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Agronomy Update

Should You Spray a Fungicide?

Published on Friday, June 24, 2016

A lot of our early planted corn is already in the reproductive stage, or will be within the next week. A majority of the phone calls I’ve recently received are from farmers asking “should I spray a fungicide?” This is a tricky question. On one hand, you don’t want to throw money at a corn crop when it’s not warranted, but on the other hand you don’t want to lose potential yield by not protecting your crop. So the million-dollar question is, “what should I do?

First, there are a few questions you should ask yourself.

  1. Is there disease present? If so, what level of infection do you have?

  2. What stage is the crop in?

  3. What was your previous crop and tillage method?

  4. Do you have a hybrid that will respond to fungicide?

  5. Is the weather conducive for disease development?

Here are my answers to these questions based on what I’ve been seeing in the field.

  1. Is there disease present? If so, what level of infection do you have? I have seen very little disease pressure so far this year. There is some common rust at very low infection levels in most fields and there is also some gray leaf spot in the lower canopy as seen in the photo below.

  2. What stage is the crop in? Most of the corn that was planted in mid to late April is at or close to the VT (tasseling) growth stage. This is a critical time for fungicide application, if disease is present.

  3. What was your previous crop and tillage method? Many diseases will overwinter in the residue of a previous corn crop, so a corn-after-corn rotation is much more susceptible than a corn-after-soybean rotation. Reduced-till and no-till systems are also at a higher risk because of the amount of residue left on the soil surface.

  4. Do you have a hybrid that will respond to a fungicide? No hybrid is completely resistant to all diseases, but there are some with genetic resistance to disease. Consult your product guide for individual hybrid disease ratings.

  5. Is the weather conducive for disease development? Some of our area has been experiencing extremely hot and dry conditions while other areas have had some very timely rainfall events, so this question is very specific to each individual region. Most disease favors warm, humid environmental conditions.

While I have yet to see enough disease presence to warrant a fungicide application, it is still very early. Most corn fungicides will provide 14 to 28 days of residual control, so if we have another year of late southern rust development, an application may be warranted later in the year.

Take home message: Scout your fields! It is still early and disease pressure is light, a fungicide application may not be necessary at this point. However, if you do spray, I would recommend a product that has a QOI/Strobilurin & Triazole mixed together.

For fungicide recommendations, click below to view the Fungicide Efficacy for Control of Corn Diseases from Purdue University.


(Click chart to enlarge)

*If applying a pre-tassel fungicide, do not add non-ionic surfactant (NIS), as arrested ear development could occur.

Don’t hesitate to contact myself or your local Beck’s representative if you have any questions.


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Austin Scott
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