SUGARBEET INSECTS

Insecticide Quick Reference Chart for: Sugarbeet Insects

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SUGARBEET ROOT MAGGOT

This insect overwinters in soil at 6 to 12 inches below the surface as a mature larva in fields that had been planted to sugarbeets during the previous growing season. In late April and early May, overwintered larvae move up to within 3 inches of the soil surface to pupate. In the Red River Valley, fly emergence generally begins in late May and continues for a period of 4 to 6 weeks. Following emergence, flies move to current-year sugarbeet fields and deposit eggs below the soil surface near the base of beet plants. Egg depth is dependent on soil moisture (i.e, eggs are deposited deeper in dry soil conditions). Earlier-seeded (April - early May) plants are usually more vigorous and able to tolerate more injury than smaller, later-planted beets. Fields planted in areas with established maggot populations should be protected with a planting-time insecticide. These treatments will usually be effective with adequate rainfall during June. If dry conditions prevail, a post-emergence insecticide application may be needed. This management approach has been shown to be cost-effective during dry growing seasons and under severe maggot infestation levels. Producers should consider the following when deciding if a post-emergence treatment is warranted: soil moisture - good soil moisture with spring rains should enhance planting-time insecticide performance - extreme rainfall amounts (3" within first 24 hours or at least 6" if received in 1 or 2 rainfall events within 1 week after planting) may cause movement of the insecticide from the treated target zone; sugarbeet size - plants that have 10 to 14 true leaves at peak activity (early- to mid-June) can tolerate moderate levels of feeding injury; population level - use sticky-stake traps to monitor for development of damaging population levels.

RUP - Restricted use pesticide

^a Counter 15G, Counter CR, Lorsban 15G, Nufos 15G, and Thimet 20G may only be applied once per year.
^b Mustang 1.5EW may be applied as a planting-time or a postemergence treatment for various pests; however, total active ingredient applied per acre per season cannot exceed 0.15 pound.
^c Temik 15G can be applied once at planting and up to two postemergence treatments can be applied per season; however, total product applied per acre per season cannot exceed 33 pounds.

BEET WEBWORM

Beet webworms rarely occur in significant numbers in Red River Valley sugarbeet fields. Larvae are slender caterpillars and are very active when disturbed. Early-stage larvae are dark green. Older larvae are olive green and have a dark band flanked on each side by two light-colored stripes running down the center of their back. Full-grown larvae can be up to 1½ inches long. Adults are mottled tan and brown moths with smoky grayish wing margins. The moths first appear in late May and early June. Larvae usually cause problems during the first 3 weeks of June. A second brood is also possible during late August and September.

Threshold:
Treatment is recommended if 1 to 2 webworms are present on 50 to 75% of sampled leaves.

RUP - Restricted use pesticide

WIREWORMS

Wireworm larvae are smooth, somewhat hard-bodied worms varying in length from ½ to 1 ½ inches long. Their color can range from yellowish-white to a light copper color. Wireworms feed on a wide variety of crops and weeds, and are generally difficult to detect and control. They tend to be more prevalent in light-textured soils or in soil that has not been in crop production for several years. Fields that had grassy weed escapes during the preceding season are also at risk. Frequent cropping and working the soil helps reduce wireworm problems.

Threshold:
Currently, there is no established threshold for wireworms in sugarbeet. The following insecticides labeled for sugarbeet root maggot control will usually provide adequate protection from wireworm injury. Refer to product labels for more information.

RUP - Restricted use pesticide

Do not use lindane or any other chlorinated hydrocarbon insecticide on sugarbeet seed. Check with your company field representatives before treating sugarbeet seed with an insecticide.

CUTWORMS

Major cutworm pests of sugarbeets in the Red River Valley include the Darksided and Redbacked cutworms. Eggs of both species hatch into larvae during late May and early June. Early detection of larval feeding activity is essential to a good control program. Fields should be checked for wilting or dead plants at frequent intervals during periods of cutworm activity. Cutworms will generally be found within 1 to 2 inches of the soil surface near the base of wilting plants. Most feeding activity occurs at night. Young sugarbeet plants are often cut off near ground level. During periods of dry weather, larvae prefer feeding just below the soil surface as they move along the row. They will feed above the surface on leaves and petioles during periods of excessive soil moisture.

Insecticides generally require some moisture after application for optimal performance. Very light rain showers or heavy dew is generally sufficient. It is desirable to apply insecticides during late afternoon. This maximizes the amount of insecticide material present during the first nighttime hours following application when larvae are often most active. Applications may be repeated as necessary during peak cutworm feeding. Liquid formulations generally provide better control of cutworms, especially during very dry periods. If severe crusting is evident in the field, the crust should be broken up prior to or during the insecticide application.

In 2001, variegated and black cutworm infestations caused problems in late July and August. These insects migrate into our region as moths during the spring and are capable of multiple generations within a single growing season. Variegated cutworm larvae have a distinctive row of pale yellow spots down the middle of their backs. They are a climbing cutworm species that primarily feeds in the plant canopy during evening hours. Because they feed above ground, insecticide treatment can be effective in controlling economic populations of variegated cutworms. Black cutworms can feed more than 2 inches below ground in later growth stages when soils are too warm near the surface. Therefore, late-season control of these cutworms can be difficult to achieve.

Threshold:
Cutworm control in young beets is suggested when 4 to 5% cutting of seedlings observed in fields. A population of 3 to 5 per square foot is recommended in late summer and plant canopy is developed.

RUP - Restricted use pesticide

FLEA BEETLES

The flea beetles most frequently found feeding on beets are shiny black in color and about 1/8 inch in length. All flea beetles are oval-shaped and have enlarged hind legs. When approached or disturbed, they readily jump to escape. Flea beetles overwinter as adults and emerge in late April and May. They feed first on suitable weeds such as winter annuals, and move to field crops as weed hosts are depleted and crop plants begin emerging. Foliar feeding injury from flea beetles consists of small, rounded holes, and gives leaves a shot-hole appearance. Severe shot-holing damage can result in stunting, wilting, and even death of seedling plants. Plant responses will be most dramatic during periods of hot and dry weather.

Threshold:
Treatment is usually justified if flea beetles threaten to reduce sugarbeet plant stands to below 35,000 plants/acre.

RUP - Restricted use pesticide

GRASSHOPPERS

In the northern plains, grasshopper eggs hatch normally begins in late April to early May. Most grasshoppers emerge from eggs deposited in uncultivated ground. Sugarbeet growers should expect to find grasshopper feeding first along field margins adjacent to these sites. Beets in fields that follow late-season crops may have hatching throughout the field and should be monitored carefully if adults deposited eggs in the field during the previous fall. Later infestations may develop when grasshopper adults migrate from harvested small grain fields.

Threshold:
Grasshopper control is advised whenever 20 or more adults per square yard are found in field margins or 8 to 14 adults per square yard are occurring in the crop. (For more information on infestation ratings, see the discussion under Grasshoppers in Small Grain Insects)

RUP - Restricted use pesticide

TARNISHED PLANT (LYGUS) BUGS

Tarnished plant bugs (TPB) have caused late-season injury to Red River Valley sugarbeets since 1998. Most TPB feeding injury appears on new leaves and stems emerging from the crown region of beet plants. Feeding symptoms include curling and wilting of leaves, feeding scars on leaf petioles, and blackening of the new growth near the center of the crown. Multiple generations of TPB can develop during the growing season. Populations usually build up in other host plant habitats, then adults migrate to beets in late-July to mid-August. TPB is a sporadic pest in this region and its biological profile is not understood well enough to anticipate when or where significant infestations may occur in the future.

Threshold:
Currently, there is no established economic threshold for TPB in sugarbeets. However, after checking 30 to 50 plants in a field and at least one third (33%) of the plants are infested with one or more TPB (adult or nymph stage) and feeding injury is observed, treatment may be justified. They have usually infested beets during August. Therefore consideration of pre-harvest interval may be a critical factor in choosing an insecticide. A number of insecticides that are approved for use on sugarbeets have TPB or Lygus as a target pest in their labels for other crops; however, TPB is not listed as a target pest in the sugarbeet portion of those labels. These insecticides include Asana, carbaryl (Sevin), Lannate, Lorsban, and malathion. It is legal to apply an insecticide if it is labeled for use in the crop; however, if the target pest is not listed for that crop, efficacy is not implied by the manufacturer and growers that choose to use the product assume their own liability for any unsatisfactory performance.

RUP - Restricted use pesticide

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