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K-State Agronomy eUpdates

Department of Agronomy

Kansas State University

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Manhatan, KS 66506

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Extension Agronomy

Sunflower moth: Treatment options and pollinator safety

(Editor’s note: The following is an excerpt from a new K-State publication, Sunflower Moth, MF3108, part of the Kansas Crop Pests series of publications. The author is J.P. Michaud, entomologist at the Agricultural Research Center-Hays. You can see the full publication at: http://www.ksre.ksu.edu/bookstore/pubs/MF3108.pdf)

Last week’s issue of the Agronomy eUpdate had an article on the behavior, scouting, and management of the sunflower moth, Homoeosoma ellectellum. This week’s article discusses treatment options and pollinator safety when using insecticides to control the sunflower moth.

Treatment options

If sunflower moths are above threshold, an insecticide treatment should be applied once the majority of blooms have opened and begun shedding pollen (stage R-5.1). Most failures to obtain control result from delayed treatments.

The objective of an early application with most insecticides is to kill female moths before they lay eggs, and young larvae while they are still feeding on pollen and before they bore deep into the head. Diamide insecticides are an exception in that they do not have contact activity and thus do not kill adult moths, although they are effective against larvae.

Scouting should continue after an early treatment as additional applications may be required when moth pressure is heavy. Whereas some growers opt to spray automatically at R-5.1, the advantage of scouting is the possibility that treatment can be avoided if moths remain below threshold, or delayed until later in the flowering cycle when blooms are fully expanded, increasing the chance that a single application will suffice.

Once flower disks are fully expanded or significant numbers of larvae have entered, treatment is far more effective when applied directly into the flower faces. This is best accomplished in aerial applications by flying each pass from an easterly direction, rather than back and forth over the field. Use of a ground rig, although more time consuming, permits more effective application of insecticide in a larger volume of water to provide better coverage.

Organophosphate materials have somewhat better residual activity than pyrethroids, whereas the latter have repellent properties. Both can lose their efficacy quickly under Kansas summer field conditions. Several new formulations combine active ingredients with different modes of action (organophosphate + pyrethroid, or organophosphate + neonicotinoid) to increase efficacy. However, recent observations suggest rising levels of resistance to organophosphates may be evolving in sunflower moth populations.

Pollinator safety

The need to control pests on a crop in bloom raises concerns about potential impacts on pollinators. Sunflower growers also should be aware that most insecticide applications against sunflower moth carry a hidden cost in terms of yield reduction. Although commercial varieties have been bred to be self-compatible, and hence less pollinator-dependent, studies have shown that cross-pollination by insects improves seed weight and oil content.

Insecticide should be applied in the early morning or late evening when pollinators are not flying. Evening is preferable because this permits overnight dissipation of material before pollinators return to the field. However, the requirement for low-wind conditions is a priority that may trump this concern.

Because of their repellency, pyrethroids tend to be safer for bees than organophosphates, provided bees are not sprayed directly. Dusts and wettable powders tend to be more toxic than solutions and emulsions, and microencapsulated insecticides are especially hazardous. Studies suggest that diamides, a new class of insecticides that disrupt insect muscle contraction, have a high degree of safety for pollinators. Diamides act as ryanodine receptor modulators to paralyze insect muscles and must be consumed by the insect to reach their active site.

As of 2012, both Bayer and Dupont have registered diamide insecticides for use on commercial sunflowers in Kansas (Belt and Prevathon, respectively). Preliminary trials indicate that good levels of control can be achieved with these materials without endangering bees.

Growers and applicators should refer to the most recent edition of the K-State Research and Extension publication, Sunflower Insect Management, MF814, for a table of registered materials and application rates. See: http://www.ksre.ksu.edu/bookstore/pubs/MF814.pdf

J.P. Michaud, Entomologist, Agricultural Research Center-Hays
jpmi@ksu.edu