ISSUE 7 June 16, 2005
North Central ND
CUTWORMS INJURY IN SUNFLOWERS
There been several reports of cutworms causing stand loss to sunflowers in the North Central Region of North Dakota. In one instance, a 500-acre sunflower field had to be replanted due to cutworms near Harvey (source: D. Anderson). Continue to scout fields for cutworms through June. Foliar insecticides should provide good control with the current moist soil conditions as this causes them to feed closer to the soil surface. Watch your fields for any cut plants and dig up any cutworm larvae located under cut plants. The red-backed, Exoa ochregaster, is a common cutworm in sunflowers. Remember, early scouting and detection is critical for effective cutworm control. Treatment is warranted when one cutworm or more is found per square foot or there is a 25 to 30% stand reduction observed assuming a typical plant population of 15,000 to 25,000 plants per acre for oilseed sunflower and 14,000 to 20,000 plants per acre for non-oilseed sunflowers.
FIRST DETECTION OF SMALL GRAIN APHIDS SOUTH OF MINOT
Very low levels (1-3% incidence) of small grains aphids were detected on wheat south of Minot in McLean County this past week. Late-planted small grains fields will be more susceptible to aphid infestation and the barley yellow dwarf virus, which is vectored by the aphids. To protect small grain fields from yield loss to aphid feeding, the treatment threshold is 85% stems with at least one aphid present, prior to complete heading.
ASH PLANT BUGS IN GREEN ASH TREES
Reports of ash plant bug feeding injury to green ash trees have been report in the Minot area. Adults are tan colored with pinkish markings on the back and are about Ĺ inch long. Green to tan nymphs emerge in spring and feed on the undersides of leaves. Plant bugs pierce host tissues and suck plant sap causing yellow spotting of leaves of green ash. Severe infestations cause leaf mottling, deformed leaves, and sometimes premature leaf drop. Trees usually tolerate ash plant bug damage and it is normally not severe enough to cause defoliation or warrant control. However, control is justified when injury is common throughout canopy or on young trees with repeated injury.
YELLOW-HEADED SPRUCE SAWFLY EMERGED IN SHELTERBELTS OF NORTH CENTRAL REGION OF NORTH DAKOTA
The first spruce sawflies have been reported in shelterbelts located near Bowbells, Burke County (source: D. Folske). The yellow-headed spruce sawfly is a native defoliating insect of spruce in Canada and the Northern United States. Although it feeds on all species of spruce, feeding preference varies geographically. Eggs are laid on current yearís foliage during the last week of May through the first week of June. After about 10 days, larvae emerge from these eggs and begin feeding on the new growth. Initially larvae are 1/8 inch long and have olive green bodies with reddish heads. Mature larvae may eventually reach a length of ĺ inch. The larvae feed on the young needles first and then move to older foliage to continue feeding. Larvae stop feeding in mid to late summer, drop to the ground and spin cocoons. The sawfly will spend the winter in these cocoons and emerge the following spring as adults. There are many parasites and predators that help to keep sawfly populations in check however localized outbreaks may occur periodically. The damage to spruce trees caused by the sawfly can be substantial. Repeated defoliation causes reduced growth and at times tree mortality. Branches defoliated by the sawfly will not re-grow needles. Generally spruce trees require 5 to 7 years of needle retention for optimal growth and survival. Needle loss from sawfly defoliation reduces the trees ability to convert sunlight into energy. This stress may exacerbate other pest problems or if severe enough, can kill the tree outright. Early detection and timing are the keys to successful yellow-headed spruce sawfly management. Chemical controls may need to be incorporated if many trees are infested and the potential for damage is high. Unfortunately, most people do not notice sawfly damage until mid to late summer when defoliation has already occurred, the larvae are absent, and insecticides are ineffective. Insecticides are most effective if used to target early larval stages. Targeting the early larval stages in mid June can reduce the population before significant defoliation occurs.
(SOURCE: Michael Kangas, NDSU Extension)
Area Extension Specialist
North Central Region Extension Center
During the past two weeks (June 1 to 14), the south-central regionís rainfall ranged from 2.7 inches at Tappen to 7.8 inches at Edgeley as recorded at NDAWN (North Dakota Agricultural Weather Network) sites. Areas north of I94 and west of Hwy 281, and south of I94 and west of Hwy 3 generally have less challenges with excessive soil moisture compared to other areas in eastern ND. Growers continue struggling with completion of crop planting and timely herbicide application. Also, hail recently damaged crops in Emmons and McIntosh counties.
The regionís cool-season crop fields generally continue to have good to excellent plant stands and yield potential. Canola planted in April is in or nearing the flowering stage. The regionís abundant moisture is increasing the possibility of white mold in canola. The majority of the regionís spring wheat crop is in the jointing stage (1-2 nodes present), while early-planted wheat (first-half of April) is in or nearing the flag-leaf stage. Wheat growers should consider early-flowering stage fungicide application for scab suppression and protection from leafspot disease. Growers also are considering foliar N application for increasing wheat protein content. Small grain aphids are becoming more easily found. Soybean stands generally are adequate and the crop is in the unifoliate to 1-2 trifoliate growth stages.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center