Zane Grabau, UF/IFAS Entomology & Nematology Department & Patrick Troy, Regional Row Crop Agent

Plant-parasitic nematodes, including sting, root-knot (RKN), and stubby-root nematodes among others can cause significant damage to Florida field corn. Nematicide application is a common management practice for nematodes, but is it economically feasible for a relatively low-value crop like corn?

Terbufos (Counter 20G) and ethoprop (MoCap 15G) are granular nematicides labeled for corn, while metam sodium products (Vapam and others), metam potassium products (K-pam and others), and 1,3-Dichloropropene products (Telone II and others) are fumigant nematicides labeled for corn. I made some calls to local retailers and manufacturers to get an estimate on the cost of these products. After getting initial estimates, I eliminated Vapam and K-pam from further analysis, as these products were too expensive to consider. For the other products, I used a range of estimates for product price (not including cost of buying or running equipment) and corn prices along with labelled product application rates to estimate the yield savings that would be needed to break even applying each nematicide. Both corn grain and silage corn are included because one retailer surprised me by saying that most of his corn nematicide sales went to dairy operations for use on silage corn.

Corn silage value seems to be much less concrete, and more volatile, than grain corn. The UGA factsheet: Production Costs vs. Feeding Value of Forages provides some insight on silage value. For my calculations, I used rough low, medium, and high estimates for silage corn value. The low estimate ($25/ton) converts grain to silage value using a conversion factor of 8.3 (the average Florida yield in 2015, 141 bu/a, divided by 17 tons/a corn silage, also average) and $3 corn grain. The medium estimate ($50) is based on the UGA article’s estimates of silage value from a dairy operator’s perspective.

For a Telone II application, at 3-5 gal/a, a yield increase of about 13 to 37 bu/a (or 1230-8800 lb/a for silage) would be needed to cover the cost of the product (Table 1). For grain corn, this is a 10-26% increase, based on the average corn grain yield listed above. For silage, it is a 4-26% increase, again based on an average corn silage yield in Florida of 17 ton/a. It was a surprise to me that this crude analysis suggested nematicide application is more likely to be profitable on silage than grain corn. Since Telone is a fumigant, there would be considerable extra costs beyond product cost, since an extra pass through the field would be required and specialized equipment is needed. The prevailing wisdom is that fumigation, at least on a large scale, is not feasible for corn and that may be true. However, based on this rough estimate, Telone application for corn is much more financially feasible that I expected.

The estimate for yield savings needed to break even ranged from 11 to 25 bu/a (8-18% of average yield) for MoCap (Table 2) and 4 to 9 bu/a (3-6%) for Counter (Table 3). Estimates for silage break-even points ranged from 1020-5290 lb/a (3-17%) for MoCap and 370-2160 lb/a (1-6%) for Counter. Counter and MoCap have similar prices per pound of product, but Counter application rates are much lower, so costs per acre are lower for Counter. Based on my phone calls, Counter is the nematicide applied most often to corn in the region, and price is probably a driving factor for that trend. Applications costs are also generally lower for Counter than Mocap, as Counter is typically applied in-furrow in the same pass as planting, while two passes are often needed to apply Mocap.

Based on this rough cost-benefit analysis, a relatively modest yield bump is needed for Counter application to be profitable in the short term. So, is Counter likely to provide that yield bump? As always, a nematicide is much more likely to be effective where nematode infestations are more severe, making it important to test for nematodes. If you suspect a field is infested with nematodes, take soil samples as described in the EDIS fact sheet, “Soil Sampling for Nematode Assays“.

Nematicide testing on corn in Florida has been limited in recent years, so it is hard to say for certain what results to expect in Florida. However, Counter has been tested on corn, primarily under pressure from southern root-knot nematode, in surrounding states and these results (summarized from articles in Plant Disease Management Reports) are summarized in Table 4. Counter significantly reduced root-knot nematode densities in only one study, but was more successful at increasing yield, as there were significant increases in 6 of 15 studies (average of 7 bu/a increase across the 15 studies). Perhaps Counter nematicide application on corn would provide greater returns under more severe nematode pressure, particularly if highly damaging ones like sting nematode were present. Growers that choose to apply nematicides are encouraged to test products on a limited number of acres when applying a product for the first time. Split applications comparing multiple products can also help growers determine which product will provide the greatest return on investment.

Action summary for those considering nematicide application for corn:

1. Sample fields to determine if nematode population level justifies nematicide application.

2. Consider costs and benefits of nematicide products for corn.

3. Test or compare products on a small scale before making a large investment.

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