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Heat and humidity arrived in the state over the weekend, accompanied by multiple rounds of thunderstorms and heavy rain. Afternoon highs July 13-14 climbed to the upper 80s and lower 90s, with heat index values approaching 100 degrees in southern Wisconsin. As the week progressed, temperatures dropped to a more comfortable range in the 70s and lower 80s.
The severe weekend storms produced drenching rain that led to localized flash flooding and waterlogged fields across the southern and western regions of the state. Rainfall totals of 4.0 inches or more were reported from Arcadia (4.18”), Cashton (4.02”), and Trempealeau (4.26”) in the west-central area July 14, while nearly 3.0 inches of rain fell in Janesville (2.82”) and Madison (2.76”) in south-central Wisconsin on Saturday.
After the latest deluge, condition ratings for the state’s corn and soybeans are expected to show further decline. Currently, the USDA NASS Crop Progress & Condition Report rates 58% of Wisconsin’s corn acres and 56% of soybean acres in good to excellent condition, a four percentage point decrease from the previous week for both crops and the lowest ratings of the season so far.
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Mid-season soybean surveys across southern Wisconsin indicate that advanced fields have reached the R2-R3 (full bloom to beginning pod) growth stages and insect pressure is gradually building. Soybean aphid counts are still overall very low. The typical average is fewer than five aphids per plant (500 aphids per 100 plants), based on observations in 80 soybean fields sampled July 5-18. Aphids are not yet dispersed throughout fields and are generally colonizing less than 20% of the plants fieldwide. As populations increase toward the end of the month, growers and crop advisors are reminded that insecticide treatment should not be considered unless the economic threshold of 250 aphids per plant on 80% of the plants has been exceeded. Aphid counts have not begun to approach this level in any soybean field surveyed by DATCP as of July 18.
Soybean fields are also showing 1-10% of plants with light to moderate leaf injury caused by Japanese beetles, bean leaf beetles, green cloverworms, silver-spotted skipper larvae, and other defoliators. The sampling method for defoliators is to select 10 plants throughout the field, choosing a trifoliate from the upper, middle, and lower canopy on each plant, for a 30-leaf sample. Compare the 30 leaflets with an online defoliation estimating guide to determine the average percent defoliation. Defoliation that meets the 20% threshold between the bloom and pod-fill stages and 30% in the pre-bloom soybean may warrant control. Scouting several areas in the field interior, in addition to field edges where Japanese beetles are most numerous, is required for an accurate assessment.
Routine scouting will be most critical in the next two to three weeks as soybeans advance to the later reproductive growth stages. In addition to aphids and defoliators, soybean fields should also be scouted for soybean gall midge and the newly identified soybean tentiform leafminer, neither of which has been found in Wisconsin to date but occur in neighboring Minnesota. |
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Emergence of western bean cutworm moths increased abruptly with the high temperatures of the past week. DATCP’s monitoring network of 69 traps captured a total of 2,784 moths (40 per trap average) during the week of July 12-18, which is more than four times the 507 moths (9 per trap average) collected the week before. Eleven of the 69 traps registered 100 or more moths and three traps captured over 200 moths. These elevated counts indicate the annual flight may have peaked across much of southern Wisconsin and in areas near La Crosse.
According to the western bean cutworm degree-day model, peak moth activity, or 50% emergence, coincides with the accumulation of 2,704 degree days (modified base 38°F). Moth emergence currently ranges from 50-75% complete across far southern Wisconsin and is approximately 25% complete in the central counties south of Highway 10. Near Wausau and northward, 25% of the population should emerge next week and the flight is expected to peak August 2-8.
The window of peak moth activity now open also marks the primary egg laying period for western bean cutworm. The opportunity to scout for egg masses is quickly passing in the south but will remain an option through the first week of August in central and northern Wisconsin. For these areas, the bulk of this year’s western bean cutworm eggs will be laid in pre-tassel and pollinating corn in the next two weeks. 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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Surveys in wheat fields across the southern and east-central areas of the state in June found a marked increase in foliar disease symptoms, due in part to prevailing wet spring conditions. DATCP specialists sampled 61 fields in Brown, Calumet, Columbia, Dane, Dodge, Door, Fond du Lac, Kewaunee, Manitowoc, Sheboygan and Winnebago counties June 6-21. In each field, a sample consisting of 20 wheat heads and leaves was collected for disease testing at the Plant Industry Bureau Laboratory.
The map below shows the results of disease testing. Fungal diseases were prevalent in the surveyed fields, particularly Fusarium head blight which was found in nearly half of the fields checked (27 fields). These findings align with UW reports indicating the reappearance of Fusarium head blight this season for the first time in three years: Wheat Diseases Resurge in Wisconsin (midwestfarmreport.com). Other diseases detected on the wheat samples included Alternaria head mold (7 fields) and rust (10 fields). |
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All samples tested negative for the wheat blast pathogen Magnaporthe oryzae Triticum pathotype, a national priority pest predicted to spread through wheat-growing regions of the world under climate change conditions. Wheat blast originated in Brazil and is currently found in several countries in South America, as well as in parts of Africa and Asia. Where this disease occurs, infection can be severe with up to 100% yield loss. DATCP targeted wheat blast as part of a USDA APHIS early detection survey cooperative agreement. |
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After three years of destructive caterpillar populations and heavy defoliation, the spongy moth outbreak phase appears to be subsiding in parts of Wisconsin. The decline is due largely to two naturally occurring diseases, nucleopolyhedrosis virus (NPV) and the fungus Entomophaga maimaiga. These biological controls can become particularly effective during wet, rainy seasons and once larval populations are dense enough for the virus to spread rapidly. DATCP and the DNR have received many reports of caterpillar mortality from landowners, residents, and foresters this summer.
Differentiating the cause of caterpillar mortality is relatively easy. Caterpillars that succumb to NPV hang in an upside-down “V” orientation, as shown in the photo above. Entomophaga maimaiga fungal infection causes the larvae to become shriveled, dark, and hang vertically (see photo below). |
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 Spongy moth larva infected with E. maimaiga | Steve Katovich bugwood.org
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Preliminary reports indicate these diseases are causing larval mortality in southern and central Wisconsin, but more specific location and severity information would be useful to assess areas of spongy moth population collapse. Readers who notice dead spongy moth larvae showing symptoms of either of these diseases are asked to report observations to https://arcg.is/ni4eu. Late-instar larvae are still active in northern Wisconsin and diseased caterpillars should still be noticeable, whereas adult moths are now emerging in southern Wisconsin (beginning July 3).
More information on the spongy moth life cycle and control can be found at spongymoth.wi.gov. Questions may be directed to the Wisconsin Spongy Moth Hotline at 800-642-6684 or datcpspongymoth@wisconsin.gov. |
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