ISSUE 3 May 19, 2005
EARLY-SEASON INSECT PESTS OF SUGARBEET
This spring’s cool and wet conditions are slowing sugarbeet germination and seedling development in the Red River Valley. As a result, sugarbeet seedlings will be more vulnerable to attack by early-spring insect pests.
Soil Insects: Fields that did not receive a planting-time insecticide will be particularly at risk to damage by soil-inhabiting insect pests. Fields should be carefully monitored for failure of plants to emerge and for wilted seedling plants. Post-planting insecticide treatments are usually not effective. If an infestation is confirmed, prompt replanting and application of a registered planting-time soil insecticide or simply accepting the loss are the only practical options for management.
Important soil insect pests of sugarbeet include wireworms, springtails, and white grubs. Symptoms of soil insect injury to sugarbeet include wilting and dying seedlings, and dead patches or strips within the field. NDSU has been monitoring wireworm and springtail activity this spring using bait stations and soil samples.
Wireworm activity is currently low, but could still be a threat. Activity is likely to increase as soils warm up in the next couple of weeks. Fields can be attacked in 2 to 3 consecutive years, so growers should be on guard if they had wireworm problems in recent years.
Springtail infestations are low to moderate this year, but localized areas that recently received heavy rains may be more at risk, especially if air temperatures remain cool. Fields with a history of springtail problems should be monitored closely for stand losses, especially if no planting-time soil insecticide was used. Areas affected by springtails usually occur in multiple patches of 1 to 5 acres.
White grub problems are usually most severe within 45-90 yards of a shelterbelt of trees containing poplar, cottonwood, or willow trees. Infestations typically occur in a 3-year cycle, and this year is not anticipated to be a high year for grub problems. However, infestations of annual grubs have been reported in the vicinity of Colfax, ND and Wolverton, MN.
Stem & Leaf Feeders: Flea beetles are tiny insects with shiny shell-type wings. Their hind legs are expanded to that allow them to leap when disturbed. Major infestations in sugarbeet are infrequent and difficult to predict. They usually attack the crop during early plant development from cotyledon stage to when plants have about 2 emerged true leaves. Early detection is key to successful flea beetle control. Initial feeding injury consists of tiny rounded shot-holes in leaves. Severe injury results in leaves being almost completely destroyed. Flea beetles are capable of causing major stand reductions in sugarbeet. A foliar liquid insecticide should be applied if the infestation is likely to reduce the plant stand to below 35,000 plants /acre.
Several cutworm species are also capable of causing major sugarbeet plant stand losses in early spring. Early-season cutworms typically clip the stem of seedling plants as they feed. Most feeding activity occurs during late evening through early morning. If cutworm activity is suspected in a field, further scouting should consist of sifting through soil in the upper 2 inches near the base of plants in affected areas of the field. Cutworm larvae will curl up into a C-shape similar to white grubs, but differ from grubs by having darker coloring, a variety of markings on their body, and several pairs of prolegs (false legs) on their abdomen. Foliar insecticides are effective in managing cutworm infestations, and early detection is important for protection from major economic loss. A rescue insecticide should probably be applied if 4 to 5% of seedlings have been clipped by cutworm larvae.
The leaf feeding weevil, Tanymecus confusus, is also a spring/early summer foliar pest of sugarbeet. Infestations are sporadic and difficult to predict. Diagnosis can also be tricky because of the weevil’s small size and dark brownish grayish coloring. A key descriptive feature of the weevil is its long, narrow snout-shaped head. Damage to the plant is usually confined to interveinal areas and margins of leaves, with veins typically left intact. Foliar application of a liquid insecticide is advised if weevils are causing severe defoliation of plants. Spot treatments may be feasible in localized infestations.
For more information regarding wireworms, consult extension circular no. E-188 (revised) entitled "Wireworm Management for North Dakota Field Crops." It is located on the web at:
To learn more about springtails, see extension circular no. E-1205, "Springtails in Sugarbeet: Identification, Biology, and Management." It is also located on the web at: http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/e1205w.htm
For more guidance on identifying and managing the leaf-feeding weevil in sugarbeet, consult extension circular no. E-1273, "Leaf-feeding Weevil in Sugarbeet. It is available in print or on the web at: http://www.ext.nodak.edu/extpubs/plantsci/rowcrops/e1273w.htm
Research & Extension Entomologist
ORBATID SOIL MITES – NUISANCE FOR HOME OWNERS
If you find many tiny, little black dots, like pepper moving around in your window sills or house siding on warm days, you are not alone. These are microscopic Orbatid soil mites! Orbatid mites can vary in color (see Figure 1), but they live in the top layer of soil, leaf litter, or other debris. Hundreds of thousands of mites can live in one square meter of soil! The role of Orbatid mites is extremely important in ‘recycling’ nutrients back into the soil. Soil mites are also a food source for other arthropod predators, such as, beetles, ants, larger mites, spiders, and others. Although these mites are sometimes a nuisance in the spring as temperatures warm up, the presence of many mites are a sign of healthy fertile soil. When you are walking on a healthy lawn or field, there are millions of Orbatid mites under your feet! Remember not all outdoor home insecticides will control mites. Desperate home owners can use diazinon or dicofol (kelthane) (not Tempo).
Figure 1. Orbatid Mites
(courtesy Ray Norton)
Area Extension Specialist
North Central Research Extension Center