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Last week’s heatwave ended as powerful thunderstorms swept across the state. The storms on Friday, July 28, produced torrential rain, large hail, power outages, and widespread wind damage. Many areas recorded at least an inch of rain, with some southeastern locations receiving up to two inches or more. Unusually large hail ranging up to four inches in diameter was reported near Galesville, Holmen, and West Salem in western Wisconsin.
Dry conditions returned after the storms, while temperatures dropped to a more comfortable range in the 70s and lower 80s. The dry weather allowed hay baling and other fieldwork to resume, along with storm damage assessment and clean-up. DATCP Pest Survey activities this week included conducting seed field inspections, assessing soybeans for insect pests, and beginning the annual corn rootworm beetle survey, which will continue throughout the month of August.
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Western bean cutworm moth counts have peaked across most southern and central Wisconsin trap locations and will begin to decrease in the week ahead. In contrast, the annual flight is still increasing and should peak next week in the northern counties as degree day accumulations reach 2,704 (modified base 38°F), the point at which 50% emergence is expected.
DATCP’s western bean cutworm monitoring network traps captured a total of 2,674 moths July 28-August 3, compared to 3,431 the week before. Preliminary results of the 19th annual trapping survey show that the 2023 state count is 7,756 moths in 42 traps, or an average of 185 per trap. This season’s average moth catch has already surpassed last year’s all-time survey record of 133 moths per trap, or 4,804 in 36 traps, with two more weeks of monitoring remaining. The extremely high counts documented in the south-central and central Wisconsin zones of heaviest western bean cutworm pressure (i.e., Columbia, Dodge, Green Lake, and Marquette counties) signal that larval infestations are probable.
Although the primary scouting window for egg masses has closed across the south, there is still time to assess northern Wisconsin corn fields. Scouting entails checking 20 consecutive plants in five separate areas of the field for egg masses laid on the upper surface of the top leaves. The treatment threshold has been met if egg masses or small larvae are found on 5% or more of the plants. |
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Field surveys across southern Wisconsin indicate that the most advanced soybeans are at the R5 beginning seed growth stage and soybean aphid densities have been very low in the fields sampled. Of the 103 sites surveyed as of August 3, only three fields had a total count exceeding 100 aphids per 40 plants (three aphids per plant average). The highest count recorded was just 197 aphids per 40 plants, or an average of five aphids per plant. Aphids have generally been found on less than half of the plants in the fields checked. In addition, natural enemies were abundant at most sites, suggesting that the economic threshold of 250 aphids per plant on 80% of the plants may not be reached in the majority of Wisconsin soybean fields this season.
Routine scouting is most critical in the next two weeks. Fields most at risk of developing heavy soybean aphid infestations at this time of year are later maturing soybeans, which attract migrating winged aphids as they leave more advanced or drought-stressed fields. Soybeans should be evaluated not only for aphids, but also for two-spotted spider mites and defoliation caused by Japanese beetles, green cloverworm, and assorted caterpillars. |
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DATCP is cautioning landscapers, homeowners, and nursery industry personnel to become familiar with the symptoms of boxwood blight, a disease that poses a serious threat to the nursery trade and to boxwood landscape plantings. Caused by the fungus Calonectria pseudonaviculata, boxwood blight was recently detected at a nursery in Walworth County. This aggressive disease of ornamental boxwood shrubs leads to leaf loss, branch dieback, and shrub death. Pachysandra can also be affected by this pathogen.
Since the state’s first detection of the disease in 2018, boxwood blight has been confirmed at nurseries in Kenosha County, retailers in Dane and Portage counties, and on landscape boxwoods in Dane, Door, and Milwaukee counties. Boxwood blight remains an emerging threat that residents, retailers, and the green industry should be alert for. When purchasing new boxwoods, it is important to closely inspect the plants for blight symptoms and isolate new plants from existing boxwood and pachysandra plantings for at least one month. The most noticeable symptoms include brown leaf spots with black necrotic edges (see photo above). Black streaks on stems and branch dieback are also symptoms. During humid weather, white fungal structures may be visible on leaf undersides and on stems. A complete list of recommendations is available on DATCP’s Boxwood Blight page. |
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