Scouting for Sunflower Stem Weevil
Based on heat units to date, entomologists report that adult sunflower stem weevils are now emerging in the northern High Plains and much emergence is already complete in Colorado and Kansas. Once the adult has emerged, 10 to 14 days are required before egg laying begins. The adult lays eggs in the stem of the plant. Newly hatched larvae tunnel through the stalks and facilitate proliferation of Phoma black stem disease. Together, these can significantly weaken the stalk and infested plants may lodge as they dry down.
Eggs are mostly laid on plants with six or more leaves and treatments are best timed to coincide with the 8-10 leaf stage. Early planted fields are more vulnerable; fields planted mid-June or later will normally miss the peak of weevil activity. The threshold level is considered to be one adult per two plants, but it is important to note that adult weevils are difficult to scout. They are small and cryptic and fall to the soil quickly when disturbed. It is advisable to consider the recent history of stem weevil problems in a region when considering a treatment for this pest.
Most foliar insecticides are registered for sunflower stem weevil control.
For more detail and pictures: Go to www.sunflowernsa.com and go to the grower section.
Assefa Gebre-Amlak, CSU Entomologist at Akron: 970-345-2287
Ron Meyer, Agronomist at Burlington: 719-346-5571 or 719-346-1101 Cell
JP Michaud, KSU at Hays: 785-625-3425
Jeff Bradshaw, U of N at Scotts Bluff: (308) 632-1369