Crop & Pest Report

Accessibility


| Share

Watch for Insect Pests in Seedling Sugarbeet Fields (05/12/16)

The early start to field preparation this spring likely resulted in some sugarbeet seed being planted into cool soils.

Watch for Insect Pests in Seedling Sugarbeet Fields

The early start to field preparation this spring likely resulted in some sugarbeet seed being planted into cool soils. That, in combination with the recent cool and wet weather, could be causing moderate to slower-than-average seedling development in some areas. Delays in germination or development can make young plants more vulnerable to attack by early-season insect pests, such as springtails, wireworms, cutworms, and white grubs. 

Wireworms:  Wireworm infestations have been reported in the Drayton and Moorhead factory districts, suggesting that all American Crystal factory districts and the MinnDak growing area may be at-risk for problems with this pest group. At least two different wireworm species can damage sugarbeet in the Red River Valley, and larvae are the main damaging stage in sugarbeet. Larvae are cream- to rust-colored worm-like pests with a hardened exoskeleton (“skin“), and range from 3/8” to 1.5” in length (Fig. 1). Observations over the past several years suggest that the smaller (5/8” to 3/4”-long), pale rust-colored larvae are the most aggressive feeders that can cause stand and yield losses in sugarbeet. 

Depending on the species, wireworms can spend 2 to 4 years in the larval stage before they develop into their adult stage, the “click beetle.” Therefore, one cannot assume that risk has passed after experiencing wireworm problems in a given year.

 mark.1

Springtails:  Subterranean (below-ground) springtails could also be problematic for sugarbeet producers this year due to the cool soil conditions in some areas. They are very small (1/32 to 3/32” long), and white- to cream-colored insects with tiny, fleshy antennae that are projected forward (Fig 2). They spend their entire life below the soil surface, and their small size and subterranean habit make accurate diagnosis of field infestations difficult. Springtails pose the most threat to fields with heavy soils containing high levels of organic matter. Springtail infestations are most common following a small grain crop such as wheat or barley. Infestations usually develop in patches ranging from one to 5 acres in diameter, but patches can be as large as 15 acres.  Symptoms of springtail damage can include failure of seedlings to emerge, as well as wilting and dead plants.

 mark.2

Wireworm and Springtail Control:  Control options for both wireworms and springtails include planting-time granular and liquid insecticides (e.g., Counter 20G and Mustang Maxx), or insecticidal seed treatments (e.g., Cruiser, NipsIt Inside, or Poncho Beta). NOTE:  Although products containing chlorpyrifos (e.g., Lorsban 15G) provide good root maggot control, they do not perform well against wireworms or springtails. Also, there have been rare reports of Mustang Maxx providing less-than-optimal control of springtails. 

There are no recommended rescue insecticide options for wireworm- or springtail-damaged fields that were unprotected at planting time. As such, if significant stand losses occur from either of these pests, the best option is to replant affected areas using one of the aforementioned at-plant control strategies.

Cutworms:  A few reports of cutworm activity in sugarbeet fields have been reported in the southern part of the Valley during the past week. Redbacked and dark-sided cutworms are the most common species to cause early-season injury to beet fields, although army cutworms can also be problematic. Early-season cutworm injury in sugarbeet fields usually involves seedlings being cut off at the base of the stem near the soil surface, but can also include chewing injury to the cotyledon leaves and first few true leaves. Cutworm feeding activity mostly takes place during evening and overnight hours, so determining if cutworms are the causal agent in severed seedlings can be challenging. Scouting for cutworm infestations involves lightly digging and sifting the upper two inches of soil near the surface within rows and surrounding individual plants. 

Cutworm Control:  A rescue insecticide application is usually economically justified if cutworm injury is approaching 4 to 5% cut-off seedlings within a field.  Insecticide applications are most effective when made during late-afternoon to evening hours.  Chlorpyrifos-containing insecticides (e.g., Lorsban 4E, Lorsban Advanced, Govern 4E, Chorfos 4E, Nufos 4E, Warhawk 4E, Whirlwind 4E, etc.) and pyrethroid products (e.g., Asana XL and Mustang Maxx) should provide good cutworm control. NOTE: NDSU research suggests that insecticidal seed treatments should not be relied upon to protect fields from cutworms.

For more guidance on sugarbeet insect management strategies, consult the “Insect Control” section of this year’s Sugarbeet Production Guide.  Always remember to READ, UNDERSTAND, and FOLLOW the label of your insecticide product – it’s the law.

Mark Boetel

Research & Extension Entomologist

Creative Commons License
Feel free to use and share this content, but please do so under the conditions of our Creative Commons license and our Rules for Use. Thanks.