FROM AROUND THE STATE
ISSUE 9 June 26, 2003
Pest Update – June 23, 2003
More Grasshoppers, Grasshoppers, Grasshoppers, Grasshoppers, ... GRASSHOPPER OUTBREAK!!!
Young grasshoppers (first to forth instars) have been causing severe damage in just about any crop grown in the North Central and Northwest Regions - small grains, sunflowers, flax, canola, lentils,... Many fields are requiring an edge spray, while others need the entire field protected in localized "hot" spots.
Bertha armyworm larvae (1-3 instars) have been found in canola fields in McLean County last week. Adult moths have been flying for two weeks or more. Bertha armyworm eggs will hatch in about a week and develop into a larvae (or caterpillar). The emerging larvae (1/10th of a inch) are usually green in color and hide underneath leaf litter and clumps of soil during the day. Making them difficult to find! Mature larvae are about 1½ inch long and vary in color from green, brown to velvety black. It takes six weeks for the larvae to complete their development. So far, cumulative trap catches have been LOW in north central and northwest regions. The economic threshold is 18_22 larvae per square yard when the damage is primarily leaf feeding. Thresholds should be lowered if larvae are found feeding on maturing seed pods to 2-3 per square foot.
Diamondback moth traps catches have been LOW (averaging below 100 moths per trap week) several weeks prior to flowering canola. All life stages can be found in the field now - eggs, larvae, pupae, and adults. The larvae (or caterpillar) feed on the flower buds and flowers causing them to abort. Occasionally, diamondback moth can also damage developing pods as well. Larvae are lime green about ½ inch long with a forked posterior end. Monitor fields for diamondback larvae by beating or dislodging the larvae from plants. No threshold has been established for the early flowering stage, however, insecticide applications are likely required at larval densities of 10-15 larvae per square foot (one to two larvae per plant). The action threshold for canola at the pod stage is about 20-30 per square foot (two to three larvae per plant). Early monitoring of adults and larvae, and judicious use of insecticides only when fields are above thresholds are the best pest management practices for preventing losses from diamondback moth on canola.
Crucifer Flea beetles have subsided for the most part. With the increase in acres using an insecticide seed treatment instead of foliar insecticides, other insect pest problems like cutworms appear to be increasing in minimum/no-till canola. Cutworms were normally kept under control when the foliar insecticide was applied for spring flea beetle control.
The Ash-gray Blister beetles were reported feeding on blooming canola near Williston. The presence of large numbers of blister beetles in spots of a canola field have often concerned growers. However, adult feeding is generally not significant enough to warrant an insecticide treatment for the entire field. Spot treatment with a foliar insecticide registered in North Dakota is usually recommended and will control these beetles.
Aphids have been detected in the southern tier of north central region (McLean County). Any late planted fields will be attractive to aphids. Aphids vector barley yellow dwarf virus, which can be devastating if the crop is infected prior to heading. An economic threshold is when 85% of the stems have one or more aphids.
Wheat Midge degree days are moving along fast! Most of the North Central and Northwest Regions are above 1100 degree days when the male wheat midge emerges. The female emerges at 1300 degree days and emergence is 90% complete at 1600 degree days (degree day base = 40 degrees F). Numerous male wheat midge were reported flying in the Harvey area - already!
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
During the past week (June 18 to 24), area rainfall ranged from 0.45 (Harvey) to 3.2 inches (Streeter) in the region as recorded at NDAWN (North Dakota Agricultural Weather Network) sites. Topsoil and subsoil moisture continue to be adequate. High winds on June 19_20, followed by hail and heavy rain in localized areas have reduced crop conditions. The high winds have browned leaf tips and edges of small grain.
Hail occurred in counties including Burleigh, Eddy, Emmons, Sargent, Sheridan, Stutsman, and Wells. Lodged small grain is most common in the south-east counties of the region. Extended sunshine is welcome!
Wheat and barley growers are strongly encouraged to continue monitoring their crops in the flag-leaf to early-heading stages for leaf disease and to consider fungicide application for control of foliar and head (scab) disease. Good to excellent small grain yield potential continues to exist along with favorable weather conditions and increasing disease presence to warrant fungicide use. Also, refer to the NDSU wheat disease forecasting system for additional information on disease presence and management:
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center