Nematodes are stealing as much as 10 percent of U.S. cotton production annually and many producers are not aware that they are being robbed.
“Yield losses of 10 percent within a field are common and often go unnoticed,” says Clemson University Extension nematologist John Mueller.
“Yield losses in some fields,” he said at a recent PhytoGen field day in Lee County, S.C., “can exceed 50 percent.”
Across the Cotton Belt, nematodes may be taking close to 1 million bales annually. Root-knot and reniform species are the most common and extend from North Carolina to Texas with annual Beltwide losses averaging 5 percent.
“Cotton production in every state is affected by one or more nematode species,” Mueller says. “In addition to reniform and root-knot, South Carolina and some counties in North Carolina and Georgia also lose cotton to the Columbia Lance nematode. Other damaging species include the sting and stunt nematodes.
Mueller says nematodes may occur and limit yield on most soil textures. If plants are under stress from other factors — moisture or heat — nematode losses may increase and could be worse in coarse, sandy soils.
“Nematodes occur in scattered patches. These areas develop more slowly than the rest of the field, which makes maintenance, including herbicide application, and especially defoliation and boll opening, difficult. Often, yield is in the field but lost due to late maturity.
“Irrigating more will not eliminate damage,” he adds. “The damage from nematodes often blocks the vascular system, so, no matter how much soil moisture you have, the plant is still not taking up all it needs.”
Yield loss may come from stunted and abbreviated root systems from nematode feeding; reduced efficiency of water and nutrient uptake from impeded vascular systems; and potential increased levels of fungal root diseases and Fusarium wilt, in addition to seedling diseases.
Mueller recommends four important steps farmers should take to manage nematodes.
1. The first thing you need to do is sample all your fields, find out what you have. Submit those samples to the nematode lab; identify the species — root-knot or reniform (the main two across the Belt).
2. Follow a good crop rotation. Work with your county agent or your local consultant. Pick a rotation that will minimize the nematode buildup.
3. Use available resistant varieties if rotation is not adequate. Currently, several varieties with root-knot resistance are available and reniform resistant options are about two years away.
“That will be a great addition to fight the nematode damage in a conservative manner, no pesticides into the soil,”
4. The last resort is where you spend the most money. A nematicide is probably going to cost $30 to $50, $60 an acre.
Sample timing critical
Timing of sampling is important, Mueller says. “We need to sample between harvest and Thanksgiving in most places. Take samples in the fall and send them to your state lab or local commercial lab. Look over the numbers and design a two- or three-year plan to control nematodes in the crops that you want to plant.”
Mueller says samples should be pulled from the crop row, about 3 inches from the stalk, not the middles where producers typically collect soil fertility samples.
He recommends storing samples out of sunlight, preferably in a cool spot but not frozen.
“Send samples to a nematode laboratory as quickly as possible. They do not need to be shipped in a cooler with ice if sent in a package with numerous samples and the outside temperature is not extreme.”
Producers should “sample every field for nematodes to develop an effective nematode management scheme.”
In South Carolina, cost for nematode samples vary from $5 to $20 per sample and may be as high as $50.
“Although that seems high, it is easy to justify a $20 per sample fee,” Mueller says. “Normally, a sample represents more than 20 acres. At 20 acres per sample, that’s just $1 an acre.”
Species and population density depend on several factors, including crop, variety, weather and planting date, he says.
Crop mixes are important but Mueller cautions that eliminating nematodes by rotation may be difficult. Cotton and soybeans are hosts for root-knot, reniform, lance and sting nematodes. Corn is host to root-knot, lance and sting but not reniform. Peanut is host only for the sting nematode.
Variety selection is also important and underscores the importance of sampling to identify species. “Host plant resistance is specific to one species,” Mueller says.
Varieties first released with root-knot resistance were associated with a “yield drag,” Mueller says. “The latest Southern Root-Knot (SRK) resistant varieties (PhytoGen 480, for one) have overcome the yield drag and reduce nematode reproduction and carryover significantly.”
Nematicides, on the other hand, work across nematode species.
Mueller also cautions producers about moving nematodes from an infected field into a clean one. Nematodes may hitchhike on soil carried in mud on vehicle tires. Implements such as discs and planters or other pieces of equipment inserted into the soil are potential nematode movers.
Wind may bring in nematodes. Also, birds and mammals and any movement of water that carries soil may transport nematodes. “Flooding will not kill off a nematode population,” Mueller explains.
Need to know
The critical first step in managing nematodes, Mueller says, is knowing what’s in the field — population density and species. Next is realizing how damaging the pests can be.
The life cycle of a nematode from egg to egg is less than 28 days and one female can produce more than 200 eggs with multiple generations per year. The female dies after producing eggs and once a female infects a root, she cannot move to another location.
Knowing the population dynamics of nematodes and the amount of loss a cotton farmer can incur should encourage producers to manage the pests.
Control costs may seem high, he says, but are also justifiable. The $20 per sample, for instance, adds just $1 per acre to production costs.
Nematicide treatments range from $5 to $60 an acre. “In two-bale cotton, a 10 percent yield loss will cost at least $60 per acre,” Mueller says. “You can spend $1 per acre to help make decisions that could cost you $5 to $60 in nematicide cost or lost yield.”
Unless producers sample, they don’t know if nematodes are costing them lost pounds and if so, which species is doing the damage. A modest investment at least provides information to make informed decisions.