Local Tar Spot
October 25, 2021
Tar spot has been the hot topic this summer! If you’re like me, your Twitter feed has been filled with photos of corn leaves with black specks for the last two months. Okay, but how bad is it really? Do we even have it in this area? Is the hybrid I’m growing tolerant? There are a lot of questions amongst growers, rightly so!
Our team has been in several corn fields from London up to Ripley over to New Hamburg in the last few weeks. We have found tar spot in every single field, regardless of hybrid or fungicide use. The incidence of disease was not severe enough that it would have caused yield loss this season but the inoculum now on crop residue will pose future problems. Moving forward, we will have both local inoculum as well as wind-blown spores to contend with, meaning that we will likely see conditions show up earlier in the season. That said, disease relies on the correct environment. Tar spot thrives under wet, humid conditions like we had this season.
How bad can it really be? Our team toured Albert Tenuta’s tar spot trials in Elgin County about a month ago. In that area, where they have had the disease present for two years now, the results of the disease are devastating without the use of fungicides. I would estimate 50-100 bu/ac losses where the corn was not sprayed or ineffective fungicides were use. Keep an eye out for Albert’s work this winter. Hybrid tolerance will help. As an industry we are just beginning a long process of breeding for tolerance. In the mean time, both extension and seed companies will be working to rate the hybrids in their current lineup to provide reference of each hybrid’s susceptibility.
Fungicides are the answer for the foreseeable future. Plan on your current R1 fungicide but plan to scout fields in the weeks leading up to this application for earlier infection. The current fungicides on the market will provide 2-3 weeks residual control. Late season scouting will be required to check for later infections. Under the right weather conditions and heavy inoculum like we saw in Elgin county, a second fungicide application will be warranted.
I really wish that there was better news but that is the current situation we are facing. Strategic fungicide use will be our best bet going into 2021!