Vegetable Crop Update – Aug 30, 2026
In this issue:
Vegetable Production Update
Yi Wang, Associate Professor & Extension Potato and Vegetable Production Specialist, UW-Madison, Dept. of Plant and Agroecosystem Sciences, 608-265-4781, Email: wang52@wisc.edu.
Weather outlook
Based on the UW-Madison Extension Weather Outlook, temperatures were cooler than normal across the state last week, about 1-4°F below average. Northwestern state was the driest last week, receiving less than ¼”. In other parts of the state, total precipitation ranged from ½” to 2″. The total 30-day precipitation were 1.5″ or less across the northwest, which was about 50% of normal or less. Over the state, satellite-based soil moisture estimates suggest that severe dryness is common across northwest, north-central, and east-central counties. Southern counties also remain drier than normal.
Extreme drought now covers 15% of the state, all in the northwestern part. In the next week, there are rain chances in portions of Wisconsin every day from 8/29 to 9/3. Chances are higher in southern counties, especially in the southeast. The outlook for early September demonstrates that temperatures will likely be warmer than normal. September temperatures are uncertain statewide with equal chances. Rainfall is leaning slightly towards below normal along the northern border. Fall temperatures are leaning towards above normal for almost all parts of the state. Precipitation is uncertain statewide except for the far northeast.
Potato harvest
For homegrown potatoes, it is the time to harvest the full-season varieties. You can begin by checking on tubers’ maturity. Dig up a couple of tubers and rub the skin. If the skin peels easily, wait another week or so before harvesting. Tubers with broken skin are highly susceptible to pathogen infection during storage, but it is ok if you consume them immediately.
To prepare potatoes for storage, reduce irrigation amount immediately to allow vines to senesce and die back completely before harvesting. When harvesting, if your soil is coarse-textured and sandy, gently brush off the soil; in fine and clayey soil, washing the tubers is needed. Either way, tubers should be completely dry before starting to store. Minimize light exposure during the entire process because light can increase the accumulation of chlorophyll on the tuber skin (Figure on the right), which is accompanied by the synthesis of solanine and chaconine, both are toxins.
Newly harvested and cleaned potatoes should be cured in a dark, well- ventilated place with moderate temperatures (around 55°F) and high humidity for one to two weeks. Curing can help extend storage life. After curing, the storage temperature can be reduced to 40 – 46°F. Potato tubers have more than 80% of water content, and therefore high humidity (above 90%) is essential to prevent weight loss and shriveling during long-term storage. Potatoes should be stored in perforated plastic bags or well-ventilated containers for maintaining humidity. Refrigerators set to 40 – 46°F, insulated garages, or cool dark basements are good suitable storage areas. It should be noted that temperatures below 38°F can cause sugar accumulation and sweetening. Tubers stored at lower temperatures will produce dark products during frying (for fries or chips). However, higher storage temperatures above 40°F can lead to decay, sprouting, and shriveling of the tubers.
Red and yellow potatoes typically have thin skins and shorter storage life compared to thick-skinned russets. Late-maturing full-season varieties store better than early ones. Please check on the label of the variety to make sure their maturation length. With good storage management, mature-skinned, full-season varieties can be stored for up to eight months. If the storage temperature is above 46°F, storage life will drop to about two months, and sprouting and shriveling will take place afterwards. Stored tubers should not be replanted the following season. Even they look healthy, they might carry soil borne pathogens on their skin or internally. Always plant certified healthy seed tubers.
Vegetable Disease Update
Amanda Gevens, Professor & Extension Vegetable Pathologist, UW-Madison, Dept. of Plant Pathology, 608-575-3029, gevens@wisc.edu
Current P-Day (Early Blight) and Disease Severity Value (Late Blight) Accumulations
Thanks to Ben Bradford, UW- Madison Entomology for supporting this effort and providing a summary table: https://agweather.cals.wisc.edu/thermal-models/potato. A Potato Physiological Day or P-Day value of ≥300 indicates the threshold for early blight risk in potato and triggers preventative fungicides. A Disease Severity Value or DSV of ≥18 indicates the threshold for late blight risk and triggers preventative fungicide application in potato. Data from the modeling source: https://agweather.cals.wisc.edu/vdifn are used to generate these risk values. I’ve estimated early, mid-, and late planting dates by region based on communications with stakeholders. These are intended to help in determining optimum times for preventative fungicide applications to limit early and late blight in Wisconsin.
| Location | Planting Date | 50% Emergence Date | Disease Severity Values (DSVs) through 8/29/26 Season total (additional DSVs over past week) | Potato Physiological Days (P-Days) through 8/29/26 Season total (additional P-Days over past week) | |
| Spring Green | Early | Apr 10 | May 7 | 56 (1) | 920 (60) |
| Mid | May 5 | May 20 | 54 (1) | 848 (59) | |
| Late | May 16 | June 2 | 54 (1) | 752 (69) | |
| Arlington | Early | Apr 12 | May 8 | 30 (1) | 921 (60) |
| Mid | May 6 | May 23 | 30 (1) | 846 (61) | |
| Late | May 20 | June 4 | 30 (1) | 749 (61) | |
| Grand Marsh | Early | Apr 13 | May 9 | 51 (3) | 888 (57) |
| Mid | May 6 | May 22 | 51 (3) | 829 (57) | |
| Late | May 21 | June 5 | 51 (3) | 724 (57) | |
| Hancock | Early | Apr 14 | May 11 | 32 (1) | 882 (57) |
| Mid | May 10 | May 30 | 31 (1) | 768 (57) | |
| Late | May 23 | June 6 | 30 (1) | 714 (57) | |
| Plover | Early | Apr 15 | May 12 | 27 (1) | 882 (56) |
| Mid | May 10 | May 30 | 26 (1) | 772 (57) | |
| Late | May 25 | June 6 | 25 (1) | 718 (57) | |
| Antigo | Early | May 12 | May 29 | 34 (3) | 735 (44) |
| Mid | May 25 | June 5 | 41 (4) | 690 (45) | |
| Late | June 8 | June 20 | 30 (4) | 578 (45) | |
| Rhinelander | Early | May 15 | June 6 | 23 (3) | 671 (50) |
| Mid | May 28 | June 10 | 21 (3) | 634 (50) | |
| Late | June 9 | June 25 | 15 (3) | 538 (52) | |
Late blight of potato/tomato
Wisconsin potato production regions have accumulated only 1-4 Disease Severity Values or DSVs over this past week. All locations with the exception of the latest plantings in the Rhinelander area, are at or surpassing the action threshold of 18. Fields with ≥18 DSVs should receive preventative fungicide applications to manage for late blight. A current list of fungicides for management of potato late blight in Wisconsin 2026 is provided here: https://vegpath.plantpath.wisc.edu/resources/late-blight-fungicides/.
Late blight in the US 2026. Again, this week, there have been no new findings of late blight on potato, or tomato, in MI or anywhere in the midwestern region. There was confirmation of late blight on tomato in North Carolina in Henderson County (south central NC) last week. Extension scientists involved with the case confirmed the finding on 8/21 and they were in the process of determining genotype/strain type, but suspected US-23.
Early blight of potato
All Wisconsin potatoes have surpassed the treatment threshold of 300 P-Days. Continued preventative fungicide applications are warranted for these fields. In the past week regions of the state accumulated between 44 and 61 P-Days, very similar to the previous week. For support in selecting fungicides, please consult the A3422 Commercial Vegetable Production in Wisconsin: https://vegpath.plantpath.wisc.edu/resources/a3422/.
Cucurbit downy mildew
Cucurbit Downy Mildew on cucumber has been reported in several additional counties in MI this past week (see map below from Dr. Mary Hausbeck’s Michigan State University Cucurbit Downy Mildew Reporting website https://veggies.msu.edu/wp-content/uploads/downy-mildew-confirmed-reports.pdf ). Additional reports were made out of NY, OH, and PA on primarily cucumber (https://cdm.ipmpipe.org/) suggesting broader spread of the Clade 2 pathotype of the downy mildew pathogen. The green counties indicate confirmations of downy mildew of over one week ago and red indicates confirmation within the past 7 days. There were no field disease confirmations from Wisconsin. Fungicide considerations were discussed in a previous newsletter and can be found here: https://vegpath.plantpath.wisc.edu/2026/07/12/vegetable-crop-update-jul-5-2026/
More information on cucurbit downy mildew & management: https://vegpath.plantpath.wisc.edu/diseases/cucurbit-downy-mildew/