Late-Season Sunflower Stem Diseases (09/15/16)
Late-Season Sunflower Stem Diseases
Over the last several weeks, several stem diseases of sunflower have showed up prominently in some areas of the state. There is nothing that can be done to manage these diseases now, but it is important to accurately identify the diseases in order to manage them in the future (if possible and if needed). Below is diagnostic information and images of three key stem diseases that are appearing. More information about these and other diseases are available in the original publication: Sunflower Disease Diagnostic Series - PP 1727.
Phoma Black Stem
Importance: Very common stem disease but rarely economically important.
Key Symptoms: 1-2 inch coal-black lesion centered on a petiole, usually superficial. Many lesions may occur on the same stem
Phomopsis Stem Canker
Importance: Disease appears to be increasing in the region. Lesions may degrade the pith, resulting in yield loss and lodging. High disease pressure early in the season can devastate a crop.
Key Symptoms: Large (often greater than 6 inches) brown lesion centered on a petiole. Stem becomes hollow underneath the lesion, and is easily punctured with thumb pressure. Lodging may occur.
Sclerotinia Mid-Stem Rot
Importance: Common disease that causes can cause yield loss and lodging, high disease pressure will result in yield loss. Caused by the same pathogen that causes head rot in sunflower and white mold in other broadleaf crops (for example, soybean, dry bean, canola, pulse crops, etc.).
Key symptoms: Large (often greater than 6 inches) tan to cream colored stem lesion centered on a petiole. White fungal growth and black fungal bodies may appear on or in stem. Stem frequently shreds and lodges.
Extension Plant Pathologist, Broad-leaf Crops