There’s More to “Sorry Dirt” Than Meets the Eye
What you don’t know can hurt you.
What you can’t see can hurt you.
Over the years, many cotton farmers learned that the hard way when nematodes stole yield, quality, and crop resilience from their crop. Many of those farmers now know about nematodes. They not only stopped the pain of lost yield and quality; they also added the joy of crop resilience and increased profit opportunity.
“Growers in the Southeast are paying more attention to nematode issues, and I am thrilled by that,” University of Georgia Extension Plant Pathologist Bob Kemerait says. “Farmers have come so far from a time when poor production and growth was simply cast off as ‘sorry dirt.’ It’s hard to think too much about something over which you have no control, but today’s chemistries, resistant varieties, and education efforts capture the attention of growers.”
The first step toward controlling nematodes, however, is unchanged: soil sampling to determine which type of nematodes are in a field and at what level.
Increased yield is probable when farmers do three things, Kemerait says:
- Sample for nematodes to discover the type present and the population size. “No sense using a root-knot nematode resistant cotton variety if you are fighting sting nematodes.”
- Choose the product and rate that makes the type of nematode and the size of the population. “You can’t be “Goldilocks” when it comes to fighting nematodes; you must be ‘just right’.”
- Applications must be timely. “You can’t fix missed opportunity.”
Kemerait advises farmers to sample after harvest before soil temperatures fall below 65 F, then again during the season, to set the stage for planning nematode management for the following crop.
“Samples collected during the season are for troubleshooting to identify why plants are stunted or struggling,” Kemerait says.” It may not be ‘todes, but it might be. It will be too late to do anything, but it helps prepare for next time.”
Pre-season planning is the time to decide which fields to rotate to which crops and whether to use a nematode resistant cottonseed variety.
Rotate to Non-Host Crops
Kemerait calls rotation to non-host crops during spring and summer months “the single most effective tool to lower populations of plant-parasitic nematodes in coming seasons.”
Consider Planting Nematode-Resistant Cotton Varieties
Planting nematode-resistant cotton varieties can provide yield advantages and decrease crop input costs. But again, the only way to make the right call on a variety is to know which nematodes are in the field and at which population level.
“Resistant varieties work for any population size of the right nematode(s),” Kemerait says. “But, when populations are low or moderate, a grower may prefer a favorite susceptible variety plus a nematicide.”
Growers who consider resistant varieties must calculate anticipated yield as well as the opportunity to save on inputs when they estimate gross profit opportunity. “It’s also savings on the cost of nematicides and the impact on next season when nematode populations crash,” Kemerait says. “If you only think yield equals profit, then you need to change your equation.”
Plan for Site-Specific Management
“Done correctly, site-specific management always pays off,” Kemerait says. For that to happen, however, certain pre-season activities are foundational.
“It is important to ground truth,” he says. “First, develop risk management zones, largely based on mapping soil particle size, then focus nematode sampling efforts on high-risk zones.”
From there, put the appropriate nematicides to work where they are most needed.
“Effective use of risk management zones is an awesome way to put nematicides where they are needed and to save the expense where they are not,” he says. “Research behind use of site-specific management is clear in the benefits toward profitability.”
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