Corn Rootworm Protection

Quite a few years back, an industry person gave me a little vial of corn rootworms. Not only does it contain actual rootworm larvae (worms), it also includes some tiny little rootworm eggs. The significance here is that corn rootworms are the single largest insect problem in corn production in the United States.

The corn rootworm larvae feed mainly on corn roots in the mid to late spring. The feeding negatively impacts corn plants in a couple of ways.

1. Physical loss of roots – less root mass to take in water and nutrients while providing the structure to hold the plant upright
2. Introduction of diseases – any open wound gives disease a chance to enter

Many American farmers are planting corn hybrids with biotech traits to help fight corn rootworms. We plant these on some of our acres. On the Blank Slate field my intention this year is to plant a hybrid without a corn rootworm biotech trait. It’s not a protest against biotech traits or anything. The hybrid I really think will perform the best on this ground isn’t available with a biotech rootworm trait. That’s no big deal to me. Instead, I plan to fight corn rootworms the old-fashioned way: with insecticide. The next paragraph is really the most important thing I’ll write today.

“Plant the best base germplasm for your farm. Then choose the right trait package it’s available in. Just because a hybrid has all the biotech traits inserted into it doesn’t make it a good hybrid.” I may take that topic up on a future blog post.

With corn rootworm, the only way to protect your crop is either with a biotech trait in the seed itself or with an insecticide applied at planting time. There’s no scouting for rootworms and then treating them later. Since I don’t have a corn rootworm trait, I’ll use a full rate of insecticide when I plant my corn. There are dry granule products like Force, Aztec, and Lorsban; and there is also a liquid product, Capture LFR.

The dry insecticides have performed better over the years in university trials and in the field. Part of the reason is the slower release of the insecticide off the dry granule compared to the liquid product where the insecticide is theoretically all available at once. Slow release is nice because we’ll plant corn the last 2 weeks of April and rootworms won’t begin their attack on corn plants until late May and early June. The other reason may be due to placement. There are 3 methods farmers use to place insecticides.

1. Band – all the insecticide is left on the soil surface in a 4 to 8 inch wide band directly over the row. This allows the insecticide to move down with rainfall. It also provides the best control for insects such as cutworms who work mainly at or near the soil surface. The other thing I like about leaving insecticide in a wider band is that is can protect up to an 8 inch wide profile of roots as it moves down in the soil.

2. In-furrow – all the insecticide is placed in the seed furrow. This is the best protection for seed-attacking insects such as seed corn beetles and seed corn maggots. The protection for rootworms is optimized in a couple inch diameter around the seed. It leaves roots that are further off to the side considerably more exposed to rootworm feeeding than a banded application in my opinion.

3. T-Band – a combination of the above two methods. Some of the insecticide is placed in-furrow and the rest is left in an above ground band. This is my favorite application method.

Of the dry products, Force and Aztec have done a little better job than Lorsban. All the dry products have been slightly better than the liquid Capture LFR. However, many farmers are not set up to apply dry insecticides, so the liquid is a great choice for them.

The other tempting thing is to mix liquid insecticide with liquid fertilizer to do two jobs at once. Capture LFR is FMC’s newest formulation. The “LFR” stands for “liquid fertilizer ready” indicating that it mixes much easier with fertilizer than previous formulations of Capture. My experience is that they are correct. The new formulation is much better, but still not perfect. We’ve found that temperature is a big factor in mixing. If the fertilizer is warm and the Capture LFR is warm, the products mix very well. If things are cold, like early in the corn planting season can often be, then you have to be pretty careful.

The other safety precaution we use is to jar test the fertilizer blend with the Capture. Basically you just mix up a small batch in a mason jar and see if they mix well or if they turn to something with the consistency of cottage cheese.

The safest alternative is to have two separate tanks: one with fertilizer and the other with insecticide. If you run two lines back to each row, you never have to be concerned with mixing issues.

I’ve had a lot of questions about Capture LFR this year, especially from Agro-Culture Liquid Fertilizer users and other farmers set up to apply a liquid starter. You can try mixing them if you want. I’d prefer to see guys set up with a two-line, two-tank system. As we do more variable rate fertilizer applications, this gives us the most flexibility to do what we want. Like on the Blank Slate for example, I plan to bump the fertilizer up 50% in some areas. If the insecticide was already mixed in the tank, I’d be forced to up that rate 50% as well which would not be a legal application.