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I'm obsessed with nematodes

Brad Haire brad-haire-farm-press-cotton-planting-ga-2-15-z-1.JPG
Unmanaged, plant-parasitic nematodes can rob yield from large sections of an infested field. Management opportunities for nematodes are largely over when the furrow is closed.

My buddies out in Texas call them “rib-eyes in the sky," but when I recently heard the rolling call of sandhill cranes, I thought of nematodes.

I am obsessed with nematodes. It may be guilt that I didn’t talk enough about the damage to corn from nematodes. It could be my renewed focus on soybean cyst nematodes through the Soybean Cyst Nematode Coalition. Very likely, the release of reniform-resistant cotton varieties and changes in our nematicide arsenal have fueled my fascination. The biggest reason I talk about nematodes is that I don’t want you to forget about them. Ever!

On a recent Saturday I received a text message from my UGA colleague, Dr. Glen Harris.  It read, “Sandhill cranes circling and heading north.  They should be over you pretty quick; check them out!”  Hearing and eventually spotting sandhill cranes are things many in Tifton look forward to as annual rites-of-passage in the fall and late-winter.  However, seeing cranes heading north on Jan. 23 was troubling as winter doesn’t officially end for nearly two more months. To be honest, I was quickly thinking more about nematodes and less about cranes.

If nematodes were as infamous as boll weevils or as big as glyphosate-resistant pigweed, things might be different.  But because nematodes are nearly microscopic and create symptoms that can be easily confused with other causes, to include herbicide injury, drought, and soil fertility problems, it is easy to miss them.  Overlooking nematodes can be a costly mistake.  Unmanaged, plant-parasitic nematodes can rob yield from large sections of an infested field.  Also, best-management opportunities for nematodes are largely over when the furrow is closed.

Getting the most from a nematode management program requires that you know something about what’s wiggling through your fields.  Two things of greatest importance are "what kind(s) is/are in the field?" and “how many of them are there?”  The best way to answer these questions is to pull soil samples for nematode testing at harvest when populations are at their peak.  I’ve recently had samples sent to me for comment.  The problem with not finding nematodes in cooler soils is that I can’t be sure if they aren’t there of if we are just not finding them during winter months. 

While nearly all fields in the Southeast are vulnerable to infestation by one plant-parasitic nematode or another, obviously not all fields have a problem.  “Common denominators” in fields where nematodes are an issue include soil type (e.g., sandy soils are more favorable for root-knot and sting nematodes, while reniform nematodes are often found in heavier soils).

Nematode problems are tied to cropping history in a field. Planting the same nematode-susceptible crop in a field year after year, season after season is a fool-proof recipe for problems with nematodes.  Rotating fields with crops susceptible to the same nematodes will also lead to problems.  Colder soil temperatures suppress growth and development of nematodes on cover crops. However, if the winter is unusually warm, or if the cover crop is especially susceptible, nematodes could still be a problem. 

For example, rye and wheat are commonly grown as winter cover crops.  While rye is generally considered a “poor” host for the southern root nematode, wheat is a “fair” host.  When winter soil temperatures approach 65 degrees, nematodes can build on wheat.  As another example, planting black oats as a cover crop may suppress lesion and stubby-root nematodes, but may not suppress southern root-knot nematodes.

Most growers are aware of the nematode-resistant-varieties available in peanut, cotton and soybeans.  For 2021, cotton growers in the Southeast will have several new nematode –resistant cotton varieties to consider. From Phytogen, PHY 545 W3FE has two-gene resistance to southern root-knot nematodes and PHY 332 and PHY 443 W3FE have resistance to root-knot and reniform nematodes. From Deltapine, DP 2141 NR B3XF also has resistance to root-knot and reniform nematodes. 

In addition to seed-treatment nematicides, cotton growers have an expanding arsenal that includes Telone II, AgLogic, Vydate, and Return XL.  In 2021, the torch from Bayer CropScience will pass from Velum Total (fluopyram + imidicloprid) to Velum (fluopyram alone).  Corn growers are familiar with Telone II and Counter 20G, but will also have Propulse (fluopyram + prothioconazole) and Velum for nematode management.

I believe that growers must be especially vigilant for nematodes as we head into the 2021 season.  Anticipation of a fairly mild winter suggests that nematodes could be hungry and active when the first seeds are planted.  Volatility in commodity prices brings uncertainty as to “what,” “how much” and “where” crops will be planted and this may affect crop rotations.  As I was told earlier today by a grower anxious to protect his crop, “Nematodes could be a problem anywhere and everywhere on my farm.”  I think that’s what the sandhill cranes were trying to tell us one Saturday afternoon in January.

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