Monday, May 2, 2016

These Pesky Bugs Can Really Gum Up Your Almond Crop

 It glistens in the streams of sunlight penetrating the canopy of the almond trees. You could see the small sap-like glob stuck to the green peach fuzz of a young almond hull.
To field scout Jenna Mayfield, it’s the likely sign that leaffooted plant bugs (LPB) have found a home in the orchard. That can be bad news for the grower. A small number of bugs can cause a lot of damage.

Gummosis on the hull of an almond.  
During her scouting rounds last week, Jenna found a few orchards troubled by the LPB. In each instance, the orchards were bordered by grape vineyards. Jenna suspects the deep ridges of the canes of the grapevines were an ideal place for overwintering adults. In March and April, the bugs head out to the orchards looking for a meal of fresh nuts.

Jenna points out these pests will feed on young nuts before the shell becomes hard, causing the developing embryo to wither or gum inside. Nuts also can drop.

Leaffooted bug damage on a kernel.
After the shell hardens, the leaffooted plant bug can continue to feed on the nut, causing black spots on the kernel, wrinkling to misshaping the nutmeat. The damage can lower the quality, or grade, of the nuts.

An almond cross section.
Jenna collected some samples and will be cutting a cross section of the damaged side to look for a puncture mark from the bug’s mouthparts to make sure the outside gumming – called gummosis – isn’t caused by bacterial spot. You can tell by the color – gummosis caused by leaffootedplant bugs is clear to amber in color while bacterial spot damage is a dark amber to orange color.

UC IPM recommends growers check weekly for leaffooted plant bugs this month and every one or two weeks through June. A visual inspection is the best way to look for the bugs in the trees. Use a long pole to knock branches in the top part of the canopy and look or listen for the bugs to fly around.
Farm advisors also say growers should inspect the fruit for gummosis on the almond hull. However, damage has probably occurred if you already see evidence of gummosis.

Close-up of a leaffooted plant bug.
“Treatment thresholds have not been developed for this pest in almonds, but low numbers of bugs can cause substantial damage. If bugs and their damage are evident, consider a treatment,” UC IPM says. Jenna notes that some growers have been treating for leaffooted plant bugs.

Meanwhile, Jenna points out almond growers also need to be on the watch for European red mites. There have been reports of red mite pressure in some orchards in the region, she says.

European red mites.
These mites usually don’t reach damaging levels, according to UC IPM. In fact, low numbers can be beneficial because they can serve as a food for mite predators. But orchards with a high population over a long period can experience leaf drop, especially in trees that are stressed.

Yes, says Jenna,  “there is always a bug to be on the look out for during the season.”

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