Weekly Pest Report highlights new insects, pressure changes
The hot and dry weather that persists in major regions of Wisconsin is proving to be favorable for several insects, which are seldom found or rarely cause problems in the state's crops while the populations of others are being suppressed by the weather.
For instance, the third weekly Wisconsin Pest Bulletin (WPB) for July published by the Department of Agriculture, Trade, and Consumer Protection reported that the false chinch bug has been found in some south central counties, mainly Columbia.
The pest prefers mustard and beet family plants but will migrate to no-till soybeans and corn. It had not been noticed in the state since the droughty period in 1988 and 1989.
The two-spotted spider mite, which thrives under current weather conditions, has created significant damage in some southwestern and southern Wisconsin soybean and corn fields, the WPB reported.
Severe infestations were noted during the third week of July at field edges in Richland, Sauk, and Juneau counties.
Fond du Lac, Manitowoc, Rock, Washington, Vernon, Grant, and Lafayette counties were also mentioned in the WPB update as having infestations of the spider mite.
It noted that the insect will feed on cucumbers, squash, and other vegetables and suggested a treatment with insecticidal soap (five tablespoons to one gallon of water) with particular attention to applying the solution to the bottom of leaves.
In some southern Wisconsin apple orchards, a dogwood borer population has arrived, the WPB reported. It noted that the pest is a threat at the graft union points on apple rootstock and warned that this threat could continue for another five weeks.
Potato leafhopper populations exceeding the economic damage threshold were counted in 35 percent of the alfalfa fields surveyed in southern and central counties. Counts were highest in Green Lake and Marquette counties with catches in the overall survey running at averages of two to five leafhoppers per net sweep.
Grasshopper populations continued to build in most areas, threatening a wide variety of crops, the WPB indicated. Catches averaged 17 per net sweep near Mauston in Juneau County.
On the flip side, Japanese beetle emergence has been both low and late in areas where that insect caused lots of damage in recent years, the WPB observed. It suggested that the drought was responsible for reducing the threat from the Japanese beetle this year.
The heat is definitely limiting the population of the soybean aphid this year and few if any growers need to be concerned about a foliar insecticide treatment, the WPB stated. It described the aphid population as "remarkably low for this time of year."
A similar pattern exists with some orchard pests, the WPB noted. Red-banded leafminer populations are low because of the drought and apple maggots pose a potential threat mainly where there has been irrigation.
European red mites, seldom mentioned in the WPB section on fruit trees, have established a presence at some sites. Their effect is a bronze color on the leaves and a treatment is recommended if the population reaches 7.5 per leaf.
Among the more common crop pests, corn rootworm beetles are appearing in large numbers this summer. Populations of 13 to 15 beetles per corn plant were observed in some fields in Dodge, Washington, and Green counties.
Of the corn fields surveyed during the reporting field that ended on July 18, populations topping the economic loss threshold of .75 beetle per plant were found in 63 percent of the fields.
Insecticide treatment was advised in corn not yet completely pollinated if populations are five or more plant and corn silks are being cut to less than one-half inch.
Corn earworm moths were caught in five of the 10 traps during the July 12-18 period with catches totaling 22-83 at Ripon, Hancock, and Janesville.
The WPB advised sweet corn growers to consider such counts as an early warning for earworm problems in fields that were still in the silking stage.
With the moth flight of the Western bean cutworm nearly over for the year in most areas, corn growers can expect larvae to emerge in the next two weeks, the WPB indicated.
Catches for the reporting week were led by 135 at Sparta and 96 at Wautoma but the week's total of 518 in 124 pheromone traps was down by 60 percent from the previous week and put the year's pheromone and black light trap catch totals at 2,574 moths.
European corn borer egg deposition increased during mid-July as the second generation moth flight passed its peak in at least the southern half of the state. Snap beans and potatoes are also vulnerable crops, given the rise in moth catches as indicated by the 168 during the week at the Chippewa Falls trap compared to 18 the previous week, the WPB observed.
Among other crops, the WPB reminded potato growers to use a different insecticide mode of action if applying a second treatment for the Colorado potato beetle.
Onion growers were advised to dispose of culls when harvesting in the wake of the third and last flight of the onion maggot fly for the season.