For the most part, damage from insect pests has not been a big problem for Wisconsin's major crops this summer. That's the good news in the weekly Wisconsin Pest Bulletin (WPB) for the first week of August issued by the Wisconsin Department of Agriculture, Trade, and Consumer Protection.
Catches of western bean cutworm moths in 103 pheromone traps through August 6 totaled only 409, the WPB reported. This was the lowest number since tracking of the insect began in 2005.
As of August 6, the primary migration of corn earworm moths had not yet been documented, the WPB indicated. The weekly tally was 16 moths in 11 pheromone traps compared to 40 in the previous week.
About two more weeks remain for treatment of European corn borer second generation larvae in southern and western regions of the state and for longer periods in other areas. The WPB advised growers of sweet corn and non-Bt field corn hybrids to check for egg masses and small larvae.
After a couple of years of major outbreaks of Japanese beetles in many parts of Wisconsin, reports indicate that the populations are down almost everywhere this year, the WPB stated. It noted, however, that some apple orchards and nurseries have populations high enough to warrant an insecticide treatment.
In corn fields, the economic threshold is three beetles per corn ear, the WPB noted. It pointed out that an insecticide treatment would be needed before the end of pollination to minimize yield losses.
With soybeans, defoliation by Japanese beetles has reached 2-15 percent in some fields compared to the 20 percent threshold for economic loss, the WPB observed. It suggested scouting for the insect on grapes and other susceptible crops and applying insecticide on a warm, sunny afternoon when the beetles are likely to be the most active.
The critical time has arrived for monitoring soybeans for infestations of aphids, the WPB remarked. That's because of the combination of the start of pod filling time and the early August temperatures in the 70s and 80s that accommodate the most rapid reproduction of the soybean aphid, it explained.
So far, the average population has remained at less than 20 aphids per plant, the WPB noted. The only exceptions in 188 fields surveyed during the reporting week were single fields in La Crosse, Wood, and Waupaca counties with average per plant counts of more than 40 aphids. The economic threshold for likely yield losses is 250 or more aphids on at least 80 percent of the plants.
A few whiteflies were noticed in soybean fields in western and southwestern counties. The WPB pointed out that they are found most often on vegetable and household plants.
In alfalfa fields, the counts of potato leafhoppers, plant bugs, and pea aphids continue to be well below levels of concern, the WPB stated. It noted the discovery of some striped blister beetles in western counties — an insect that usually follows a grasshopper infestation.
Numerous reports are being received about blossom rot on tomatoes, peppers, melons, and squash, the WPB stated. In most cases, the disease is due either to a shortage of calcium in the soil, inconsistent moisture, or a combination of them.
Of greater concern is the confirmation of late blight in two potato fields in Portage County and on tomatoes in Milwaukee County, the WPB observed. It advises growers to consider fungicide applications every five-seven days and to destroy any infected plants.
Dane, Marathon, Sauk, and Vernon were among the counties reporting high populations of squash bugs on vined plants. High counts of larvae were found on cabbage plants at a few locations in southern Wisconsin.
The WPB also advised apple orchard owners to be on the alert for apple maggots, codling moths, and the white apple leafhopper. It added that those who had stink bug infestations in 2013 should be watching for them this year.