Corn

Virginia growers are over the hump so far as corn disease management is concerned.  Late season diseases such as tar spot and southern corn rust have not been observed in Virginia at this time and we are past the R3 (milk) stage which is the cutoff for making effective fungicide applications for each disease.  Click the link for updated maps showing where each disease is currently in the U.S. https://corn.ipmpipe.org/diseases/

Peanuts

As of August 1st, peanut growth and development is a little behind in areas that have experienced periods of severe drought.  Heat units for peanuts planted on May 1st so far are on par with 2021, which was a record-breaking year so far as yield is concerned.  Growers in Virginia have made at least one fungicide application for leaf spot by August 1st, and many have made 2 applications.  The risk of Sclerotinia blight has been variable based on the differences in vine growth due to drought in certain areas, however, recent rainfall events have been more numerous in the region and I expect disease pressure will continue to increase.  Increased rainfall and relative humidity will shorten the LESD (last effective spray date) for leaf spot for most fungicide chemistries and growers using Miravis should consider spraying at 21 days after the first application if disease risk for leaf spot is continually high since the last spray of that product.  Growers that have already made applications of Miravis tank-mixed with Elatus will have some protection against Sclerotinia blight and growers that are opting for Omega 500 should be scouting fields with histories of that disease, especially in those fields where peanut canopies are dense, to make applications at disease onset.  If Miravis or the Miravis/Elatus combo was not applied as the first or second fungicide application I do not recommend using it in August or later due to concerns with fungicide resistance and the lack of curative or “kick back” activity associated with those chemistries.    If peanut leaf spot severity becomes high due to weather and the inability to get equipment in fields to make timely fungicide applications, rescue treatments using Microthiol Disperss or chlorothalonil tank-mixed with Group 3 fungicides, such as Provost Silver, to reduce defoliation prior to digging.

Soybean

Fungicides have recently been going out for foliar diseases recently as most soybeans are in the R1 – R5 growth stages.  Recent weather patterns have brought and continue to bring rain events and high relative humidity which favor the development of frogeye leaf spot and other foliar diseases.  My main concern for fungicide applications is to avoid using Group 11 (strobilurin) fungicide chemistries alone as fungicide resistance to those has been previously documented in the frogeye leaf spot pathogen in Virginia.  There are plenty of Group 3 (triazoles), Group 7 (SDHI) and Group 11 fungicide combinations available to manage foliar soybean diseases.  Also, I’m thinking of naming August as “SDS (sudden death syndrome) month” as that is when SDS usually starts showing up.  The first clinic sample with SDS came in Tuesday on soybeans planted April 15th.  Typically, SDS symptoms occur in early planted and early maturing soybeans first and continue as soybeans mature.  Soybeans planted early in cool (at or below 60°F), moist soils are more at risk of infection by the pathogen that causes SDS, Fusarium virguliforme.  The most visible symptoms occur at the late R5 growth stage and into R6.  Managing this disease is strictly preventive through the use of crop rotation, delayed planting, resistant varieties and the fungicide seed treatments ILeVO and Saltro.  We are gathering data on SDS outbreaks in Virginia so please contact us if you suspect this disease in your fields.

As always, feel free to contact me if you have questions regarding disease and nematode issues in your fields. e-mail: dblangston@vt.edu, cell: 757-870-8498