ISSUE 13 July 28, 2005
THE NEW GENERATION OF CRUCIFER FLEA BEETLES IS EMERGING NOW
The new generation of crucifer flea beetle adults (or offspring of the spring flea beetle adults), begins in late July and lasts 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 during swathing and cause 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, Proaxis and Decis have the shortest preharvest interval of 7 days; in contrast, Capture has a preharvest interval of 35 days. It is common to get complaints from homeowners about flea beetle infesting their vegetable and flower gardens during swathing in ND. Plants in the Crucifer or Cabbage family (cabbage, broccoli, cauliflower) are preferred hosts of flea beetles. In early fall, these beetles move to shelterbelts and grassy areas for overwintering.
BIOLOGICAL CONTROL IN ACTION IN SUNFLOWER FIELDS
It is easy to find diseased thistle caterpillars (larvae of painted lady butterfly) on sunflower leaves. This is a nuclear polyhedrosis virus that causes the infected caterpillar to become sluggish and eventually a dead gooey blob! Unfortunately, the viruses often do not destroy larvae until considerable crop damage has occurred.
Remember to protect honeybees when spraying any blooming crop and only spray when it’s absolutely necessary. If it is necessary to spray, apply insecticides when there is minimal bee activity, preferably during the evening hours. During most summer evenings, honeybees leave fields by 8 PM and do not return until 8 AM or later the following day. Be sure to know the location of beehives. A list of the locations of 2005 beehives by county can be obtained from the ND State Department of Agriculture:
TIME TO SCOUT FOR SUNFLOWER HEAD INSECT PESTS
Red Sunflower Seed Weevil:
Reports of adult seed weevils on early blooming sunflower fields indicate the beginning of weevil emergence. This is a reddish-brown weevil of about 1/8 inch.
Red sunflower seed weevil
Newly emerged adults feed on the bracts, floral tissue, and pollen. The female seed weevil must feed on pollen for fertile egg development. 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. Spray the sunflower heads and wait 15 or more seconds for the adult weevil to move to the front of the head. Count the number of adult weevils per plant at several locations in the field and then calculate the overall field average. The typical 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. If spraying is done too early, weevils can re-infest a field requiring a second treatment.
Banded Sunflower Moth:
Adult moths have been observed along field margins and eggs can be found on the bracts of sunflower heads. Pheromone trap captures indicate peak activity this week. Fields should be monitored when plants are in the late bud (R-4) to early bloom stage (R5.1). The economic threshold based on monitoring for adult moths, during dusk or dawn, is one adult moth per 2 plants; or use the new egg-sampling method (see last week’s Crop & Pest Report). 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 mainly a pest problem in confection sunflowers causing kernel brown spot. Adults are about ¼ inch in length, and pale green, light brown, or dark brown with a distinctive triangular marking on its back.
Lygus bug adult
Immature nymphs hatch from these eggs and look like aphids. Field reports indicate that Lygus bugs are common in sunflower fields. 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.
Lygus bug nymph
Area Extension Specialist
North Central Research Extension Center