Early applications of foliar fungicides to corn?
Recently, there has been interest in making early season fungicide applications to corn – at the V5 to V7 stages. This concept has been promoted by some fungicide manufacturers. There has been some research on this by universities in the Corn Belt, but not much.
There is little question that fungicide applications made at the traditional time, VT – R1(tasseling through brown silk), will usually have a much greater effect on corn yield than an application at V5 to V7 – assuming disease pressure is heavy enough to justify a fungicide application at all!
But early fungicide applications are made using low rates and can be done at comparatively little cost, especially if they are combined with a postemergence herbicide application. So the question is whether producers would get enough of a yield increase from a low-rate, early application of fungicide to justify the low cost and potential disease resistance risk. Corn producers looking at this option would probably be thinking about using it as a supplement to a VT/R1 application, not a replacement.
To address the question of early fungicide applications to corn, we have to start by looking at what is going on with corn plants at that stage of growth, and what diseases might be expected to be present early in the season in Kansas.
Kernel row number determination of the uppermost ear begins shortly after the ear shoot is initiated (V5 to V6) and continues through at least V8. Anything from about V5 to V12 that severely limits photosynthesis, such as loss of leaf tissue, can result in fewer kernel rows or, more likely, fewer kernels per row. Although such early stress can be important, it will have much less potential to reduce yield than the same level of stress that occurs shortly before to shortly after pollination.
From this perspective, it might seem to make some sense to apply a low rate of fungicide to help protect the plants from disease stress at V5 to V7, and for the period of time following application consistent with the level of residual activity from the fungicide being used.
But what diseases might be present at these stages of growth? The most common early season diseases on corn in Kansas would be anthracnose leaf blight and possibly common rust.
Anthracnose leaf blight is most commonly found in continuous corn fields under no-till or strip-till residue management systems. The disease infects corn most often in the seedling stage, prior to V5, so a fungicide application made at V5 will usually be too late to help control anthracnose leaf blight. Contrary to popular thinking, controlling anthracnose leaf blight will not help reduce the incidence of anthracnose stalk rot since the pathogen overwinters in corn residue. Anthracnose stalk rot typically occurs later in the season, since the stalk rot pathogen is caused by an infection through the roots, not the leaves.