Pest problems minor on state's major crops

Some insects pose concerns in the future

Ray Mueller


The major part of Wisconsin's growing season has passed without any widespread serious damage to crops from pests. But that doesn't mean that there aren't a few concerns on the horizon, according to the last weekly issue of the Wisconsin Pest Bulletin (WPB) for 2016.

Among the state's major crops, there is still a concern for the coming weeks with earworm infestation of sweet corn, the WPB indicated. It reported the catch of 2,865 moths in 17 pheromone traps during the final week of August, bringing the year's count to 6,372 moths. Fond du Lac, Columbia, and Dane counties registered the highest totals.

The 75th year of European corn borer monitoring in Wisconsin tracked 2nd generation infestations in 15 of 73 fields that were checked. In what the WPB attributed to the growing of more conventional corn hybrids in anticipation of lower corn prices, counts of close to two larvae per plant and two borers per ear were tallied in fields near the Holmen and Centerville areas in La Crosse and Trempealeau counties.

Corn rootworm beetle shifts

Significant changes in corn rootworm beetle populations have been tabulated in four of Wisconsin's nine agricultural districts this year, the WPB pointed out. The state average for 2016 is .5 beetle per plant compared to .6 in 2015.

But there are major geographical shifts in the numbers. This was most noticeable in the northeast district with an average count of .7 beetle per corn plant compared to .2 in 2015. There were also increases in the west central and northern districts while the southeast district dropped from .7 beetle per plant in 2015 to .2 and the south central district was down from .8 to .4.

Western bean cutworm larvae were found in 15 of the 229 fields surveyed during the last week of August. The WPB described the populations in some fields in Chippewa, Dunn, Eau Claire, Green Lake, Juneau, and Marquette counties as being “medium to heavy.”

Northern corn rootworm beetles were found on soybeans in Richland County with 10 to 40 percent of the plants having some defoliation. For soybean aphids, the year's final count was an average of 8 per plant compared to 35 in 2015.

New insect concerns

The August 5 collection of two-banded Japanese weevils from ornamental plants at a residence in Dane County was the first detection of this insect in the state although it has been in the United States since 1914. The WPB noted that the weevil has spread to much of the eastern part of the United States during the past century.

The WPB indicated this pest can be destructive to more than 100 landscape plants. At the Dane County site, two-banded Japanese weevils were found on columbine, coral bells, Japanese anemone, ligularia, pulmonaria, Siberian blugloss, snow on the mountain, spirea, rock iris, and several weed species, the WPB reported.

Dane County, along with Rock County, is also the location of confirmed populations of the brown marmorated stink bug, which the WPB indicated has become “a severe pest” in fruit, vegetable, and field crops in the mid-Atlantic states and now has the potential to do the same in Wisconsin within 5 to 10 years. It asks anyone seeing a swarm of this bug to call the Department of Agriculture, Trade, and Consumer Protection's pest survey program at 1-866-440-7523.

Fall seasonal pests

Yellowjacket hornets are beginning to dine on ripening vineyard grapes in Wisconsin. The WPB advises vineyard owners that applying an insecticide is not effective in that setting and to harvest ripening grapes instead.

In addition to the brown marmorated stink bug, nuisance insects such as multi-colored Asian lady beetles, boxelder bugs, and western conifer seedbugs will soon be congregating on the southern and western sides of buildings and preparing to move indoors, the WPB advised. It said severe infestations can be treated by a licensed pest control technician but suggested sealing cracks in windows, doors, or siding in most cases to exclude the pests, which do not reproduce while inside.

Late blight has been confirmed on tomatoes in Polk County and on potatoes in Dane County. Because it is not possible to save infected plants, the WPB recommends disposing of their foliage in plastic bags.

Northern corn rootworm beetle.