The relatively wet summer weather we’ve had this year, combined with high temperatures, have created ideal conditions for crown rust in ryegrass in the upper North Island.
In such a favourable environment, all ryegrass cultivars will succumb to this fungal disease. Old varieties, such as Nui, would have been infected months ago with the weather we’ve had this season. More modern cultivars hold out much longer, but they too will eventually become infected as disease pressure is high and this puts considerable stress on the plants.
Rusty pastures look bad; they don’t grow very well and palatability suffers but it is a temporary problem.
The best way to manage rust is to hard graze affected pastures, then apply some N fertiliser if you can to stimulate healthy re-growth. New growth should show little rust. To prevent rust in the first place, remember to graze pastures at the correct time – don’t let them get too long.