Fungicide: Timing is Everything


by: John Woerner

Fungicides prevent infections better than they cure infection.  If spores land on a plant that has already been treated, they will be killed as they start to infect.  If a plant is treated after infections are about more than 3 days old, these infections will continue to develop into lesions.  Effective disease control requires that the plant be treated just as the disease is becoming established.


I base my treatment threshold on proximity to the ear leaf.  From the ear leaf up is the area of the plant I want to protect.  Yes, the fungicides that are available today do better just preventing versus curing, but these fungicides do have both capabilities.  In reality, the corn plant can survive just fine with some lesions on the bottom portion of the plant.  Therefore, I can cure that are below the ear leaf and then prevent disease from developing above the ear leaf with the proper timing of a fungicide.


What should you keep in mind.  Is the hybrid susceptible to one or more leaf diseases, are leaf diseases currently present, are you following a corn crop, and does the field have a high yield potential.   Also, consider the pollination success.  If the hybrid has pollinated successfully out to the tip of the ear, your goal should be to protect as much as the leaf area as possible.  To reduce the risk of kernel abortion, help the plant retain as much leaf surface area as possible.  More leaf area equals more photosynthesis, more photosynthesis equals more sugar generated in the plant, more sugar equals more carbohydrates which equals better kernel fill.


How late can I spray?




Spraying after R2 (blister) reduces the chance for the best economic return.  This does not mean that a fungicide cannot be sprayed past R2.  Some fungicides are labeled up to within 14 days of harvest.  However, the potential for a yield increase reduces dramatically.


Other benefits can include; enhancing crop yields even without the presence of any significant leaf disease.  These chemicals have a direct effect on the physiology of the plant, promoting plant health and yield.  However, this needs to be further researched.  Please treat in regard to the prevention or treatment of disease.

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March 23, 2020


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