BOM recently updated its seasonal outlooks to reflect the El Nino conditions and as a consequence its effect on temperature and rainfall patterns across Australia.
Two of the worrying weather map forecasts show the chance of temperatures exceeding median maximums up into the 80% range across a majority of our major tree cropping regions.
Another crop stress & sunburn season
If you combine these temperature outlooks with the lower than average rainfall predictions, Australia’s tree crop industry is potentially in for a another crop stress and sunburn season.
Now is the time to be thinking about ways to mitigate the impacts of heat, water and salinity stress on your crop.
Soil preparation
As a tree crop specialist you know what you need to be doing with your irrigation scheduling to get a good deep base of sub-soil moisture into the profile.
However, due to variability in soil chemistry and structure some soils may suffer from preferential flow which means irrigation and rainfall uptake is not uniform throughout the soil profile. This can lead to a poor moisture profiling and poorly developed root systems which puts the tree under stress.
Consider the injection of liquid gypsum (Gyp-flo Liquid) into your irrigation to improve soil structure in areas where salinity stress may exist.
If your soils suffer from localised dry-spot conditions caused by areas of hydrophobic soil particles, you should consider adding a soil wetting agent to your irrigation system (HydraSoil®).
This will help to move the moisture more deeply and uniformly through the profile.
Plant preparation
Nutrients
It goes without saying that nutrition plays a major role in plant stress tolerance.
Managing nitrogen levels to allow for optimum leaf expansion to provide shading to fruit and the soil helps to reduce heat build-up in the canopy and moisture evapotranspiration under the canopy.
However, this must be balanced with not applying too much nitrogen that can lead to excessive leaf expansion and high transpiration loss from leaves and leaf drop.
Potassium and chlorine levels need to be monitored to ensure optimal guard cell and stomatal function is maintained which is supported by other micronutrients like iron, copper, manganese and boron.
Make sure these key nutrients—that are responsible for regulating photosynthesis and cell wall integrity—are well monitored and provided for in your nutrient program.
Biostimulants
There is a significant focus on research in the field of how to manipulate genes to make plants more drought tolerant.
The 'holy grail' of enhancing global plant production in a warming planet with less water, is discovering how plants regulate water loss and maintain cellular integrity under drought conditions.
A great deal of work in this area has been conducted with extracts from Ascophyllum nodosum kelp (STIMPLEX®).
Researchers have discovered that compounds like betaines, polybetaines and other oligosaccharides, that are abundant in products like STIMPLEX, can induce plants to express genes responsible for coping with elevated levels of drought and salinity stress.
This makes sense when you consider how Ascophyllum nodosum has evolved, firstly to cope with living in a highly saline environment but also to survive the extreme inter-tidal zones of the Nova Scotian coastline.
The tides rise and fall by as much as 15 metres leaving the kelp baking in the sun without access to any soil moisture for hours at a time. So what does this mean for tree crops?
The foliar application of products like STIMPLEX can be used to assist with mitigating the effects of drought and saline stress on trees.
STIMPLEX also provides a full range of the essential micronutrients needed for optimum plant function.
STIMPLEX also has been shown to improve root growth which is important with a predicted increase in severe storms: a larger root mass will better anchor the tree against high winds but also provides the tree with more effective uptake of key nutrients like calcium and greater access to soil moisture.
Adding 2–4L/ha of STIMPLEX to your nutrient program will ensure your trees are functioning at optimum levels.
When entering into the high stress period it would also be a good insurance policy to put STIMPLEX on the list of tools you can call on to minimise fruit/nut abortion and downgrading of the crop.
Canopy heat relief
The build-up of radiant heat in the canopy leads to crop stress.
There are many fancy imported heat and sunburn protection products on the market these days but one of the most tried and proven Australian-made products for sunburn and heat protection is Crop Block®.
No matter how you slice it, sunburn protection is simply about creating a reflective barrier to reduce heat building in the canopy and on the skin of fruit. Crop Block is like zinc on your nose—sun protection for your crop.
Let’s hope that this season is not as bad as predicted and we all get through it with a good crop in the cool-room.
Only time will tell, but it is always good to prepare for the worst and I hope some of the tips I have provide in this article are of value to you.
For information phone 1800 634 204
See this article in Tree Fruit Jan 2019
