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An unsettled weather pattern brought cooler conditions and rain chances each day this week, though the rain was generally too light to alleviate the impacts of the summer drought. A few locations in northern and eastern Wisconsin received more than 0.50 inch over the last seven-day period ending July 13, while most areas recorded less than 0.10 inch. Daily temperatures were seasonable for early July, with afternoon highs mainly in the 70s to mid-80s and overnight lows ranging from the 40s to mid-60s.
The rapid intensification of drought in June is reflected in the weekly crop condition ratings reported by the USDA National Agricultural Statistics Service (NASS). Corn rated as “good to excellent” fell from 72 percent at the start of June to 45 percent as of July 10. Similarly, the condition of soybeans decreased from 69 percent “good to excellent” early last month to 42 percent this week. Severe drought (D2) has expanded across most of southern Wisconsin, and extreme drought (D3) has been introduced for most of Dane County and parts of surrounding counties, where June 2023 was the fifth driest on record. Currently more than half of the state’s corn, hay, oats, and soybean crops are rated as fair, poor, or very poor.
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The annual emergence of Japanese beetles is well underway. Beetles are common at low levels in corn, soybeans, and fruit crops, and the effects of their feeding may be exacerbated by this season’s drought. For corn, the primary concern is silk clipping during the first five days of silk emergence, which can impair pollination and cause reduced seed set—especially if plants are under severe drought stress.
Treatment of corn for Japanese beetle control is generally not needed in Wisconsin, but may be considered for fields showing:
- three or more beetles per ear and
- the majority of silks clipped to ½ inch during the pollination window and
- pollination less than 50% complete
Although Japanese beetle infestations often appear heavy based on pressure observed along the field perimeter, silk feeding rarely extends more than a few rows from the edge, emphasizing the importance of obtaining a representative sample from several areas throughout the field before making control decisions. Spot treatment (only during early silking) is sufficient if the above-threshold numbers of beetles and damage are confined to the field edges.
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Early corn earworm migrants are arriving in Wisconsin, according to reports from DATCP’s corn earworm monitoring network. The pheromone traps located near Beaver Dam, Marshfield, Mayville, and Ripon registered counts of 1-12 moths this week. The total catch is 20 moths in four traps as of July 13.
For fresh market sweet corn, 5-10 adult earworm moths per night for three consecutive nights is the standard treatment threshold (when green silks are present). The treatment threshold for tomatoes is seven moths per pheromone trap per week.
Moth counts for the state’s 16 pheromone trap monitoring sites will be published each Thursday through mid-September on the DATCP Corn Earworm page. |
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The western bean cutworm moth flight period began by June 21 this year and trap counts have been very low thus far (<four moths per trap per week). As of July 13, only 31 moths have been collected in 10 of DATCP’s survey traps.
Based on the UNL-UMN degree-day model for this pest, 25% emergence of the moth population should occur across the southern half of the state over the next two weeks. Oviposition on corn and dry beans is expected to increase as the moth flight gains momentum. In fields where egg masses and small larvae are found on 5% or more of the corn plants, a treatment applied at 90-95% tassel emergence will optimize caterpillar exposure to the insecticide. Routine scouting for egg masses and small larvae should begin in the week ahead and continue through the end of the month. |
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Captures of apple maggot flies on orchard traps have increased despite dry conditions, with reports of flies appearing on traps at four of 24 cooperating locations in Fond du Lac, Iowa, Ozaukee, and Racine counties. The highest count for the week was a total of eight flies on an unbaited red sphere trap, apparently all in the same Lodi apple tree. Maintaining traps will be important as emergence continues and oviposition on apples intensifies in late July and early August.
The current recommendation for apple maggot monitoring is to place an average of three red sphere traps per 10 acres. The threshold is an average of one fly per trap across all three traps if the traps are unbaited. When red spheres are baited with an ammonium enhancer, the threshold increases to an average of five flies per trap.
In addition to apple maggot flies, Japanese beetles are also appearing in higher numbers in Wisconsin apple orchards and vineyards. Damage to fruits, ornamentals and field crops is likely during the second half of the month. Insecticide options for this insect are limited and most chemical treatments offer only short-term repellency when applied before large aggregations of beetles begin to appear. For large populations, spot treating the blocks or perimeter areas with the highest beetle pressure with a “knock-down” or contact insecticide may offer temporary control. Strategies for reducing Japanese beetle damage without use of insecticides are discussed here: https://fruit.wisc.edu/2022/07/28/japanese-beetle-management-without-insecticides/.
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This destructive lawn grub has been confirmed in Marathon County for the first time. Several adult beetles were captured in the Wausau black light trap and identified by UW-Madison Entomologist PJ Liesch on July 10.
The European chafer has been established since 2013 in Door County, where it has caused extensive lawn damage in Sturgeon Bay and surrounding areas. Many yards have been reduced to patches of dead grass due to the combination of root feeding by the chafer larvae and scavenging by birds, skunks, and other animals. This invasive scarab beetle was also documented in the Antigo area of Langlade County in 2019.
Larvae of the European chafer are considered a more serious pest of home lawns than Japanese beetle because they feed later into the fall and earlier in spring, and may even resume activity during warm periods in winter. Property owners or lawn care companies who suspect European chafer damage are encouraged to send a specimen to PJ Liesch at the UW Insect Diagnostic Lab for verification. |
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