Model of stripe rust infection and control on irrigated wheat in the murrumbidgee irrigation areas of new South Wales

A well-developed epidemic of stripe rust on a field crop of a susceptible wheat cultivar (cv. Avocet) led to significant yield reductions compared to plots which were protected with regular applications of the fungicide triadimefon (Bayleton®). A modified logistic transformation of the leaf infection data provided values of apparent infection rate, r, which are required for use in simulation models of disease progress and predicted yield loss, such as epidemic and epipre. Flagleaf area at early water stage of the kernels (86 days following sowing, DFS; Zadoks growth stage 70), afforded a good prediction of grain yield. Stripe rust infection of the flag leaf had a strong negative effect on final grain yields larger than would have been predicted solely from a loss of photosynthetic area. Flood irrigation did not affect the level of disease on the flag leaf at 86 DFS nor the apparent infection rate of stripe rust on the flag leaf. Irrigation gave increased grain yield only in sprayed treatments. Conversely, while there was a yield response due to fungicide application to cv. Avocet in both irrigated and non-irrigated plots, the cost benefit of spraying the latter was marginal.