Pistachio trees may just be pushing out leaves in early April, but it’s not too early to begin scouting for insect pests and planning effective control strategies.
Pest control adviser Justin Nay of Integral Ag., Inc. in Butte County lists small plant bugs, including lygus, calocoris, and phytocoris; plus Gill’s mealybug, scales, and occasionally katydids as early spring pests which can invade pistachio orchards.
Considering the large amount of vegetation this spring, calocoris could be common this spring. The plant bug can be found on mustard, wild radish, and vetch in northern pistachio growing areas. Calocoris migrate into pistachios when native weed hosts dry up or are cultivated in the spring.
David Haviland, University of California (UC) Cooperative Extension (UCCE) farm advisor at Kern County, suggests that pistachio growers begin setting traps in April for Navel orangeworm (NOW). Also, small bugs and false chinch bugs could begin building in numbers in spring vegetation.
NOW monitoring with egg traps help determine the starting point in calculating degree days to the first flight of adults.
While Haviland is not making predictions on NOW pressure this year, the UCCE entomologist believes the wet winter may have had some effect on the viability of eggs laid in mummy nuts on the ground. The farm advisor has seen plenty of mummy nuts sprouting this season. Mummies left on the tree are a NOW source.
“The problem is not going away,” he warns.
Meanwhile, Integrated Pest Management Specialist Kris Tollerup at the UC Kearney Ag Center believes leaffooted plant bug numbers could also increase this year, due in part to the wet winter.
Bob Beede, UCCE farm advisor Emeritus, says calocoris is the predominant plant bug present prior to shell hardening. Most growers routinely add a pyrethroid to their mid-April nutrition spray to take care of the pest.
Meanwhile, phytocoris overwinter in the egg stage in pistachio. These insects are a short-term threat to pistachio from bloom through shell hardening.
There is also the potential this year for lygus to move from drying foothill vegetation into pistachio orchards, says Haviland. The lygus bug also poses a threat prior to shell hardening. Growers should be diligent in scouting for lygus and treat groundcover.
False chinch bug numbers could also increase this season. London rocket and spotted spurge are preferred hosts for false chinch bug. When weeds dry out, false chinch bugs can move into young budded trees and potentially kill the trees with a toxin as the pest feeds.
Gill’s mealybug, first found in California in the 1990s in Tulare County, has spread to all pistachio growing regions in the state. The pest feeds on immature nuts, intercepting carbohydrates needed for kernel development. Adult females emerge in late April and May.
The best time to find new mealybug infestations is from early fall through mid-winter when the numbers are highest. Sooty mold on leaves and adults within clusters are signs of infestation. Locations should be noted for inspection in the spring. At bud break, examine the base of new bugs for this mealybug.
Small, black nut clusters on the ground in late April and May are signs of leaffooted bug (LFB) feeding. Tollerup says mild temperatures last fall and few freeze events over the winter added another generation of leaffooted bugs. The potential exists for large populations this growing season, especially where pistachio orchards are adjacent to pomegranates, a preferred host for leaffooted bug.
A good way to scout for LFB is by examining the edges of orchards on the sunny side of the tree for signs of LFB. If present, eggs and nymphs can be found when nutlets form.
All scouting for leaffooted bug is visual. Tollerup says pheromone traps for this pest are still in the developmental stage. Eggs are fairly easy to see on leaves or twigs – barrel-shaped and lay in a line.
Tollerup notes that this pest can damage nuts at all stages of development and spread disease.