As many growers will have seen, there is a heavy load of early, out-of-season flower on orchards in the Northern Rivers (Alstonville, Dunoon, Fernleigh). This coincides with the main flowering, which is currently moving through raceme elongation and is presumably on track for peak bloom around the end of August into the first week of September. We’ve also just come through a cool, showery period – the sort of conditions that suit the development of Botrytis. Botrytis is a flower disease mainly associated with older, denser canopies where air flow through the tree canopy is limited.
The disease needs two things to get going: susceptible flowers and sustained wet, mild conditions. Showery weather over three or more days, with cool temperatures roughly in the 10-22°C range, is enough to trigger an outbreak if flowers have been wet for six to eight hours or more. The past two weeks have certainly seen those types of conditions.
Racemes aren’t equally vulnerable to Botrytis throughout their development. From bud break through raceme elongation, and into the expansion of flower buds to the “punching bag” shape, they are not vulnerable. However, from early flowering (when flower parts begin to push through the buds – the “bent elbow” stage) through peak flowering and into sepal drop and ovary swell, they are vulnerable. Right now the main flowering is still in the elongation stage, and so, theoretically, isn’t at risk.
However, as noted in the first paragraph, we are currently seeing a lot of early or out-of-season flower, which right now is in the susceptible stages for Botrytis. If this flower gets infected with Botrytis, it won’t necessarily cost much yield on its own, since a large amount of flower loss can be tolerated without a major hit to the crop. The real concern, however, is that infected, decaying racemes can carry viable spores for several weeks, building up inoculum in the orchard. If that carries through to the main flowering event, the risk to this year’s crop becomes very real.
Lace bug is also active on flower buds at this time of year, feeding by sucking sap and causing buds to desiccate – damage that tends to show up more in elevated blocks. Similarly, with the potential for carryover of Botrytis into the main flower, there is also a risk that lace bug populations could build up in this early flower and carry over into the main flower.
Given the combination of heavy early flower and recent weather, it’s a good time to get an orchard inspection done, specifically to establish what stage your flower racemes are actually at, block by block and also by variety. From there, ongoing weather monitoring through to the main flowering period will tell you whether conditions are tipping toward a moderate or higher disease risk.
If you’d like a property assessment to establish flower staging across your blocks and varieties, or want a second set of eyes on your pest and disease management program heading into the main flowering, please get in touch. This is exactly the kind of seasonal risk that orchard monitoring and good macadamia orchard management are built to catch early – a conversation and inspection now costs a lot less than a compromised level of nut set at the end of flowering.
Allen Agri Consulting provides macadamia agronomy and farm management services across the Northern Rivers and Northern NSW, including Lismore and the surrounding growing districts.