Craig Kallsen

UCCE Farm Advisor, Kern County

Citrus, Subtropical Horticulture, Pistachios

November 19, 2001

FALSE CHINCH BUG SUSPECTED OF DAMAGING CITRUS FRUIT

The adult false chinch bug, Nysius raphanus, is a grayish-brown plant bug about1/8 inch or 3 mm long. The legs and antennae of chinch bugs are relatively long and are darker than their bodies. The adults, unlike the immatures, have wings and are slightly larger than the nymphs. The nymph is somewhat lighter-colored than the adult and its abdomen has more of a reddish tinge. During spring, summer and fall, the nymphs and adults can be so numerous that it appears the ground is moving in infested areas. The adults when disturbed can produce clouds of insects so thick that they may make breathing difficult.

False chinch bugs breed on weeds. Weeds that serve as host plants for these insects include wild mustards, wild radish, shepherds purse, London rocket and, especially, spurge. The eggs are laid randomly on the soil or within soil cracks. They overwinter as nymphs. As weeds dry up in late spring, or are cultivated or killed by herbicides, false chinch bugs may move to adjacent tree crops such as citrus.

The ability of false chinch bugs to damage young citrus, pistachio and other fruit trees is fairly well documented. Their feeding can cause young trees to wilt and die. The decline of young trees is often so rapid that the presence of a toxin in false chinch bugs has been hypothesized. Now, observational evidence strongly suggests that false chinch bugs can seriously damage mature citrus fruit as well. The damage occurs in progression. Typically, in the presence of high populations of false chinch bugs, the green fruit on the skirts of the trees turn prematurely yellow. Darker discolored brown patches appear within the yellowed areas of the fruit rind. Light stippling may be visible in these brown areas. The damage at this stage appears similar to that which might be done by sunburn, herbicide, or by leafhoppers.

Under light feeding pressure from false chinch bugs, the areas of the fruit rind where the oil glands appear to be damaged may not be visible in the green fruit picked during the early navel orange harvest, but appear as green-spotting after the fruit is treated with ethylene gas. Under conditions of high pest-feeding pressure, the fruit on the tree may become more brightly colored with brighter hues of yellow and reddish oranges. At this stage the fruit falls easily from the branches. Leaves adjacent to the fruit do not, generally, show much damage.

False chinch bugs were commonly seen in the southern San Joaquin Valley this season. When large numbers of false chinch bugs are present in orchard weeds, and the weeds are scheduled for treatment, it may be advisable to include a properly labeled insecticide with the herbicide to prevent a migration to citrus or other tree crops. This pest may also be present in neighboring rangeland, and move into bordering crops once the summer dry season commences and range plants dry out. False chinch bugs often appear suddenly and may disappear just as quickly, leaving growers, pest control advisors and packinghouse managers wondering just what caused the damage to oranges crossing the packline.