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Curtailing the Cutworm Threat

Saturday, December 1, 2007
filed under: Insects

I operate a diversified grain farm near Steele, in south central N.D. We produce eight different crops, including oil- and hulling-type sunflower.

In the past five years we have moved from conventional till and soil-incorporated herbicides, to direct seeding and pre-emergence surface-applied herbicides. I usually plant my sunflower into small grain stubble with a row-crop planter equipped with a residue manager, or with a shank-type air seeder.

All sunflower ground is treated in the fall prior to seeding with a glyphosate/ dicamba tank mix. Prior to seeding with the row-crop planter, I apply one quart of glyphosate and one ounce of Aim. When seeding with the air seeder, I apply one quart of glyphosate, one ounce of Aim and five ounces of Spartan. I do this after seeding because of the soil disturbance caused by the air seeder. If the planter and drill are properly adjusted and calibrated, I should have a uniform population of 18,500 plants in rows or 22,000 with the air seeder. These populations have provided us with even drydown, satisfactory weed control and good yields on our farm.

Increased Cutworm Populations

One of the side effects of switching to this reduced tillage system appears to be cutworms. I have noticed increasing populations since I made the switch. If not controlled, this insect can wreck my uniform stand, causing spotty weed control and reduced yield. Under moderate to heavy pressure, the Cruiser® seed treatment will still result in too much stand loss. Sunflower can compensate for stand loss to a point before yield is adversely affected. But fewer and larger heads can result in lodging, slow drydown and a weedy field. A uniform canopy is my weed control insurance policy if and when my herbicides break down.

Cutworm’s effect on stand reduction can be managed in either a defensive or offensive way.

First, the defensive route: This has been my choice in prior years because of my conservative Dutch heritage and my inclination to minimize my costs. Defense includes scouting fields, counting insects, looking at the threshold level and then applying an insecticide. I certainly prefer this method; but it is labor intensive and can be more costly.

My cutworm monitoring system has consisted of an ATV-mounted sprayer. I treated an eight-foot swath diagonally across the field with an insecticide labeled for cutworm. This was done pre-emergence, late in the evening. Then, early the next morning, I retraced the path, counting dead cutworm larvae. If the count exceeded the threshold level, I treated the entire field. This system does work and reduces costs in some years, but it requires scouting time and interrupts my small grain weed spraying. Yet if I depend on a custom applicator, I can end up with some real damage should delays occur due to scheduling and weather.

The second plan is to go on the offense. For seeding with a row-crop planter, FMC will have a system to apply a T band for in-furrow application of Mustang Max® for control of cutworm and other soil insects. This label is not yet official, but is expected this coming spring. The estimated cost per acre would be about $6 to $7 and should provide up to 30 days of control. So it would be one pass at planting over the field, and I am done.

When planting with the air seeder, I am planning to tank mix Baythroid® or Warrior® with our Spartan pre application. Again, this will omit another pass over the field, eliminating the worry and providing a good stand. This is a higher-cost option than the defensive plan, but it does reduce time, labor and fuel. It also eliminates the consequences of missing an infestation, having to deal with a poor stand, or even the possibility of a replant — all of which are costly alternatives.

Going back to tillage is not an option for me. If cutworms are a consequence of reduced tillage, then I am prepared to deal with the pest by going on the offensive. I plan to treat all of my sunflower fields without waiting to see if I have a problem. My history tells me I have a very high probability of having a cutworm problem each year. Delaying planting and waiting out the cutworm population is another defensive option. However, in my narrow planting window, this is not an alternative either, since cutworm larvae are active for about 30 days.

The Decision to Replant

Deciding to replant due to emergence or cutworm problems is always the most challenging for me when using the air seeder. An evaluation system I use is the 1/1,000th-acre sampling throughout the field. There are 43,560 square feet in one acre, so 43.5 square feet is 1/1,000th of an acre. One square 6.2 x 6.2 feet is 43.5 square feet. This is generally about two paces.

Once I have determined my square, I count the seedlings and multiply by 1,000. A square containing 15 plants equates to 15,000 plants per acre. I drive my ATV across different parts of the field to make my counts and then take an average. — Tim DeKrey

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