SUGARBEET INSECTS

Insecticide Quick Reference Chart for: Sugarbeet Insects

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SUGARBEET ROOT MAGGOT

This insect overwinters in soil at a depth of 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. Females deposit eggs below the soil surface near the base of beet seedlings with egg depth being dependent on soil moisture (i.e, eggs will be deposited deeper in dry soil conditions). Earlier-seeded (April - early May) plants are generally more vigorous and are able to tolerate more injury than smaller, later-planted beets. Severe feeding injury and major plant stand losses can occur in untreated beets planted during mid- to late-May since young seedlings cannot withstand early-season feeding pressure. Therefore, 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 the month of June. However, when dry conditions prevail, a post-emergence insecticide 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 trying to determine if a post-emergence treatment is needed: Soil moisture - good soil moisture with spring rains should enhance planting-time insecticides, however, extreme rainfall amounts may cause movement of the insecticide from the treated target zone; Sugarbeet size - plants that have 10 to 14 true leaves at peak flight (early June) can tolerate some feeding pressure; Population level - monitor sticky-traps in individual fields to estimate relative numbers of egg-laying females.

    RUP - Restricted Use Pesticide

^aCounter 15G, Counter CR, Lorsban 15G, and Nufos 15G can be used as either planting-time or postemergence treatments but only oneapplication of either insecticide is allowed per season.
^b Mustang 1.5EW may be applied as a planting-time or a postemergence treatment for various pests; however, total active ingredientapplied 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 seson; however, total product appliedper 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 they 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 1� inches long. Adults are mottled tan and brown moths with smoky grayish wing margins. The moths first appear in late May and early June, and larvae can cause problems during the first 3 weeks of June. A second brood is also possible during late August and September.

Threshold:

The recommended treatment threshold is 1 to 2 webworms on 50 to 75% of the leaves sampled.

    RUP - Restricted Use Pesticide

WIREWORMS

Wireworm larvae are smooth, somewhat hard-bodied, worms varying in length from � to 1 � 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. Frequent cropping and working the soil helps reduce wireworm problems.

Threshold:

Currently, there is no established threshold for wireworms in sugarbeets. Most insecticides used for sugarbeet root maggot control will help control wireworms. Refer to product labels for more information.

    RUP - Restricted Use Pesticide

Do not use lindane or any other chlorinated hydrocarbon insecticide on sugar beet seed. Check with your sugar beet company field representatives before treating beet 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 beet rows; however, they will feed above the surface on beet leaves and stems during periods of excessive soil moisture.

Insecticides generally require some moisture after application for optimal performance. Very light rain showers or even heavy dew at night is generally sufficient. It is desirable to apply insecticides during late afternoon. This procedure maximizes the amount of active insecticide material in the field during the first nighttime hours following application. Bait 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 begin migration 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, therefore, control can be difficult to achieve.

Control of cutworms 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 beetle most frequently found feeding on beets will be shiny black in color and about 1/8 inch in length. Flea beetles, in general, are oval-shaped and the hind legs are enlarged. When approached, these beetles jump readily. These flea beetles overwinter as adults, emerging in late April and May. They feed first on suitable weeds, moving to crops as they emerge. Injury consists of small round holes chewed in the leaves giving the foliage a shot-hole appearance. When shot-holing is severe, plant growth is retarded and wilting or death of seedling can occur, particularly in hot, dry weather.

Threshold:

    If flea beetles threaten to reduce sugar beet plant stands to below 35,000 plants/A, treatments are justified.

    RUP - Restricted Use Pesticide

GRASSHOPPERS

In the northern plains, grasshopper egg 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 laid eggs in the field 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 BUGS (LYGUS)

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, 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