With pesticide resistance on the rise, it’s becoming harder for growers to rely solely on chemicals to control disease. And on top of increasing resistance, there are also concerns with the potential impacts of chemicals on water supplies, soil health and the increasing cost of production. So, are there other pest-reduction strategies that could be used in a broader approach to management?
One grower determined to find a better way of doing things is David Giumelli, manager of Eastwind Orchard, in Balingup. David says that soil-borne diseases are becoming increasingly prevalent and the effectiveness of intensive pesticide programmes is declining.
“The way we deal with these problems is a real issue for me,” David said.
“Everything seems to be evolving around chemical control and less so around biological control. We are using more and more chemicals. The cost is one thing but the damage is another. As far as I’m concerned, the soil is becoming sterile.”
David has been trialling various non-chemical approaches over the past two years with the support of South West Catchments Council (SWCC).
The partnership has connected David with Queensland-based nematologist, Dr Graham Stirling, a specialist in soil-borne disease and integrated pest management and Fellow of the Australasian Plant Pathology Society. Dr Stirling is the author of several books including Soil Health, Soil Biology, Soilborne Diseases and Sustainable Agriculture, and has developed tests using pest and beneficial nematodes to assess the biological status of soils.
Dr Stirling is analysing the nematode community in David’s soils prior to visiting the orchard for a field day on 25 October 2017. Preliminary results using soil samples from an area where trees have died appears to confirm that soil health at that location is in bad shape.
“The number of dagger (Xiphinema spp) and ring (Criconematidae) nematodes was high in both samples,” Dr Stirling said. “These (pest) nematodes will certainly be damaging the root system. Root-lesion is also present, which not only damages root systems but also provides entry points for other pathogens.”
The number of free-living nematodes was also assessed. These beneficial nematodes feed on other soil organisms and don’t damage roots, so healthy populations indicate that a healthy food-web is present in the soil. Results supported conclusions that soil health is poor, possibly reducing nutrient cycling.
“(Beneficial) nematode numbers are low and there are few omnivores and predators,” Dr Stirling said.
Low numbers of omnivorous nematodes can indicate that the soil biology is affected by pollutants or excessive fertiliser inputs. Disturbance through tillage can also reduce numbers but is less likely to be the cause in an established orchard (Ref).
David says that most growers can’t work without chemicals because they are vital in reducing the fear of crop failure, and he would have a lot to answer for if an outbreak occurred.
“Farmers don’t like to feel vulnerable because we are already vulnerable in so many ways,” David said.
But over the past few years, David has found little ways to adjust his system without putting his head on the chopping block.
“A lot of stuff goes out that doesn’t need to, or it goes out too late. I try not to do any more weed spraying than I have to and try to use the minimal amount,” he said.
“Even with fungicides, if we’ve got the right weather conditions and the numbers are down, I’m not going to spray just for the sake of it. I might leave it for 25 days if the weather hasn’t been good for spores to form. In winter, you normally put insecticides out, but we are trying to improve timing and precision by monitoring for insects first. So I’m just trying to draw back where I can.
“With nutrition, I’m using more foliar sprays at smaller quantities rather than through the irrigation that is leaching out. I’m doing smaller waters more often as well.”
Most of Dr Stirling’s research has been directed towards the development of non-chemical controls for plant-parasitic nematodes. He found that a soil food web that suppresses bad nematodes can be fostered by eliminating practices that are detrimental to predators, such as aggressive tillage and excessive inputs of fertilisers and pesticides.
Also, using organic inputs from composts and rotation crops can maintain a food supply for beneficial organisms. For example, research into the management of lesion nematodes (Pratylenchus jordanensis) on replanted apple trees suggested that these nematodes could be managed through a combination of allowing more time between the removal of the previous orchard and replanting, incorporating animal manure or a green manure crop with urea, choosing appropriate rootstock, and maintaining a layer of organic mulch around trees.
Dr Stirling warned against looking for silver bullets, which aligns with David’s approach.
“The more I look, (I realise) it’s more of a whole system and touching up the way of doing things.” David said. “We’ve got to condition the soil and get the organic matter and environment right for micro-organisms to thrive.”
Other ways that managers can foster a healthy and diverse community of microorganisms is to manage soil acidity and compaction, maintain permanent groundcover between orchard rows, and increase the diversity of plant residues, including leguminous residues.
David has begun implementing some of these concepts in his orchard. For example, he is now planting mixed leguminous cover crops between orchard rotations, preparing soil by mixing in biochar to retain soil structure, and promoting clover growth beneath trees, which he later sprays out to create a mulch.
“A lot of farmers are worried about soil and waterways and the sustainability of it all, but most are unsure about which way to go with it. I’m trying to figure that out to create a system for my farm that’s more sustainable, profitable and more environmentally friendly.”
Dr Stirling will be at Eastwind Orchard’s field day on 25 October.
This article first appeared in WA Grower magazines Spring 2017 edition.