The high risk of back to back chickpeas
GroundCover™ Issue: 121
Pulse pathologist Dr Kevin Moore urges growers to resist the temptation to plant chickpeas in 2016 into paddocks with a recent history of chickpeas
Most growers are aware of the recommendation not to plant chickpeas into paddocks with a recent history of pulse crops. The current high chickpea price, however, is very attractive and some growers may be wondering if the risk is worth the potential financial gain.
The reality is that the risk is far too high – not just for the individual crop and grower but for the whole industry.
Planting chickpea on chickpea will favour ascochyta blight, phytophthora root rot (PRR), sclerotinia rot and root lesion nematodes and, if conditions are conducive, the first three have the potential to cause 100 per cent crop loss.
Even if there was no sign of these diseases in the 2015 crop it is not safe to plant chickpeas on chickpeas in 2016. There are two significant cases from recent years where severe outbreaks of disease occurred in paddocks where it appeared safe to plant.
The first case was in a paddock planted mainly to PBA HatTrick in 2013, with a strip of the new variety PBA Boundary. Although the soil was a grey clay vertosol, no PRR was observed in either variety in 2013. In 2014, the whole paddock was sown to wheat and then to PBA HatTrick chickpeas in 2015. In September 2015 a laboratory test confirmed that phytophthora was the cause of plant deaths in the strip that had previously been sown to PBA Boundary, a variety that is susceptible to PRR. The affected crop area was so severely diseased that it was not harvested in 2015 while the remainder of the paddock yielded more than two tonnes per hectare.
In the second case, several paddocks on one farm were planted to Kyabra in 2014, and because ascochyta blight was not detected on the farm or in the district and El Niño conditions were expected, some of these paddocks were sown to KyabraA again in 2015. Since Kyabra is susceptible to ascochyta blight the plan was to manage the disease with fungicide should it become a problem in 2015.
Even though the disease was not detected in 2014 it was clearly present on the farm and plants were infected in late autumn or early winter 2015 and wet weather prevented the application of fungicides until mid-July.
By this time the disease was well established in all chickpea crops on the farm and was particularly severe in paddocks sown to chickpeas in 2014. Although no more rain fell after the end of July, the badly affected areas yielded just 0.6 to 0.8t/ha compared with Kyabra planted into wheat stubble, which yielded 1.0 to 1.5t/ha.
Wide scale risk
So, we know the risk is real for back-to-back chickpea crops, with financial losses expected due to lost yield or quality and higher production costs. There are also longer-term consequences, particularly for diseases such as sclerotinia that have a wide host range. The survival structures (sclerotia) remain viable in the soil for many years and could potentially affect many crops including faba beans, canola, lupins, field peas and cotton.
Planting back-to-back chickpeas also has significant implications for the industry. The first is the increased risk of the pathogen becoming more virulent and aggressive. The second is the increased level of pressure on the resistance genes in new varieties as crops are subject to earlier infection and potentially more disease cycles within a season. The third industry risk is the increased risk of the pathogen developing resistance to fungicide.
The ‘best’ place to look for chlorothalonil resistance isolates of ascochyta would be in early-sown back-to-back KyabraA. It would be unlikely for any such isolate to be confined to the paddock or farm as the resistant isolate could spread from a single farm to the whole cropping area of the Darling Downs, northern and north central New South Wales within a few seasons.
The resounding advice then is that planting chickpeas on chickpeas is far too risky and the risks to the grower and the industry far outweigh any potential gain. Seed treatments and fallow cultivation do not reduce the risks associated with back-to-back planting. The best-practice recommendations for disease management in chickpeas are to:
- maintain a one-in-four-year rotation;
- avoid planting next to the previous year’s chickpea stubble if possible;
- ensure all planting seed is pickled; and
- follow the recommended in-crop ascochyta fungicide strategy for the sown variety.
Do not even consider planting back into the previous two years’ chickpea country. It is not worth the risk. As well as increased risk of disease in back-to-back chickpeas, the management of weeds and insects will also be more challenging. At $800/t likely for chickpeas in 2016 it will pay to do everything possible to reduce risk and maximise yield and quality.
More information:Dr Kevin Moore, senior plant pathologist,
NSW Department of Primary Industries,
02 6763 1133
GRDC Project Code DAN00176, DAN00151