Fungicides don’t always do their stuff: it depends on the wheat variety. But under some circumstances their guarding action can help boost yields up to 40 per cent.
These findings come from a WA project identifying best practice in disease control, supported by growers and the Federal Government through the GRDC.
The study found that control differs for the varieties affected — with susceptibility a regulating factor.
Jatinderpal Bhathal, Kith Jayasena and Robert Loughman of AGWEST, working with the Mingenew-Irwin group, found that wheat response to fungicide treatment depended on its initial rust resistance.
For example, Ajana, a susceptible variety, responded routinely to fungicides, while resistant varieties, such as Camm, were generally unresponsive.
The response of intermediate (e.g. Brookton) and moderate (e.g. Carnamah) resistance varieties corresponded to disease pressure. However, in most scenarios, one spray prevented most yield losses.
While successful spraying of susceptible varieties could virtually halve yield loss, a second spray may be required, at a cost of $13—17/ha, to arrest rust after an early infection.
Other factors in management strategy
Factors other than varietal resistance also affected yield response to fungicide treatment.
Things such as disease spectrum and severity, crop potential and future disease risk as a result of weather and the costs of fungicides should be considered when devising fungicide rates and number of applications.
As a guide, the trials found that, in an average season, a single application of fungicide at full flag leaf emergence (Z39 growth stage) provided the most economical disease control.
However, when under threat of early infection, an application at early stem elongation (Z31), followed by another at normal timing (Z39), was better than seed treatment or in-furrow fungicide.
In a dozen trials on leaf rust, effective management of the disease had lifted profit an average of $40/ha for susceptible cultivars.
Results showed propiconazole to be best at controlling yellow spot, while triadimefon provided the most cost-effective control of leaf rust and powdery mildew.
While past research suggests aeroplanes can be as effective as ground booms, grower experience in 2000 found the higher water volumes in booms helped control high disease pressure situations.
Using a Rogator helped to minimise boomspray wheel damage, with the Mingenew-Irwin group reporting just 0.7 per cent yield loss from wheel tracks over three harvest trials, when spraying at flag leaf emergence.
Contact: Dr Jatinderpal Bhathal 08 9956 8540
Dr Kith Jayasena 08 9892 8477
Dr Robert Loughman 08 9368 3691
North, South, West