Vegetable Crop Update #10
Updates provided by Amanda J. Gevens, Associate Professor & Extension Vegetable Plant Pathologist, Interim Co-Director of Wisconsin Seed Potato Certification Program, UW-Madison, Dept. of Plant Pathology
While it is only June 12, Disease Severity Values have exceeded the threshold of 18 for potatoes planted on/around May 1-15 in the Grand Marsh area. This means that weather conditions (moisture and temperature) have favored the development of late blight for crops with emergence dates established for these two planting dates. We presume presence of late blight pathogen inoculum with this Blitecast risk tool – and – as such, recommend preventative application of fungicides for managing late blight in potatoes at this time. This presumption is conservative, but given that inoculum can be harbored in multiple places within/around the production environment (seed potato, volunteer potatoes, nightshade weeds, infected tomato/potato harbored in compost piles), and experience with this disease in past years, it is reasonable to be proactive in early season management.
The attached newsletter provides updates for DSVs for all in-field locations, PDays for Grand Marsh and Plover, and additional information for identifying late blight in potato, and selecting fungicides.
We now have the weather data provided at the UW-Potato and Vegetable Pathology website. My apologies for delay in posting these this year. There was a need to upgrade modems on the stations within the month of May which delayed our generation of values. While PDays don’t typically hit threshold of 300 until late June early July, DSVs for late blight risk can certainly reach threshold in early June and we hope not to miss these critical periods. I have provided proxy DSVs from our relatively new Vegetable Disease and Insect Forecasting website which can source DSVs for specified dates anywhere within Wisconsin. Link here: https://agweather.cals.wisc.edu/vdifn/maps
*Please note, and excuse my error, DSVs are over threshold of 18 for potatoes that were at 50% emergence on 5/15, 5/28 in Grand Marsh WI. My newsletter identified these as planting dates which is inaccurate. General planting dates for early and mid planted potatoes were 5/1 and 5/15.