Early development of ascochyta blight leaf lesions. Crops should be carefully inspected 10 to 14 days after each rain event. (Photo: G. Cumming)
Protecting chickpea crops from ascochyta blight
by Gordon Cumming, Pulse Australia, National Development Manager
Many chickpea crops are now emerging and it is time to focus on the management of ascochyta blight. The susceptibility of the variety to disease and other risk factors will help determine the need for a prophylactic fungicide spray program.
The pathogen that causes ascochyta blight is endemic to the northern grain-growing region and must be considered a threat to all chickpea crops.
Under ideal conditions, the pathogen can complete its lifecycle in 5–7 days, so crop inspections should occur 10–14 days after each rain event. Multiple cycles of infection will occur during the growing season, whenever environmental conditions are favorable.
No chickpea variety is immune to ascochyta blight. However, varieties do differ in the amount of disease that develops and in the impact of the disease on yield.
Current varietal ratings (susceptible/resistant) to ascochyta blight are based on the amount of damage the pathogen causes during the vegetative phase. Pods of all varieties are considered equally susceptible to infection and need to be protected from infection through the use of fungicides to ensure maximum grain yield and quality.
The recommended fungicide management program for ascochyta blight is based on varietal resistance and risk assessment.
Susceptible (S) varieties (e.g. Jimbour, Kyabra, Moti, PBA Pistol) If the season favours ascochyta, regular fungicide sprays will be needed from emergence until four weeks before maturity. Do not wait until you find the disease. Timing of the first two sprays is critical, because control is difficult or impossible after the disease has taken hold. The first spray must be applied before the first post-emergent rain event, or three weeks after emergence or at the three-leaf stage, whichever occurs first.
The second spray should be applied three weeks after the first spray. However, apply the second spray if two weeks have elapsed since the first spray and rain is forecast. Continue monitoring the crop 10–14 days after each rain event. If ascochyta is found, additional sprays will be required. If it has been two weeks or longer since the last application, spray again just before the next likely rain event.
Moderately Resistant to Resistant (MR/R) varieties (e.g. PBA HatTrick, PBA Boundary) In most seasons, disease development will be slower and there will be no or minimal yield loss in these varieties. In such seasons there is no cost benefit in applying a fungicide during the vegetative stage. However, despite good foliar resistance to ascochyta, the flowers and pods of MR/R rated varieties can be infected.
Infection of pods can result in poor quality, discoloured seed or seed abortion and yield loss in severe situations. Under high disease pressure, a reactive foliar fungicide strategy may be warranted during the vegetative period of the crop. Monitor the crop 10–14 days after each rain event. If ascochyta is present in the crop, apply a registered fungicide at early podding prior to rain to ensure pods are protected, and high quality, disease-free seed is produced.
High risk situations In areas where high ascochyta blight pressure was experienced in the previous season, a prophylactic application of a registered fungicide three weeks after emergence may be warranted for MR/R rated varieties. Especially if early winter rains are expected.
Please discuss your specific situations with your chickpea agronomist to ensure the development of a suitable ascochyta blight management strategy for your crops.
Detailed information concerning disease management strategies can be found in a series of ‘Northern Pulse Bulletins’ on the Pulse Australian website www.pulseaus.com.au by clicking on the ‘Publications’ button or feel free to call me on 0408 923 474.