FROM AROUND THE STATE
ISSUE 7 June 14, 2001
INSECT AND DISEASE PEST UPDATE
Too Many Cutworms!
More reports of cutworm damaged fields (i.e., mostly canola, sunflower) are coming in from the North Central Region! One can find several different sizes of larvae (worms) now -- ¼ inch to the mature 1½ inches long larvae. The smaller cutworms have 6-8 weeks of feeding, mostly at night to complete its development. The larger cutworms will become dormant and pupate within 7-10 days or so depending upon temperature. The Red-backed cutworm is the most common species.
Diamondback moths (DBM) feeding can be easily observed in canola fields now. Look for the small irregular holes in the leaves. DBMs often eat the upper and lower epidermis (green tissue) leaving the leaf membrane untouched – "window effect." Although most of the canola escaped damage in the earlier stages, the canola will need to be monitored as it approaches flowering and young seed pods. Feeding damage during the early flowering stage can be very damaging. Feeding on the flowers will delay plant maturity, cause uneven crop development, and significantly reduce yields. The treatment threshold for later growth stages (flowering to pod fill) is 2 to 3 larvae per plant or 20 per square foot.
Thistle caterpillar (larvae of the Painted Lady Butterfly) was observed in Divide County feeding on Canada Thistle in a canola field (K. Brown). Unfortunately, the thistle caterpillars had completely devoured the thistle, and had moved over to the canola plants for food. Some areas of the field had up to 6-8 larvae per foot of row, and the larvae were causing close to 25% defoliation. In this situation, the grower had decided to spray the field by adding Capture to his tank mix during his second application of Roundup. This is a first for Thistle caterpillar in canola! It prefers thistle plants, but will also feed on sunflowers, borage, legumes and many other Compositae. The larvae are dark and spiny with yellowish lateral stripe and spines, and they live singly in silk nests on the leaves.
Sunflower beetles are causing significant damage on sunflowers in the seedling to 4-leaf stage. Several fields are being sprayed for beetles in Burke-Renville-Bottineau Counties. Scout fields for 1 to 2 adults per seedling as a guide to determine whether or not a field needs to be treated (see Entomology for additional threshold information). This time of year (weed spraying), growers may consider a tank mix of insecticide with the herbicides being applied for weed control.
Tree & Shrubs
Ash plant bugs have been observed feeding on ashes near Rugby in Pierce County (C. Erickson). Look for the green to tan colored nymphs or adults. The feeding damage is caused by the sucking mouthparts that remove plant sap. Severe infestation causes a mottling of the foliage, and may cause premature leaf drop.
More reports of Yellow-headed Spruce Sawflies are being observed now – north of Minot! Look for chewed spruce needles in your shelterbelts and ornamental plantings.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
Rainfall amounts over 2" were common the last few days with areas receiving more than 3". Some light hail was reported near Cando. Planting is nearly complete .It appears that there will be several pockets where planted area will be near 60% with most other areas nearing 95% planted. Emergence of crops is good with some of the best stands established in years. Overall development of plantings is later than typically desired but a normal summer will allow maturity before Sept. 20 killing frost. Winter wheat is in the boot stage. Stands are less than desired with some fields being kept with marginal stands .
Light tanspot infection on wheat on wheat plantings. Weed spraying is common. Scattered reports of wireworm damage to row crops with some acres being reseeded. Flea beetle feeding on Canola is generally light due to the cool rainy weather with only scattered reports of economic damage. Monitoring Canola fields is essential as feeding activity increases dramatically during warm days. Sunflower beetle adults are feeding on volunteer and newly emerging sunflower plantings.
Area Extension Specialist/Cropping Systems
During the past week (June 6 to 12), rainfall recorded at NDAWN sites in south-central North Dakota ranged from 0.8 inches (Linton and Oakes) to 2.3 inches (Edgeley and Streeter). Reports of rain exceeding 5 inches in Burleigh County were received during the June 9 storm. Hail and wind damage occurred on June 9 in Burleigh, Emmons, Logan, McIntosh, and Dickey counties. Crops most adversely affected were early-planted small grain (jointing stage and beyond), emerged beans and sunflower, and hay. The region generally has moisture-saturated soils. Dry and warm weather is needed!
Grain crop seeding is essentially complete. Annual forage crops will be planted when soil conditions allow the work. Warm-season forage crop seed supplies are short. Crop stands generally are adequate, especially cool-season crops. Based on growing degree day units, wheat emerged on May 1 was in the flag leaf stage and wheat emerged on May 15 was nearing the jointing stage as of June 12. In Dickey County, winter wheat is heading and early-planted spring wheat is in the boot stage. Warmer air temperatures are desirable to promote growth of corn, beans, and sunflower.
Reports of crop insect and disease problems are low. Weekly counts of flea beetle in sticky traps at the Carrington Research Extension Center (CREC) have increased to an average of over 300/trap on June 11 versus an average of 15/trap on June 4. Fortunately, area canola fields are well past the susceptible stage to this insect. Sunflower beetles are easily detected in volunteer and planted sunflower. Young grasshoppers are being detected in field margins. Downy mildew can be found in early-emerged sunflower.
Potential for an increase in tan spot incidence in wheat is likely due to the wet conditions. Finding sustained periods to apply POST herbicides continues to be a challenge due to windy and wet weather conditions.
Area Extension Specialist/Cropping Systems
NDSU Carrington Research Extension Center