- Author: Ben Faber
So after five years of drought a grower told me he finally gets it. Farming avocados in Goleta with limited well water and poor quality and expensive, rationed delivery, he has finally cut out trees that were not performing well. These were wind sept trees, areas with root and crown rot. Tree were either stumped or removed altogether. The idea is to focus on those trees that are productive, and are they ever. They are getting the water they need and their schedule has been changed. Previously irrigation had been on a fixed schedule of 2 weeks and got 24 hours per set. The schedule was dictated by the time it took to get around to all 300 acres. Now trees are irrigated one to two times per week with shorter sets, from 5-8 hours depending on the time it takes to get 18 inches of penetration in sandy ground. Yields per acre have significantly increased, largely because non-productive areas have been eliminated and the remaining trees are getting what they need.
He is also anticipating irrigation needs – projecting a schedule.
The driving forces for water loss in avocados in decreasing effect are sunlight (day length, cloud cover), wind, humidity, and temperature. More light, more transpiration. More wind, more water loss, lower humidity, more water loss. And least of all if temperature which is what we normally respond to, but which the tree responds the least. Usually, though the most desiccating conditions occur during periods of high, dry winds that blow out of the Great Basin – the dread Santa Anas or in the case of Santa Barbara the Sundowners. When they start blowing, it's hard to play catchup. It takes a while for water to infiltrate and for the roots to start taking it up and filling all the drained leaves and stems. Now the grower more carefully watches the forecasts and makes sure to get water on before the high demand conditions arrive. With multiple blocks he wants to get all of them wetted to a normal irrigation depth and then it's time to start the cycle over again. He keep an eye on the nearest CIMIS station to see how much the water demand is increasing and adjusts the irrigation frequency. Importantly, h keep your eye on how fast the soil in the root zone is drying out and then makes even smaller and more frequent applications.
When it comes to making the water meet the needs of the trees, he is really customizing each irrigation.
- Author: Ben Faber
I've been getting calls and have gone out to see several avocado orchards in the Ventura/Santa Barbara area and the comments are that the trees look worse this year than they normally do. When I see the trees, it's clear that they don't look in the best shape. This time of year, when there are old leaves that have accumulated salt all through the irrigation period and the trees are getting ready to flower, the leaves just don't have much energy. Also, two years of drought with no rain, means that salts have probably accumulated more by this time of year, than in a year when we do have “normal” rain to leach the soil. The accumulated salts can lead to water stress which also brings on stem and leaf blight, along with salt burn. With the bicarbonates in the water, the pH may have rise as well, inducing some iron chlorosis. Compounding the leaf damage is some frost burn, which was not cold enough to kill the leaves. Any dead tissue, also makes the leaves look more ratty, because with Santa Ana winds earlier, those dead areas have often blown out, making them look like they have been nibbled on by insects. Further adding to the stress was a huge crop year that put a lot of stress on the tress. When clearing the leaves to look at roots, it has often been hard to find viable roots. All these stresses are going to make the trees more susceptible to root rot. So it's going to be necessary for growers to keep their eyes out for further disease symptoms and to be ready to treat with phosphites when the soil warms up enough for the roots to start growing again.