Corn development as fungicide application timing approaches

With Hayden and Liam's help, Grandpa's two junior agronomists, let's look at corn development this year as fungicide application timing approaches.

Key Points.

1.    Physiological development of corn planted in the month of May is on schedule.  A number of fields in the area are just coming into tassel and will be in full tassel through next week.  I have witnessed many years that corn tassels in early August and still put up an excellent crop.  I think we all know that September weather will need to co-operate for this to happen.  There is no reason at this time to doubt that a nice September is in the cards.

2.    Corn that tassels in the first half of August is worth protecting.  The yield potential is there.  There is still time for diseases like northern leaf blight, eyespot, leaf rust and gibberella ear mold to develop.  Fungicides are preventative, not curative.  They need to be in place and protecting the plant before the disease can be seen with our eye.   

3.    What about fungicide causing elevated grain moisture at harvest? This is true. Our many years of experience has taught us that corn will usually be 2-4 pts wetter at harvest with fungicide which increases drying costs.  However, 5 points of moisture adds 10 cents per bushel to the drying bill.  If you have produce a 180 bushel crop that 10 cents will add $18 per acre in to the cost of production.  It is normal to expect 7-10 bushel yield response to fungicide use.  The net return is easily in favour of fungicide.

4.    Is there a date when it may not be worthwhile applying fungicide?  Yes, I believe so.  The middle of August is our best estimate of the date when it may not pay to apply fungicide.  In other words the moisture penalty may be too great and the yield return may be too low if our crop tassels in late August.  We are going to do some side by sides to see if we are right.       

5.    The best timing for application is at full green silk.  This is especially true if we are trying to reduce the potential for gibberella ear mold infection.  Gibberella ear mold infects through the silk channel and needs fresh silks to aid infection. 

6.    I strongly suggest using a member of the triazole family of fungicides, Proline, Caramba, or MiravisNeo because in addition to providing acceptable leaf disease control, they are the only products that have effect on gibberella ear mold. 

7.    The biggest struggle in many fields will be timing the spray to coincide with green silk.  The variability in silk development across many fields is problematic. We are used to dealing with this same issue of variability in wheat at heading time too.  Many times the front of a field is ready and the back of the field is not, so there is a tendency to spray too quickly.  Brian and I tend to believe that spraying a couple of days late is preferable to spraying too early. 

Russ Barker – CCA-ON 4R NMS

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