Update 7 – June 11, 2022

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

This week, the early emerging potatoes reached tuber initiation and we have seen hooking (Figure 1) on Colomba in our research plots. Overall for commercial growers in the Central Sands, most people have finished their N fertilization at tuber initiation. Canopy closure is about 30 – 40% on average (Figure 2). Looking at the weather forecast for the next 10 days, it will be wet until early next week, followed by warm days for the rest of the week, so we should expect to see rapid tuber bulking and growth.

Figure 1. Bulking tip of Colomba.


Figure 2. About 40% canopy closure observed on a commercial field with Lakeview Russet.

This year we had some emergence issues at Hancock. Varieties like Colomba, Dakota Russet, Dakota Trailblazer, and Reveille Russet showed decayed / un-sprouted seed tubers (Figures below) with symptoms from dry rot and soft rot. One thing to notice was that we cut seeds for those varieties. Although we suberized them under 55°F for about 16 days, we still had issues. Similar problems have been reported by commercial growers. Possible causes include unfavorable weather conditions right after planting (too cold or too hot) or diseases on the seed.

Some updates on our remote sensing research. This past week we flew two commercial potato fields for the first time. We have noted that we could fly at 400’ with a resolution of 1.4’’, and it took us about 45 minutes with 2 batteries to fly an 80-acre field, and we used 3.2 gb of memory.  The big factor that determines the turnaround time is still the image processing. It took us about 24 hours to precisely stitch the raw pictures together, and we are working hard on making the following steps including data extraction, vegetation index (like NDVI) calculation, and field map generation with predicted yield (or other traits) as short as possible.

Some growers who are using UAV-based remote sensing pay less attention to precision stitching of the images, and instead they just use the images to identify possible problematic spots within the field so they can go and check on those plants before any further damage occurs. Other growers who are using sensors mounted on center pivots like the idea of getting high-resolution pictures of their field when the pivot was moving around, and typically they can receive info on AI-identified problems of bugs/diseases/weeds/nutrient deficiency from those pictures with GPS coordinates within a week. In general, remote sensing is really helping growers to make their production more efficient, and hopefully it will help reduce the production inputs like field scouting someday.



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 2022.  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, once available.  Data from an alternative modeling source: https://agweather.cals.wisc.edu/vdifn will be used to supplement as needed for missing data points.  Data are available in graphical and raw formats for each weather station at:  https://vegpath.plantpath.wisc.edu/dsv/.

Location Planting Date 50% Emergence Date Disease Severity Values (DSVs) 6/10/2022 Potato Physiological Days (P-Days) 6/10/2022
Grand Marsh Early Apr 5 May 10 7 222
Mid Apr 20 May 15 7 181
Late May 12 May 25 7 122
Hancock Early Apr 7 May 12 1 200
Mid Apr 22 May 17 1 166
Late May 14 May 26 0 121
Plover Early Apr 7 May 15 3 178
Mid Apr 24 May 20 3 144
Late May 18 May 27 2 107
Antigo Early May 1 Jun 3 1 46
Mid May 15 June 10 0 5

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 2022 Commercial Vegetable Production in Wisconsin Guide, Extension Document A3422, linked here: https://learningstore.extension.wisc.edu/products/commercial-vegetable-production-in-wisconsin


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

Colorado potato beetle (CPB) – (https://vegento.russell.wisc.edu/pests/colorado-potato-beetle/). Overwintered adults continue to be active in nearly all fields within Wisconsin. In southern Wisconsin, we are very likely near 50% egg hatch and 50% early larvae (Fig. 1). In central Wisconsin, we are around 10-20% egg hatch and adults will continue to mate and lay eggs over the next 10-14 days. In northern Wisconsin, adults continue to emerge and colonize fields with only a few egg masses being laid toward the end of this last week. Forecast high temperatures in the coming week will change this trajectory, and will hasten the development of populations very rapidly.

Figure 1. Vegetable Disease and Insect Forecasting Network (VDIFN) map of Colorado potato beetle population development, https://agweather.cals.wisc.edu/vdifn (sourced 06/11/2022). Notice we are at the peak of early larvae risk with accumulated Fahrenheit Degree Days, using a base temperature of 52F (FDD52). Users are able to select any cell in the VDIFN map(s) and obtain locally relevant DD for their farms. Areas within the ‘red shaded’ and high risk zone are either at, or very near to the 400 FDD52 which signifies the predicted temperatures required for early larval presence and associated egg hatch.

Now is the time to begin looking for small larvae (1st and 2nd instars) on the crop, and now is the time to implement control using reduced-risk (RR) insecticides (click here for a list of reduced-risk insecticide options for CPB in Wisconsin). Do not utilize older, defoliation-based thresholds (5-10% defoliation) for the purposes of making control decisions. By the time potatoes reach 5-7% defoliation (in about 7-10 days), populations will have progressed through early larval stages and will be nearing the 3rd and 4th instar stages. This will be too late to effectively manage the populations with RR options including novaluron (Rimon), abamectin (Agri-Mek) and spinosad (Blackhawk) or spinetoram (Delegate). This timing is especially true for organic producers who need to focus the use of materials like Entrust SC (spinosad), Trident (Bacillus thuringiensis subsp. tenebrionis) or Venerate (heat-hiller Burholderia spp.) on these early larval populations. Don’t wait! Remember also that the first application should be followed up in 5-7 days with a second application of the same compound depending on the formulation and label restrictions. With warmer day and nightime high temperatures forecast for the coming week, it will be critical to initiate first larval sprays soon in central and southern Wisconsin. Careful scouting will reveal the exact timing!


Seedcorn maggot ‘Round #2’ across Wisconsin and upper Midwest – (https://vegento.russell.wisc.edu/pests/seedcorn-maggot/). The second generation of the seedcorn maggot has entered southern Wisconsin and is progressing northward. Recall that seedcorn maggots (SCM) have a large host range including numerous common vegetable crops. In high numbers and when peak SCM are predicted (again in southern Wisconsin, Fig 2.), egg laying and larval development can decimate entire crop stands if left untreated. Larvae will feed in the cotyledons and below-ground hypocotyl (stem) tissue of seedling plants, resulting in a variety of damage symptoms. Feeding damage in germinating seeds will often kill seedlings before they emerge. Poor germination or poor stands of susceptible crops may indicate a SCM problem. Since adult SCM is attracted to decaying organic matter, do not plant susceptible crops in fields where animal or green manure has recently been incorporated. The faster planted seeds germinate and grow, the less opportunity the maggots have to damage the crop.

Figure 2. Peak flight activity for 2nd generation of seedcorn maggot in the upper Midwest and across southern Wisconsin. First generation peak is illustrated across southern Canada and has already passed. The risk of infestation from the developing 2nd generation is illustrated by the warm colors (reds, oranges, yellows) on the map. The 3rd generation is currently across southern Illinois and this risk interval will be moving northward in the 10-14 days to come. This population is typically not an issue as most planted crops have developed through susceptible stages (Source: https://agweather.cals.wisc.edu/vdifn).


Brown Marmorated Stinkbug (BMSB) Wisconsin and upper Midwest – In addition to being a conspicuous household nuisance pest in the winter and spring, BMSB is a serious agricultural pest of numerous crops during the summer months. After emerging from shelters in late spring, BMSB adults begin mating and laying eggs on various trees and host plants in late May and June, and early nymph populations become conspicuous (Fig. 3). Overwintering adult BMSBs emerge when day length reaches 13.5 hours in the spring (approx. mid-April). Adults will begin laying eggs at around 148 FDDs after spring emergence. Egg hatch occurs at around 686 FDDs. All life stages can damage plants and fruit.

In most of its range in North America, BMSB completes only one effective generations per year, progressing through an egg stage and 5 nymphal instars before molting into a fully-winged adult. This development can take 4-5 weeks and adults typically emerge in mid-July. Nymphs and adults of the BMSB will attack most vegetables to include okra, bell pepper, green bean, tomato, eggplant, sweet corn, asparagus and Swiss chard. Only infrequent damage has been observe on cucurbits such as squash and cucumber and brassica vegetables such as broccoli, and collards.

Nymphs and adults injure vegetables by inserting their piercing-sucking feeding stylets into fruit, pods, buds, leaves, and stems. Feeding can also open the path for secondary pathogens, further reducing the marketable yield. In Wisconsin, the highest pest pressure to vegetablescoccurs in July and August, with special reference to crops directly bordering woodlots. These sections of the field are at the highest risk of attack as a large portion of the BMSB population disperses from wild tree hosts in the summer.

Figure 3. Peak egg hatch activity for the 1st generation of Brown Marmorated Stinkbug is predicted soon in Wisconsin and the upper Midwest. The appearance of early season nymphs is illustrated by the warm colors (reds, oranges, yellows) on the map. Border sprays to control early nymphs may be a practical option, especially in areas where the pest is known to occur and become problematic later in the season. For most vegetables, control measures should be initiated if bugs (nymphs or adults) are present in fields and the crop has initiated fruit development. (Source: https://agweather.cals.wisc.edu/vdifn).


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