FROM AROUND THE STATE
ISSUE 15 August 14, 2003
TIME TO SCOUT FOR SUNFLOWER HEAD INSECT PESTS
Sunflower Seed Weevil:
Reports in the North Central Region indicate sporadic infestations of seed weevils. Field counts have been higher in field edges, up to 20 seed weevils per head, while the interior of fields have had 0-3 weevils per head. Field scouting for adults should begin when plants are showing yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3), and should continue until most of the plants have reached 70% pollen shed (R5.7). The easiest method for scouting for adult seed weevils is using a can of insecticide/mosquito spray with DEET like Deep Woods Off. Spray the sunflower heads and wait 15 or more seconds for the adult weevil to move to the front of the head. Then, count the number of adult weevils on numerous sunflower heads at several locations and calculate the average number of adult weevils per head. The economic threshold is only one adult weevil per head for confections and about 8 adult weevils per head for oils. The best time to treat is when more than half of the plants in a field are beginning to show yellow ray petals (R5.0) to 30% of the head shedding pollen (R5.3) and the rest of the plants in the field are still in the bud stage.
Banded Sunflower Moth:
Adult moth activity has been observed in field margin and sunflower fields. Pheromone trap captures indicate peak activity last week. Small cream-colored larvae with a brown head capsule can be found on face of sunflower heads. Later silken webbing on mature sunflower heads indicate the presence of banded sunflower moth larvae within the head. Larvae will change colors from cream to pink to red to green as they mature about 0.5 inch long. Fields should be monitored when plants are in the late bud (R-4) to early bloom stage (R5.1). The economic threshold is based on monitoring for the adult moth during dusk or dawn – one adult moth per 2 plants. The best time to treat is when the sunflower plant is R5.1 or when the plant has just begun to shed pollen. Most insecticides being applied for banded sunflower moth are edge treatments with several passes into the field.
Lygus bug is only a pest problem in confection sunflowers causing brown spot on kernel. Field reports indicate that lygus bug is numerous in sunflower fields, and some fields were sprayed over past week. Scout for adults or nymphs on the sunflower head or foliage. Only one Lygus bug per plant is an economic threshold. Spray timings coincide with timings for control of banded sunflower moth and sunflower seed weevils – early pollen shed. A second application, seven days later, is recommended for optimal control of lygus bugs in confection sunflowers.
Large Numbers of the New Generation of Crucifer Flea Beetles Are Emerging Now! High population of flea beetles are being observed in swathed canola fields this week. This is the new generation of adults (or offspring of the spring flea beetles), which begins in late July until early September. These beetles feed on the epidermis of green foliage and pods of canola, mustard, and cruciferous weeds. The crop is usually mature enough that feeding damage is usually minimal. If pods are heavily covered with flea beetles and the epidermis is completely stripped, shattering may occur causing some yield loss. There has been very little research conducted on the impact of pod feeding by flea beetles on canola yield/quality. If an insecticide is needed to protect canola pods, Warrior has the shortest preharvest interval of 7 days; in contrast, Capture has a preharvest interval of 35 days. There has been numerous complaints from homeowners about flea beetle infesting their vegetable and flower gardens. Plants in the Crucifer or Cabbage family (cabbage, brocolli, cauliflower, ...) are preferred hosts of flea beetles. In early fall, these beetles move to shelterbelts and grassy areas for overwintering.
APHIDS, APHIDS, APHIDS AND MORE APHIDS
Aphids have been reported in large numbers on many crops including canola, mustard, peas, small grains, for example. Timing for control of aphids is usually during vegetative to boot in small grains, or flowering in other crops. Most crops are past the optimal time for control making insecticide applications. Fortunately, many ladybird beetle adults / larvae, lacewing larvae, syrphid fly larvae, and other beneficial insects have also been observed feeding on these aphids – biological control in action!
SOYBEAN APHIDS FOUND IN NORTH CENTRAL NORTH DAKOTA
Low levels of soybean aphid have been detected south of Minot in soybean. This is the first confirmed reporting of this pest infesting soybeans in the North Central Region of North Dakota.
GRASSHOPPERS CONTINUE TO BE A PROBLEM IN MATURE CROPS IN THE NORTH CENTRAL AND NORTHWEST REGIONS
Adult grasshoppers are very mobile and moving into fields like flax, small grains, sunflower that have been sprayed before in some instances. It is important to continue monitoring fields for grasshopper movements. Remember when grasshoppers start to clip bolls or heads, the usual thresholds of 8 -12 per square yard do not applied. Control of adult grasshopper is more difficult than young grasshoppers, so check the label for the proper rate of insecticide. Preharvest intervals should also be checked, and it is getting too late for some insecticides to be a control option. Some complaints have been coming in about poor control of adult grasshoppers, long preharvest intervals, and the lack of insecticides available on some crops like mustard, flax, or barley. Several dead grasshoppers have been observed with their legs wrapped around the plant stalk and head pointed upward near the tops of plants. This is Summit Disease, a common and widespread fungal disease, Entomophaga grylli, that infects and kills grasshoppers under the right environmental conditions.
Janet J. Knodel
Area Extension Specialist Crop Protection
North Central Research and Extension Center