NDSU Extension - Ramsey County

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July 5, 2010 Agriculture Column

Howdy!!!

Growing degree  days are accumulating sounds like we will gain many units over the next couple of weeks.  To date, using May 1 as the starting point, we have garnered 717 units.  Compared to norm we are 18 units ahead of norm.  Remember, as we calculate Growing degree days we do not use the high of the day if it is over 85 degrees.    Growing degree days are calculated using either 85 degrees, if over 85, or the number under 85 degrees.  Example:  92 degrees outside temperature we would use 85 as the high of the day, if the outside temperature was 76 we would use 76 for the calculation number.  The same holds true for the low number of the day.  The whole formula is based on 55 degrees and over.

One last note and that is we have a group of 4 young men and two coaches attending the National Shotgun completion in Texas.  They are doing great and showing the rest of the country that we do exist and can very compete.

 

DOWNY MILDEW IN SUNFLOWER APPEARING

Downy mildew is starting to appear in sunflowers. The disease is more common when soils are wet, so the appearance of the disease is no surprise. The disease causes a thickening of the leaves and stunting of the plant. The upper side of the leaves will become yellow from the stem outward), and on the undersides of the leaves you may see a white cottony appearance (spores). An extension publication with detailed information and numerous photos of downy mildew is available at www.ag.ndsu.edu/pubs/plantsci/rowcrops/pp1402.pdf

 

The pathogen is soil-borne, and the infection takes place through the roots. No foliar fungicide application will rescue a plant from downy mildew. Downy mildew infected plants will usually have significantly reduced yield. However, since downy mildew plants are usually stunted and unthrifty, nearby non-infected plants may compensate. The biggest yield losses are observed when

large patches of sunflowers are infected.

 

Many downy mildew resistance sunflower hybrids are available and widely used. However, a new race that can overcome the resistance was identified last year. It is unlikely the race is widespread, but if a downy mildew resistant hybrid has symptoms, the new race may be present. Dr. Tom Gulya is will be coordinating a survey effort this summer to try and assess the geographic

distribution of the new race. However, if you observe downy mildew in a resistant hybrid, your help in this process would be greatly appreciated. If possible, please place sporulating leaves (leaves with the white cottony

growth) leaves in a zip lock bag, keep cool, and mail as soon as you are able to Tom Gulya at the address below. Dr. Tom Gulya, Research Plant Pathologist USDA,ARS,NCSL; 1307 18th St. N.; Fargo, ND 58102-2765

Thomas.Gulya@ars.usda.gov

 

 

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