Georgia Cotton: Nematodes – What You Do Now Affects Everything You Do Later

    Cotton roots infected with root-knot nematodes swell in response to the infection. These knots serve as feeding sites where nematodes (microscopic worms) grow, produce more eggs and stunt the plant's growth. Photo: University of Georgia

    We had a very mild winter this year.  Mild winters may be nice in reducing our power bill; however extended periods of very cold soil temperatures are essential for reducing nematode populations in the upcoming field season.  I don’t believe we had enough cold weather this year and it could make nematode problems more severe for our cotton farmers.

    If plant-parasitic nematodes are likely to be a problem in a cotton field this season, then the grower has a very brief window of opportunity to effectively manage this pest.  Southern root-knot, reniform, sting, and Columbia lance nematodes all damage our cotton crop in Georgia and, while growers may not find management options convenient, protecting the crop from nematodes is an essential step to protecting yield.

    Nematodes begin to affect the root system of the cotton crop very soon after germination.  If the developing taproot and root-system is not protected, then all other production efforts throughout the remainder of the season are compromised as the damaged plants can never fully recover.

    There are important steps necessary to reduce the risk of nematodes to a cotton crop and to protect the crop once the seed is planted.  It is critical to remember that once the furrow is closed, nearly every management decision has been made and the grower will have to “live with” the results throughout the season and on to harvest.

    Step 1.  Practice good crop rotation to reduce parasitic nematode populations in a field.  Peanut is an excellent rotation crop for cotton as peanut is not a host for the reniform, Columbia lance, or southern root-know nematodes. Corn is not a host for the reniform nematode.  Soybean is a host for the southern root-knot and reniform nematodes; however if a grower planted a “nematode-resistant” variety in the previous season, then the impact of the nematodes on the future cotton crop should be reduced.

    Step 2.  Take soil samples, optimally in the fall of the previous cropping season, to assess both the types of nematodes and population size in a field.  To be able to make the best management decisions, it is important to know not only which kinds of nematodes are in a field, but also how many of them are there.  Growers could take samples now that soil temperatures have risen; however nematode counts may still be deceptively low and misleading as far as best management options.

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    Step 3.  Consider planting a root-knot nematode resistant variety, such as DP 1747 B2RF, Phytogen 480 or Phytogen 580.  These varieties are not resistant to reniform, sting or Columbia lance nematodes; however they can have a tremendous impact when planted where southern root-knot nematode is a problem.  Planting one of these resistant varieties in a field infested with root-knot nematodes will accomplish two things.

    First, damage from root-knot nematodes will be minimal, if it occurs at all.  No nematicides are needed.  Second, the root-knot nematodes will be unable to build in the field, so populations will be lower for the next cotton crop.

    Step 4.  If a grower chooses not to plant a root-knot nematode resistant variety, either because he preferred another, susceptible, variety or because reniform, sting or Columbia lance nematodes were the problem in the field, then he must consider using a nematicides to protect the crop.  To make the most informed decision about which nematicides to use, the grower should have some idea about the size of the nematode population in the field.

    This is best accomplished with results from fall nematode counts.  Samples taken in the spring before planting, but after soils warm, could give some information if nematodes are found in the sample.  However if nematodes are not found in the sample then this may simply be because they have not yet built to a detectable level following the colder winter months.

    Where parasitic nematodes are well-above “threshold” levels, there is no nematicides that can perform as effectively as Telone II (3 gal/A).  Telone II is a fumigant that must be applied when the soil is neither too wet or too dry.  Typically Telone II is applied 7 to 14 days ahead of planting; however when soil conditions are right and heavy rain is not expected within 3-4 days following planting, Telone II can be applied at the same time as the seed is planted.

    In fields where Telone II will not be used, or where nematodes are at a “moderate threat”, growers should consider using AgLogic (5-7 lb/A) or Velum Total (14-18 fl oz/A).  Both products protect the cotton crop against nematodes and thrips.  Though results from nematicide trials are notoriously variable, I am comfortable with the recommendation that Velum Total (16-18 fl oz/A) is gernally equivalent in performance to AgLogic (5 lb/A).

    Where pressure from nematodes is severe, it is my observation that AgLogic (7 lb/A) offers greater protection than does Velum Total.  But, of course, that additional protection comes at a cost.

    Seed treatment nematicides, to include AVICTA Complete Cotton, COPeO Prime, Bio ST, Nemastrike all are convenient tactics for managing nematodes; however they may not be enough.  I have significant data for AVICTA Complete Cotton and COPeO Prime and an increasing volume of data for BIO ST.  I have limited data for Nemastrike.

    Seed treatment nematicides are most appropriate for low levels of nematodes in a field.  As populations of nematodes increase, the benefit of the seed treatments, as compared to Telone II, AgLogic, or Velum Total, is lost.  Also, performance of some seed treatment nematicides in Georgia may not match that reported in advertisements.

    I do not have data to show the value of combining use of a seed treatment nematicide with either Velum Total or AgLogic; however I generally do not think any additional benefit in yield will offset the added cost of the combination treatment.

    Once the furrow is closed, growers have only one additional treatment option and that is either Vydate-CLV or RETURN XL as a foliar-applied nematicide at approximately the 5th to 7th true leaf stage.  This treatment should be in addition to an earlier nematicides treatment and not as a “stand alone” treatment.  Results with Vydate-CLV have been mixed, but it seems most promising where reniform nematodes are a problem.

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