FROM AROUND THE STATE
ISSUE 13 July 29, 2004
DIAMONDBACK MOTH LARVAE CAUSING DAMAGE TO CANOLA BUDS, FLOWERS AND PODS
Trap catches for adult diamondback moth have been high in the north central and northwest regions of North Dakota for the past several weeks (>100 moths per trap week). Late-planted canola (June) will be more susceptible to infestations. Fortunately, most of the canola crop was planted in May. Larvae feeding and injury to buds/flowers have been reported from Fortuna, Divide County this week. Larvae feed on the leaves, buds, flowers, seed pods, the green outer layer of the stems, and occasionally, the developing seeds. The amount of damage will depend on the crop stage and the larvae densities and size. Extensive feeding on the buds or flowers will delay plant maturity, cause the crop to develop unevenly, and significantly reduce seed yield.
Producers can scout for larvae of diamondback moth by beating plants and dislodging the larvae from plants into buckets or onto the roof of a vehicle. Larvae are about ½ inch long, pale yellowish-green caterpillars with a forked posterior end. When disturbed, the larvae thrash backwards violently and often drop from the plant on a strand of silk. The action threshold for canola at the pod stage is about 20 per square foot (two to three larvae per plant). For the early flowering stage, insecticide applications are likely required at larval densities of 10-15 larvae per square foot (one to two larvae per plant). Capture or Warrior are the registered insecticides.
FIELD OBSERVATIONS OF WHEAT MIDGE CONTINUE TO BE LOW
The north central and northwest regions range from 1783 degree day accumulations in McLean County to 1578+ degree day accumulations in Bottineau, Renville, Burke, and Divide Counties. In other words, the southern section is near the end of wheat midge activity, while the northern section is near 90% of the females emerged and will have flight activity for another week depending on temperatures. Producers should continue to monitor wheat and durum if it in the susceptible crop stage, heading to 50% flowering, and you are in an area with active wheat midge flight (1300 to 1900 DD).
SPOTTED SUNFLOWER STEM WEEVIL DETECTED IN NORTH CENTRAL REGION OF ND
Low levels of spotted stem weevil were observed in sunflower fields this past week. The spotted sunflower stem weevil is difficult to scout for due to their small size, cryptic color, and "play dead" behavior. Adult are about 3/16 inch long and grayish-brown with varying-shaped white spots on the wing covers and thorax. Being a weevil, it has a snout that protrudes down and backwards from the head. The economic threshold is 1 adult weevil per 3 plants. This weevil can cause significant stalks breakage and lodging, and vector the sunflower pathogen Phoma black stem and charcoal stem rot.
SUNFLOWER MAGGOTS COMMON IN SUNFLOWER FIELDS
Sunflower maggot flies are easy to find in sunflower fields now. Three different species occur: Gymnocarena diffusa, Strauzia longipennis, and Neotephritis finalis. Each species ranges from ¼ to 5/8 inch in size and has a different yellowish-brown pattern on its wings (called Picture Winged flies). Larvae of each species also damage a different part of the sunflower plant: Gymnocarena usually damage the area behind the sunflower head; Strauzia the stalks; and Neotephritis the seeds in head. Fortunately, sunflower maggots usually cause negligible injury and no economic threshold has been established. Recently, observers have been confusing another common fly in sunflower fields, the Lauxanid flies for sunflower maggot flies. The Lauxanid fly has a yellow body and wings are often spotted, but it is smaller (< 1/10 to 1/6 inch) than the sunflower maggot flies. Lauxanid larvae live on decaying vegetation and or leaf litter. This is the same Lauxanid that one can confuse with the wheat midge.
SUNFLOWER BEETLE LARVAE FEEDING UNDERWAY
A few reports of sunflower beetle larval feeding have come in this past week. Larvae are 1/16 to an inch long and yellowish-green with a brown head capsule. Most larval feeding occurs at night. During daytime, larvae can be found resting in terminal growth area of leaf axis and flower buds. If larvae feeding is severe, defoliation can reduce yield by poor seed set or fill. The economic threshold is 10-15 larvae per plants and 25% defoliation on top 10-15 leaves or "active" growing point.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
Rainfall has been more abundant in July than in June over most of southwest North Dakota. To date (July 27), all NDAWN locations except Bowman and Hazen have reported rainfall amounts in excess of 2 inches. Bowman reported 1.96 inches and Hazen reported 1.08 inches. The Dickinson Research Extension Center has received 2.13 inches as of July 27 and Hettinger has received 2.95 inches. The 105-year mean July precipitation for Dickinson is 2.23 inches and the 48-year mean at Hettinger is 2.08 inches. July precipitation came late for many cereal and grass hay crops and can not make up for the lack of rainfall in April, May, or June but will help corn and sunflowers. Some areas received more than four inches of rainfall and can probably expect a second cutting of alfalfa hay. July also brought with it warm weather and helped speed the rate of crop development. July 18 was the warmest day so far this month with Bowman, Dickinson, Hettinger, Mandan, and Mott exceeding 100oF.
Canola seed in the lower pods of the plant are changing color in some of the fields. We have a few reports of canola being swathed in the southern areas of southwest North Dakota. Also winter wheat harvest has begun in some areas with barley harvest likely to begin in some areas late this week or early next week.
Sunflowers are in the R-3 stage (immature bud elongates more than one inch above the nearest leaf) and producers should increase scouting trips to fields to look for crop damaging insects. Scouting should continue through to R-5.9 (90% of the disk flowers have completed flowering). Insects to look for include Sunflower Moth, Banded Sunflower Moth, Red Sunflower Seed Weevil, and Sunflower Beetle. When insect populations reach treatment thresholds pesticide applications should be considered for control. Last year sunflower long horn beetle were found in many fields at high incidence levels. Though no pesticide has been found to control this pest effectively, producers should still scout fields for this pest. If high incidence levels of this pest are found producers should plan for an early harvest to avoid lodging.
Roger O. Ashley
Area Extension Agronomist
Dickinson Research Extension Center