Spotted wing drosophila, soybean aphids highlight weekly Pest Bulletin update report
The first catches of spotted wing drosophila flies this year in Wisconsin and the first economic threshold count of soybean aphids highlighted the weekly Wisconsin Pest Bulletin (WPB) edition for the middle part of July.
Spotted wing drosophila (SWD), which infest a variety of ripening berries and other fruit with white larvae, were first identified in Wisconsin in 2010 and were found in nearly corner of the state in 2012.
The WPB noted that this year's collection of adult specimens was the earliest such observation of the pest in the state.
University of Wisconsin researchers caught a pair of adult SWD in Vernon County on June 24, the WPB reported. Later catches of SWD flies occurred in Crawford County.
The presence of the white larvae in raspberries, blueberries, strawberries, grapes, and other fruits makes them unmarketable and tends to spoil the fruit. As measures of protection, the WPB suggest covering vulnerable fruits with a barrier net, placing sugar and yeast traps, or applying an insecticide according to conventional or organic standards every four to five days.
Michigan State University, which has been tracking the widespread SWD infestation of blueberries in its state, recommends a trap consisting of a solution of apple cider vinegar with a drop of unscented dish detergent inside covered containers with holes punched in the upper half.
During an inspection of 48 soybean fields during the reporting week, a field in Calumet County was found to have a per plant soybean aphid population averaging above the 250, which is the threshold for expecting economic damage, the WPB indicated.
Fields in Fond du Lac and Chippewa counties also had elevated aphid counts.
Despite the average of 50-142 aphids per plant in those instances, the WPB pointed out that the average count in field surveys through the period ending on July 17 was still running below 10 per plant.
It, however, urged consistent monitoring of aphid counts until soybeans reach their reproductive 5.5 stage of growth in August.
Japanese beetles were beginning to leave their mark with 1-10 percent leaf defoliation in more than one-half of the 48 soybean fields surveyed during the reporting week.
The WPB noted that an accumulation of 20 percent defoliation from all pests before pod fill begins could result in yield losses.
Green cloverworm larvae were also being detected in some soybean fields. The WPB reported average catches of four larvae per 100 sweeps in Lafayette, Monroe, and Vernon counties.
Corn Pest Reprieve
Among corn pests, the pressure has been relatively low. For instance, only a total of 26 Western bean cutworm moths were caught in pheromone traps at 12 of the 103 monitoring site compared to 2,574 moths by the same time in 2012.
With the rapid growth of corn during the past three weeks, most fields have passed the V7 growth stage at which the stalk borer is a concern.
The WPB noted that larvae damage was detected on less than 15 percent of the corn plants in most cases with only a few fields showing whorl damage on 20-30 percent of the plants.
The WPB pointed out that moths from the relatively low population of first generation European corn borer pupae began to emerge during the past week in southern Wisconsin.
It cited more concern with the corn earworm, as indicated by the 6-18 percent infestation in some Dane and Green County fields.
Although no active infestations of true armyworms were listed during the reporting week, the WPB nonetheless suggested maintaining a watch in the wake of the very hot third week of July.
As a result, it said that second generation larvae would develop very rapidly.
Heat Hatches Hoppers
Corresponding with the heat, potato leafhopper populations were increasing in nine surveyed counties in the western and southern parts of the state but the average catches remained at less than two per net sweep.
Pea aphid populations were jumping with 5-10 being caught per net sweep in Rock and Dane counties. Plant bug totals were staying well below the economic loss threshold level.
Numerous reports were received about squash vine borer, squash bugs, and the bacterial wilt that is caused by striped and spotted cucumber beetles.
Unlike in 16 other states, no downy mildew on cucurbits had been reported in Wisconsin so far this season.
Another piece of good news for the reporting week was that no new identifications of late blight were made in either potatoes or tomatoes around the state.
In apple orchards, apple maggot flies were caught at 8 of 30 monitoring sites, the WPB reported.
It noted that leafminer flights were peaking, larvae of the leafroller were emerging, and codling moths had also advanced to the larvae stage.