ISSUE 13 August 2, 2007
SUNFLOWER MOTH BLOWS INTO NORTH DAKOTA
The migratory sunflower moth has been observed in Bismarck / Hazelton area in high numbers and in Prosper, Cass County. So, it’s time to get out and scout more sunflowers! The adult is a shiny gray to grayish tan moth about 0.38 inch long, with a wingspan of about 0.75 inch (see photo). When at rest, the wings are held tightly to the body, giving the moth a somewhat cigar-shaped appearance. The larva has alternate dark and light-colored longitudinal stripes on a light brown body and about 0.75 inch long at maturity (see photo).
Adult sunflower moth (photo by L. Charlet)
Sunflower moth larva (photo by L. Charlet)
Life Cycle: The moths are highly attracted to sunflower that is beginning to bloom. Individual female moths will deposit up to 30 eggs per day on the surface of open sunflower heads. The eggs hatch within 48 to 72 hours and the newly emerged larvae feed on pollen and florets. The larvae begin tunneling into seeds upon reaching the third instar (larval growth stage). This tunneling continues throughout the remainder of larval development. Larval development from hatching to full maturity takes about 15 to 19 days.
Damage: The young larvae of the sunflower moth feed primarily on florets and pollen. Older larvae tunnel through immature seeds and other parts of the head. A single larva may feed on three to 12 seeds and forms tunnels in both the seeds and head tissue. Larvae spin silken threads, which bind with dying florets and frass to give the head a trashy appearance. Severe larval infestations can cause 30 percent to 60 percent loss, and in some cases, the entire head can be destroyed. Sunflower infested with sunflower moth has an increased incidence or risk of Rhizopus head rot.
Scouting Method: Sampling sites should be at least 75 to 100 feet (23 to 31 m) from field margins. The X pattern should be used in monitoring a field, counting moths on 20 heads per sampling site for a total of 100 heads. Scouting is most accurate in the early morning or late evening, when moths are active.
Economic Threshold: The economic threshold for sunflower moth is one to two adults per five plants at the onset of bloom or within seven days of the adult moth’s first appearance.
SOYBEAN APHID UPDATE
There have been many recent inquiries about "What are we seeing for soybean aphid populations in North Dakota’s soybeans?" So far, populations of soybean aphids have been hard to find and definitely below the economic threshold (<250 aphids per plant) in most areas (see IPM maps for last two weeks). However, there always one exception to the rule and soybean aphids have reached treatable levels in Dickey County in the southeast region. Fortunately, the ‘hot’ weather conditions have not been favorable for aphid reproduction and build-up. Be vigilant and continue to monitor for any aphids in soybeans until the pod-fill stage, especially in late planted fields. We may get lucky this year and escape any major infestations of soybean aphids!
SUNFLOWER MAGGOT CAUSING INJURY IN DEVELOPING SUNFLOWER HEADS
Injured sunflower heads that show tunneling from the sunflower seed maggot (see photo), Neotephritis finalis, have been reported from throughout the state. These ‘picture-winged’ flies have brown lacelike wings with a wing span of approximately 0.28 inch and a body length of about 0.25 inch. The small, brown pupa (see photo) of N. finalis is what is found in the face of the sunflower head, usually surrounded by a small number of damaged florets.
Injured sunflower head (photo by D. Markle)
Sunflower maggot pupa (photo by D. Markle)
The magnitude of damage to sunflower seeds by N. finalis larvae depends largely on the stage of larval and seed development. Seed sterility occurs when newly hatched larvae tunnel into the corolla of young blooms. Observations indicate that a single larva feeding on young flowers will tunnel through 12 ovaries. Mature larvae feeding on older sunflower heads will destroy only one to three seeds. A scouting method has not been developed for sunflower maggots because its damage has been negligible. Although the injury can be alarming, no insecticide treatment is recommended for control of sunflower seed maggot. Please send in any reports of high populations.