If grain growers in the northern region are not already convinced about the presence and impact of root lesion nematodes (RLN) on crop production they should attend the next nematode field day.
The impact of nematode activity on crop yields can be difficult to assess visually. Their impact is definitely less striking than a field full of whiteheads which can be the result of unmanaged crown rot inoculum.
In trial situations where you have tolerant and intolerant varieties growing side by side the impact of RLN becomes far more obvious.
Recent Grains Research and Development Corporation (GRDC) funded research activities conducted by the Department of Agriculture, Fisheries and Forestry (DAFF) and Northern Grower Alliance (NGA) has shown that the impact of RLN on yields of winter crops including wheat, barley and chickpeas can be even more significant than the impacts of crown rot on wheat yields.
If growers do not recognise that they have an issue with RLN on their farms they are unlikely to implement appropriate management programs and production losses will accumulate.
At low to moderate levels of RLN, their relatively minor impacts can be attributed by unsuspecting growers to other causes such as dry conditions or nutritional impacts.
However, as numbers of RLN can rapidly explode under inappropriate management programs, growers can be unwittingly exposing their intolerant crops to very high levels. It is under these regimes that recent research has shown up to 50 % loss in grain yield.
At MCA we have been monitoring RLN numbers on behalf of our grower clients since the late 1990s and have used the data to help design appropriately tailored management programs.
In fields where the presence of RLN has been confirmed we have promoted the use of varieties with some tolerance and resistance. We have also altered the recommended rotation to help in managing their numbers.
Our monitoring has shown that there are still a reasonable percentage of fields in the region that do not have any RLN issues.
This presents an opportunity for those growers to continue with their current cropping programs without major concerns to RLN management practices.
However, the majority of fields monitored do have RLN at various levels. For these growers, this information provides an opportunity to tap into some production that had been otherwise lost due to unmanaged RLN.
Pratylenchus thornei (P. thornei) has definitely been the dominant RLN species in our operational region. However we have noticed more recently that the number of fields which also have pratylenchus neglectus has increased significantly.
Our monitoring over time has shown that to bring P.thornei numbers down significantly, several resistant crops (in our cases predominantly sorghum) need to be grown consecutively.
The practice double cropping of chickpeas into sorghum has been shown to negate the P.thornei benefit of sorghum in the rotation. Also the use of very susceptible wheat varieties such as Strzelecki has proven to lead to a rapid escalation in RLN (P.thornei )numbers.
We have also shown however that the presence of RLN is not a death sentence. With the adoption of appropriate management practices their impacts can be minimised.
The saying “you can’t manage what you don’t measure” definitely applies to RLN as the early impacts can be relatively subtle and we would encourage all grain growers to have background RLN data on their fields and to monitor numbers over time. This is now most conveniently achieved by submitting soil samples to SARDI for PreDicta B testing.
Paul Castor, MCA senior agronomist, Toowoomba
Sarah Jeffrey, Senior Consultant Cox Inall Communications