Corn
Some corn may have been sprayed as early as V5 but now we are approaching tasseling and some fields have already begun to tassel. With the corn prices being what they are more growers are inclined to apply a fungicide. Multiple studies have shown that a single application of a DMI (FRAC Group 3) + QoI (FRAC Group 11) fungicide at VT-R1 provide the best chance of return on investment. The Corn Disease Working Group of the Crop Protection Network updates the corn fungicide efficacy table in the following link.

https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-corn-diseases-filename-2021-03-09-163332.pdf

The last few years we’ve seen more Gray leaf spot on corn in Virginia than other foliar disease. Be aware that if you used Xyway in-furrow you may not be protected against Southern corn rust that comes in later in the season some years. Typically, by the time Southern corn rust is observed in Virginia it will not impact yield greatly. However, for late-planted corn fungicide application must be made by R3 (milk stage) to limit yield loss due to Southern corn rust.

Soybeans
In Virginia, our primary foliar disease of soybean are frogeye leaf spot, Cercospora leaf blight and Septoria brown spot. Scouting for these diseases at or prior to beginning flower (R1) will give an estimation on the amount of disease pressure in a given field if diseases are present. Fields with disease pressure early are more likely to benefit from a fungicide application. Fungicides have the best chance of potentially reducing yield loss to foliar pathogens when sprayed beginning at pod initiation (R3) through seed initiation (R5). If dry conditions are prevalent during this spray window a fungicide spray is not advised. Be aware that foliar fungicides do not offer much protection against seed decay organisms or soilborne pathogens of soybeans. Below is the link for the Crop Protection Network’s soybean fungicide efficacy table.

https://crop-protection-network.s3.amazonaws.com/publications/fungicide-efficacy-for-control-of-soybean-foliar-diseases-filename-2021-03-12-182833.pdf

It is not advisable to spray QoI (FRAC Group 11) fungicides alone as fungicide resistance to this group has been observed in the fungal pathogen that causes frogeye leaf spot.

If you have questions or concerns please don’t hesitate to contact me.

David B. Langston, Jr.
Professor and Extension Plant Pathologist
Tidewater Agricultural Research and Extension Center
6321 Holland Rd., Suffolk, VA 23437
Office (757) 807-6536
Cell (757) 870-8498
FAX (757) 657-9333
e-mail dblangston@vt.edu

After looking at some wheat fields this morning I believe most of Virginia’s wheat is between head emergence (Feekes 10.3) and flowering (10.5.1). Wheat disease pressure has been low but with rain chances increasing by the middle of next week that could change. I have seen some physiological damage caused by weather or hypersensitive responses (resistant responses) to disease but no real disease outbreaks. With the flowering stage here we typically begin spraying for wheat scab or Fusarium head blight (FHB). Right now risk of FHB is low. The risk of FHB can be monitored by the FHB Risk Assessment Tool provided by Penn State (http://www.wheatscab.psu.edu/). Fungicides such as Caramba, Prosaro, and Miravis Ace are recommended for FHB and DON control. Caramba and Prosaro will provide better control when applied at flowering while Miravis Ace has a wider window of activity from heading to 6 days after flowering. Remember to avoid using strobilurin (FRAC Group 11) fungicides after flag leaf as these fungicides can increase DON levels in grain. Fungicides applied for FHB will control the other major foliar wheat diseases. The 2019 Fungicide Efficacy for Wheat Diseases can be found at the following link. NCERA 184 Wheat fungicide table 2019_Final

If you have questions about wheat diseases you can reach me, David Langston, via e-mail or phone.

e-mail dblangston@vt.edu
office phone (757) 807-6536
cell phone (757) 870-8498