Figure 2. Crown rust inoculum observed on buckthorn leaves on June 8, 2021 (A) compared to about the same time on June 10, 2019 (B).
Unlike other cereal rusts, the crown rust pathogen overwinters in South Dakota on buckthorns. The pathogen survives as hardened spores called teliospores on oats residue and on other grass hosts. In spring, the teliospores produce another type of spores called basidiospores that infect the buckthorn (Figure 2). The basidiospores on the buckthorn produce another type of spores called aeciospores and it is the aeciospores (primary inoculum) that infect oat. Infection of oat can produce secondary spores called uredospores that infect other oat leaves. The dry and warm weather conditions have limited crown rust inoculum to build-up hence the low levels of this disease currently in oat.
A fungicide at flag leaf is usually recommended to manage crown rust in oat. Given the low levels of the disease and the advancement of the crop, a fungicide may not be needed in oat this year. Planting a crown rust resistant oat variety is the best practice to manage crown rust. Two new cultivars, Saddle and Warrior are resistant to crown rust.
Source : sdstate.edu