Understand fungicides before you spray

Are you going to spray fungicides? Can you mix other products with it? These are all common questions of the new fungicide era.This month, Indiana Certified Crop Adviser panelists address two specific issues related to fungicides.

My crops consultant says I have a moderate amount of gray leaf spot and some northern corn leaf blight already showing up low in the canopy. Should I spray a fungicide that stops these now, or one that prevents future infection?

Steve Dlugosz, agronomist with Harvest Land Co-op, Wayne County: Susceptibility of the hybrids and amount of hot, humid weather has the largest effect on development of a yield-limiting problem. The objective is to protect the upper leaves from significant infection. The ideal time to spray is from tassel until brown silks form. Spraying a protective and/or curative fungicide earlier than that will not protect upper leaves, since they aren’t yet emerged.

Gene Flaningam, Flaningam Ag Consulting LLC, Vincennes: Applications of fungicides before pollination is complete can be justified as a preventive measurement of disease management. Corn following corn would be a good example of an environment that would justify an early application. A second application to the same field may be justified following pollination if leaf diseases continue to develop. These situations will greatly depend upon a hybrid’s tolerance to various leaf diseases.

Willis Smith, Senesac Inc., Fowler: If it’s mid-July, a moderate amount of disease below the leaf, if it stays below the leaf, shouldn’t be a concern, as only leaves above the ear contribute to ear development. However, the chances that the disease will move up the plant are pretty good. Also, the symptoms you see will always be 10 to14 days behind infection. So if you have disease present and it’s probably going to get worse, I would recommend a fungicide that is both curative and preventive. Possible choices are Amp, Quilt, Quilt Xcel and Stratego Yld.

Fungicides and insecticides

I’m spraying fungicides where the hybrid isn’t as resistant to gray leaf spot as I would like. Can I add insecticide for rootworms and Japanese beetles on the same trip to stop these silk clippers?

Dlugosz: An insecticide can be used with fungicide if silks are being clipped shorter than one-half inch, and the field isn’t pollinated. Adding insecticide “just in case” isn’t a sound approach.

Flaningam: The silk-clipping pest must be present, and the application must be timed with fresh silks. Research says a fungicide application prior to pollination with an oil-based product can cause corn ears to become deformed. Applications of fungicide with surfactant or an oil-based product are recommended only after pollination is complete, at or near “brown-silk” formation.

Smith: Scout fields at the first sign of disease. If the corn is within labeled growth stage, apply a fungicide. Applying at the wrong stage could cost yield. If disease never shows up, you can still apply. Some companies tout that their fungicides improve plant health and yield even without disease. If silks aren’t clipped within one-half inch and pollination is over, save your money. If you do apply a combination, check labels to make sure they’re compatible. It only takes three extra kernels per ear to increase yield a bushel per acre. I usually lay out facts, especially cost-to-benefit ratio, and let the grower decide.

This article published in the July, 2011 edition of INDIANA PRAIRIE FARMER.

All rights reserved. Copyright Farm Progress Cos. 2011.