Issue link: https://www.e-digitaleditions.com/i/1268831
A L M O N D O R C H A R D 2 0 2 5 G O A L S WATER USE Almond Board of California 4 "Each almond variety has its own hull split timing, which is also impacted by irrigation decisions and nutrient management," Milliron said. With the seriousness of hull rot in mind, how can strategic RDI help combat this disease? As with all aspects of responsible management, it comes down to balance and a plan. 2 Make a plan "Growers should be thinking about irrigation throughout the crop year," said UC Davis plant science professor Ken Shackel, Ph.D., who is an industry expert on water and plants' ability to access it. "They should be aware of the amount of water stress their trees are experiencing throughout the year before practicing RDI to ensure their trees are in a 'good zone' or experiencing mild-to-moderate stress." According to Shackel, at least two weeks before hull split starts growers should be checking their trees' water stress levels to determine if the trees are already experiencing mild-to-moderate stress. If the trees are experiencing that level of stress before growers start RDI, there may be a problem. "Your trees may already be too stressed at that point. That's why it's so important to monitor their water levels throughout the year as a gut check on how the trees are feeling and what their needs are," Shackel said. At the onset of hull split, to succeed in combatting hull rot and stress the trees to the correct amount, growers should implement RDI by reducing their irrigation levels for two-to-four weeks. This will result in a 10-20% reduction in applied water. The maximum amount a tree may be water stressed before negative impacts – such as threats to crop yield – may occur is a 30% reduction in applied water. How can growers best measure tree stress not only leading up to hull split but year-round? Shackel, Yaghmour and Milliron each said they would like to see more almond growers use a pressure chamber to routinely measure tree stress. A pressure chamber measures plant water stress by applying pressure to a sampled leaf enclosed in an airtight chamber. The pressure required to force water out of the petiole of the leaf is measured with a pressure gauge and demonstrates how much tension the leaf (and tree) are experiencing. A high value of pressure equals a high degree of water stress. 2 Tree stress is best monitored by measuring midday water potential to ensure the trees are moderately (-14 to -18 bars), but not excessively, water stressed during hull split. 3 Prime your trees for harvest Shackel said that RDI also plays an important role in priming trees for harvest 2 For more on how to use a pressure chamber, check out ABC's Irrigation Station video "Using a Pressure Chamber" at https://youtu.be/iDgPG88ie18. Check out page 132 of ABC's Almond Irrigation Improvement Continuum to learn how to interpret a pressure chamber reading. Continue on page 5 "Irrigation systems are like a car – you need to regularly check the filters and flush out the pipes once in a while. There's a reason you do maintenance instead of repairs – it's always preferred and more cost friendly." — Sebastian Saa Hull rot is especially threatening as it can occur year after year in an orchard.