|
Driving directions
Portageville, Pemiscot County
Field Day
*Our next field day will be held September 2, 2008.
News
Research
People
Crop & Pest Information
Weather
Contact us
Director:
Jake Fisher
P. O. Box 160
Portageville, MO 63873
Phone: 573-379-5431
Fax: 573-379-5875
Email:FisherJ@missouri.edu
|
Agricultural publication G04259---Reviewed March, 2008
Cotton Nematodes In Missouri:
Your Hidden Enemies
Allen Wrather,
University of Missouri Delta Center and
Mike Milam, Regional Agronomy Specialist
In 2005, diseases, including nematodes, reduced the United
States cotton crop by 2.4 million bales valued at $1.05 billion
according to estimates by the Disease Loss Committee of the
National Cotton Council. Plant parasitic nematodes alone
accounted for an estimated yield suppression of 562,000 bales.
What is a nematode?
Nematodes are worm-like animals that are mostly invisible,
ranging in size from microscopic to more than 10 feet in length.
There are more than 10,000 known species of nematodes.
Fortunately, only a limited number cause problems to humans and
domesticated plants and animals.
Cotton Nematodes in Missouri
Members of the Cotton Foundation, recently decided that too
little was known about cotton nematode problems in the United
States. They asked scientists from each cotton producing state
to form a committee and conduct studies, including surveys of
cotton fields for nematodes. University of Missouri scientists
surveyed for cotton parasitic nematodes in Dunklin, New Madrid,
and Pemiscot counties, which produce about 98% of Missouri's
cotton. They sampled 90 fields in this three-county area. Lance
nematodes were found in two fields and reniform nematodes were
found in three fields, but root-knot nematodes were present in many
fields. The percentage of cotton fields where root-knot nematodes
were found was in Dunklin 45%, 20% in New Madrid, and 26% in
Pemiscot. Fortunately, only a few fields had enough root-knot
nematodes to cut yield.
Root-knot Nematodes
Root-knot nematodes were first recorded as parasites on
vegetables in 1885. They are called root-knot nematodes because
the galls they produce on roots look like knots in a rope. Five
years later, they were observed attacking cotton in the southern
United States. Root-knot nematodes, which include more than 60
species, attack nearly all crop and weed species. The most
common species of root-knot nematodes are Meloidogyne incognita,
Meloidogyne arenaria, Meloidogyne hapla, and Meloidogyne
javanica. These nematode species are generally considered to be
among the 10 most important plant pathogens in the world and are
responsible for hundreds of millions of dollars in crop losses
annually. All four species occur in the U. S. Cotton Belt, but
only some populations of the species Meloidogyne incognita (also
know as the southern root-knot nematode) attack cotton. Recent
survey data show populations of this nematode are widespread
throughout the Cotton Belt. More than 75% of the cotton fields
in some areas are infested. The southern root-knot nematode was
the only type found in Missouri.
Biology of root-knot nematodes
Like all other plant parasitic nematodes, root-knot
nematodes must have a plant to feed upon to complete their life
cycle. The simple life cycle has four juvenile stages in
addition to egg-laying adult female. Egg production occurs
without sexual cross-fertilization of eggs. Even though adult
males may be present, they are not required for reproduction.
The number of days required for this nematode to complete its
life cycle depends on soil temperature. One life cycle,
from egg to reproducing adult, will occur every 28 days when the
soil temperature is 80oF. However, little or no development
occurs at soil temperatures below 50oF or over 100oF.
After the second stage juvenile hatches from the egg, it
migrates through the soil in search of a cotton root. It usually
enters a root near the tip and begins feeding. Since the
nematode is much smaller than the root tip, it can completely
embed itself within the root. Once feeding begins, it loses its
ability to move within the root. As many as 20 juveniles may
invade a single root tip. Second stage juveniles cause little
physical damage to the roots during the penetration process.
Most damage to the cotton plant results from chemical changes
caused by nematodes feeding
The plant root cells near the nematode's head are not killed
by the feeding, but they are transformed. The cells enlarge many
times their normal size and are called "giant cells." Giant
cells, which are approximately 10 times larger than normal root
cells, interfere with the development of the root. The damaged
root cannot transport water and nutrients from the soil to the
developing leaves and bolls. In addition, some of the sugars the
plant produced by photosynthesis to support normal root growth
are diverted to the giant cells to sustain the developing
nematode.
Approximately three weeks after root penetration, the female
becomes swollen, and pear-shaped. The male at the same time
reverts to its previous worm-shape and exits the root without
feeding. The adult female deposits eggs in a mass; an egg mass
contains from 500 to 3,000 eggs. Eggs may hatch immediately and
juveniles may reinfect the root, or may overwinter and hatch next
spring. The female dies soon after laying eggs.
The number of nematodes in a field varies throughout the
year. Populations usually are lowest at planting and greatest at
crop maturity. Root-knot nematodes have limited ability to
survive in frozen soil. Populations decline in the winter when
soils freeze. As much as 99% of the nematodes in a field may die
during the winter. However, the population can increase rapidly
during the summer. It is not unusual for populations to increase
more than 100 times between planting and harvest. Because
population densities can fluctuate greatly and detection
procedures are less than 100% accurate, it is important to sample
fields when the population densities are expected to be the
highest, August to mid-September in Missouri.
Distribution of root-knot nematode and estimates of losses
Root-knot nematodes will be a greater problem when cotton is
planted year after year and the soil is sandy. Root-knot
nematodes are best adapted to coarse-textured, sandy soils rather
than fine-textured silty or clay-based soils. The presence of
root-knot nematodes in a field does not always mean they are
causing significant yield loss. Cotton plants can usually
tolerate a small amount of damage from root-knot nematodes before
yield loss occurs. Many factors influence the amount of crop
damage that will occur with a given population of root-knot
nematodes. Factors to be considered include soil type, soil
fertility levels, moisture availability, and presence of other
pathogens or pests.
Beltwide cotton losses due to root-knot nematodes are as
variable as the distribution of the nematode. The Cotton Disease
Council's annual estimates of total yield losses caused by all
nematode species from 1952 to 1990 ranged from 1.2% to 2.5% per
year. However, losses may exceed 50% of the yield potential in
severely affected fields.
Interactions with other pathogens
Cotton is susceptible to several different pathogens.
Root-knot nematodes are noted for interacting with other pathogens to
cause disease complexes. In most instances, disease complexes
result when soil-born fungal pathogens are present in addition to
root-knot nematode. The Fusarium wilt/root-knot nematode complex
is an example in which the nematodes increase the incidence of
the fungal disease and the severity of the disease symptoms. It
usually requires 100 times more of the individual Fusarium wilt
pathogen to cause the same amount of damage to cotton as when
root-knot nematode is also present. The Fusarium wilt/root-knot
nematode disease complex frequently results in the death of large
numbers of plants in a field. When the nematode is present
alone, it is quite capable of causing yield losses; however,
plants are not normally killed. The absence of Fusarium wilt
symptoms does not indicate an absence of nematode problems.
Cotton root rots caused by several different fungi are affected
similarly by the root-knot nematode. However, the pest does not
interact with the Verticillium wilt pathogen.
Symptoms
Root-knot nematodes are not uniformly distributed in soil;
they occur in irregular patches. These patches may be small and
limited in number, or they may be large and widely distributed.
Depending on the nematode population, plants in these patches may
be damaged and show symptoms ranging from mild to severe
stunting and a reduced rate of development . Leaves on
infected plants may wilt at mid-day more readily than healthy
plants.
Root-knot nematodes cause visible galls or knots on roots
. Swellings of the infected root tissues can be found
on the cotton tap root and the lateral roots from about six weeks after
emergence to harvest. The galls are easier to detect if cotton
plants are carefully dug (not pulled) from the soil.
Root-knot Nematode Management and Control
There are two strategies for managing cotton nematode
problems; rotating cotton with resistant soybean varieties, and
using nematicides. An integrated approach that uses both methods
usually is the most effective and profitable. Strategies that
may be practical for one grower may not be feasible for another.
Crop rotation- Southern root-knot nematode populations can
be reduced by rotating cotton with a resistant soybean cultivar
like Manokin. Maintaining a clean, fallow field will also reduce nematode
populations. However, this practice is impractical because of
the loss of revenue during the fallow period. These nematodes can attack susceptible
soybean varieties, all varieties of potato and corn are susceptible so rotating
these crops with cotton will not reduce the damage these nematodes cause on cotton.
Biological Control- No reliable biological control systems
are currently available, although research is being conducted.
Resistant Varieties- Unfortunately, no cotton variety
currently available has a high level of tolerance or resistance
to the root-knot nematode. Cotton cultivars with resistance to
the fusarium wilt/root-knot nematode complex do not show any
significant resistance to the nematodes. Although some
cultivars are resistant to Fusarium wilt, it is important to
understand that root-knot nematodes alone can and do cause
substantial yield losses to these cotton cultivars. In research
at the University of Arkansas, Stoneville 5599 was the variety
most tolerant of root-knot nematode. Unfortunately, this variety
matures very late in Southeast Missouri and may not produce a
harvestable crop.
Nematicides- Chemical nematicides are widely used to control
root-knot nematodes. Numerous studies show that when nematicides
are used to control nematodes, yields increase significantly.
Yield increases of more than 50% are common in severely infested
fields. The objective for using chemical nematicides is to
protect the seedling roots from nematodes for four to six weeks.
By protecting the roots during early development, yield losses
will be reduced substantially even though nematodes may penetrate
the roots during the latter part of the season. Several
nematicides labeled for use on cotton include seed treatments,
soil fumigants and contact non fumigant products
(click here for list). All pesticides
should be used only in accordance with label instructions.
Sampling for Nematodes
Nematode distribution in a field is generally irregular
and uneven. Populations may be very high in a localized area of
a field and low in the remainder of the field. Because irregular
nematode distribution affects the accuracy of population density
estimates, it is necessary to collect several composite samples
from a single field. Good soil samples that accurately represent
nematode populations are essential for prudent management
decisions. Collecting several samples from each field may
increase cost of sampling, but it is more valuable because the
estimate is more accurate and reliable. Nematode populations
usually are low in the spring and build through the growing
season to reach peak densities at harvest. Nematodes populations
are easier to detect when bolls begin to open than at any other
time. Samples should be collected from within the row because
the nematodes are concentrated there. Generally, a sample should
represent about 10 acres of similar soil type and should consist
of at least 20 individual soil cores in that area. Soil probes,
which are steel tubes about one-inch in diameter, are commonly
used to extract soil cores. Insert the probe 6-12 inches deep
into the soil. Soil cores are collected in a bucket and
thoroughly mixed. About a quart of mixed soil is then placed in
a plastic bag and sealed to inhibit drying. Nematode samples
require special care, because nematodes are living creatures. A
nematode sample should not be handled like a soil fertility
sample. For example, if a sample dries or is placed in the sun,
the nematodes will die. The laboratory information on a dried
sample will not accurately reflect the field situation. A
nematode sample should be handled like a carton of milk. It
should be kept cool, but not frozen. During sample collection,
it is important to keep the soil sample in a cool location, such
as an ice chest with ice. The sample should be transported in a
pre cooled ice chest to prevent overheating. Samples should be
delivered to the diagnostic laboratory as soon as possible.
Overnight delivery service should be used if feasible.
* Issued in furtherance of Cooperative Extension Work Acts of May 8 and
June 30, 1914, in cooperation with the United States Department of
Agriculture. Ronald J. Turner, Director, Cooperative Extension Service,
University of Missouri and Lincoln University, Columbia, Missouri 65211. *
University Extension does not discriminate on the basis of race, color,
national origin, sex, religion, age, disability or status as a Vietnam-era
veteran in employment or programs. * If you have special needs as addressed
by the Americans with Disabilities Act and need this publication in an
alternative format, write ADA Officer, Extension and Agricultural
Information, 1-98 Agriculture Building, Columbia, MO 65211, or call (573)
882-8237. Reasonable efforts will be made to accommodate your special
needs.
|
