Update 23 – Sep 18, 2022

Save the date for the 2023 Wisconsin Agribusiness Classic (January 11th and 12th).  The Wisconsin Agribusiness Classic is Wisconsin’s premier agribusiness industry event drawing interest and participation from all confluences of the industry from throughout the Midwestern states.  The program is held at the Alliant Energy Center each January and boasts an attendance of over 1,000 attendees. The conference and tradeshow is a collaborative effort between the Wisconsin Agri-Business Association and the University of Wisconsin.  The depth of coverage and exhibits provided through the conference and tradeshow make it clear why the Wisconsin Agribusiness Classic is Wisconsin’s premier industry event.  Registration coming soon: agclassic.org


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.  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 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.  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.  Data are available for each weather station at:  https://vegpath.plantpath.wisc.edu/dsv/.

Location Planting Date 50% Emergence Date Disease Severity Values (DSVs) 9/17/2022 Potato Physiological Days (P-Days) 9/17/2022
Grand Marsh Early Apr 5 May 10 81 961
Mid Apr 20 May 15 81 920
Late May 12 May 25 81 862
Hancock Early Apr 7 May 12 52 955
Mid Apr 22 May 17 52 935
Late May 14 May 26 52 876
Plover Early Apr 7 May 15 123 905
Mid Apr 24 May 20 123 871
Late May 18 May 27 122 836
Antigo Early May 1 Jun 3 54 776
Mid May 15 June 15 50 702
Late June 10 June 24 50 617

Accumulations of P-Days were 43 to 48 over the past week. Potatoes should continue to be on a preventative fungicide program with effective disease management selections to limit early blight in long-season potatoes with persistent green foliage.

All monitored Wisconsin locations accumulated 0-4 DSVs this past week indicating a relatively low risk week for promoting late blight in potato.  A fungicide list for potato late blight in Wisconsin was provided in a past newsletter and is available here:  https://vegpath.plantpath.wisc.edu/2022/07/03/update-10-july-3-2022/

I will discontinue the DSV and P-Day reporting in the coming week or so as the field in which the weather stations are housed are vine killed and advanced to harvest. 

To my knowledge, there have been no reports of late blight in Wisconsin on potato or tomato so far this season.  Michigan reported potato late blight in a few additional fields over this past week.  The genotype is US-23.  According to usablight.org there were no other diagnoses of late blight in the US in the past week.  Previous diagnoses in the US this season included those in NC, FL, CA, TN, and Ontario Canada.  These have been primarily on tomato, with only the FL report on potato in early spring.

Cucurbit Downy Mildew:  During this past week, cucurbit downy mildew was confirmed in MD, NJ, SC, and AL this past week.  Previously this growing season, the disease was confirmed in AL, CT, DE, FL, GA, KY, MA, MD, ME, MI, NC, NH, NJ, NY, OH, PA, SC, VA,WI, and WV.  Red counties, on the figure below, indicate recent reports (less than 1 week old) of cucurbit downy mildew.

Cucurbit downy mildew confirmed infections as of Sep 18, 2022. This year (green), and past years (red). https://cdm.ipmpipe.org/

As a reminder, the pathogen is now known to have two ‘strains’ for clade types.  The type (Clade 2) which infects cucumber, can also infect melon.  Due to fungicide resistance within the downy mildew pathogen population, especially in Clade 2, selection of fungicides is important.  Management of cucurbit downy mildew requires preventative fungicide applications as commercial cultivars are generally susceptible to current strains (Clades) of the pathogen.  Management information can be sourced here:  https://vegpath.plantpath.wisc.edu/2022/07/03/update-10-july-3-2022/


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