Lygus Bug in Sugarbeet

E-1289 Mark Boetel, Research and Extension Entomologist NDSU Department of Entomology Phillip Glogoza, Extension Specialist University of Minnesota Extension Service Justin Knott, Plant Protection Specialist North Dakota Department of Agriculture ▲ Figure 1. Adult tarnished plant bug on sugarbeet leaf. Lygus bugs have long been recognized Lygus nymphs (Figure 2) are pale to as pests of sugarbeets grown for seed yellow green and very small (only 0.04 production in North America. Three lygus inch long) during the first few days after ▲ bug species, the tarnished plant bug hatching. Older nymphs are larger (0.06 Figure 2. (Lygus lineolaris), pale legume bug to 0.20 inch) and usually bright green. Newly (Lygus elisus) and Western tarnished Last-stage nymphs can be mottled and hatched plant bug (Lygus hesperus), have been occasionally more tan. Lygus nymphs and late- documented as injuring beets grown for often are mistaken for aphids due to instar sugar processing. Damaging infestations their color and rounded body shape. Up lygus of tarnished plant bug (TPB) first were to four black spots appear on their backs nymphs. observed in eastern North Dakota and as they progress through later develop- western Minnesota sugarbeet fields in ment stages. A centrally located scent to six weeks to complete a generation 1998. Since then, the insect has caused gland opening, which looks like a spot, and produce two to three generations per economic losses for many area produc- is on the back of the abdomen in all lygus year. Adults are mobile and readily take ers due to yield reductions and control nymphs. The scent gland and spots help flight when disturbed. Their mobility costs. confirm that they are lygus bugs. Nymphs allows for short-range movement within can move quickly on the plant. They fields and longer, field-to-field flights. sometimes drop to the ground beneath Description Adults are quick to move from a field the sugarbeet canopy when disturbed, Adult TPB (Figure 1) are about 0.25 inch to find a more suitable host for feeding making identification and counting long and half as wide. Their flattened and egg laying when the original habitat difficult. bodies are tapered slightly toward the becomes unsuitable due to stress or head and more so toward the hind injury (from flooding, drought or frost), end. They have a pair of long, tapered Biology and Life History or as host plants dry down after reaching antennae, slightly protruding eyes and a Lygus bugs overwinter as adults in physiological maturity. four-segmented needlelike beak. Body leaf litter and other plant debris in field More than 300 plant species, including colors vary from tan or pale green to margins, shelterbelts, ditch banks, fence several weeds and about 50 cultivated mottled reddish brown or dark brown. rows and other protected areas. Rising crops, can serve as lygus bug hosts. Adults have a prominent triangular plate spring temperatures prompt the adults Weeds in North Dakota and Minnesota on their backs between the wing bases. to become active in mid-April to late sugarbeet production areas that com- Two sides of the triangle are yellowish May, and mating occurs soon thereafter. monly harbor lygus bugs include redroot white, giving adults a characteristic Females lay eggs by inserting them in pigweed, common lambsquarters and V-shaped marking on their backs. petioles and stems of actively growing kochia. plants (mostly weeds in the spring). Eggs hatch into tiny nymphs in one to three Third-generation lygus adults typically weeks, depending on air temperatures. infest sugarbeet fields late in the growing This begins the first true generation of season (mid- to late August) after a the season. Nymphs cannot fly. They reservoir host crop (such as alfalfa or usually remain on the plants from which canola) is harvested or other hosts they hatched. Nymphs feed on plants become less suitable for feeding. and develop through five instars before Sugarbeet fields adjacent to these turning into adults. In North Dakota and hosts can be at elevated risk for lygus Minnesota, lygus bugs typically take four infestation. Extended periods of warm, JULY 2005 dry weather also can lead to lygus population increases and subsequent movement of adults into sugarbeet fields. ▲ Figure 3. Lygus injury to Damage petioles and new growth with Adults and nymphs damage sugarbeet leaf curling and seepage of plants by feeding on petioles of new and black exudate. emerging leaves near the crown with piercing-sucking mouthparts. Feeding begins with the insects injecting plant- toxic saliva that “pre-digests” plant tissue. They then suck up the resulting fluid and plant sap. Females also damage plants by depositing eggs in petioles. Plant Injury and Symptoms Symptoms of recent feeding injury include new leaves wilting and curling, and blackened exudate seeping from ▲ feeding sites on leaves and petioles Figure 5. Healed lygus feeding scar on (Figure 3). ▲ Figure 4. Leaf tip yellowing and necrosis sugarbeet petiole. Occasional leaf tip yellowing and brown- following lygus bug feeding injury to sugarbeet ing (Figure 4.) appears to be an indirect petioles. result of lygus feeding injury. Often only a few plants in a field will show this symptom. Frequency of its occurrence typically infest beets late in the season. Treatment threshold: Treatment with an may be variety-specific. Use caution when tank mixing foliar insecticide is advisable if the infestation insecticides with certain fungicides exceeds one TPB per plant (nymphs or Older feeding sites appear as raised labeled to control cercospora leaf spot adults) and if the field is three weeks or necrotic scars as shown (Figure 5). Yield because of the potential for crop injury more from harvest. Insecticide recom- impact is believed to be largely due to and significant yield loss with some mendations are available in the “Insect late-season development of new leaves combinations. Control” section of the Sugarbeet from crowns in response to feeding injury. Production Guide or the North Dakota Carbohydrates are depleted from storage Scouting: Careful field scouting helps Field Crop Insect Management Guide roots to produce new leaves, resulting in determine the need for an insecticide (publication E-1143). Both are available stored sucrose reductions. application. Scouting involves randomly at county Extension offices or the selecting and examining plants from top NDSU Agriculture Communication office. to bottom, including the ground surface Management Online versions of these resources immediately below the canopy. Adults Cultural practices: Effective manage- are at www.sbreb.org/Production/ usually will be on outer leaves. Most ment of small-seeded broadleaf weeds production.htm and www.ext.nodak.edu/ nymphs will be on newer leaves and from early spring to midsummer may help extpubs/plantsci/pests/e1143w1.htm. petioles, especially near the crown. reduce lygus buildups. Burning weedy Lygus adults that leave a plant selected field margins and roadside ditches in the for sampling should be included in counts fall may help because it destroys lygus Photo credits: Jack Kelly Clark and UC if they are positively identified. At least 50 overwintering sites. Statewide IPM Program (Fig. 2.), Mark to 100 plants should be sampled in a field Boetel (Fig. 3), Justin Knott (Fig. 4), and Chemical control: Foliar insecticides to estimate an infestation, although more Robert Dregseth (Fig. 5). are the most common tool to manage samples per unit area will provide a more Reference: Knott, J.O. 2005. Bionomics of lygus bugs in sugarbeets. Insecticide accurate assessment. Sampling should the tarnished plant bug in the northern preharvest intervals require careful represent the whole field and not just Great Plains. M.S. Thesis. North Dakota consideration because these pests field edges. State University, Fargo. 68 pp. For more information on this and other topics, see: www.ag.ndsu.edu NDSU Extension Service, North Dakota State University of Agriculture and Applied Science, and U.S. Department of Agriculture cooperating. Duane Hauck, director, Fargo, N.D. Distributed in furtherance of the acts of Congress of May 8 and June 30, 1914. We offer our programs and facilities to all people regardless of race, color, national origin, religion, sex, disability, age, Vietnam era veterans status or sexual orientation; and are an equal opportunity employer. 5M-7-05 This publication will be made available in alternative format, upon request to people with disabilities, (701) 231-7881..

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