As the 2014 growing season progresses for Wisconsin's crops, the threats they face from insects continue to be monitored by weekly Wisconsin Pest Bulletin and its private and public sector cooperators.
The WPB for the first full week of July issued by the Wisconsin Department of Agriculture, Trade and Consumer Protection focused heavily on insects affecting the state's corn crop.
One of them is the European corn borer, from which feeding injury by larvae on 1 to 14 percent of the whorls was detected in 33 of the 86 fields that were checked during the reporting week. The WPB noted that it was too late for chemical treatment in the parts of the state where the degree day total (on a base of 50) had reached 1,100 for the season.
The treatment window remained open through this week in the southeastern, central and northern counties where the degree day totals were lower. The WPB also urged growers with Bt corn hybrids to check the effectiveness of that trait in controlling the corn borer.
Stalk borers should be monitored until corn reaches its V7 growth stage, the WPB suggested. In what was probably an exceptionally high infestation, it cited the report of stalk borer damage to 2 to 43 percent of the corn plants near Deforest in Dane County.
A catch of 82 true armyworm moths in black light traps near Janesville during the reporting week raised concerns about new outbreaks of the insect's larvae in corn and winter wheat that is lodged. Many of the surveyed corn fields had ragged leaves and defoliation traced to the true armyworm larvae on 1 to 6 percent of the plants.
The WPB reported that corn rootworm beetles were already emerging in Dane and Rock counties although, the peak emergence isn't expected until mid to late August. Growers of corn hybrids with Bt traits for controlling rootworms were advised to notify their seed company representative if unexpected lodging occurs as a result of storms or heavy rains.
Western bean cutworm moths have been caught in pheromone traps in Adams, Columbia, Dane, Fond du Lac, Green Lake, Marquette, Monroe, Sauk and Walworth counties this month. The WPB predicted another 25 percent emergence of the moth population as far north as Waushara County the end of next week.
Corn earworm larvae were already found in Richland and Sauk counties. Populations of Japanese beetles have been feeding on corn and soybean plants, the WPB added.
Soybean plants can tolerate defoliation of up to 30 percent from beetles or other insects before they bloom and up to 20 percent later, the WPB explained.
Although soybean aphids were found in only 18 of the 87 fields that were inspected during the reporting week, the WPB cautioned that population density could increase rapidly. It advised monitoring populations until the plants reach the 5.5 reproductive stage and applying an insecticide if per plant population averages top 250 aphids compared to the average of 14 counted in the most recent surveys.
One encouraging item in the latest bulletin was the low population of most insects that affect alfalfa. Potato leafhopper populations had increased in southern counties, but of the 84 fields that were checked, only seven yielded an average of 1.1 to 1.7 leafhoppers per net sweep while another 26 had an average of 0.6 to 1 per sweep.
The WPB also noted that alfalfa weevil and plant bug populations were low and the pea aphid population had crashed rapidly due to fungal pathogens that developed during wet and humid periods.
The first spotted wing drosophila flies of the season were detected in Vernon County on June 30, the WPB reported. This insect, whose larvae infest ripening raspberries and other fruits, can be controlled with barrier netting to keep out the flies or with the application of an insecticide every 4 or 5 days.
Timely updates and alerts were also issued for codling moths and San Jose scale in apple orchards and about the grape phylloxera.
Current vegetable plant threats include the squash vine borer and squash bug. Bacterial wilt on cucumbers caused by beetles was reported in Dane and Sauk counties. Squash bug outbreaks on cucurbits were noted from Grant to Monroe counties.
Despite an adequate accumulation of the environment factors that cause the disease, the WPB stated that no late blight has been diagnosed on potatoes or tomatoes in Wisconsin.