How We Grow

Spotting damage in the orchard From March to early May, BMSB and LFB can feed on young nuts before the shell hardens, causing the embryo to abort and drop to the ground. "We've gone into orchards along Interstate 5, west of Fresno, and we suddenly see a tree where all the nuts have dropped off like a shaker shook them off the tree – green," said Patrick Romero, an almond grower and independent pest control advisor. "These are green nuts; I mean they haven't even started to hiss or crack. I think this is more common in dry years because the weeds dried down early and the insects need a host plant to live on." Growers will see the telltale sign of gummosis on the nut. LFB usually feeds on one or two spots per nut, resulting in thread-like gumming. BMSB feeding results in multiple gumming spots per nut, with glob-like gumming. Based on field observations by PCAs, UC Cooperative Extension and handler field staff, certain varieties of almonds tend to be more susceptible to damage from BMSB and LFB, including Price, Fritz, Aldrich, Sonora, Monterey and Butte. After the shell hardens, BMSB (and native stink bugs, mainly green stink bug) can still cause damage to nuts late in the growing season, through July. The bug can probe through the hull and shell with its piercing-sucking, needle-like mouth, injecting a digestive enzyme upon feeding to liquify plant tissue. This leaves a brown spot on the kernel – damage nearly identical to that caused by the green stink bug. Brown spot from insect damage should not be confused for hull rot, but Romero says there's a way to distinguish between the two. "When the nut begins to crack, it becomes very susceptible to any humidity and the shell can start to rot in the green hull, which can stain the kernel," Romero said. "You can tell if you take a knife and cut through that spot. If it's a deep, recessed brown injury, then it's an insect. If it's just superficial, just under that brown skin of the kernel, then it's hull rot." A brown spot on growers' bottom line Mel Machado, vice president of member relations at Blue Diamond Growers, has closely monitored the uptick of brown spot damage caused by insects. "We're seeing up to 30% of the total rejects caused due to brown spot. So, if you have 1 to 2% overall rejects, then about a third could be caused by leaffooted bugs or stink bugs and the brown spot they leave. There's been cases where if a grower didn't have brown spot, they wouldn't have had a reject problem. I have been watching this trend grow and it scares me." Machado says he has seen some growers lose their entire load due to brown spot, a huge economic loss. "There were guys that had 15-20% total rejects and it was all brown spot," Machado said. "My goal is to have growers at 2% or less on reject damage because that's where the premiums really kick in. If you're at 15-25% damage, that's a couple thousand dollars of loss per acre." Romero echoes Machado's sentiment, encouraging growers to manage for BMSB and LFB to protect their bottom line. "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." Managing for BMSB A close look at or removal of potential BMSB overwintering sites, such as structures and woodpiles near to the orchard, help to reduce the BMSB population. "If you have early season hosts, such as trees of heaven (Ailanthus trees), near the orchard, that tree species most likely supply BMSB to the orchards," Rijal said. "We have observed this in many orchards where tree of heaven is nearby. It is the most preferred non-crop host of BMSB." According to Rijal, growers can use a trap baited with a BMSB aggregation pheromone and pheromone synergist, methyl decatrienoate, to monitor adults and nymphs all season long. "Fortunately, we have a trap for BMSB, which we don't have for the rest of stink bugs," Rijal said. "Several PCAs and growers are using it once they find they have damage." However, Rijal notes that a treatment threshold has not been developed for the pest. The recommended best management practice at this time for growers who have BMSB in traps and confirmed visual surveys is consideration of a spring application for control. "The best insecticide to use in the early season to control BMSB is a broad spectrum pyrethroid, but these are also the ones that can kill beneficial insects" PEST MANAGEMENT Continued from page 2 Adult LFB feeding on green almonds. Courtesy: Jhalendra Rijal, UCCE 3

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