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Scout for Banded Sunflower Moth Eggs (07/15/21)

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Based on pheromone trap catches, banded sunflower moth (BSM) and Arthuri sunflower moth (ASM) have emerged this last week. Trap catches are low at most trap sites except Cass County. Sunflowers were in the late vegetative to R2 stages.

 

The egg sampling procedure for BSM and ASM is simpler and quicker than sampling for adult moths, and may provide more time to react if a treatment is needed. See NDSU Extension YouTube video for a demonstration. Because the eggs are very small, you need a magnifier to count the small eggs accurately, such as head-mounted magnifier. Egg scouting is conducted when most of the plants in the field are at plant stage R3 (distinct bud elongated ¾ inch above the nearest leaf, yellow ray petals not visible). Steps for egg sampling are:

 

1) Divide each side of the field into two sections.

2) Sample the center of each section at 20 feet into the field from the field edge.

3) Randomly select five buds.

4) From each bud, randomly select six bracts (Figure 1) from the outer whorl and count the eggs on each bract.

5) Average the egg counts from the five buds

The economic injury level (EIL) is used to determine if an insecticide treatment is warranted. The EIL is the average number of eggs per six bracts and considers treatment cost ($/acre), market price ($/pound) and plant population per acre. The EIL for $8 and $10 treatment costs are shown in Tables 1 and 2. For example, the EIL would be 2.1-2.6 eggs per 6 bracts for $8/acre (Table 1, red box) and 2.7-3.2 eggs per 6 bracts for $10/acre (Table 2, red box) insecticide cost.

If the number of BSM eggs is above EIL, insecticide should be applied at the R5.1 sunflower plant growth stage (when 10% of head area has disk flowers that are flowering or completed flowering) for optimal control of BSM-ASM and other head-infesting insect pests, including the red sunflower seed weevil. One red sunflower seed weevil was observed by the CREC IPM Scout, Carrie Nichols, in Stutsman County last week.

Banded Sunflower Moth Trapping Network map from July 5-9, 2021
BSM eggs on outer bracts of sunflower
Table 1. Number of eggs of BSM per 6 bracts for the economic injury level when the cost of control equals $8 per acre

 

Janet J. Knodel

Extension Entomologist