1. Life Stages of the Sugarbeet Root Maggot

The mature maggot overwinters in the previous season's beet fields 6 to 10 inches below the soil surface. During late April and early May, the maggots move to within 1-3 inches of the soil surface to pupate. In the Red River Valley, emergence generally begins during late May and continues for a period of 4-6 weeks. Following emergence, mated female flies are found in sugarbeet fields depositing eggs below the soil surface at the base of sugarbeet seedlings. Eggs hatch in 3-7 days, depending on soil temperature and moisture, and the newly hatched maggots move down immediately to begin feeding on the root surface. Severe damage can occur in untreated beets planted during mid-May since young seedlings cannot with stand early season feeding pressure and heavy stand losses can result. Early planted beets, seeded in April through early May, generally are able to withstand some feeding pressure because of additional growth prior to maggot fly emergence and oviposition. In this case, stand loss is not a significant factor but yield reduction at harvest generally results. Because of the long period of adult emergence and oviposition, maggots of various sizes can be found on injured beets from early June through August. Mature maggots, after completing their feeding, move away from the beet root and deeper into the soil during August and September, where they will spend the winter.

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2. and 3. Typical Sugarbeet Root Maggot Damage

Wilted plants during June and July are a sign of root maggot damage. Digging will reveal moist feeding tunnels and maggots in the soil around the root. Damaged roots are blackened and if maggot populations are large, the tap root may be severed.

Click here to see Typical Sugarbeet Root Maggot Damage (Foliage)

Click here to see Typical Sugarbeet Root Maggot Damage (Root)

4. White Grub

Grubs move up in the spring of their second season to begin feeding on beet roots, cutting them off below the soil surface. Feeding continues through the summer with grubs again moving deeper in the soil to overwinter. Feeding activity and damage in sugarbeets is most severe during the second year of the cycle. Feeding activity resumes the spring of their third year and continues into early summer after which the grubs mi.grate downward to 6-8 inches below the soil surface where they form a cell in which they pupate. In late summer they change into the adult and remain in the soil over the winter, emerging the following spring. White grubs feed on the roots causing wilting and stand loss in sugarbeets. Typical damage in fields is wilted or dead beets in patches or areas generally close to shelterbelts. Digging will reveal the white grubs just below the soil surface in close association with the wilted plants.

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5. Cutworm Damage and Mature Cutworm in Sugarbeets

Cutworms feed at night just below the soil surface during dry periods. Typical damage will be areas of wilted or dead beets in the fields. Large areas can be damaged within a beet field overnight if cutworm populations are high. With sufficient moisture, cutworms will climb and feed on leaves at night returning to the upper 1 inch of soil during the day. Daily surveillance is essential to detect damage during the early growing season and when symptoms appear, treatment should be applied immediately.

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6. Beet Webworm Adult

Beet webworms overwinter as larvae in the soil and pupate in late spring. Adults first appear in late May and early June and the small smoky colored moths are active at night. During daylight hours the adults hide beneath beet foliage. Adult webworms are readily observed when beet foliage is disturbed since they will make short flights within the field to find new hiding places.

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7. Beet Webworm Larvae and Typical Damage in Sugarbeets

Early instar beet webworms are slender, active, dark green colored larvae. As they mature, they turn darker green with a black stripe down the middle of the back and wavy white lines on each side. Larvae will often migrate to sugarbeets when weed hosts are depleted. In heavy infestations total sugarbeet defoliation can occur. Hot weather increases food intake and will contribute to a rapid rise in webworm populations. A second brood is possible in late August and September.

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8. Wireworm

Wireworms are usually hard, smooth, wire-like worms frequently encountered in light textured soils. Wireworms attack seeds and beet seedlings, causing reduction in stand. Wireworms overwinter as larvae and adults spending 2 to 6 years in the soil feeding on seeds and roots during spring and summer.

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9. Flea Beetles and Damage

Flea beetles are small, shiny black beetles most common in sugarbeets during the early spring. Typical damage produced is small round holes in young beet leaves giving a shot-hole appearance. With severe shot-holing, retarded plant growth and wilting are evident during hot, dry weather. Flea beetles overwinter as adults in plant trash or other suitable sites.

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10. and 11. Sugarbeet Root Aphid

Sugarbeet root aphids suck the sap from beet roots. Heavy infestations will destroy rootless causing the plant to wilt and eventually die. Infestation and damage is most common during dry periods when cracks in the soil develop around beet roots, allowing root aphids to become established. Above ground symptoms include leaf yellowing and wilting. Roots from these plants will be covered with patches of white mold-like material produced by the aphids. Sugarbeet root aphids overwinter in the soil or in shelterbelt trees, particularly poplar. Winged forms are produced in June or July and disperse into sugarbeets. Wingless generations occur on beets which produce economic damage. Winged forms produced in late fall migrate back to poplar trees to lay eggs. On poplar, wingless generations develop in galls formed as leaves open in the spring.

Click here to see Sugarbeet Root Aphids on Beet Leaf

Click here to see Beet Root Damaged by Root Aphids(undamaged root on the left)

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NDSU Extension Service, North Dakota State University to Agriculture and Applied Science, and U.S. Department of Agriculture cooperating. William H. Pietsch, Director, Fargo, North Dakota. Distributed in furtherance of the Acts at Congress at May 8 and June 30, 1914. We offer our programs and facilities to all persons regardless of race, color, sex, religion, age, national origin, or handicap; and are an equal opportunity employer.

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