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Seed Bait For Soil Insects

Use this sampling technique to estimate underground pest pressure.

By Dr. Ayanava Majumdar “Dr. A,” Extension entomologist and state sustainable agriculture coordinator, Auburn University; and Rudy Yates, regional Extension agent, Alabama Cooperative Extension System print email

This past year was a difficult one for peanut producers because of wireworm, lesser cornstalk borer and rootworm outbreaks that resulted in severe yield losses in many states.

Wireworms are the immature stages of click beetles, and they overwinter very deep in sandy soils. Wireworms make large feeding holes and deep tunnels on peanut pods that completely destroy the produce.

Being soil pests, wireworms may be overlooked and go undetected unless special monitoring systems are placed in the ground. Germinating seed bait stations are an inexpensive relative sampling method for many species of wireworms inhabiting the soil.

A Complement To Other Techniques
The term “relative sampling” refers to the ability of the seed bait station to attract a small population of wireworms in the area and provide an estimate of real pest pressures.

For producers with wireworms, the goal should be to put as many seed bait stations as possible in different parts of the field to get a reliable result. The seed bait technique also can complement other sampling techniques used popularly, such as shovel sampling.

Germinating seed bait sampling methods have been used successfully in agronomic and vegetable crops, pasture and fields under the Conservation Reserve Program. A producer can deploy these bait stations without the need for special equipment.

Materials Needed
To create the seed bait, collect the following items: untreated corn, wheat or sorghum seeds; water; black plastic trash bag; colored flag or marker; shovel; large Ziploc bags (optional).

The step-by-step procedure for creating the seed bait, as shown in the picture, is as follows:

1. Use a mixture of seeds to increase the attractiveness of seed baits to different wireworm species. The most common seed mixture is wheat and corn, but others may be added.

2. Pre-soak the seed mixture for 24 hours before placement to encourage germination.

3. Dig a pit about nine inches wide and four inches deep in the soil and put a handful of seed mixture in the pit. Wireworms in the planting zone will be attracted to the heat and carbon dioxide released from the seeds. Bait stations over six inches deep attract few insects because most grubs inhabit the upper two to three inches of soil.

4. Cover the seeds with a shallow layer of soil and put a 15 inch by 15 inch piece of black plastic trash bag on the top to trap heat and promote germination of seed in the pit. Use soil to seal the edges. The plastic will help deter animals from disturbing the bait. Put a color flag to mark the position of the bait stations across the field to ensure the bait can be found and that no one runs over the bait until it is taken out.

5. Although it is difficult to recommend a specific number of baits per acre, use as many bait stations as you can handle without forgetting about them. Remember that accuracy of a scouting procedure improves with increasing number of samples or bait stations.

6. It is recommended that seed baits be maintained for at least one week in spring or up to one week prior to planting crops. If feasible, seed baits should be deployed throughout the production season in fields with a history of wireworms in order to monitor the peak larval activity period. Knowledge of peak insect activity could facilitate the development of a site-specific pest management plan.

7. At the end of the sampling period, dig out the germinating seeds along with the soil surrounding the seed bait. Sometimes wireworms collect just under the seed bait; hence, collecting surrounding soil improves pest detection. Carefully go through the sample by manually sorting through the seedlings or by using a pressure washer.

Whatever the method used, be sure that wireworm specimens are not removed or damaged before the count is complete.

8. For an intensive sampling program with a large number of samples, seed baits retrieved from the ground can be stored in Ziploc bags, frozen and checked at a later date (freezing slows down insect development). Refrigerated bags should be processed as soon as possible.

9. Attractiveness of seed bait to wireworms could be affected by the distribution of baits, seed quality and species present. Keep good records of the location of baits on paper. If you are in doubt about identifying the insect, bring a pest sample to your county Extension office.

Sampling sites can be marked with a GPS to develop field maps for insect pressures based on data from many years.

Action Threshold
In the case of peanuts, the economic threshold is one or more wireworm per bait station. A band application of chlorpyrifos over the row may help reduce wireworm pressure to some extent, but don’t expect complete control. Follow proper crop rotation and plant non-host crops to reduce wireworm populations. PG

Contact Dr. A at 251-331-8416 or by email at bugdoctor@auburn.edu.

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