Amanda Gevens, Dept. Chair, Professor & Extension Specialist, UW-Madison Plant Pathology, gevens@wisc.edu, Cell: 608-575-3029.
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). A P-Day value of ≥300 indicates the threshold for early blight risk and triggers preventative fungicide application. A DSV of ≥18 indicates the threshold for late blight risk and triggers preventative fungicide application. Red text in table indicates threshold has been met/surpassed. TBD indicates that data is To Be Determined as time progresses. Weather data used in these calculations comes from weather stations that are placed in potato fields in each of the four locations. Data are available in graphical and raw data formats for each weather station at: https://vegpath.plantpath.wisc.edu/dsv/
| Location | Planting Date | 50% Emergence
Date |
Disease Severity
Values 7/6/20 |
Potato Physiological
Days 7/6/20 |
|
| Grand Marsh | Early | Apr 17 | May 18 | 49 | 363 |
| Mid | Apr 25 | May 26 | 46 | 308 | |
| Late | May 6 | June 1 | 43 | 267 | |
| Hancock | Early | Apr 8 | May 18 | 27 | 377 |
| Mid | Apr 20 | May 25 | 25 | 326 | |
| Late | May 4 | May 30 | 22 | 288 | |
| Plover | Early | Apr 10 | May 23 | 37 | 330 |
| Mid | Apr 20 | May 30 | 31 | 276 | |
| Late | May 5 | June 1 | 31 | 263 | |
| Antigo | Early | May 14 | June 5 | 21 | 238 |
| Mid | May 24 | June 10 | 21 | 201 | |
| Late | Jun 1 | June 17 | 19 | 153 | |
Late Blight Management: Our DSVs are reported here from emergence to July 6. Over the past few days we have accumulated near maximum DSVs for several sites/emergence dates due to heat and rains (albeit spotty). All plantings of potatoes in the Grand Marsh, Hancock, Plover, and Antigo areas have exceeded threshold and should receive routine (~weekly) preventative fungicide application for late blight management.
Early Blight Management: PDays are exceeding the threshold of 300 for early planted potatoes in Grand Marsh, Hancock, and Plover areas. Totals are rapidly accumulating with higher temperatures. For more information about fungicide selections, please see the Potato section of the A3422 Commercial Vegetable Production Guide for Wisconsin, 2020. https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A3422-2020.pdf
As a reminder the UW Plant Disease Diagnostic Clinic is open for sample processing, but they cannot take walk-in samples; all must come in the mail or connect with a UW representative to have samples brought directly to the lab. We have a 1-2X weekly drop off from the UW Hancock ARS to Madison. E- mail diagnostics have been on the rise and can be very useful in narrowing causes of challenges in potato and vegetable crops. Please send pics and descriptions to me by email and we can get the dialogue going.