Downy Mildew


Left Photo: Bare patches are from damping off caused by downy mildew. The surrounding sunflowers survived, but did not recover.

Right Photo: Downy Mildew can be recognized by the stunted and yellowing of veins.

The weather this past week has not been good for sunflowers when it comes to downy mildew prevention. The cool and wet weather this past week has been a happy place for this devastating foliar disease of sunflowers. Looking at NDAWN’s and SDSU’s soil temperature report for June 1st in the state of ND I am seeing temperatures in the mid to high 50s from North Central South Dakota to the Canadian border. The organism is microscopic and needs water to swim to its target. Some seedlings are killed right away from damping off and others survive, but never fully recover. Those plants that survive are typically stunted, have yellowing along the veins and if the plant does put on a head, it doesn’t yield well. Once a plant is infected there are no management practices that can help the plant to recover. For the future, a grower should plant a hybrid with genetic resistance or at least a seed treatment that can help to suppress the disease (or both!). Unfortunately this disease is genetically variable, which means it can change and overcome the genetic resistance or the seed treatment over time. A good rotation can help to prevent catastrophes, but once it is in your soil, the disease can live for at least 10 years. On a positive note, Nuseed is working hard to incorporate the newest genes available into our hybrids and testing new fungicide seed treatments as they come available.