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2018 Insect Thresholds for Sunflowers (07/26/18)

The USDA NASS reports that 28% of the sunflowers were blooming in North Dakota as of July 23rd, compared to only 14% last year (USDA NASS News Release).

2018 Insect Thresholds for Sunflowers

The USDA NASS reports that 28% of the sunflowers were blooming in North Dakota as of July 23rd, compared to only 14% last year (USDA NASS News Release).

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Red sunflower seed weevil: Red sunflower seed weevils (RSSW) are emerging and will fly to the nearest flowering sunflowers. Low numbers of RSSWs are present in sunflower fields from southeast ND (Cass County) and southwest ND (Grant County). Please send me your reports, including locality and numbers, when you start finding more.

Identification: RSSW are small (⅛ inch long) weevils with a snout and reddish-orange.

Scouting: When sampling, use the X pattern and begin counting at least 75 to 100 feet into the field to avoid field margin effects. Count the number of RSSW adults on 5 plants at 5 sites for a total of 25 plants. Scout for adults in the early blooming sunflower fields when the yellow ray petals are just beginning to show. RSSW is attracted to early blooming sunflowers, as females must imbibe pollen before laying eggs. A NDSU YouTube video is available on Scouting for Red Sunflower Seed Weevil in Sunflowers.

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Scouting should continue until the economic threshold is reached or most plants have reached 70% pollen shed. At 70% pollen shed, plants are no longer susceptible for egg laying or significant damage. On older flowering plants (after R5.7), larvae of RSSW (and banded sunflower moth larvae) will be feeding inside the seeds and protected from the insecticide. By then, much of the feeding damage has already occurred.

 

Banded sunflower moth (BSM):

Identification: Banded sunflower moth can be identified by its small size (¼ inch long), and its forewings with a triangular, dark brown band across the middle of the wing.

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Scouting: When sampling, use the W pattern and begin counting at least 75 to 100 feet into the field to avoid field margin effects. Count moths on 20 plants at 5 sampling sites to obtain the total number of moths per 100 plants. When scouting during the day (late morning to early afternoon), the moths remain quiet, resting on upper or lower leaves of sunflower plants or other neighboring broadleaf plants like soybeans. Look for the moth fluttering from plant to plant when disturbed.

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Trap counts for BSM from the NDSU IPM Survey insect trapping networkindicate that banded sunflower moth increased this past week, probably a peak emergence. Scouting is key now, and it should be conducted from the late bud stage (R3) through early flowering. If treatment is warranted, it should be delayed and applied at the R5.1 sunflower plant growth stage (when 10% of head area has disk flowers that are flowering). At R5.1, most BSM eggs have hatched and young larvae are feeding on the florets on the face of the sunflower head.

Sunflower moth:

Sunflower moth migrates to North Dakota from states to our south. Because of the migratory nature, it is usually not a major problem for sunflower production in North Dakota. However, recent low trap catches of the sunflower moths were observed at trap sites in Cass, Foster and Renville Counties (Source: NDSU IPM Survey insect trapping network). All traps catches were <7 moths per trap per week, so the infestation is considered non-economic (so far).

Identification: The adult moth is about ⅜ inch long, grayish-tan and has a cigar-shaped appearance when at rest.

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Scouting: Moths move into fields during early bloom. They deposit eggs on the face of the flower. Damage is caused by the larval feeding on seeds and tunneling in heads. Using the same scouting method as described for BSM, walk a W pattern in the field and count moths on 20 plants at 5 sampling sites and calculate an average number of moths per 5 plants. Since female moths lay eggs on the face of sunflower heads, insecticide should be applied during early flowering (R5.1 - R5.3).

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Lygus bug:

Identification: Lygus bug is primarily an insect pest concern in confection sunflowers only. Adults are small, cryptically colored insects with a distinctive yellow triangle or “V” on the wings, and are 0.2 inch in length. They vary in color from pale green to dark brown. Lygus bugs insert their mouthparts into developing sunflower seeds and inject a toxic saliva into the seed causing a brown to black spot called “kernel brown spot.”

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Scouting:Count the number of Lygus bug adults on 5 plants at 5 sites for a total of 25 plants. Scout for Lygus bugs during flowering. Sunflowers are susceptible from feeding injury during flowering through seed hardening.

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Insecticide spray timing for most sunflower seed-feeding insect pests:

Once the decision to treat has been made, it is critical to time the spray application correctly to get effective management of all sunflower head insects, including RSSW, BSM, sunflower moth and Lygus bug (for confection sunflowers only).

The best sunflower plant stage to treat for all these head-infesting insect pests is when the majority of the plants are in the early flowering R5.1 growth stage (when pollen shed on 10% of the outer rim of the sunflower head).

Scheduling an airplane may take a week or more if ag pilots are busy spraying, so we recommend planning for your insecticide application when only 30% of the plants in a field reached the R5.1 growth stage. If it’s hot, flowering will progress more rapidly and one week may not be enough lead time. Getting the timing right in this situation is difficult - but making arrangements when 5-10% of plants are at R5.1 may be more prudent. Last year at Casselton, sunflower progressed from 1% at R5.1 to 50% at R5.1 in just a few days. Insecticides should be targeted at the adult RSSWs to prevent egg laying; at the adult and early larval stages of BSM and sunflower moth; and at the adult or nymph stages of Lygus bug.

Please see the 2018 ND Field Crop Insect Management Guide for insecticides registered in sunflower.

 

Janet J. Knodel

Extension Entomologist

This site is supported in part by the Crop Protection and Pest Management Program [grant no. 2017-70006-27144/accession 1013592] from the USDA National Institute of Food and Agriculture. Any opinions, findings, conclusions, or recommendations expressed are those of the website author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.

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