to "hold it back." Just don't overdo it, Shroyer says.

"Producers should watch their wheat crops for insects and diseases, and make every effort to get on their topdress nitrogen soon, before the crop reaches the jointing stage -- if they haven’t already done so," he says. "Other than that, there’s not much that producers can do to stop the development of the crop. Grazing the wheat can hold back its development, but grazing may not be possible much longer this winter. Cattle should be pulled off before first hollow stem, and this will be occurring soon in southern Kansas, if it hasn’t already occurred."