Sunflower producers may want to start scouting earlier than usual this year. The Panhandle Research and Extension Center in western Nebraska has noted the early occurrence of sunflower rust on volunteer sunflower plants this spring.
Many years’ low levels of sunflower rust can be found on confection and oilseed sunflowers in South Dakota late in the season. This type of late infection rarely results in yield damage, especially in our dry climate. However, if the disease were to infect sunflowers early in the season, there is potential for yield loss.
Sunflower rust is specific to cultivated and wild sunflowers. The onset and spread of sunflower rust is usually dependent on the environment and inoculum source. Environmental conditions that are conducive to the spread of this disease include temperatures of 55-85 degrees F and free moisture. To date this disease has not been observed in South Dakota this spring. However, with its early appearance in NE, it could also appear early in the season in South Dakota as well, especially if the weather is conducive to its spread. Early infections allow more time for secondary and tertiary infections to occur during the season.
Growing hybrids that are resistant to rust is an important management tool. However new races of the pathogen can develop and overcome the genetic resistance. Rust spores can travel across long distances, therefore crop rotation will not prevent rust. However, crop rotation can break up the rust life cycle and delay onset of the disease. Controlling wild sunflowers in and around fields can also help to slow the spread of the disease. All species of wild sunflowers found in North America are hosts to the rust pathogen.
Fungicide applications are very effective in slowing the progression of this disease. A fungicide application is recommended when the disease covers 1% of the leaf area on the four uppermost, fully unfolded leaves. Applications are most economical when made prior to or during bloom (R5). For a list of products labelled to control rust in sunflowers, view the 2018 South Dakota Pest Management Guide: Alfalfa & Oilseeds.
Source: Ruth Beck, iGrow