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Mid-June heat accelerated crop emergence and growth across Wisconsin. Afternoon temperatures were the hottest of the year so far, with highs on June 18-19 exceeding 90°F in the southern areas and lows in the 60s to mid-70s providing little overnight relief. Milwaukee set a new daily record high minimum temperature of 78°F on June 18, breaking the previous record of 74°F set in 1995. In addition to the heat and humidity, scattered showers and storms occurred each day and were particularly heavy (over 2.0 inches) in the northwest region. A few locations, including Bayfield, received more than 3.5 inches over the seven-day period ending June 20, though most areas recorded 0.25-1.50 inches.
The rain eased heat stress on emerging crops and maintained abundant topsoil moisture supplies, which currently average 60% adequate and 40% surplus statewide (USDA NASS Crop Report). Pest survey activities for the week included scouting alfalfa and wheat fields, setting pheromone traps for western bean cutworm, placing apple maggot red ball traps in apple orchards, and beginning early detection efforts for the invasive box tree moth. Spongy moth mating disruption treatments are underway in the western counties.
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The annual flight of western bean cutworm (WBCW) moths has started in Wisconsin. The season’s first pheromone trap captures were registered near Darlington, Janesville, Sheboygan, and Waupun June 13-19. Last season, the flight began about a week later, from June 23-29.
Based on the UNL-UMN cumulative flight model for this insect, 25% emergence of the moth population should occur July 1-15 across the southern two-thirds of the state (areas south of Highway 29). Scouting corn plants for egg masses and small larvae is recommended once fields enter the late-whorl and pre-tassel stages. The eggs are laid on the upper surface of the top 3-4 leaves, often on the flag leaf, and the larvae can be found in developing tassels. In fields where egg masses and small larvae are found on 5% or more of the corn plants, an insecticide applied when 90-95% have tasseled is most effective.
Moth counts will be available through mid-August on the DATCP Western Bean Cutworm monitoring network page. In addition, WBCW degree day accumulations are provided in the modified base 38°F column in our degree-day table. The lower threshold for WBCW is 38°F while the upper threshold is 75°F. Once 2,577 degree-days are reached, 25% of the WBCW flight has occurred and scouting should begin. |
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Heavy June rainfall has provided favorable soil moisture conditions for emergence of apple maggot flies. Growing degree-day (gdd) accumulations (modified base 50°F) as of June 19 have exceeded the threshold required for fly emergence (900 gdds) near Beloit, Madison, Racine, and throughout much of the southern half of the state. The first apple maggot fly captures on orchard traps are anticipated over the weekend of June 22-23.
At this time, DATCP apple pest monitoring network cooperators should set out sticky red sphere traps in trees along the orchard perimeter (especially next to wooded edges) since the source of apple maggot flies is often nearby wild hosts. A perimeter trapping density of 6-12 unbaited red spheres per acre is suggested. The density can be reduced to one trap every 20 trees along the perimeter when the traps are baited. Orchards with a history of apple maggot problems should also place a few traps in the orchard interior in blocks with the earliest maturing apple varieties. The red visual traps mimic a ripened apple and attract mated female flies ready to lay eggs. The number of flies caught on a trap per week can help with management decisions and will provide an overall indication of apple maggot pressure this season.
In conventional programs, the initial treatments begin immediately after the first apple maggot fly is captured on a red sphere, with later sprays following at 10- to 14-day intervals as long as above-threshold numbers of flies are appearing on traps. The economic threshold for apple maggot control is one fly per unbaited trap per week or five flies per baited trap per week. Baits commonly used with apple maggot traps are ammonium acetate, ammonium carbonate (food odor), and butyl hexanoate (fruit odor). The traps supplied by DATCP do not include bait.
Home fruit growers can also use the red sphere traps to reduce apple maggot pressure in backyard apple trees or in very small orchards. The UW Extension recommends a trap density of one trap per small tree, two to four traps per medium-sized tree, and six to eight traps for a large apple tree for apple maggot control. Additional guidelines are to position the traps at eye-level in the tree canopy where they are not obstructed by foliage and to clean and reapply the sticky coating weekly, or as needed. Disposable and reusable versions of the red traps are available online through Great Lakes IPM and Gemplers. |
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True armyworm larvae are active but not abundant in corn and wheat fields. Surveys of wheat in the east-central region this week found very low counts of 1-6 larvae per 100 sweeps in about 25% of the 50 sites sampled, with the highest counts recorded in Fond du Lac and Kewaunee counties. The levels noted were well below the economic threshold of three larvae per square foot for small grains.
Armyworm larvae are also feeding in the perimeter rows of corn, although no significant infestations were observed as of June 19. As a reminder, counts must reach two or more armyworms (0.75 to 1.0 inch or smaller) per corn plant on 25% of the plants, or one worm per corn plant on 75% of the plants to qualify for treatment. Continued scouting is recommended since this month’s prevailing wet, weedy conditions are suitable for localized armyworm issues. |
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