Leaffooted plant bugs and stink bugs are capricious pests in San Joaquin Valley almonds and occur on a hit-or-miss basis, says David Doll, University of California Cooperative Extension farm advisor for Merced County.
“These two insects seem to cause a little damage every year,” he says “Some growers have them every season and know they’re coming. For the most part, however, they sneak up on other growers and the next thing they know they are seeing stings throughout their orchards.”
Leaffooted plant bugs and stink bugs overwinter in undisturbed ground, under shingles on outbuildings, and even in asparagus patches, Doll says. The migratory insects can move in quickly and cause severe damage within an orchard, if not controlled.
“If you have them, they can be pretty devastating,” he says. “With a heavy infestation, you can lose a lot of crop fairly quickly.”
Last year, he received calls from growers on both the eastern and western edges of the Central Valley, as well as western Fresno County, where plant bugs were common. Most of the damage was where orchards interfaced with rangelands.
Overall, damage from these pests is increasing, he says. “We don’t have enough data to know whether that’s due to more acres of almonds being planted or to higher populations of the insects.”
There is no way to accurately gauge the likely threat of a leaffooted plant bug or stink bug infestation in advance, Doll says. “We just don’t have a lot of good information for modeling or predicting outbreaks of these insects.
The damage caused by leaffooted plant bugs and stink bugs in almond orchards in the San Joaquin Valley is on the rise, saysVern Crawford, PCA with Wilbur-Ellis, based in Shafter, Calif. He works with growers in Kern, Kings and Tulare counties.
Asked if they caused problems last year, he responded: “Did they ever! We had a lot of problems with them.
“We’re beginning to recognize that the leaffooted plant bugs and stink bugs that hang out over winter are becoming a greater concern. In talking with my counterparts elsewhere in the valley, it’s interesting how much of a problem these insects are causing in Modesto and farther north.”
The insects move into the valley from the eastern Sierra Nevada foothills, overwintering in urban areas, particularly yards with cypress and conifer types of plants. They also overwinter in pomegranates, as well as almond and pistachio orchards.
“Three years ago, some almond growers suffered huge amounts of damage from leaffooted plant bugs, losing as much 40 percent or more of the crop,” he says. “The next year, there seemed to be fewer of the pests, but a lot more damage from stink bugs. Last year, depending on location, some growers had a fair amount of leaffooted plant bug damage.”
Increasing outbreaks coincide with growers’ move away from using broad spectrum insecticides in their dormant spray to more selective, softer products, Crawford says.
Years ago, growers weren’t aware of leaffooted plant bugs and stink bugs, he explains, because they were using materials, like parathion, that killed the damaging insects as well as the beneficial ones. As a result, leaffooted plant bug and stink bug populations didn’t build up to the point where they caused many problems.
“Now, we’re using products in our dormant sprays that target only certain pests, like scale, navel orangeworm or peach twig borer,” Crawford says. “So, more leaffooted plant bugs and stink bugs are surviving overwinter in much higher numbers than they used to.”
Pressures from the insect have increased to the point where some of his growers treat their almond orchards every spring as the nutlets are filling and the hulls become soft enough to be punctured.
“I’m always looking for damage,” Crawford says. “When I see it, I recommend growers be ready to treat their orchards immediately. With the market value of almonds today, growers won’t tolerate too much damage to their crop.”
Last year, that approach protected 100 acres of almond trees for one of his growers in Tulare County whose orchards were invaded by leaffooted plant bugs. He and the grower found leafooted plant bug eggs, larvae and adults throughout the orchard when nutlets were in the milky stage of development.
The first of two insecticide applications was made immediately. Two weeks later, after more fresh damage was found, the second treatment was combined with a spider mite spray. No further treatments were needed to control the insect.
Neither the leaffooted plant bug nor the stink bug caused any problems in the almond orchards observed in 2011 by PCA Sara Savary, Crop Care Associates. Based in Fresno, Calif., most of her growers are in Madera County.
“I didn’t see any of the insects in fields last year,” she says. “In the past, the only areas where I’ve seen them have been on the east side of the San Joaquin Valley near the foothills.”
Problems with these pests have been few and far between in recent years. Savary attributes that to the increased flow in the San Joaquin River, which has kept nearby vegetation green through much of season. This has provided enough suitable habitat that the insects have had no need to move elsewhere in search of hosts, including almonds and pistachio orchards, she says.
Continued dry weather into spring could reduce the leaffooted plant bug threat for almond and pistachio orchards this year, by reducing refuge habitat, Savary says.
A University of California survey of lygus bugs in the foothills finds larger populations in wet winters due to more vegetation to support the insect, she says. “It would seem logical that other plant bugs that overwinter in non-croplands and migrate out of the winter refuge will have the same pattern.”
Like Savary, PCA Rene Forbes sees the leaffooted plant bug and stink bug only on the east side of the valley. As owner of Forbes Consulting, Inc., Dos Palos, Calif., she also works with growers in Madera County.
The insects move down creeks and rivers from the foothills, and when brush in those areas dries up, they migrate into almond and pistachio orchards, she says.
There’s no set pattern to the frequency of infestations, Forbes says. “It’s random from year to year. They may be in orchards one season, but not the next.”
In the past five years, stink bugs have become more prevalent in almond orchards in the areas where she works, but she’s not sure if that reflects a bigger population base of the insects.
The increasing pistachio acreage might also explain the growing numbers of stink bugs in almond orchards over the past few years, Forbes says. In fact, last year, the only case where she needed to treat for the insect involved two blocks of almonds about three miles apart owned by a grower in eastern Madera County. Both blocks bordered a pistachio orchard on one side. At the same time, she saw no stink bugs in any of the other almond orchards where she works in the county.
Last year, she became aware of stink bugs in the two infested orchards on April 10. That’s when she saw the first telltale sign of their presence — curly strands of gum spiraling out of newly-forming nuts where the insect had stung the nutlets.
“It’s very difficult to actually see stink bugs in an orchard,” Forbes says. “So, when I saw the tail of gum from the nutlets, I looked closely at other nutlets for similar damage. Also, I shook the limbs, as when looking for leaffooted plant bugs to confirm that the insects were in the orchards. The stink bugs dropped from the shaking foliage.”
Forbes treated the orchards with Belay, which she describes as soft on predators, effective in controlling stink bug and leaffooted plant bug, and not expensive.
“The infestation in both blocks was light, and we didn’t want it to get bigger,” she says. “So, we applied the insecticide the moment we found the stink bugs.
“I don’t know of a threshold pest count to determine when to treat. But, if I see the gumming damage and then find stink bug or leaffooted plant bug, I treat. Last year, it was April when I found the problem, but everything was late last year. March is the normal time to find the pest and problems when the nutlets are at their most vulnerable stages. The untreated nutlets drop and crop yield losses can be great.
That single treatment was enough to eliminate the threat last year. Had the insect come back later in the season, Forbes says, she would have continued treating as often as needed to control them.
June is another time when damage can be found. Controlling stink bugs and leaffooted plant bugs isn’t always that easy, she says. “You never know if, or when, they could become a problem, so I watch for them throughout the season, until shells harden enough that they won’t be damaged by the insects.”
She’s found that some varieties, particularly Butte and Fritz, seem to be more attractive to leaffooted plant bugs and stink bugs. The bugs don’t feed as much on Nonpariel and other varieties, she says.
Forbes isn’t making any predictions about how much threat, if any, either insect could pose to almond and pistachio orchards this year. However, she points out that almond trees are advancing earlier this year than in 2011.
“Development of pests usually tracks development of the orchards,” she says. “The trees bloomed earlier this year, so the pests probably will be earlier, too.”