How We Grow

PEST MANAGEMENT ALMOND ORCHARD 2025 GOAL ABC, Industry Partners Marshal Efforts To Combat Insects Causing Brown Spot Brown spot damage caused by plant bugs is on the rise, resulting in higher rejection rates and blemishes on the bottom line for growers. Since 2017, the most severe cases of brown spot accounted for nearly half of the damage experienced by some growers. In extreme instances, kernel deliveries to handlers were rendered as oil stock, where the crop was discarded and growers were left without a return on their monthslong investment. Latest culprit: Brown marmorated stink bug Brown spot can be caused by a variety of true bugs, such as native stink bugs, which use their needle-like mouth to probe through the hull and into the kernel. Across the industry, experts are seeing two types of bugs increasingly responsible for brown spot damage in almonds, one of which is the brown marmorated stink bug (BMSB). "The brown marmorated stink bug is a relative newcomer," said Dr. Jhalendra Rijal, UC Cooperative Extension integrated pest management advisor for Merced, Stanislaus and San Joaquin counties. "We first saw it in 2017 in only one orchard, and now we're seeing it more frequently, and in more orchards and more counties." BMSBs are approximately 3/4-inch long with brown marmorated — or marbled — shading on their upper body surface. The bug feeds exclusively on the reproductive structure of plants, such as fruit, and in some cases flowers, causing significant economic damage to a variety of crops. The first reported BMSB infestation of an almond orchard occurred near Modesto and has since spread to orchards in the northern San Joaquin Valley, where it has caused the most damage over the past six years. "It's established in the majority of counties along Highway 99, from Butte — even Colusa and Glenn counties — all the way down to Fresno County," Rijal said. "The tricky thing about BMSB is that it can establish in an urban area because it feeds on ornamental trees and we may not see it in a crop at first in many cases." Warmer winters in California may be one possible reason for the recent geographic spread and rise of the BMSB population. "The BMSB adults overwinter in relatively warmer places, using people's houses or any kind of structure, such as wood or junk piles," Rijal said. "So, when there is a mild winter, there's less overwintering mortality, and they might come out early because of the warmer conditions." Due to its penchant to overwinter in undisturbed areas, the BMSB invades orchards quickly and in large populations. "BMSB just doesn't go to the orchard, feed and stay there," Rijal said. "They come to the orchard, feed and then fly back." Within two weeks after emergence in the spring, overwintering adults will mate, with females laying a cluster of around 28 eggs on the underside of leaves. Eggs are light green when first laid, gradually becoming whiteish near and after hatching. A single female BMSB can produce more than 480 eggs in a lifetime. On the rise: Leaffooted bugs As with the brown marmorated stink bug, higher instances of brown spot caused by the leaffooted bug (LFB) have been reported in recent years. The LFB is about 1 inch in length, with a narrow brown body and a yellow or white zigzag line across its flattened back. LFB has also benefited from recent mild winters, allowing a higher percentage of its adult population to survive into the spring, enabling a larger March or early April flight. "Late in the fall, LFB moves from almond or pistachio orchards to some other hosts, like pomegranates," Rijal said." After they feed there, they go somewhere else. It's not exactly clear where they overwinter, but we do see them in cypress trees and in some bulk, dense trees where they can hide." Following their overwintering period, LFB moves into orchards, with females laying strands of usually 10 to 15 eggs, often found on the sides of almond hulls. One LFB adult female can lay more than 200 eggs in the first two months of spring. Continue on page 3 BMSB nymphs feeding on green almonds in Hughson, California. Courtesy: Jhalendra Rijal, UCCE "If you don't bring into the processor a clean crop, you tend to lose more money than the drop in the price. You're going to get paid less per pound because you didn't spend another hundred or two hundred dollars an acre trying to control an insect or a disease." — Patrick Romero Almond Board of California 2

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