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Western bean cutworm moth populations on the rise in Colorado PDF Print E-mail
Written by Holyoke Enterprise   

Western bean cutworm moth populations continue to grow in the pheromone traps in most of the locations. Other pests to pay attention include sunflower head moth and sunflower stem weevils.

In corn, growers should scout fields until eight or more percent of the plants have egg masses or small larvae in the tassels, and the crop is at least 95 percent tasseled. Chemical control should be initiated after 95 percent tasseling but prior to larval entry into the ear. If tasseling is much less than 95 percent, the percentage plants infested should be raised, as fewer larvae are likely to reach the ear. Keep in mind those hybrids containing the Herculex corn borer trait.

Damage by young western bean cutworm larvae in dry beans is not very noticeable, as they feed primarily on tender leaves and flower parts. Pod feeding generally begins about three weeks after the peak pheromone trap catch. Feeding occurs primarily at night and during cloudy days. As pods form, worms chew holes in the pod walls and feed on developing seeds. Some mid-sized worms may remain in the pod during the day, but larger cutworms will hide in the soil at the base of the plants.

Two pheromone traps per field are used to monitor western bean cutworm moth in dry beans. On the date of peak pheromone trap catch, if the seasonal cumulative total catch averaged across the two traps for a field is: between 700 and 1000 moths per trap, the risk of significant damage is low to medium and above 1000 moths per trap the risk is high.

If counts are high enough to warrant treatment, treatment should be applied 10 to 20 days after the peak flight. This allows for all eggs laid in beans to hatch, is early enough to avoid damage from large worms and results in maximum control.

Sunflower head moths have been detected in pheromone traps in Kit Carson, Washington and Weld counties this week. However, most of the sunflower fields have not reached the susceptible stage yet (vegetative to R2). If the moth flights do not coincide with early bloom sunflower (stages R-5.1 to R-5.5), damage due to this insect will be minimal.

Most of the planting date studies indicate that early planted fields (fields bloom before late July) stand the greatest chance of developing significant head moth infestations. Planting after June 1, will reduce but not eliminate the potential for sunflower moth damage, because moth flight activity will be decreasing when sunflowers begin blooming.

If you have early planted sunflower fields blooming now, you should start scouting for sunflower head or banded moth.

There are two types of sunflower seed weevils that infest sunflower seed (red and gray). Both red and gray seed weevils are small weevils found in sunflower heads, although the gray sunflower weevil is larger. The red seed weevil is more damaging than the gray species.

Adults may be found from June 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.

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 (R4) 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. Red sunflower seed weevils can be counted by rubbing the face of the head. An alternative is to spray the head with an aerosol containing the insect repellent Deet. This will flush the weevils from their hiding places, allowing them to be counted easily.