Growers and pest control advisers (PCAs) in the southern San Joaquin Valley should keep their eyes peeled for wilting and scorching in one to two-year-old grape vines and almond, pistachio, citrus, and pomegranate trees.
The possible culprit is heavy infestations of false chinch bug, Nysius raphanus. “Aggregations of false chinch bugs can quickly result in plant and tree decline,” said David Haviland, University of California Cooperative Extension (UCCE) Kern County farm advisor.
“There are reports of the heavy bug populations causing severe damage to young almond, pistachio, citrus and pomegranate trees.”
All leaves on border grape vines can be killed by false chinch bugs in a few hours, according to the UC Davis Integrated Pest Management Program.
As of late June, spotty, but heavy migrations of false chinch bugs were found in Fresno, Tulare, Kings and Kern counties. Haviland expected the buildup to end in early to mid-July.
Haviland has fielded numerous phone calls from growers, PCAs, and residents across Kern County from Delano to the north, Buttonwillow to the west, and Arvin to the south. Homeowners were hit hard as waves of bugs enveloped garden and landscape plants. Homeowners said the insect masses resembled “moving ground.”
“The problem is bad enough in some Kern County agricultural areas that if farmers didn’t spray they would lose a lot of young trees,” Haviland said. “In other areas you may find several false chinch bugs here and there. It depends on the vegetative areas around the orchard.”
The infestation failed to move south into citrus in the Coachella and Imperial valleys and the Yuma area, according to Cooperative Extension specialists.
Major weeds which serve as preferred hosts for the false chinch bug include London rocket, wild mustard, wild radish and shepherd’s purse.
Why the sudden explosion in false chinch bug numbers?
Above average rainfall this spring increased weeds and grasses in areas with natural vegetation. Cool spring and early summer temperatures extended the weed-grass growing season which fueled the false chinch bug buildup. The plants are now dying off due to hotter summer temperatures. The insects headed to orchards and vineyards to feed.
The adult false chinch bug is grayish brown, slender, and about 3 millimeters (eighth of an inch) long. The insect resembles the lygus bug. The nymph is gray with a reddish-brown abdomen. Chinch bug legs and antennae are longer and darker than the body.
Immature stages lack wings and resemble coffee grounds. Immature and adult insects feed on plants through their straw-like proboscis which probes into the plant tissue to drink plant fluids. Plants are unable to replace lost tissue and fluids.
The time frame from first infestation to scorching and wilting is two to three days.
“Such rapid damage suggests the false chinch bug injects a toxin into the plant,” Haviland said. “While not proven, there is consensus in the industry that the insect releases a toxin as it drinks plant juice.”
The false chinch bug can withstand 100-degree temperatures.
Haviland is not surprised by the heavy false chinch bug outbreak this year. False chinch bugs appear annually. The last heavy infestation occurred following the mild, rainy winter in 2005-2006.
Nut and citrus trees three years and older are more resistant to insect damage.
Haviland says the best treatment for false chinch bug includes broad spectrum insecticides including organophosphates, pyrethroids, and carbamates. Reduced-risk insecticides or bio-control products are not available.
“Catching the insect early on the field perimeter is best,” Haviland said. “Keep spraying the field edges to keep them from moving in. Once they are in the entire field then spray everything.”
Haviland suggests applying insecticide sprays by air or ground application at night or early in the morning. False chinch bugs hide during the middle of the day under weeds and inside the cardboard trunk guards (milk cartons) around the base of new trees and vines. The guards help protect the young trees from sunburn and herbicide damage.
“These bugs love to hide down in the milk cartons,” Haviland said. “Hundreds of the insects will hide inside the carton during the middle of the day. In the evening they come out and feed on the plant all night. Sprays are less effective when the bugs are inside the milk cartons.”
As the weather stays hot, Haviland expects the chinch bugs to disappear.
Fall migrations of false chinch bugs can occur in September and October.
“Basically it boils down to watch your blocks,” Haviland said. “If you have enough bugs to see wilting or scorching then you need to treat. Make sure treatments do not run off into waterways. That’s not a problem with micro sprinklers.”
The UC Davis’ IPM program offers these false chinch bug control suggestions for grapes. If false chinch bugs have been a problem in the past, disk under stands of London rocket and other host weeds about three weeks before bud break in grapevines. Do not delay disking until after bud break since it could result in the heavy movement of the bugs from the weeds to the vines.
A treatment may be necessary if weeds were not disked and high populations of false chinch bugs are found on weeds at bud swell or after bud break.
If nymphs are found moving onto vines, spot treat the vines and adjacent weeds. Bugs migrate mainly in one direction. Wilted vines along the edge of the vineyard will indicate the line along which they are moving. A chemical barrier about 30-inches wide can prevent further migration.
Citrus damage from false chinch bugs includes the premature yellowing of green fruit on the skirts of the trees, according to Craig Kallsen, UCCE Kern County farm advisor.
Darker discolored brown patches appear within the yellowed areas of the fruit rind. Light stippling may be visible in the brown areas. The damage at this stage is similar to damage from sunburn, herbicides, or leafhoppers, Kallsen says.