Scouting sunflower for insect pests and diseases

By D. Bruce Bosley

Extension Agent/Cropping Systems

Many insects are attracted to sunflowers. Most of them either don't harm or are actually beneficial but a few insect species can damage the sunflower crop. The three primary insect pests of flowering sunflower in the west central High Plains region are: Sunflower moth, banded sunflower moth, and red sunflower weevil. These insect pests are attracted to sunflower fields during the late bud stages of growth and early flowering. Most importantly, insecticides are most effective in preventing the economic yield losses when applied in early bloom.

Scouting for these insects starts when sunflower buds are fully developed and at or just before the time when a few early flowers are beginning to open. When scouting, sample sites should be at least 75 to 100 feet from the field edge. Use an X pattern when sampling making counts at the five points.

Both red sunflower seed weevil and grey sunflower seed weevil occur regularly. These insects are about 1/8th of an inch long with the grey weevil being larger than the red seed weevil. However, grey weevils rarely cause economic losses while red seed weevil can cause significant damage. Female red seed weevils require feeding on pollen before they can develop eggs.

Weevils hide in crevices on the flower head but can be drawn out during the mid part of the day with light brushing or spraying with an insect repellent containing DEET. Count five sets of five plants, distributed across the field in an X pattern.

The oilseed economic treatment threshold is ten red seed weevils found per head at or after 30 percent of the plants are at early bloom (R5.1 stage). The confection economic threshold is reached at one per head at or after 10 to 15% early bloom. Stop scouting for red weevils when most plants have reached 70% pollen shed (R5.7 growth stage).

Sunflower Moth adults have tan or grey wings with a 0.5 inch wingspan. Banded Sunflower moth adults are straw colored and have only 0.5 inch wingspan. Both roll their wings over their back (cigar like) when resting. Female moths of both species prefer to lay eggs on sunflower plants in early flowering growth stage. The moth larvae for both species feed on seeds and create webbing on the flower surface. They also provide an introduction site for head rot fungus. Treat for sunflower and banded sunflower moths when treatment thresholds have been reached.

Scouting at this stage should be frequent because large numbers of moths can migrate into fields overnight. Scouting is best done with calm winds and near dawn or dusk when moths are most active. It is best to scout for resting moths on flower heads during the dark using a flashlight. Count five sets of twenty plants traveling in an X pattern. The economic treatment for sunflower moth is when two are found per five plants while that for the banded sunflower moth is one is per two plants.

Using pheromone traps for monitoring sunflower moth activity provides an alternate method for determining when to treat fields for this insect. One or less moth trapped per night is considered low risk, while more than four moths trapped per night is considered high risk and justification for treatment. Pheromone traps have not been successfully demonstrated for monitoring banded sunflower moths. Remember to treat as early as the action threshold is reached.

Other insect pests are often found during early bloom growth stages of sunflower: Head clipper weevil, sunflower midge being the most common. These insects rarely impact yields enough to justify treatment. It is at this time that the beginning stages of sunflower diseases may be noticed.

Pictures of these and other insect pests as well as more information regarding their identification and biology are on the Web at www.highplainsipm.org or in the High Plains Sunflower Production Handbook. These references are also available at Cooperative Extension offices throughout the western High Plains.

Please contact me with your cropping systems or natural resources questions: 970-522-3200 extension 285. Thank you!

Date: 7/26/06

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