How to Manage Pests
UC Pest Management Guidelines
Scientific names: Lygus hesperus, Lygus elisus, and Calocoris norvegicus
(Reviewed 4/10, updated 4/10, pesticides updated 9/15)
In this Guideline:
Adult lygus bugs are somewhat variable in color and size. In general the adults are about 0.20 to 0.25 inch long. Lygus hesperus adults vary from yellowish to reddish brown and the adults of Lygus elisus are pale or yellowish green. A distinctive yellow triangle is located in the middle of the back. Overwintering males of both species are mahogany colored, while the females are reddish. Eggs are slightly curved, elongated, flattened on one end, and inserted into plant tissue. Nymphs are pale green in color. Later instar nymphs have circular, black spots on the dorsum.
Lygus bugs overwinter as adults in plant debris, in the crown of plants on the orchard floor, and in uncultivated areas outside the orchard. As temperatures rise, females begin laying eggs on a wide range of plants, especially mustards. As plants begin to dry up in uncultivated areas, lygus adults migrate to irrigated areas where mating occurs. It is believed adults are chiefly responsible for damage to fruit orchards, as nymphs are rarely found in trees. There may be as many as 6 to 10 overlapping generations per year.
Calocoris adults are about 0.25 inch in length with a green-colored body. The wings have a reddish brown tint and are black where they overlap. There are also two black dots on the thorax. Calocoris is usually found on mustard, wild radish, and vetch hosts and is most common in the northern San Joaquin and Sacramento valleys. Populations of Calocoris may build up on cover crops, especially purple vetch. There is only one generation a year so late season problems do not occur with this pest.
Adult Calocoris can be distinguished from lygus bugs by the presence of two black dots on the back just behind the head. Calocoris nymphs do not have red-tipped antennae and black spots on the back as do lygus nymphs. Calocoris nymphs tend to be longer and narrower than lygus nymphs and have fine black hairs on the body.
Damage to rapidly growing shoot tips can begin as early as mid-May in most years, when adult plant bugs begin laying eggs and feeding in the soft tissue at the tips of the shoots. They can also insert eggs in fruit at this time. Severely damaged terminals may resemble peach twig borer and oriental fruit moth shoot strike, but there is no tunneling in the shoot tips and damage generally occurs lower in the tree. Affected growing tips may die, causing lateral buds to push and shoots to become bushy.
Plant bug feeding on green fruit may result in gumming, but gum is usually absent on nearly ripe and ripe fruit. On green fruit, feeding stings cause the outermost cortical cells of peach flesh to die, resulting in small, bluish green spots. The skin then develops a small, dead area that often splits as the fruit grows, frequently causing it to be misshapened. On nearly ripe fruit, feeding is characterized by small, dead areas where a small cavity has developed beneath the skin. Fruit damage is sporadic and doesn't occur every year; however, in some years severe economic losses can occur. In general, plant bug populations are highest in years where there is lots of lush vegetation growing in and around the orchard.
Generally speaking, plant bug damage is worse in orchards planted near wild or uncultivated areas or in orchards near a host such as alfalfa, cotton, safflower, or tomatoes. Damage is often heavier on outside rows or in areas of the orchard that are nearest to a source of migrating adults. Anticipate migrating adults as other hosts begin to dry or are cut or harvested. Calocoris damage is a problem mostly in orchards where there is a legume cover crop other than subclover.
Cover crop manipulation is important in plant bug management. In orchards located away from an outside plant bug source, clean cultivation or a weed-free orchard floor will aid in suppressing these pests. Where hard-to-kill broadleaf perennials are present, treat the orchard floor with an insecticide when sweep net counts indicate a potentially damaging population is present in the weeds.
Where migration is a problem, destroy as many surrounding hosts as possible in early spring before first generation nymphs complete their development. If you own or manage the adjacent fields, another alternative is to treat these areas with pesticides, although there may be hazards to foraging bees. If it is impossible to keep plant bugs from moving into an orchard, a lush, well-managed cover crop might help to keep them on the orchard floor. Care must be taken to keep the cover crop attractive to the plant bugs; if it dries up, plant bugs will move up into the trees. New orchards that are planted next to weedy areas are especially susceptible to damage from both plant bugs and thrips as the weeds dry out. If an orchard is near an alfalfa field, strip-cutting the alfalfa or leaving a strip uncut nearest to the orchard will help prevent migration out of the alfalfa. If Calocoris bugs are feeding in a legume cover crop, be sure not to mow it until the adults are gone (there is only one generation a year).
Monitoring and Treatment Decisions
Examine fruit on trees every other week after color break (see PREHARVEST FRUIT SAMPLES) to detect any developing problems in the orchard and take a fruit damage sample at harvest to assess the effectiveness of the current year's IPM program and to determine the needs of next year's program (see FRUIT EVALUATION AT HARVEST). Record results for the harvest sample.
UC IPM Pest Management Guidelines: Peach
Insects and Mites
J. K. Hasey, UC Cooperative Extension, Sutter and Yuba counties
Acknowledgment for contributions to the Insects and Mites:W. J. Bentley, UC IPM Program, Kearney Agricultural Center, Parlier
C. Pickel, UC IPM Program, Sutter and Yuba counties
R. E. Rice, Kearney Agricultural Center, Parlier
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