Managing Wireworms in Spring-planted Small Grains
Managing wireworms depends upon correct insect identification and effective monitoring of your fields. Certain seed-treatment insecticides and proactive planting strategies can suppress wireworm activity.
Monitoring for Wireworms: Stocking Traps
It is common for wireworms and other soil-dwelling pests to be underdiagnosed because they are difficult to observe directly. Stocking traps are a useful, low-cost tool for assessing wireworm presence and estimating their density.
Step 1: Choosing the site. As soon as soil temperature nears or reaches 45°F at a depth of four inches, wireworms become active and will be attracted to stocking traps. You will need a minimum of ten stocking traps per average-sized field, as wireworms are patchy by nature. Fields that have previously had patches of sparse and stunted growth, and fields that have been continuously cropped, are at the highest risk for wireworm damage.
Step 2: Making the stocking traps. Put ½ cup of wheat seed in a nylon stocking, and tie it off with string, leaving a tail of about 15 inches. (NOTE: The stockings are the type used by shoe stores. You may be able to buy a small quantity from a local business; or, search online for “disposable foot sox” and buy them in bulk.)
Step 3: Soaking the traps. Just before use, the traps need to be immersed in water for 12 to 24 hours. This step is important to start the germination of the grain, making it attractive to wireworms.
Step 4: Burying the traps
- 10 stocking traps (step one)
- 10 flags
- 10 1x1-ft2 black plastic sheets
- 40 landscaping staples
Dig a hole in the soil about 3 to 5 inches deep and 8 to 10 inches wide. Drop a nylon stocking in the hole and press it down to spread the grain mixture across the bottom of the hole. Leave the string above the soil to help relocate the stocking later on. Cover the stocking with 1 to 2 inches of soil over the bait. Do not pack the soil over the bait.
Cover the soil with a piece of black plastic, and secure the edges with rocks or with landscaping staples to keep the plastic from blowing away. The plastic keeps the soil warm and moist, which is attractive to the wireworms. Place a flag in the corner of the plastic to relocate the site later on.
Leave the trap in place for 10 to 14 days. Wireworms within a radius of about six feet will migrate to the trap. A few may penetrate into the trap, but many will be concentrated in the soil directly surrounding the trap (within a halo of about two inches).
Step 7: Collecting the stocking traps. Traps are picked up in 10 to 14 days. Wireworms may be located inside the stocking, caught in the stocking mesh, or (more frequently) found in the surrounding soil.
Step 8: Count the wireworms at each bait station. Determine the average number of wireworms per trap. An average of 1-2 wireworms per trap is considered the threshold for using an insecticidal seed treatment.
If you are going into the planting season with a known wireworm problem, manipulating certain planting practices can discourage damage:
- Rotate infested grain fields to non-grassy crops such as alfalfa, buckwheat, or sunflower (visit OMAFRA for more info).
- Plant later when the soil is warmer, to expedite growth and reduce the window of time that wireworms have to feed on the vulnerable seedlings.
- Increase seeding density by 10% to compensate for projected losses.
Wireworms can continue to feed and cause damage into late June and early July depending on soil conditions. Currently there are three neonicotinoid active ingredients available for seed-treating small grains (Tables 1 and 2). Higher rates of insecticidal seed treatment provide a longer window of protection. However, research has demonstrated that these products do not directly kill the wireworms but rather act as feeding deterrents. This means that, in spite of feeding suppression, wireworm populations may continue to increase in the field from year to year. Also, note that seed treatment of fall-planted grains is not recommended for wireworm control because efficacy is not expected to persist over the winter.
Table 1. Products labeled for seed treatment of small grains
|Trade Name||Active Ingredient||Labeled Rate
|Cruiser® 5FS||thiamethoxam||0.19 - 1.33|
|Gaucho® 600*||imidacloprid||0.13 - 2.40|
|Nipslt Inside®||clothianidin||0.25 - 1.79|
*generic formulations are available
Table 2. In small grains the economic threshold is a field average of one to two larvae per trap
|Average Number of
Wireworms Per Trap
|0||Continue periodic monitoring for damage and larvae|
|0.1 - 0.9||Survey field for standing thinning during establishment and monitor larvae each year|
|1.0 - 3.0||Continue monitoring and consider applying Cruiser® 5FS, Gaucho® 600, or NipsIt
at 0.5 oz. / 100 lbs. of seed
|> 3.0||Higher rates are recommended if damage has been severe. Use Cruiser® 5FS (1.0-1.33
Gaucho® 600 (1.8-2.4 oz.), or NipsIt Inside® (1.3-1.79 oz) per 100 lbs. of seed