Pest Alert: Seed Treatments for Corn, Cotton, and Soybean Nematode Control
Date: January 31, 2011
From: Steve Koenning, Corn, Cotton, and Soybean Pathology Specialist; Jim Dunphy Soybean Specialist Crop Science; Ron Heiniger Corn Specialist Crop Science; and Keith Edmisten Cotton Specialist Crop Science
A number of seed treatments that claim to aid in nematode management are rapidly emerging. Naturally we are beginning to field a number of questions about these treatments and hope to provide answers. Before we start however some definitions are needed:
- Fungicide – Any seed treatment will almost always contain a fungicide and usually two or three to control post- and pre-emergence damping off. The basic fungicide chemistry differs little between one company and another. They are designed to control the same two to three soil borne diseases. They rarely affect nematodes or insects.
- Neonicotinoid insecticide – thiamethoxam in Cruiser, imidacloprid in Gaucho, and clothianidin in Poncho are common examples of insecticides used on cotton and soybean. These systemic insecticides have averaged about three weeks of protection against thrips. NCSU testing has generally not shown a positive growth response to neonicotinoids in the absence of insects. They have little if any activity against nematodes.
- Polymer – a polymer is a complex chemical that is used in seed treatments to insure that the pesticide additives as well as other materials adhere to the seed and allow for easier and safer handling, as well as insuring that seed flows through equipment.
- Colorant – a dye added to the polymer to identify the components of the additives (will likely vary by company).
- Biological – A number of bacteria, actinomycetes, and some fungi that may be added to enhance disease and or nematode control. They may be stand-alone treatments for “organic” agriculture or be adjuncts to traditional chemical control agents. Many are bacteria in the genus Bacillus. Bacilli are the preferred type of biological because they form spores which are relatively stable and resistant to degradation over time. A strain of Bacillus subtilis is the active ingredient in Kodiak and Bacillus fermis is the active ingredient in Votivo. Another biological is known as Messenger or N-Hibit when used as a seed treatment. This is the Harpin protein that stimulates plant defense mechanisms to protect against attacking pathogens. This Harpin protein was discovered through its ability to protect against bacterial plant pathogens, its efficacy against fungal or nematode pathogens is less clear.
- Avicta or Abamectin is an organic fermentation product that comes from a soil inhabiting actinomycete (Actinomyces avermitilis). Since this is a biological there are various strains which may be more or less potent as toxins to the mites insects, or nematodes. Overall, these Ivermectins are extremely toxic to nematodes at very low doses with very little mammalian toxicity. They are however nearly insoluble in water and are not systemic, so activity is limited in soil.
- Aeris is a carbamate insecticide (thiodicarb – also marketed as the insecticide Larvin). It has good nematicidal activity and limited systemic activity.
We have evaluated a number of nematicidal materials on corn, cotton, and soybean. The most extensive North Carolina research was supported by the North Carolina Soybean Producers Association Check Off program. The results were disappointing. It’s not that they didn’t work, just that they didn’t work as well as we had hoped. At the rate they will be applied to seed, there likely will be no negative effects (phytotoxicity or stunting, and we don’t foresee negative interactions with herbicides). Next, we must consider the crop and species of nematode involved.
In the case of Cotton, both Aeris and Avicta have been approximately equivalent to 5 to 7 lbs/acre of Temik for nematode control. Neither product controls thrips, thus on cotton they should be used in combination with insecticidal seed treatments (Cruiser or Gaucho) or a systemic insecticide to control thrips such as Temik in furrow. Avicta may be weaker on reniform nematode than some other products.
A limited number of tests with Avicta on corn have generally resulted in increases in yield roughly equivalent to that achieved with Counter for root-knot, Columbia lance, and stubby root nematode.
Trials on soybean have shown yield increases equivalent to those achieved with Temik for root-knot nematode. Yield increases with seed treatments for soybean cyst nematode (the most common problem) have not been statistically significant. That does not mean that they will not improve soybean yield. We have seen yield increases on the order of 1/2 to 5 bushels/acre, but the increases have not been consistent over locations and conditions. One to two bushel yield increases are more common, but in no trial have we seen that these products actually control nematodes. None of these products have had any impact on the numbers of nematodes we find.
Control vs. Management
Are we controlling pests (pathogens, weeds, insects) with our practices or pesticides? The answer is a definite NO! At best, we manage pests. Control implies elimination of the pest or completely removing adverse effects of the pest. At best, we suppress plant pest populations and this allows us to produce a crop profitably. These materials are more properly considered aids to pest management. In the case of nematicidal seed treatments they may act more as repellents that allow us to improve growth under nematode pressure in order to improve yield potential.
When one considers the number of potential compounds and possible combinations that can be applied to seed, we obviously we cannot evaluate them all. This said, evaluating claims is a difficult task at best. What is a grower, agent, or consultant to do?
- Have a soil sample processed by NCDA & CS Agronomic Testing in order to determine if a nematode problem exists.
- Evaluate the product literature provided and compare to competing claims. Since these nematode control measures will probably come with other pesticides that may or may not be needed, this may become an expensive nematicide.
- Consider potential yield increases; it’s easier to make a profit on better land than on poor land.
- Even a small yield increase with current prices can improve profitability.
- If possible, evaluate the results yourself if you have a yield monitor. Order some treated and untreated seed and place one in one hopper to see if there is a visible difference in treatment (note: perceived growth increases or lack thereof do not mean a yield increase).
- Remember, for the most part these treatments are good, but are not guaranteed to improve profits. Seed treated by a reputable dealer is the way to go. You can treat your own seed, but there is enough art and science involved that you are unlikely to beat the big guys.