June-July, 2003 - Leafminers in Sugarbeet

There have been isolated reports of leafminers in sugarbeets around the Grand Forks area. These are likely to be either spinach or sugarbeet leafiners, the two are similar in appearance and life history. Adults are small flies with brown or grayish brown bodies, hairy spines on their backs and clear wings. They look like small house flies. Females lay eggs directly on the plant’s leaves. Eggs hatch into small whitish maggots which tunnel into the leaf and begin to feed on the plant material inside the leaf, decreasing the photosynthetic material. This feeding results in small, serpentine tunnels (mines) in the leaves. These tunnels get larger to accommodate growth of the larvae, the newest tunneling is larger than earlier feeding. Larvae can be found at the terminal end of the tunnel, unless they have already dropped out of the leaf to pupate in the soil. There are 2-3 generations per year in the RRV, with late June – early seeing the end of the 1^st or beginning of the 2^nd generation. The literature indicate that leafminers rarely cause economic damage after the 1st generation. By this time, beets are undergoing such rapid vegetative growth, they are usually capable of outstripping any damage caused by the tunneling larvae.

Click on any of the photos for a close-up of the damage (all detail photos ~100K)

Leafminers tend to be problems in isolated fields with widespread outbreaks being rare. Scouting consists of sampling several sets of 10 random plants in several representative areas within a field. As with scouting other insects, the more areas sampled, the more accurate will be the population estimate. Treatment is recommended if 50% or more of the plants sampled have egg masses and small tunnels are present.

Product	Rate
Lorsban 4E	1 pt/A (2/3 pt/A band)
D-Z-N Diazinon 50W (Syngenta)	¾ - 1 lb/A
Diazinon 50W (UAP)	¾ - 1 lb/A
Diazinon 50 WP (UHS)	¾ - 1 lb/A
Diazinon 500AG (Helena & UAP)	¾ - 1 pt/A
D-Z-N Diazinon AG500	¾ - 1 lb/A
D-Z-N Diazinon AG500 WBC	9 ½ - 12 ¾ fl oz/A

** All are Restricted Use Pesticides

Selected Past IPM Updates

June 20, 1999 - Potato Leafhopper, Grasshoppers, Cereal Insects
Sept 12, 1999 - Impact of Aster Yellows on Canola May be Greater Than You Think
Aug 31, 1998 - Lygus in Sugarbeets
July/Aug, 2000 - Armyworm Outbreak in RRV
Fall, 2000 - Soybean Aphid, A New Insect Pest in Minnesota Soybeans
Fall, 2001 - Soybean Aphid in NW Minnesota
August, 2001 - Lygus in Sugarbeets
May 2002 - Cutworms in Sugarbeets
July 2002 - Armyworms in Small Grains July 2002 - Grasshoppers in The Red River Valley

Publications Available for Download

Insects

Grasshoppers -
Minnesota Grasshopper Management - 2002 with color graphics
Minnesota Grasshopper Management Brochure with scouting and control information (available as a PDF file designed to be 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.
Early Season Scouting for Soybean Aphids - A guide to scouting early season soybeans for soybean aphid.

Questions? Comments? E-mail us at:

imacrae@tc.umn.edu