Sunflower Stem Diseases
A visit to sunflower fields at this time of year can provide information on what disease(s) you might face in future years. This is particularly true with stem diseases.
Two stem diseases (Charcoal rot and Verticillium wilt) tend to be more common in dry years, while Phoma, Phomopsis and Sclerotinia stalk rot tend to be more common in years with adequate or excessive moisture.
A brief description of importance and symptoms is below. More information about these are other diseases are available in the original publication: https://www.ag.ndsu.edu/publications/landing-pages/crops/sunflower-disease-diagnostic-series-pp-1727
Stem diseases that tend to show up in drier seasons
Importance: More common in dry years. Yield loss can occur. Can also infect soybeans and corn.
Key Symptoms: Premature senescence, gray lesion at the soil line appearing to be spreading up the stalk (Figure 1), small black specks (microsclerotia) in the stem (Figure 2).
Importance: Often appears in spots in a field but occasionally can be widespread. Where it appears, complete wilt and premature plant death can occur.
Key Symptoms: Mid-season – Interveinal chlorosis and necrosis most severe in lower canopy, with brown ring in pith and inside of pith still white (Figure 3). Late-season – external gray lesion on stalk with shrunken pith covered with black microsclerotia (Figure 4).
Stem diseases that tend to show up in wetter seasons
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: Severe yield loss can occur with adequate moisture. 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 (Figure 6). Stem becomes hollow underneath the lesion, and is easily punctured with thumb pressure (Figure 7). 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 (Figure 8).
Extension Plant Pathologist, Broad-leaf Crops
Source: North Dakota Extension