CSU Ext: Time to monitor your sunflower fields for head infesting insects
by Assefa Gebre-Amlak, Extension Specialist, Colorado State University Extension
The three major sunflower head-infesting insects, namely sunflower head moth, banded moth and seed weevils are expected to be seen in sunflower fields early this month. According to pheromone based monitoring both sunflower and banded moths populations peak around the early part of 2nd week of August in most of the Front Range Area and northeastern Colorado http://northernipm.colostate.edu/monitored/insectpests.htm.
Sunflower moths: Younger sunflower moth larvae feed primarily on florets and pollen. Older larvae tunnel through immature seeds and other parts of the head.
Scouting for the moth is recommended the next three weeks. Insecticide applications are made at early bloom (R5.1) to prevent moths from laying eggs. If you are using pheromone traps for monitoring the moth activity, less than one sunflower moth trapped per night is considered low risk, while more than four moths trapped per night is considered high risk and justified for treatment. If visual scouting is used instead of pheromone traps, consider treatment if more than two sunflower head moths per five plants is observed while scouting during early bloom.
Banded sunflower moths: Adults are most active during the early morning and early evening. During the day they rest quietly underneath the lower leaves of sunflower plants, but flutter from plant to plant when disturbed. Larvae feed primarily on seed and florets in the central portion of the head. A single larva may feed on from three to five seeds.
Colorado State University field studies showed banded moth is less important in term of damage despite its significantly large population. Insecticide applications made at early bloom (R5.1) to prevent moths from laying eggs. Scouting in the early morning or early evening will provide the most accurate counts, since moths are most active at these times. Pheromone traps can be used to determine when scouting should be started, but a pheromone-based treatment threshold is not available. When scouting, sample sites should be 75 to 100 feet from the edge of the field. Use an X-pattern, counting moths on 20 heads per sampling site for a total of 100 heads. One moth per two plants is the currently accepted economic threshold level.
Sunflower seed weevils: Egg laying begins at the outer edge of the head and progresses inward, following seed development. Adults may be found from July to September. If seed weevil infestations are encountered late in the year, harvest may be delayed to avoid bringing infested seed into storage. Larvae emerging in storage will not damage additional seeds, but their bodies will remain in the storage.
Insecticide applications are made to prevent adults from laying their eggs. Treat red sunflower weevil on oilseed sunflower when about 30 percent of the plants have reached the R 5.1 stage. The economic threshold ranges from 5 – 15 weevils per head, depending on plant population and market conditions (see the High Plains IPM guide for details).
Confection sunflower should be treated to avoid quality penalties if less than 10 to 15 percent of the plants have reached R 5.1 and one or more red sunflower seed weevil can be found per head. Gray sunflower seed weevil is thought to be economically insignificant under most conditions.
Scouting for red sunflower seed weevil can be difficult because of its distribution in the field and because of its habit of hiding in the heads. Start scouting when the yellow ray petals are first visible and stop when the majority of the plants in the field have passed 70 percent pollen shed (R 5.7), or when the action threshold has been exceeded. Avoid taking seed weevil counts from plants in field margins as they tend to congregate in these areas and counts will not be representative of the entire field. Count five sets of five plants, distributed across the field in an X-pattern.
Effective products for management of sunflower pests can be found the High Plains IPM Guide at: http://wiki.bugwood.org/HPIPM:Crops.
Written and submitted to The BARN by:
Assefa Gebre-Amlak and Frank Peairs, Colorado State University Extension