We are seeing Lygus bugs in sugarbeets again this year. Most fields in the northern Red River Valley have populations close to or exceeding the threshold of 33% of all plants infested. There are Lygus in sugarbeets every year, but rarely do their populations get large enough to be a problem. Lygus bugs attack more crop species than any other insect pest in the US, and they are likely moving in from other crops, weeds, and grasses as they are harvested or dry off. Unfortunately, sugarbeets represent one of the last sources for a decent meal for these bugs.
Lygus (also called Tarnished Plant Bug) is 1/4" long when grown, adults are brown with a yellowish white "V" behind their heads (although this sometimes appears as only 3 white spots). The adults will darken as they get older and end up being a dark bronze color. Immatures are yellow to green, with 4 black spots on their backs. These green nymphs can often be mistaken for aphids, but they move more readily and are faster. Adults and immatures move quickly on leaves and the adults readily fly, generally in a wandering flight path close to the top of the canopy. The species currently attacking beets in the Red River Valley likely has 3 generations per year which overlap, causing a continuous presence of immatures and adults. They overwinter as adults in leaf litter or under bark.
Click on picture for larger image. Photo from Mark Boetel, Dept. of Entomology, NDSU.
Lygus feed by piercing the plant and sucking plant juices. In addition, they inject saliva into the plant to pre-digest plant sap in the plant before they suck it up. This saliva is toxic to the plant and acts like a growth regulator, causing curled, yellow leaves. Feeding locations often appear as black dimple. In addition, there is a black, tarry substance associated with Lygus that stains leaves. This is caused by a fungus that grows on Lygus excreta.
Lygus feed preferentially on new growth and will kill new leaves in sugarbeet. To scout for Lygus, randomly select plants in the field, and quickly open the canopy to examine new growth near the crown. Lygus bugs move quickly and the adults will readily fly. If there are more than one Lygus bug per plant, count the plant as infested. If more than 30% of the plants are infested, treatment is considered economically viable. Registered treatments include Lorsban (1/2 pt per acre, but 30 post harvest interval), Asana (0.03 - 0.05 lb. per acre, but 21 day post harvest interval), Carbaryl (Sevin) (1 lb. per acre, but 28 day post harvest interval), and methyl parathion (0.5 – 0.75 lb per acre, but a 20 day post harvest interval). The proximity to pre-pile and harvest should be considered when making treatment decisions.
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, treatment may be justified. TPB have usually infested beets in August. Therefore consideration of pre-harvest interval may be a critical factor in choosing an insecticide. Also, border treatments may be effective if the majority of TPB are along the edges of a given field. This threshold is based on tonnage damage data from Michegan.
PLEASE NOTE
Although the following insecticides are registered for use in sugarbeets, none have a specific recommendation for Lygus on their sugarbeet label. This means that although it is legal to use these products in sugarbeets, there is no assumption of liability by the producer of the insecticide for failure to control Lygus. Growers choosing to use any of these products for the control of Lygus in sugarbeets assume all risk for failure to control Lygus. It is especially important to check Malathion labels as some manufacturers of Malathion have chosen not to pursue re-registration in sugarbeets. Make sure the label states the product is registered for sugarbeets or beets (a registration only for table or vegetable beets means the product is NOT registered in sugarbeets). Listing of insecticides on this page does not imply recommendation but simply to provide options.
| INSECTICIDE | DOSAGE IN LB AI/ACRE |
PRODUCT PER ACRE | RESTRICTIONS ON USE |
| Asana XL RUP | 0.03 - 0.05 | 5.8 - 9.6 fl oz | Do not apply within 21 days of harvest |
| Sevin XLR | 1.0 - 1.5 | 2 - 3 pts | Do not apply within 28 days of harvest. |
| Lannate LV
RUP (water soluble liquid) |
0.22 - 0.9 | 0.75 - 3.0 pts |
Do not apply within 7 days of harvest. Do not feed tops to livestock within 30 days of last application. Field re-entry interval is 48 hours. Fields must be posted. |
| Lannate SP
RUP (water soluble powder) |
0.22 - 0.9 | 0.25 - 1.0 lbs | Do not apply within 7 days of harvest. Do not feed tops to livestock within 30 days of last application. Field re-entry interval is 48 hours. Fields must be posted. |
| Lorsban 4E RUP |
0.25 - 0.5 |
0.5 - 1.0 pts |
Do not apply within 30 days of harvest. Do not apply more than 8 pints/acre (broadcast basis) per season, or make more than 4 applications per season. |
| Malathion 57 EC | 1.0 - 1.25 | 1.5 - 2.0 pts | Do not apply within 7 days of harvest |
| Dibrom 8 Emulsive | 0.94 | 1.0 pts | Do not apply within 2 days of harvest |
RUP - Restricted Use Pesticide
From: North Dakota Field Insect Management Guide - Sugarbeet Insects.
Grasshoppers -
Minnesota Grasshopper Management - 2000 with
color graphics
Minnesota Grasshopper Management Brochure with
scouting and control information (available as a PDF file designed to be as a
tri-fold brochure).
Scouting -
Scouting for Insects in Wheat, Alfalfa, and Soybeans
- a manual prepared for the University of Minnesota Extension Service Field
School, held at the Northwest Experiment Station, Crookston, MN, July 7-8,
1998.