MANHATTAN, Kan. -- Kansas enjoyed a mild, albeit dry, winter through much of the state, but that does not necessarily mean farmers will see more insects in their corn this year, a Kansas State University entomologist said.
"Populations of most below-ground insects, such as wireworms and white grubs, probably were not greatly affected," said Randy Higgins, field crop entomology specialist with K-State Research and Extension.
The mild winter may have an impact on other insects, however. Higgins provided the following information on several pests common in Kansas cornfields:
Weed cover at or before planting can lead to increased cutworms because egg-laying female cutworm moths are attracted to weeds. But, moths must move through an area and find a field before laying eggs on a favorable site. If this happens and large numbers of cutworms start feeding on the weeds, problems in the crop could develop, particularly if a tillage operation or a burn-down herbicide eliminates the weedy food source before they have finished feeding.
One potential issue involves the southwestern corn borer in north central and northeast Kansas. Typically, this pest is more of a problem in the sandy areas south of Great Bend and in some southwestern counties. Reports last fall and winter, however, indicated good numbers had, in fact, been present in some non-Bt corn fields (including refuge and white corn sites) within Clay, Jewell, Osborne, Republic and Marshall counties.
Close inspections of lodged plants revealed that non-Bt cornstalks had been extensively tunneled in a few locations. So, this might be a year to keep an eye out for the pest in north central and northeast Kansas.
"Now is a good time to evaluate whether winter was harsh enough to kill SWCB larvae that tried to overwinter outside their traditional range," Higgins said. "Split several stalk bases from plants that were girdled and determine if the large whitish larva inside survived.
"Even if the SWCB larvae are still alive and eventually produce adult moths, they may or may not develop into a problem within nearby fields during midsummer. In most years following a fall problem in the north, the local larvae do not survive, and if that's so now, the species will need to reinvade northern counties to be an economically important problem for corn growers."
Cultural practices such as rotations also can have an influence on insect pests expected to be of concern in this year's corn fields, Higgins said. If corn is planted after a non-corn crop, for example, rootworms should not be a problem, although other pests could still be a concern.
Rootworms lay eggs in the soil during the late summer and fall, he explained. In Kansas, they prefer to lay their eggs in existing corn fields. As a result, when a grower rotates to another crop, rootworm larvae emerging from eggs laid in last year's corn ground should starve, because suitable food sources are unavailable.
Fortunately, Kansas does not yet have the strain of rootworm that prefers to lay many eggs in nearby soybean or other non-corn fields.
That problem occurs in some eastern and northern U.S. corn production regions, Higgins said. Growers there may be treating for rootworms every year, regardless of their rotation schedule.
In contrast, wireworms and grubs seem to be more of a problem when corn follows some type of grass or sod.
But, where corn follows corn, rootworm protection of some type is often justified unless the field was scouted last year and low levels of rootworm adults were present -- which means low egg laying potential and relatively low populations of larvae will be present.
Paying for additional protection also may not be justified where moderate to high adult rootworm populations were developing last year, but timely and effective adult control treatment(s) was(were) applied. If frequent scouting through the end of the egg laying period showed the egg-laying adult population did not rebound to threatening levels through immigration from surrounding fields, treatment this year may be unnecessary.
Several management options are available that can suppress root pruning by rootworm larvae and lessen other types of plant damage that corn pests can inflict, the entomologist said.
Growers can refer to the K-State Research and Extension "Corn Insect Management 2006" recommendations, publication MF-810, for information on seed treatments, planting time insecticides, post-planting rescue and foliar treatments, and host plant resistance (including the use of BT corn) as insect management tools.
This publication is revised annually and is available on-line. Printed copies can be picked up at most county or district K-State Research and Extension offices.
Mild weather likely aided beneficial insects' survival
Mild winter weather throughout much of Kansas may have helped some insect species that provide natural control of crop pests through predation or parasitization, said Randy Higgins, field crop entomology specialist with Kansas State University Research and Extension.
"In addition to being concerned about what effect the mild weather had on pest species, it is important to realize that beneficial insects probably survived the winter in higher numbers than is typical," Higgins said. "This is something that we don't often recognize. But in terms of pest suppression it can be important in limiting the development of economically important problems caused by crop-damaging insects."
SOURCE: K-State Research and Extension news release.