Beneficial bacteria and chloropicrin vie for honoursResearch & Extension
Chloropicrin was the standout performer in the first year of a Future Orchards trial of pre-plant treatments of old apple ground in Manjimup, WA. Pomewest project manager and Future Orchards front line advisor for Western Australia Susie Murphy White revisits the trial to see how trees performed in the second year.
A Future Orchards® demonstration site was set up in 2017, testing the effectiveness of different pre- planting treatments when planting Fiero® Fuji onto old apple ground at Trevor and Carmel Fontanini’s Orchard in Manjimup in south west WA.
Old apple ground can harbour apple replant disease (ARD) which reduces new tree growth and production by around 20 per cent per annum for the whole tree’s life. The demonstration site tested biofumigants as two different mixes of mustard and rocket (David Grays’ Green Fume), and mustard and Ethiopian cabbage(PGG Wrightson Seeds BQ Mulch); a beneficial bacteria product (Serenade® Prime from Bayer); and the chemical fumigant Chloropicrin (as Rural Telone C-60 applied at 300litres/ha by an accredited contractor) against the standard grower practice treatment of Metham Sodium.
It was expected that all these treatments would improve tree survival rates when planting new varieties of apples into old apple ground. But it was thought that the beneficial bacteria and biofumigation options would be better for soil health.
Year 1 Results
Trees on the Chloropicrin-treated ground produced amazing growth in the first year, with the stem elongation at first leaf six times longer than, and the amount of leaders on each tree more than double, that of trees on the other treatments.
The trees on the Chloropicrin-treated ground also had trunk diameters at first leaf that were greater by more than 5mm compared with the trees on ground treated with the other products, trees on which had only small differences between them.
Year 2 Monitoring Results
After the second growing season monitoring of the trunk diameter and stem elongation was undertaken. This clearly shows which treatments have given the trees the best start and enabled good growth into the second leaf stage. The trees on the Chloropicrin-treated ground still have a larger trunk diameter by 5mm followed by those on the beneficial bacteria treatment Serenade® Prime and then the biofumigant Green Fume (mustard and rocket).
Stem elongation in the second leaf was strongest in trees on the beneficial bacteria-treated ground, followed by those on the biofumigant mustard and rocket, then the standard practice of Metham Sodium and then the Chloropicrin, with least growth on the ground treated with cabbage and mustard. The Chloropicrin still had a lot more leaders than the other treatments. These leaders were smaller in length and diameter, but overall had a greater shoot length mass than trees on the other treatments.
What is surprising to see is the poor growth rate of the trees on the Ethiopian cabbage and mustard (BQ Mulch)-treated ground. This poor growth rate is seen in the trunk diameter, stem elongation and number of leaders per tree.
Each treatment block was soil tested and had a free-living nematode (FLN) test in Autumn 2017 before planting and after the treatments and planting in Autumn 2018. The FLN tests show that the Ethiopian cabbage and mustard had higher amount of fungal feeding nematodes before treatment but after the biofumigation treatments both biofumigation treatments had reduced the fungal feeders. But the Ethiopian cabbage and mustard ground had the biggest increase in numbers of Pratylenchus penetrans (root lesion nematode) after the treatment in Autumn 2018, and has shown the poorest growth rate.
ARD is a complex interaction of the nematodes, fungi, bacteria and microfauna that slow root growth and function. While biofumigation crops can be used to increase the beneficial nematodes and control the plant parasitic nematodes with the release of the glucosinilate gas, it appears our demonstration has shown the increase in the root lesion nematodes to slow the growth of the trees on ground treated with the Ethiopian cabbage and mustard.
The two treatments which have performed well are the Chloropicrin and the beneficial bacteria, showing both impressive growth in stem elongation and truck diameter.
Chloropicrin is still out in front at the end of the second year with more shoots and shoot mass and larger trunk diameter, while the beneficial bacteria Serenade® Prime is just behind.
What is interesting to note is the difference between the two biofumigation treatments, and the link to root lesion nematode and amount of free-living nematodes in the soil treatments after treatment.
It will be interesting to see whether the trees on the beneficial bacteria-treated ground outperform the Chloropicrin trees in year three, or whether they all reach equilibrium in the third season.
Long term implications
While the Chloropicrin treatment has given the trees a good start by reducing the effect of possible ARD, the biofumigation and beneficial bacteria treatments have the potential to improve soil health by improving organic matter, soil biology, nutrient cycling, water infiltration and holding capacity and overall microbial activity. Time will tell if the benefits of improved soil health will enable the trees to become good producers of quality Fiero® Fuji apples.
Acknowledgement: Thank you to our suppliers of the products used in this trial; David Grays, PGG Wrightson Seeds, Bayer and A-Gas Rural. Thank you to Pomewest for funding the soil and nematode tests, to APAL’s Future Orchards project, Steve Spark, AgFirst NZ, and to growers Trevor, Carmel, Joe and Lucy Fontanini for implementing the trial in their orchard.
Note: This article is an abridged version of the Apples on Apples trial Final Report. The full report with details of the treatments and methods is available in the Future Orchards Library on the APAL website.