Ascochyta blight in chickpeas has been a major disease threat to Victorian cropping regions. With limited varietal resistance and the risk of developing fungicide resistance thus the crop resistance breakdown, it is important to develop integrated disease management strategies to maximise the longevity of the varietal resistance. Hence the aim of this study was to identify if sowing time can be brought forward but reducing or maintaining the current fungicide applications for the new resistance. Three experiments (2022-2024) were conducted in Wimmera to test sowing times (May and July) against no and complete fungicide treatments in variety Genesis 090 (MS). A second experiment was conducted in Wimmera in 2024 to test six fungicide treatments (4 node+early flowering, 4 node+mid flowering, early flowering+podding, post infection+podding, 4 node+mid flowering+podding, and podding) with two controls (nil and complete control treatments) against varieties, Genesis 090, PBA Striker (S), PBA Magnus (S), CBA Captain (S), and CBA2051 (advanced breeding line). Disease severity was measured as %plot area affected with stem breakages and/or pod infection and yield was estimated.
In all years, there was higher disease severity (P <0.001) in the May sown chickpeas as compared to July sown, with the fungicides holding the disease at very low severity. With a longer wet season (2022) these results indicated a trend towards decreased grain yield (P=0.089) with May sown yielding 1.30 t/ha compared to July sown at 1.47 t/ha, regardless of fungicide treatments. With a drier start in 2024 but with more rainfall days later in the season May sown chickpeas with no fungicides produced significantly (P<0.001) less yield (1 t/ha) compared to July sown (~1.3 t/ha). In contrast, a drier spring season (2023) showed increased (P <0.001) grain yield in the May sown chickpeas with fungicides (3.67 t/ha) compared to July sown with (2.54 t/ha) and without fungicides (2.62 t/ha). The sowing time experiments over years highlighted that though the severity was always higher in May sown chickpeas, the yield can be season dependant with more rainfall events likely leading to reduced yield due to Ascochyta blight.
In the second 2024 experiment, low disease severity (stem breakages <4.25%, podding infection <1.75%) was observed for CBA2051 for different fungicide treatments, but the differences were not significant. Treatments, 4 node+early flowering, 4 node+mid flowering, early flowering+podding and podding demonstrated significantly lower disease severity, and higher yield for CBA2051 compared to PBA Striker. In addition, fungicide treatments at podding indicated significantly lower disease severity for CBA2051 compared to Genesis 090, although there was no significant difference in yield. The results suggest that new chickpea line CBA2051 in a below average rainfall season like 2024 will still require multiple fungicides to prevent grain yield loss. Further studies will be conducted to validate this observation, understand gross margin changes and the effect of any seasonal changes. Overall, the present study suggests that by delaying the sowing time and with minimal use of fungicide applications it is likely to manage Ascochyta blight in the new chickpea resistances and to improve its durability.