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Number of crop pests on WPB report increases at end of the growing season

Sept. 5, 2013 | 0 comments

Although the growing season is approaching the final weeks for most field and garden crops, the number of pests mentioned in the Department of Agriculture, Trade, and Consumer Protection's Wisconsin Pest Bulletin (WPB) for late August reached a season high for the weekly report.

According to the year's final round of field surveys for soybean aphids, the August average population was the highest in the past five years, the WPB reported.

Six percent of the soybean fields - all in the western one-third of the state - checked from Aug. 6-28 had average aphid densities of 250-587 per plant but 72 percent of the fields had an average of less than 49.

The WPB predicted that many of the late-planted soybean fields could still reach per plant averages of 250 aphids, which is the number at which an insecticide treatment is advised.

It noted, however, that no yield benefit is realized if the plants are already at the R5.5-R6 growth stage by the time aphid populations mount.

Corn Earworm Moths

An increasing surge in catches of corn earworm moths continues to create concern for infestations in sweet corn, the WPB indicated.

The reporting week catches of moths totaled 613 near Green Lake, 428 at Byron in southern Fond du Lac County, and 227 in northern Dane County.

The WPB observed that the latest moth flights mean that larvae will be feeding on corn well into September.

Its surveys indicated moderate-severe infestations of larvae in 10-31 percent of the corn plants in a few fields surveyed in Buffalo, Chippewa, Clark, Dunn, and Waupaca counties.

Damage from Western bean cutworm larvae was observed on two-six percent of the corn plants in fields in Buffalo, Chippewa, and Clark counties.

The WPB noted, however, that the catch of 655 moths in 117 traps was the lowest in the nine years the pest has been tracked in the state.

Corn Rootworms

With final data still awaited from Wisconsin's north central and northeast agricultural districts, this year's count of corn rootworm beetles is down slightly from 2012 but up somewhat in the northwest counties, the WPB stated.

The central and southern districts had lower counts.

As of Aug. 29, the surveys found that 38 of the 213 corn fields had averages about the .75 beetle per plant that suggests economic loss due to root damage for corn in the following crop year, the WPB indicated.

But the 18 percent of fields above the average of .75 beetle per plant is below the five-year average of 25 percent, it added.

Late maturing corn is vulnerable to fall armyworms, whose larvae look similar to those of the corn earworm, the WPB pointed out. It noted that fall armyworm moths were laying eggs on corn in the southwest and south central counties.

Among forage crop pests, grasshoppers were being caught at the rate of two-three per net sweep in grasses at the edge of alfalfa fields in western counties but were not considered to be a threat to crop loss.

Counts of potato leafhoppers and pea aphids continued to be low in alfalfa.

Fruit Pests

Japanese beetle counts were down in field crops but they were still attacking grapes, apples, and raspberries in several areas, the WPB reported.

Stink bugs were damaging apples and peaches in Trempealeau County.

Orchard growers were reminded that the flights of codling moths were unusually high for late August.

Updates were also given on the late season status of apple maggots, leafrollers, and leafminers in orchards.

The WPB noted that the spotted wing drosophila, whose main target in Wisconsin is raspberries, has been confirmed in 20 counties this year. It advised growers of raspberries and other sweet fruits to repeat insecticide treatments every four-five days to protect their crops.

Vegetable Pests

With the harvest season having arrived for most onions, the WPB reminded growers to be aware of the year's third generation of onion maggots and dispose of culls and bulbs to take away a large portion of the insect's overwintering opportunity.

Crop rotation is another way to cope with the maggot.

The same point applies to the overwintering chances for squash bugs, the WPB continued. It urged growers of vined plants to dispose of foliage, plant debris, and spoiled fruits to make overwintering more difficult for the pest.

Tomato growers were asked to watch for fruit worm infestations. The WPB pointed out that tomatoes become an attraction once egg laying is completed in sweet corn fields.

Late blight was confirmed on tomatoes in Milwaukee County. That raises the state's number of counties with late blight confirmed on potatoes or tomatoes to 10 for this year.

Autumn Pests

In a special section, the WPB addressed the imminent autumn invasion of residences and other buildings by several insects.

That list includes boxelder bugs, multi-colored Asian beetles, western conifer seedbugs, and possibly marmorated stink bugs.

Boxelder bugs could arrive in high numbers this year because the year's dry weather limited the outbreak of fungal diseases, which regulate the population, the WPB observed.

Property owners concerned with invasions should seal cracks or other openings on buildings or have a synthetic pyrethroid applied in September or early October at likely entry points by a licensed operator only, the WPB advised.

It emphasized that those chemical insecticides should never be used inside of a building.

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