Major crops free of most pest threats in 2016
Madison — For a majority of Wisconsin's major crops in 2016, pest infestations were no more than a minor concern during the growing season.
That was the message in the Wisconsin Pest Bulletin's (WPB) report for the year that is prepared by Department of Agriculture, Trade, and Consumer Protection entomologist Krista Hamilton with input by numerous other cooperators from both the public and private sector.
While the threats from the most familiar crop pests were not great during the year, concern is building about nematodes, plant diseases, and insect pests that have been identified for the first time in the state during recent years.
In one of its major projects during 2016, the WPB tracked the presence of soil nematodes in the major winter wheat growing areas of the state (mainly in the southeast one-third of Wisconsin). Soybean cyst nematodes were found in 29 fields, clover nematodes in 5, and other nematode species in 12 fields.
A particular concern of this project was the search for cereal cyst nematodes. The WPB reported that no positives were found in soil samples taken from 89 winter wheat fields, 21 corn fields, 3 oats fields, and 1 soybean field.
However, the laboratory analysis identified other types of nematodes in 28 percent of those soil samples. Of particular concern was the finding of a nematode which is a threat to barley in Mexico. It was the first finding of that nematode in the United States, the WPB pointed out.
In another analysis overseen by DATCP plant pathologist Anette Phibbs, a new species of phytophthora root rot was found in soybean plant roots in a Dunn County field in 2016. This was the 5th finding of a new phytophthora root rot species in Wisconsin since 2012. For all phythophthora root rot species, the disease was found in 17 of 53 soybean fields surveyed this year compared to 19 of 50 fields in 2015.
Corn leaf samples from 105 fields did not have any outbreak of Xanthomonas leaf blight. But there were late season outbreaks of southern rust in Grant, Rock, and Lafayette counties.
In seed corn fields, the report by Phibbs indicated that 11 of the 78 leaf samples tested were infected with Goss's wilt. The infected samples were found in Dane, Eau Claire, Fond du Lac, Grant, Pierce, and Walworth counties.
On the positive side, the 2016 infestation of Goss's wilt was down from the finding of it in 15 of the 39 samples tested in 2015, Phibbs observed. No Stewart's wilt was found in Wisconsin during 2016 but outbreaks of northern corn leaf blight and anthracnose were common and widespread.
Corn tar spot was identified on leaf samples collected in Green and Iowa counties in September. Tar spot, which was previously confined to Latin America, was first identified in Indiana and Illinois during 2015 and then again in those states plus Iowa, Michigan, and Florida this year, the WPB reported.
One plant disease which was a problem in 2016 was white mold in soybeans. The WPB noted that many fields, especially the later planted ones, had infections in at least 10 percent of the plants.
Beetles and bugs
Although the counts were not high, there were some significant changes in corn rootworm beetles populations within Wisconsin's nine agricultural districts of county groups during 2016. The state average dropped to .5 beetles per corn plant from a .6 average in 2016.
Within the districts, however, the significant changes were beetle population downturns from .7 to .2 per plant in the southern district and from .8 to .4 in the southeast from 2015 to 2016. In the northeast district, the population jumped from .2 beetle per plant in 2015 to .7 this year.
During the 75th year of European corn borer (ECB) population surveys in Wisconsin, the state's average rose to .11 per plant in 2016 compared to as low as .02 in some recent years. No ECB were found in the east central and northeast districts but the adjoining central district had its population jump to .24 per plant this year compared to .01 in 2015. The WPB attributed the increase in ECB to corn grower decisions to grow conventional hybrids in order to reduce their input costs for seed.
After a three year low, western bean cutworm moth numbers returned to what the WPB termed “moderate levels” during 2016. The 75 traps set out during the migrating season caught 1,530 moths compared to the 644 caught in 96 traps in 2015.
Although the early season tracking of black cutworm moth arrivals caught 1,835 moths in 43 traps, the infestation in young corn plants were found to be quite limited in 2016.
The year's catch of 6,402 corn earworm moths in 16 traps during August was concentrated in Fond du Lac and Columbia counties. In addition to sweet corn, the WPB indicated that snap beans and tomatoes faced “moderate to severe” threats from the earworms until mid-September in the few areas with significant populations.
Japanese beetle populations were the highest in several years, the WPB reported. It cited the above average rainfall, which supports the beetle's larvae, and the lack of natural predators for the abundant numbers in 2016.
Surveys of soybean fields in late July and during August found that 74 percent of them had some defoliation but not up to the 20 to 30 percent level at which a treatment is advised. The WPB noted that the Japanese beetle once preferred fruit plants but has increasingly being found in soybeans and corn.
Soybean aphids were not a problem in 2016. Hundreds of field surveys found an average of only 8 aphids per soybean compared to 35 in 2015 – both well below the 250 per plant which is the working number to suggest yield and economic losses.
In early August, Wisconsin's first confirmation of the presence of the two-banded Japanese weevil occurred. The pest was found on numerous ornamental plant species and some weeds in the Madison area but nowhere else in the state.
A lily leaf beetle was found in early August at Plover in Portage County. This marked the southernmost detection in the state of the pest, which the WPB describes as a “striking red insect.” This beetle, which was first discovered in the state in 2014, has reproducing populations in Marathon, Lincoln, and Portage counties.
Based on a multi-agency monitoring survey in 2016, the WPB observed that the brown marmorated stink stink bug (BMSB) has firmly established populations in Dane and Rock counties.
This year's trapping effort caught 185 adults and nymphs in seven pyramid traps, including 80 near an orchard at Verona in Dane County. Because this was the first time that it was found on apples, the WPB warned that the BMSB could be evolving to become an agricultural crop pest rather than merely an urban nuisance.
Wisconsin's alfalfa stands enjoyed a virtually pest free year. Alfalfa weevils were a problem only early in the season in a few fields while potato leaf hopper and pea aphid populations were very low all summer.