Cereal Diseases

CEREAL DISEASES Stripe rust has been confirmed on flag leaves in a crop of Wyalkatchem close to Minnipa on the Upper Eyre Peninsula. Hotspots have also been reported in Mace crops at early head emergence close to Yaninee, south east of Minnipa. These crops were reported to also have some leaf rust and were sprayed with Cogito on Monday 28th. Stripe rust was also confirmed in a Mace crop at flag leaf emergence near Long Plains, north of Dublin. Infection levels at this site were low and no hotspot was seen. From these observations it appears likely that stripe rust survived through the summer on the Upper Eyre Peninsula. The region around Minnipa had many volunteers following summer rains and so the presence of stripe rust cannot be a great surprise given that Mace, Scout and Wyalkatchem have been widely grown in the region. It is also likely that stripe rust will be present in susceptible varieties over a wide area downwind of Minnipa and possibly also throughout the Mid and Lower North. All crops should therefore be closely monitored and fungicides applied at an early opportunity. Early applications of fungicides will help suppress spread of the disease and also reduce head infections which are otherwise hard to control and which are likely to occur in Mace and Wyalkatchem. Wheat leaf rust has been observed in crops across the eastern Eyre Peninsula since the first report at Wharminda on 25 May, but only at low levels. The cold weather will not be favouring leaf rust as much as stripe rust, but as the temperature warms leaf rust will become more evident. A significant area is now sown to varieties that are MS or worse to leaf rust. Yield losses in these varieties could reach 15-20% if the rust becomes severe and fungicides are not applied. Net form net blotch and spot form net blotch are very common in barley crops throughout South Australia but have largely been kept under control with early applications of fungicides and cold temperatures. Many of these crops are due for second applications and particularly net form net blotch which is likely to cause considerable damage once the weather warms up. Once infection levels get high it becomes very hard to control the disease with fungicides. Early protection is a much more reliable management option.

PULSE AND CANOLA DISEASES Blackspot in field peas is severe in many districts due to frequent rain events that create spore splash. Fungicide sprays may be economic in crops that have a yield potential of more than 2 t/ha. Mancozeb should be applied at 2 kg/ha at around the 9 node growth stage and again at early flowering. No disease spread will occur in extended dry periods, so fungicides should be applied ahead of rain events. Chlorothalonil is registered in field peas but stock cannot be grazed on stubbles treated with this chemical and so it is not usually recommended.

Botrytis grey mould is severe in vetch crops in the mid north of SA. The unusually mild conditions at the beginning of the season allowed infection to occur, and the disease is continuing to develop over winter. Fungicide (carbendazim) sprays may not be economic in feed crops but are an option for seed crops.

Ascochyta blight and chocolate spot are present in many faba bean crops. Fungicide sprays for chocolate spot should be applied before canopy closure to ensure protection of flowers which are especially sensitive to infection. Once canopies close over, the disease will rapidly spread in crops with dense canopies and wet soils if left unchecked. A mix of fungicides may be necessary where ascochyta blight has infected crops. Note that the cvs. Farah and PBA Rana are susceptible to a new strain of ascochyta blight which is now widespread across the mid north of SA.

Beet Western Yellows Virus (BWYV) in canola Laboratory testing has shown that this virus is widespread across the southern cropping region (i.e. South Australia, Victoria and southern New South Wales). Due to the widespread nature of this virus we are discouraging further testing of canola crops and industry should focus on monitoring and managing aphid spread in individual crops if warranted. BWYV may be transferred into pulse crops when aphids fly in late winter/early spring and crops adjacent to virus infected canola may require insecticide sprays. Details on monitoring and insecticides were supplied in the PestFacts issue 6, and follow up information will be provided in the next Pest Facts article. If virus testing is required for pulse crops then South Australian samples can be sent to Jenny Davidson SARDI at Locked Bag 100, Glen Osmond, 5064.