Avowest Netting Trial review
Year 2020 it began … our first Review 2022 …
The 3.5Ha of netting that we installed at Carabooda has been in place for 2 years now. It is still early for the trees to be producing avocados but courtesy of the WA Department of Primary Industries and Regional Development (that’s a mouthful – DPIRD) there is a lot of environmental data that we can analyse. There are now three weather stations inside the netted area and one outside.
Most of the weather station data is not showing huge differences due to the netting. There is a reduction in solar radiation of about 15-20% which is a bit more than expected with the netting theoretically having 10% shading. Average temperature differences are less than 1oC and are erratic across the site. The highest temperatures over summer are actually inside the netting near the edge, where the hot easterly winds create havoc.
Vapour Pressure Deficit (VPD) is a measure of how suitable conditions are for stomata to be open, which in turn affects how well the avocados can operate. Differences in VPD across the sites are small and once again the worst conditions are inside the netting where the easterly winds are strongest.
Differences in average wind speeds are also small but the netting does have a consistent effect in slowing the wind down.
Evaporation is one area where there is a large difference due to the netting. Evaporation data is related to how much water the avocado trees will use. In the chart below, the red and yellow bars are inside the netting. It can be seen that evaporation in the centre of the netted area is about half that of trees outside the netting. This is encouraging as using less water is one of the reasons Avowest wanted to trial netting.
Generally, the trees inside the netted area look happier than trees outside. We will be measuring growth parameters to quantify this but haven’t done so yet.
The summer of 2021/22 has been truly awful and some of the weather stations have recorded up to 47oC. We have lost trees that were around 1 year old in the netted area but mostly on the east and north edges of the structure where the winds are hotter and stronger. Outside the netting we have had significant burning of trees, including many that were larger and stronger. Establishing the trees has not been helped by the fact that a high proportion of the weeds there are tolerant of glyphosate. This has made weed control difficult.
Despite some tree mortalities, the trees inside the netting look healthier.
When we investigated netting in other crops and areas it became obvious that there could be changes in pest management. This has certainly been the case at Avowest.
Late in 2021 there was a persistent problem with Ivy leafroller (Cryptoptila immersana). This is an occasional problem at Avowest but is easily controlled with a single spray of Bacillus thuringiensis, which is an organic spray. In the netted area the caterpillar damage was more severe and took more spraying to control them.
Overall, it’s been a mixed bag of results for the netting trial. There is a high degree of variability within the netted site. The edges exposed to hot winds are recording data that is less favourable to avocado production than outside the netted area. Further inside the netting conditions seem to be much better for the avocados to grow.
When the netting was set up we knew the site was exposed to strong winds and chose a heavier netting on the sides than on the top. In hindsight we needed more protection.
At another netted site at Moora Citrus there are large Casuarina trees surrounding the netting. Despite having misgivings about the Casuarinas stealing water, they would be beneficial in slowing wind. We could have used even heavier netting but had one side blow out over winter. Heavier netting would have only made this worse.
To try and overcome the damage that hot winds are causing we have planted sorghum in exposed areas to protect the young avocados. At Avowest we have always planted sorghum as a windbreak for new trees. We didn’t do it in the netted area as we were expecting the netting to significantly slow the wind.
The netting trial is an exciting project for Avowest. We will continue to monitor the large amounts of data that are being generated.
Very soon sap flow sensors will be installed in trees so we can measure how much water they are using. At the moment we are evaluating a lot of parameters that could impact on the trees water use. The sap flow sensors will enable us to measure this directly.
We are at least a year away from being able to measure the most important parameter of all – yield. Some of the trees were large enough at flowering to start producing avocados. Unfortunately for us, Perth had its wettest October on record. Conditions at flowering were very bad for setting fruit. All the trees at Avowest have a poor crop as a result.
I am very happy to discuss the trials if anyone wants more information. Send me an email via our contact page.
Alan