|
|
Mostly dry weather in Wisconsin during the week ending May 16 allowed crop planting to proceed at a faster-than-normal pace. Conditions were warm and overall suitable for seasonal fieldwork, though skies were overcast and parts of the state were under an air quality alert as smoke from wildfires burning across Canada drifted south over the weekend. Statewide planting progress continued to advance ahead of last season’s rate and the five-year average, with 40% of the state’s intended corn acreage and 37% of soybeans planted by May 13. On the same date last year, corn and soybeans were 28% and 20% planted, respectively. The week’s field activities included monitoring insect survey traps, sweeping alfalfa fields, and assisting with spongy moth aerial spray work.
__________________________________
|
|
|
DATCP’s 2024 early-season moth monitoring networks are the largest in Pest Survey Program history thanks to many volunteer cooperators throughout the state. The 76 black cutworm traps and 39 true armyworm traps distributed across 29 counties are providing moth capture data that will help crop advisors and growers optimize the timing of field scouting for larvae and damage this spring.
The DATCP black cutworm monitoring network has to date captured a cumulative total of 1,523 moths in 76 traps, or an average of 20 moths per trap. For context, this preliminary average count is well below both the 10-year average of 36 moths per trap and the 72-per-trap average recorded in 2017, the last time serious black cutworm infestations were documented in the state. It is also far less than the 2023 count of 2,307 moths in 50 traps, or 46 moths per trap. In short, black cutworm counts have generally been lower this season in comparison to last year’s levels and the long-term average.
Nevertheless, it is important to recognize that the exact number of moths captured regionally or in individual pheromone traps does not directly predict potential for black cutworm damage in local fields, but instead points to the most effective scouting window. Based on intense moth captures in the state on April 10, 14 and 27, it is estimated that larvae produced by moths arriving since mid-April are now reaching the destructive fourth-instar cutting stage of development in advanced areas of the state. The primary seedling corn damage window for black cutworm is expected to open by May 19 in far southern Wisconsin, May 25 near La Crosse, and May 30 near Hancock.
Crop consultants and growers are advised to begin inspecting corn (including Bt hybrids) for leaf pinholes and other signs of cutworm feeding during early season stand assessments. Scouting a few days before estimated cutting dates is recommended. Recall that Bt hybrids and corn treated with seed-applied insecticides are at reduced risk of cutworm damage, but the larvae are still capable of cutting young plants. The economic threshold for black cutworm is reached if 3% of plants have been cut and larvae are still present in the field.
As mentioned in the previous issue of Field Notes, severe black cutworm infestations are infrequent in Wisconsin, and trap counts are not a reliable predictor of outbreaks. Scouting emerging corn should be prioritized in the next three weeks. Crop advisors and producers who observe black cutworm larvae or damage are asked to please report observations to DATCP Entomologist, Krista Hamilton, at Krista.Hamilton@wisconsin.gov.
|
|
 __________________________________
|
|
Alfalfa growth has been rapid this spring and harvesting of first-crop hay is beginning ahead of schedule. As anticipated, alfalfa weevil larvae and their distinctive tip feeding injury are appearing in fields. This early-season alfalfa pest characteristically hatches in May, develops through four larval stages (or instars), and completes the damaging larval phase of its life cycle by early June. The weevil feeding season in Wisconsin is brief and only extends for about four to five weeks depending on spring temperatures.
As shown in the sine base 48°F column in the DATCP degree-day table, alfalfa weevil growing degree-days (gdds) throughout the state range widely from 141 at Bayfield to 494 at Beloit. Accumulations across much of southern Wisconsin are adequate for larvae to have reached the intermediate second and third instars. Alfalfa tip feeding damage is becoming visible in southern fields and will be more pronounced next week as a greater proportion of the larva reach the later third and fourth instars. In contrast, egg hatch has just started in central Wisconsin and larvae are still mostly in the first instar. Defoliation is not yet noticeable but will start to become visible next week.
Peak alfalfa weevil populations and tip feeding damage customarily occur in Wisconsin between 600 and 800 gdds. For the 2024 season, the last two weeks of May and into the first week of June (May 19-June 2) will be the most opportune window for alfalfa weevil scouting and decision-making. A defoliation level of 40% of stems with weevil feeding in the first crop signals the larval population is high and an early harvest would be beneficial. Sweep net sampling for alfalfa weevil larvae should be underway in areas of the state where gdd accumulations are approaching or have exceeded 300 gdds. As of May 16, this includes all alfalfa acreage south of Highway 10. |
|
 __________________________________
|
|
Spring codling moth emergence began on May 5 in southeastern Wisconsin orchards. To date, four of 29 cooperator sites have recorded significant counts of 6-16 moths per trap and the first codling moth biofix. Apple growers in the DATCP Apple Pest Monitoring Network who have not yet trapped any codling moths are advised to continue checking their traps daily until the “biofix” is established. Consistent mild evening temperatures this spring should lead to a fairly predictable emergence in most locations. The biofix is either the date of the first sustained flight of moths captured multiple days in a row or 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.
In addition to codling moth emergence, another key spring 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.
Perimeter sprays can be used as an alternative to full cover sprays if plum curculio injury is restricted to the border rows. However, if egg laying scars are found beyond the first 4-5 rows of trees, a cover spray is the better approach. Organic growers have the option of applying Surround® (kaolin clay). Another strategy is to leave untreated trap rows of early varieties that are later sprayed with an insecticide such as PyGanic at night when the weevils are active.
To protect bees and other pollinators during the bloom window, delaying treatments until 100% of petals are off of trees is recommended before applying perimeter or cover sprays. Applications made between the hours of 7:00 pm and 7:00 am will avoid peak bee activity. Spraying when temperatures are below 50°F or on overcast days will also reduce risk since honey bees do not fly during low sunlight conditions. |
|
 __________________________________
|
|
|
|
