Update 2 – May 28, 2023

In this issue:

  • Potato production progress updates
  • Asparagus beetles, Colorado potato beetles, and seedcorn maggot updates
  • Potato and vegetable disease model updates
  • WI DATCP Special Local Need Registrations (24c) and Emergency Exemptions (Section 18) authorized for use in WI 4/20/23


Yi Wang, Assistant Professor & Extension Potato and Vegetable Production Specialist, UW-Madison, Dept. of Horticulture, 608-265-4781, Email: wang52@wisc.edu.

The weather has been good enough to encourage smooth tuber sprouting and emergence (Figure below). Farms in Central Sands have completed hilling or are close to being done.

In our HARS research plots, we have observed 100% emergence on some early-season red and yellow varieties. The full-season russets are either cracking or very close to cracking. With the weather forecast, I would expect to see 100% emergence on all our varieties sometime this coming week.

As you may see from the weather figure above, we have been having a dry spell over the last couple of weeks. Based on the U.S. drought monitor website (https://droughtmonitor.unl.edu/ConditionsOutlooks/Outlooks.aspx), Wisconsin shouldn’t have soil moisture anomaly in the upcoming month (Figure below), as long as we manage irrigation scheduling well. As most plants are at the stage between emergence and tuber initiation, which is the log phase of vine growth, roots are in the second half of their growth, and the vines grow very rapidly, as much as doubling the canopy every week. Starts at 1’’ every week, and gradually increase every week by about 0.5’’. Soil moisture should be maintained at 75% to 85% field capacity, and less than 65%FC would be considered a deficit. Soil moisture deficiency during this stage would inhibit canopy and root growth, and indirectly encourage weed growth due to small ground cover. However, excessive soil moisture would retard root branching by water-logging root hairs, and promote nitrogen leaching (N applied at hilling). In summary, with the increase in foliage and thereby crop ET, as well as the ongoing drought, irrigation should be applied regularly and gradually increase as the canopy develops.


Vegetable Insect Update – Russell L. Groves, Professor and Department Chairperson, UW-Madison, Department of Entomology, 608-262-3229 (office), (608) 698-2434 (cell), e-mail: rgroves@wisc.edu. Vegetable Entomology Webpage: https://vegento.russell.wisc.edu/

Common asparagus beetle adult (Crioceris asparagi) Photo: Mark Rowland

Asparagus beetle – (https://vegento.russell.wisc.edu/pests/asparagus-beetle/). The common and spotted asparagus beetles have been infesting asparagus in southern Wisconsin for the past 3 weeks, and emergence is now underway in much of northern Wisconsin. The common asparagus beetle is the most prevalent and the only one that causes economic damage to asparagus due to its relative earliness in colonizing the crop. Adults of the common asparagus beetle feed on the plant’s spears and ferns. Disfigured and unmarketable spears can result when the beetles feed or lay eggs on the spears. Spotted asparagus beetle larvae feed more on the berries rather than the ferns of asparagus and are most often present later in the spring and early summer. Large populations of asparagus beetles, if left unchecked, can defoliate the plants.

If you are seeing early damage from common asparagus beetle, sample twenty plants each at five different locations, and consult the infestation thresholds below following scouting. Spring sampling thresholds are designed to reduce spear damage, and scouting should occur in the afternoon when the beetles are most active.

Peak activity for common asparagus beetle in Wisconsin has already been surpassed . First generation peak (and subsequent risk) is illustrated across central and northern Wisconsin, and the risk of infestation is illustrated by the warm colors (reds, oranges, yellows) on the map. (Source: https://agweather.cals.wisc.edu/vdifn).

Asparagus beetle risk model, May 27, 2023


Colorado potato beetle (CPB) – (https://vegento.russell.wisc.edu/pests/colorado-potato-beetle/). Check for CPB adults now after potato plants have emerged and during hilling operations. Emerging adults are colonizing fields now in southern and central Wisconsin. Appearance of the very first egg masses is predicted for southern and central Wisconsin. Producers in these areas may be thinking about initial perimeter spray applications of the insect growth regulator, novaluron (Rimon® 0.83EC), together with a tank mix of (Avaunt® eVo 30DG). Treatments in select fields could be initiated in the next 7-10 days, especially with predicted warm temperatures into the 1st week of June.

Peak emergence activity for 1st generation of Colorado potato beetle in the upper Midwest. First generation emergence (and subsequent risk) is illustrated across central and southern Wisconsin. (Source: https://agweather.cals.wisc.edu/vdifn).

Colorado potato beetle risk model, May 27, 2023


Seedcorn maggot– (https://vegento.russell.wisc.edu/pests/seedcorn-maggot/). The population of seedcorn maggot are between generations in central Wisconsin. The larvae damage the germinating seeds and young seedlings of a wide range of vegetable and agronomic crops. In addition to corn, seedcorn maggots (SCM) have a large host range including numerous common vegetable crops. SCM can cause economic damage to the seed of artichoke, beet, Brussels sprouts, cabbage, cantaloupe, carrot, cauliflower, cucumber, kale, lettuce, bean (lima, snap, red), onion, pea, pumpkin, tomato, and turnip. Management for SCM is only effective when used in a preventative manner. Once direct larval damage is detected there is no control option for the pest. Therefore, there are no economic thresholds for this insect pest. SCM forecasting models predict peak flight windows and are very useful for growers. Documenting peak flights can help to forecast subsequent generations of SCM. Following are a few strategies to hasten germination and lessen direct damage:

  • Delay planting until soil temperatures are at least 50°F before planting most susceptible crops. Peas and radish may be planted when soil temperatures are above 40°F.
  • After peak adult activity has passed, do not plant until 450 FDD has accumulated and passed (see risk colors below that follow peak adult emergence).
  • Plant seeds as shallowly as agronomically possible to speed germination.
  • Soak untreated pea and bean seeds in water for 2 hours before planting to soften the seed coat.
Seedcorn maggot risk model, May 27, 2023

Peak flight activity for 1st and 2nd generation of seedcorn maggot in the upper Midwest. First generation peak (and subsequent risk) is illustrated across very northern Wisconsin and surrounding Lake Superior, and the risk of infestation is illustrated by the warm colors (reds, oranges, yellows) on the map.  Second generation peaks are currently across central Illinois and this risk interval will be moving northward in the next 7 days with increasing daytime and night-time temperatures. (Source: https://agweather.cals.wisc.edu/vdifn).


Amanda Gevens, Chair, Professor & Extension Vegetable Pathologist, UW-Madison, Dept. of Plant Pathology, 608-575-3029, Email:  gevens@wisc.edu, Lab Website: https://vegpath.plantpath.wisc.edu/

Current P-Day (Early Blight) and Disease Severity Value (Late Blight) Accumulations. Many thanks to Ben Bradford, UW-Madison Entomology; Stephen Jordan, UW-Madison Plant Pathology; and our grower collaborator weather station hosts for supporting this disease management effort again in 2023. A Potato Physiological Day or P-Day value of ≥300 indicates the threshold for early blight risk and triggers preventative fungicide application. A Disease Severity Value or DSV of ≥18 indicates the threshold for late blight risk and triggers preventative fungicide application.  Red text in table indicates threshold has been met or surpassed. TBD indicates that data are To Be Determined as time progresses. Weather data used in these calculations will come from weather stations that are placed in potato fields in each of the four locations, as available. Data from an alternative modeling source: https://agweather.cals.wisc.edu/vdifn will be used to supplement as needed for missing data points. We currently have our Grand Marsh, Hancock, Plover, and Antigo weather stations up and running. Data will soon be available in graphical and raw formats for each weather station at:  https://vegpath.plantpath.wisc.edu/dsv/.



Planting Date 50% Emergence Date Disease Severity Values (DSVs)
through 5/27/2023
Potato Physiological Days (P-Days)
through 5/27/2023
Grand Marsh Early Apr 5 May 10 0 98
Mid Apr 20 May 15 0 65
Late May 12 May 25 0 13
Hancock Early Apr 10 May 17 0 55
Mid Apr 22 May 19 0 50
Late May 14 TBD TBD TBD
Plover Early Apr 14 May 19 0 49
Mid Apr 24 May 20 0 44
Late May 19 TBD TBD TBD
Antigo Early May 1 TBD TBD TBD
Mid May 15 TBD TBD TBD

In addition to the potato field weather stations, we have the UW Vegetable Disease and Insect Forecasting Network tool to explore P-Days and DSVs across the state (https://agweather.cals.wisc.edu/vdifn).  This tool utilizes NOAA weather data (stations are not situated within potato fields). In using this tool, be sure to enter your model selections and parameters, then hit the blue submit button at the bottom of the parameter boxes. Once thresholds are met for risk of early blight and/or late blight, fungicides are recommended for optimum disease control. Fungicide details can be found in the 2023 Commercial Vegetable Production in Wisconsin Guide, Extension Document A3422, linked here: https://learningstore.extension.wisc.edu/products/commercial-vegetable-production-in-wisconsin.


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