Vigilance and early treatment are the best course of action for growers facing heightened cereal disease risks this spring.
A green-bridge over the past summer, coupled with earlier sowing and a wet winter, have likely been the cause of increased observations of four major cereal diseases in 2014. SARDI Cereal Pathologist Dr Hugh Wallwork has received reports of stripe rust and leaf rust in wheat, and net form net blotch and spot form net blotch in barley.
Stripe rust and leaf rust have both been observed in South Australia. While similar, the symptoms of stripe rust will appear in a line (top), whereas leaf rust appears as single pustules or more random groups of pustules (bottom).
Potential rust spread
“Stripe rust has been observed in the past week in Mace and Wyalkatchem on the Eyre Peninsula,” Dr Wallwork said.
“It’s very unusual for stripe rust to occur in Eyre Peninsula crops this early in the season and before sightings elsewhere. The disease has also been observed near Dublin, north of Adelaide, but without a hot-spot, so there must either be a hotspot elsewhere nearby or there is a chance that this infection has come from the EP, in which case the disease would be all over the state.”
Mace is particularly susceptible to stripe rust, with a susceptible to very susceptible (SVS) rating, and is widely grown across South Australia.
A disease that has rarely been seen in SA for a number of years, but which has been spotted this year is wheat leaf rust. Unlike stripe rust, leaf rust is not as active in cold conditions, but its activity is expected to increase when the weather warms. Where varieties rated moderately susceptible (MS) or worse are grown (see Table 1), growers should be on the lookout for leaf rust.
Dr Wallwork recommends growers inspect symptoms of rusts, focusing on the differences between the two diseases.
“There has been a few instances where growers are mistaking the two rusts. Stripe rust never forms in single pustules, but instead always occurs in a whole stripe, so if there’s only single pustules, then the symptoms are indicating leaf rust. The complication is that while Mace is not as susceptible to leaf rust, the disease has been seen in Mace, so it’s not just a matter of any rust on Mace wheat being stripe rust.”
Due to the different levels of activity of the two diseases, control strategies are not the same. Where leaf rust is not highly active, growers are advised to wait until the weather warms up before spraying fungicide.
However because stripe rust is still aggressive in the cold weather, growers need to be cautious where varieties are rated moderately susceptible (MS) or worse and be prepared to spray when stripe rust is observed.
“The most effective solution would be to apply a protective spray before rust is present. However where crops have not reached flag leaf emergence then another spray could be required later so an early spray could be less economical. In this situation it may be best to delay spraying until rust is observed in the crop or in nearby crops, providing that the grower can cover the area required quickly when needed. It is not recommended delaying spraying once stripe rust is seen as the rust can develop very rapidly and also spread spores to other crops. Late sprays are less effective and may not stop rust infection in the heads of Mace and Wyalkatchem.
Net blotch infections
Widespread infections of both forms of net blotch have been largely controlled by early fungicide applications. However as the weather warms up, these diseases, particularly net form of net blotch, can cause significant damage if the current control is not maintained. Many crops are now due for a second application, and growers are advised to keep a close eye on barley to ensure the disease is treated early.
“Protection is much better than trying to control the disease later on. Once net blotch gets going in a crop, it’s very hard to keep up with control, so it’s important to protect new leaves as they come out. Especially as the weather warms up, it will progress very quickly if the leaves aren’t protected,” Dr Wallwork said.
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