ANR-1012 PLANT DISEASE NOTES ROOT-KNOT NEMATODE IN COTTON
ANR-1012, New July 1997. William
S. Gazaway, Extension Plant Pathologist,
Professor, Plant Pathology, Auburn University
Plant Disease Notes
Root-Knot Nematode in Cotton
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Root-knot nematodes rank second to reniform nematodes
in damage to cotton in Alabama. Only the cotton root-knot nematode
(Meloiodogyne incognita, races 3 and 4) attacks cotton. Other
root-knot species such as the peanut root-knot, northern root-knot,
and javanese root-knot do not attack or reproduce on cotton.
Although cotton root-knot nematodes may be found occasionally
in north Alabama, they are most common in central and south Alabama.
Root-knot nematodes are restricted primarily to sandy soils. Yield
losses to cotton root-knot nematodes can range from as little
as 10 percent to over 75 percent, depending on soil type and prevailing
weather conditions. In sandy, droughty soils, losses can approach
80 percent.
Symptoms. Root-knot nematode damaged cotton appears
as localized areas of stunted plants due to the uneven distribution
of root-knot nematodes in the field. Fusarium wilt often occurs
in association with root-knot infestations. Localized infested
areas are generally oval in the direction of the rows and may
range in size from a few feet to over a hundred feet in diameter.
If affected cotton plants are dug up and the soil carefully
removed so the secondary roots are left intact, small swellings
can be seen on the primary and secondary roots.
Since the Plant Diagnostic Laboratory here at Auburn does not
identify root-knot nematode to species, it is important to
include information regarding the field's cropping history.
Whenever possible it is also very important to check cotton
roots in the suspect field for gall or root swellings. Their
absence or presence is the best indication whether or not cotton
root-knot nematodes are present.
Persistence And Transmission. Vetch, corn, soybean,
tobacco, and many vegetables (especially legumes) are good host
crops for root-knot nematodes and will maintain or even increase
populations.
Susceptible weed hosts include Johnsongrass, pigweed, yellow
and purple nutsedge, goosegrass, bermudagrass, sicklepod, cocklebur,
cowpea, ground cherry, lambsquarter, teaweed, and smartweed.Winter
grass crops such as wheat, oats, barley, and rye are also hosts
but root-knot does not reproduce well on them since they are grown
during the winter months.Peanut is a nonhost to cotton root-knot
nematode.
Control. Root-knot nematode is best controlled by using
the following strategies:
- Use resistant or tolerant varieties. Most commercial cotton
varieties have some tolerance to cotton root-knot nematodes.
But few if any commercial varieties are completely immune to
cotton root-knot nematodes. Plant tolerant cotton varieties in
fields where cotton root-knot nematodes are found.
- Crop rotation is effective in managing cotton root-knot nematodes.
Certain grass crops or pastures, grain sorghum, and peanut can
effectively reduce cotton root-knot after a 2 to 3 year period.Corn
is a questionable non-host crop since many corn hybrids are susceptible
to root-knot nematodes and may actually increase their populations.
If corn is used in a rotation plan, make sure the hybrid has
some resistance to root-knot nematodes.
- Use nematicides in fields where root-knot nematodes cannot
be managed by tolerant cotton varieties or rotation. Certain
nematicides are cost effective in heavily root-knot infested
fields.
- Land fallow is also effective in reducing root-knot populations,
but weeds must be controlled.
Use chemicals only according to the directions
on the label. Follow all directions, precautions, and restrictions
that are listed.
For more information, contact your county Extension
office. Look in your telephone directory under your county's name
to find the number.
For more information, contact your county Extension office. Visit http://www.aces.edu/counties or look in your telephone directory under your county's name to find contact information.
Issued in furtherance of Cooperative Extension work in agriculture and
home economics, Acts of May 8 and June 30, 1914, and other related
acts, in cooperation with the U.S. Department of Agriculture. The Alabama
Cooperative Extension System (Alabama A&M University and Auburn
University) offers educational programs, materials, and equal
opportunity employment to all people without regard to race, color,
national origin, religion, sex, age, veteran status, or disability.
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