Step up sunflower scouting in July
Once sunflowers reach the bud stage of development, it’s time to initiate aggressive crop monitoring and pest scouting. Banded sunflower moth and red seed weevil are major insect challenges. In addition, lygus bugs have become a threat to confection sunflowers, and the long-horned beetle is becoming more prevalent in several areas.
Banded sunflower moth
Banded sunflower moth adults become prevalent in mid-July to August, with larvae appearing in heads shortly after adults and continuing into September. Treatments should target larvae before they reach the seed.
The optimum plant stage for insecticide treatment is pollen shed (R5.1) because most of the eggs will have hatched, and larvae will be exposed and susceptible while they are feeding on disk flowers. Confection sunflowers may require two insecticide treatments to meet the industry standard for seed damage. Male pheromone traps can augment scouting procedures to identify when moths emerge from the soil and are present in fields.
• Sunflower requires intensive scouting now through August.
• Watch for banded sunflower moth and seed weevil.
• Lygus bug and stem weevil pose special problems.
Red sunflower weevil
Red sunflower weevils normally lay eggs at pollen shed. Female moths need to feed on pollen before they can produce mature eggs. Peak emergence is in late July. Monitoring should start at late bud stage (R4).
Insecticides should be applied to prevent egg laying. Confection sunflowers need to be sprayed earlier (R5.0) than oilseed to ensure high seed quality and avoid penalties. North Dakota State University recommends treating confection sunflowers at least twice, first at early bloom and again five to seven days later.
Confection sunflowers have been plagued by lygus bug problems in the Northern Plains for the last several seasons. Oilseed sunflowers haven’t experienced an economic problem yet. Lygus bugs cause “kernel brown spot” as a result of feeding on developing seeds. Sunflowers are vulnerable to feeding from anthesis through seed hardening. One lygus bug per nine heads can result in economic loss. Organophosphate and selected pyrethroid insecticides are labeled for lygus bug control.
Sunflower stem weevil
Cancellation of Furadan for use in sunflowers has taken away the only insecticide option that offered sufficient systemic activity to contend with the extended presence of sunflower stem weevil larvae in stalks. Most of the organophosphate and pyrethroid insecticides labeled for stem weevil will provide control of adults, but none have the longevity of larval control that Furadan offered.
Economic thresholds for this insect are illusive because there isn’t a strong correlation between adult numbers and the number of larvae in the stalk. In addition, hybrid stalk size and tolerance to stem weevil can vary and is influenced by plant spacing. Stalk breakage can occur with 25 to 30 larvae in a stalk, according to NDSU research. Drought stress will increase sunflower susceptibility to stem weevil, and stem diseases infect plants through stem weevil tunnels.
Coultas is a consulting agronomist for Seeds 2000, Inc., and manages applied research projects across the U.S. Contact him at www.facebook.com/seeds2000.
This article published in the July, 2010 edition of DAKOTA FARMER.