FROM AROUND THE STATE
ISSUE 16 August 27, 1998
Summer populations of the crucifer flea beetle are abundant now especially on freshly swathed canola fields. The tiny, black beetles can be seen congregating on the tips of canola stubble and other weeds. Fortunately, no reports have been received where populations are high enough to cause serious damage like the stunted growth of the pods. The flea beetles will continue to do some nominal feeding before moving into shelterbelts and other overwintering sites. Large numbers of summer populations often indicate that flea beetle pressures may be high next spring.
Damage to late planted sunflowers from grasshopper have been reported near Washburn. The best guideline to use in making decision for management of grasshoppers is based on the level of defoliation and the amount of injury to flower heads. At the early (vegetative stages) and later stages (after R-7 - back of head is pale yellow) of plant development, high levels of defoliation usually 40-50% can be tolerated before any major impacts on seed yield (Sunflower Production Handbook, EB-25). Stages R-1 to R-6 (bud formation to flowering) appear to be the most sensitive to defoliation since the plant directs much of its energy into head development. For example, 25-30% defoliation in R-3 to R-4 stages (bud elongation to inflorescence opening) of sunflowers will cause about a 10% yield loss. If damage to the sunflower head is occurring, the number of adult grasshoppers should be used as a guide. Generally, more than eight grasshoppers per square yard is considered economic and a control is warranted. Since grasshoppers are often located primarily in the field margins, perimeter treatments minimize the migration into the field and are more cost effective. Remember to check the preharvest intervals for the insecticide.
The second flight of the bivoltine (two generations a year) European corn borer peaked last week in the Minot area. Most of the sweet corn is being picked now so the larvae (worm) produced by this generation should not damage most of the sweet corn.
GENERAL INTEREST -- FIELDS OR ROAD EDGES
The yellow or white butterflies that you see flying around belong to the Insect Family Pieridae called Sulfurs and Whites. Some of the common butterflies are the Common Sulfur (yellow colored), the Alfalfa Sulfur (orange colored with the black wing margin), and the Cabbage White (white colored). Sulfurs prefer to feed on legumes and Whites on plants in the mustard family. Swarms of male moths are often observed at mud puddles and road edges waiting for females to emerge for mating. Adult moths feed on nectar. The larvae (caterpillar) feed on their host plants, but are usually not a crop pest in North Dakota. Some, like the Cabbage White, is a pest on cabbage, broccoli, and collards, especially in the home garden.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center
Rainfall received during August 18 to 24 at south-central North Dakota NDAWN stations ranged from 0.49 inches at Harvey to 3.55 inches at Linton. Other NDAWN stations that recorded over 3 inches of rain during this period included Dazey, Jamestown, and Bismarck. Up to 9 inches of rain was reported in portions of Emmons County during the past week. Additional rainfall would generally be useful in this region north of I-94. Daily water use of alfalfa, corn, and potato at Carrington during the past week has ranged from about 0.1 to 0.2 inches.
Cool-season crop harvest is nearing completion. Barley and field pea harvest is complete and at least 75% of wheat and canola acreage is harvested. Harvest efforts currently are with late-planted small grain and canola as well as flax. In the Carrington area, barley yields are ranging from 50 to 90 bushels/acre. Wheat yield appears to average in the 35 to 40 bu/acre. Irrigated wheat at the Carrington RE Center has reached 60 bu/acre. Wheat test weight, protein, and other quality factors are generally positive and improved from last season. Reports on the region's canola yields are ranging from 1200 to over 2000 lb/acre and averaging about 1500 to 1800 lb/acre. Initial reports indicate flax yields of 20 to 30 bu/acre.
Grasshoppers should be monitored in late_season crops. Sunflower growers should be on alert for bird damage in their crop. Fields should be scouted and plans developed for fall perennial weed management.
Area Extension Specialist/Cropping Systems
Carrington Research and Extension Center
EUROPEAN CORN BORER
The second generation corn borer flight peaked on August 20 and 21, with 23 moths caught in the black light trap. Since then, borer counts have ranged between six and eight moths trapped each night.
Adult sunflower beetles are feeding on the uppermost leaves and causing significant defoliation. Fields that will likely be impacted the most are those in the R5 to R6 (blooming) stage. High adult populations in the field now indicates the potential number of adults emerging next spring. Think about management plans this fall for scouting and possibly spraying next year's sunflower fields.
I have observed many insect predators on sunflower plants in central North Dakota. Predators include "lady bugs" ( which are in both the larval and adult stages and actively feeding on the aphids found underneath the leaves, ambush bugs (they eat just about everything), lacewings (larvae and adults), and occasionally, stinkbugs. One field in northeastern Eddy County had as many as ten ladybug larvae per plant.
Grasshoppers are moving from the harvested small grain fields to the sunflowers at CREC. Grasshoppers are feeding on leaves, causing about 20 to 40% defoliation, and also feeding on the bracts. We will applying an insecticide to manage the grasshoppers.
SUNFLOWER MIDGE SURVEY
I am currently conducting a sunflower midge survey directed by Drs. Gary Brewer (NDSU) and Larry Charlet (USDA-ARS). I am surveying southern Benson, Nelson, Eddy, Griggs, Foster, Stutsman, LaMoure, and Dickey counties to find the western boundary of the midge. Any locations of midge-damaged fields would be appreciated.
Sclerotinia wilt continues to be a problem in many fields in the region and at the Center itself. This disease will likely have the largest yield impact of any of the diseases.
Downy mildew was present in four of seven fields surveyed in Wells County. However, only two plants out of 80 were counted in one of the surveyed fields for an incidence of 2.5%. We stumbled upon the other infected plants located in three different fields after taking our counts.
Sunflower rust, verticillium wilt, alternaria leafspot, and septoria leaf spot diseases are present in fields and appear to be cosmetic and not economic. Powdery mildew is present on oil and non-oil sunflowers at the Center, but control measures are not recommended (EB 25, Sunflower Production, Revised, 1994).