Blue Diamond Almond Facts November-December 2021


Dr. Jhalendra Rijal, UCCE Area IPM Advisor for San Joaquin, Stanislaus and Merced counties led a session where he discussed the increasing problem of brown spots on almonds due to insect damage and a the best ways to approach the issue.

What Causes Brown Spots on Almonds? Farm advisor offers causes and cures

With brown spot defects on almonds approaching the frequency of Navel Orange Worm damage in recent years, growers have begun looking for answers to the cause and cure. Those questions were addressed at Blue Diamond Growers ’ virtual annual growers meeting November 17. Dr. Jhalendra Rijal, UCCE Area IPM Advisor for San Joaquin, Stanislaus and Merced counties, pointed his finger at several species of Hemiptera “True Bugs” as the primary culprits who attack immature almonds early and mid-season, leaving them gummy, stained with brown spots or lying on the ground from nut drop.

Leaffooted Bugs and several varieties of Native Stink Bugs do most of the damage, Dr. Rijal noted. However, a new, invasive stink bug has found its way into the Central Valley — the Brown Marmorated Stink Bug (BMSB) which feeds on almonds throughout the season.

predators to count on for control. Only a few insecticides are available for these pests and these materials are most useful early in the season. • Bifenthrin (Brigade WSB) • Lambda-Cyhalothrin (Warrior ll with Zeon) • Clothianidin (Belay) • Esfenvalerate (Asana XL) Pest Behavior Most feeding damage from True Bugs occurs before shell hardening — early through mid-May. The bugs are equipped with sharp, needle-like feeding “stylets” that they insert through the hull as far as the kernel, release one or more enzymes that liquefy the nut material, and suck up the juice. The brown spots occur as a result of the plant fighting back by deadening the flesh around the wound to prevent the bug from causing any more damage.

But not all brown spots in almonds are created by bugs, he said. Mold, fungus, high moisture, and pathogens transmitted by large insects can also be a factor. Bug Control Prevention and control of Leaffooted Bugs and Native Stink Bugs involve early detection through visual inspection of the tree canopy looking for bugs and egg masses and applying insecticides before the bugs begin feeding on the new crop. When visually checking for True Bugs, Dr. Rijal recommends concentrating on the middle and upper canopy early in the season before the bugs damage the fruit. He says there is no economic threshold to begin control. There are not enough

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