Submitted to: Helia
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 1, 1995
Publication Date: N/A
Interpretive Summary: Larvae of the banded sunflower moth, Cochylis hospes, feed and develop within seeds of cultivated sunflower in the northern Great Plains of the United States and Canada. This research was designed to delineate larval damage to sunflower seeds from known adult populations, and develop an economic injury level (EIL) using field and cage studies. The economic injury level for the banded sunflower moth was determined to be 6 larvae per head, when the chemical application costs were $7 per acre, the market price for sunflower seed was $0.09 per pound, and the plant population was 18,000 per acre. The EIL is dynamic, so it will vary depending on fluctuating prices received for sunflower seed, application costs, and plant density. The decision on whether larval populations will reach the EIL is based on adult populations in the fields during mid-late July. A regression equation is given to predict the adult density which will result in the EIL. An adult population of 1 adult per 50-60 plants will result in an EIL of 6 larvae per head. An assessment of adult populations needs to be made prior to bloom so treatment can be made before destruction of seeds in the head. Results from cage studies infested with 1 to 10 adult banded sunflower moths per plant showed that each moth resulted in 12 larvae per plant. The higher number of larvae in the cages compared with the field is probably because adults were confined in the cages, and in the field studies adult population estimates were made during the day when fewer adults are in the fields. The cage studies also revealed that an average of 5 to 6 seeds are consumed by each larva.
Technical Abstract: Larvae of the banded sunflower moth, Cochylis hospes, feed and develop within seeds of cultivated sunflower in the northern Great Plains of the United States and Canada. This research was designed to delineate larval damage to sunflower seeds from known adult populations, and develop an economic injury level (EIL) for C. hospes using field and cage studies. Calculations showed that with aerial application costs of $17.30/ha, a sunflower market price of $0.20/kg, and a plant population of 44,600/ha, the EIL was 5.9 larvae per head. A decision of whether economic damage is likely to occur is based on known populations of adult moths. The regression equation (Y =1.69 + 23.93X) predicted a final number of mature larvae (Y) based on the average number of adults per 10 plants during daylight hours in July (X) from 1983-1985 and 1988-1989. A density of 1 adult per 56 plants resulted in an EIL of 5.9 larvae per head. Treatment is directed at larvae and is most effective when applications are made at the R5.1 sunflower growth stage. In 1990, cages infested with one adult per plant resulted in 9.3 larvae per head; cages infested with 10 adults per plant produced 55.2 mature larvae per head. The number of mature seeds damaged by feeding larvae varied from 59.6 seeds per plant in cages with infested with 1 adult per plant to 294.3 damaged seeds per plant in cages infested with 10 adults per plant. Results were similar in 1991. The regression equation to predict mature larvae per head (Y) based on adult infestation level (X) was Y=7.34 + 4.60X. Thus, each adult results in 11.94 mature larvae per head. Each larva destroyed 6.1 and 4.8 mature seeds in 1990 and 1991, respectively.