Avoid Almond Hull Rot With Deficit Irrigation
June 7, 2016 As growers approach almond harvest later this summer, strategies to reduce the likelihood of hull rot should be a top priority.
Growers can start looking for signs of rot now, but should be cognizant of possible problems before hullsplit begins. Strategic deficit irrigation (SDI) can significantly reduce the possibility of hull rot.
Trees affected by hull rot will eventually have withering and dying leaves on shoots. Fruit can have brown areas on the outside of the hull, and tan or brown areas inside or outside the hull, indicating Monilinia, or black fungal growth inside the hull indicating Rhizopus. These fungi produce toxins that can damage fruit and trees.
The process plays out before and during hullsplit, which happens around early July, says Ken Shackel, professor in the Department of Plant Sciences at the University of California, Davis.
“That fruit part of the nut starts to split open and exposes itself to all kinds of things, such as navel orangeworm and fungal spores,” Shackel says. “In addition to ruining the nut, the fungus allows a toxin to get into the plant and can ruin a whole branch. You can lose more than just some nuts.”
Shackel says almond growers nearing hullsplit should start testing water potential in trees with a pressure chamber. That measures the amount of pressure needed to force water out of a leaf.
Using SDI can stress almond trees, helping to dry the fruit more quickly during hullsplit. Shorter hullsplit times reduce the window of opportunity for hull rot fungi. Too moist, and fungi get longer to attack almonds.
“When they’re kind of under moderate stress, at the time this process is starting, the process goes quickly and the nuts aren’t susceptible for as long,” Shackel says.
The ideal pressure, Shackel says, is between 14 and 18 bars. A bar is about 14.5 pounds per square inch of pressure.
Growers can use those measurements to determine whether they should cut back on irrigation to stress the trees more. An SDI regimen can reduce hull rot by 60% to 90%.
For more information on hull rot prevention, visit the University of California’s Statewide Integrated Pest Management Program site on the topic.
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