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Mild, unsettled weather prevailed in Wisconsin since the last report. Severe thunderstorms with heavy rain impacted portions of the state on Tuesday, May 7, producing wind damage, hail, and tornadoes in Walworth County. The highest rainfall amounts (1.5 inches or more) fell across southeastern Wisconsin during Tuesday’s storms, while precipitation totals for the week were mostly between 1.0 inch and 2.5 inches. Daytime high temperatures varied widely from the mid-40s in northwestern Wisconsin to around 80°F in the southern and central areas, including Janesville, La Crosse, and Portage.
Weather conditions this spring have generally supported early fieldwork and planting, which continues at a pace ahead of average for most crops. Oat planting advanced to 54% complete at the start of the week, nine days ahead of last year and four days ahead of the five-year average. Currently, 25% of the state’s oat acreage has emerged. In apple orchards, the spring appearance of economically important pests such as the codling moth and plum curculio weevil is also beginning earlier than usual.
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The spring black cutworm migration slowed May 2-9. DATCP’s network of 76 traps collected a total of 376 moths, a decrease from the previous week’s catch of 479 moths. Intense captures of nine or more moths in two nights were recorded at 15 sites. The week’s highest count of 37 moths per trap was registered near Waupun in Dodge County.
Egg laying by spring-arriving moths has been underway for three to four weeks and larvae are currently in the early instar stages. Signs of cutworm feeding, such as small pinholes in corn leaves, should become noticeable in emerging corn fields next week. Based on 10-day forecast predictions, and using April 10 as the earliest biofix (the date of the first intense moth captures), the projected starting date for the primary black cutworm damage season is May 19 in advanced areas of southern Wisconsin.
In the central and northern regions of the state, the first major flights were documented on April 14 and April 27. Corn growers in these areas can anticipate the opening of the peak damage window on May 25 near La Crosse and May 30 near Hancock.
Severe black cutworm infestations are relatively infrequent in Wisconsin, and several factors must converge to produce outbreaks. Besides weather systems that bring heavy moth migrations into the state, conditions favorable for egg laying and survival of larvae are also required. In most years, spring cutworm problems do not materialize.
DATCP pheromone traps have captured a cumulative total of 1,192 moths in 76 traps (average of 16 per trap) since traps were set on March 31. Last season at this time, the count was much higher at 1,760 moths in 50 traps (average of 35 per trap). Scouting for early black cutworm injury can be combined with stand evaluations and is recommended for corn from emergence through the five-leaf (V5) stage.
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Spring temperatures determine when adult codling moths begin emerging in Wisconsin apple orchards, and moth flights are off to an early start this season. The orchard near Rochester in Racine County reported its first codling moth trap catch on May 5 and a few additional moths three days later. The Rochester first capture date is 11 days earlier than in 2023. In addition, the orchard near Burlington in Kenosha County also reported catches of one moth per trap on three separate traps this week.
Southeastern Wisconsin orchards along Lake Michigan customarily report the first codling moths of the season, and these early observations provide advanced warning to other growers in the DATCP Apple Pest Monitoring Network to either deploy mating disruption dispensers or to begin checking their codling moth traps daily until the “biofix” is established. The biofix is either (1) the date of the first sustained flight of moths captured multiple days in a row, or (2) when counts exceed the threshold of five moths per trap per week. This date marks the point at which to begin counting degree days (base 50°F) to determine the optimal treatment window for first-generation larvae. Mild temperatures over the next two weeks could prompt a consistent emergence and most growers are likely to see a definitive biofix this year. Apple network participants may direct questions about timing the codling moth biofix to DATCP Entomologist Krista Hamilton at Krista.Hamilton@wisconsin.gov.
In addition to codling moth emergence, another spring pest event now underway is the migration of plum curculio into orchard edges. The stings and egg-laying scars made by the female weevils will become detectable on developing fruitlets within the next two weeks. Cultivars with early-sizing fruits 5 mm or larger (e.g., Ida red, Liberty, Paula red, Zestar) are preferred for egg laying.
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