How Fungicides Work
If you have or anticipate a fungus disease in your corn, you may want to know what fungicide to apply and when. You’ll need to take into account “curative” versus “preventive” fungicides, which starts with understanding what each option is and how it works.
The first step in understanding curative vs. preventive fungicides is to understand how the disease cycle of a foliar pathogen works. A foliar pathogen can have multiple disease cycles over the course of just one season, each divided into four distinct steps: infection, colonization, symptoms, and spore production.
Growers first need to positively identify the disease they seek to control. Let’s say Southern Leaf Rust (SLR) has been identified or has been confirmed in nearby farms. SLR has the typical 4 steps of a fungus disease cycle.
Using a local fungicide guide, select the fungicide that is effective in controlling SLR. The timing of fungicide application to protect corn from SLR incidence can be accomplished two ways: the corn could be treated with fungicide before any SLR symptoms are evident, or after sporulation of SLR is evident. This is where we come to the choice between curative and preventive fungicides.
Preventive activity happens when the fungicide is present in the leaf tissue but before initial infection occurs. This type of fungicide prevents any infection from the fungal pathogen by acting as a “protective barrier.” To return to our SLR example, Strobilurin fungicide (Group 11) is a preventive fungicide that is effective in. SLR control. Strobilurin and other preventive fungicides should be applied to guard against further infections, but will not stop infections present at application.
A curative fungicide stops the early growth of the fungal pathogen after infection, the first step of disease cycle, has occurred. Most curative fungicides are also preventive if applied prior to infection. Despite their name, curative fungicides will NOT cure a plant of the disease. They are not effective against advanced disease cycles. A triazole fungicide (Group 3) is considered to be a curative fungicide. It is effective in SLR control and would be used if early symptoms of SLR are present.
Remember that corn leaves below the ear have little effect on yield. Therefore, preventing diseases from establishment on the corn leaves from the ear and above will ensure corn yield.
Getting The Most Out of Chemical Applications
We've put together a handy blog post that includes everything you need to know to make your farm's chem applications successful.
Resources:2018 Guide for Weed, Disease, and Insect Management in Nebraska. University of Nebraska-Lincoln Extension. Page 24