Cotton Nematode Management
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Cotton Nematode Management

   

Cotton Nematode Management1

Jimmy R. Rich and Robert A. Kinloch 2

Nematodes That Attack Cotton

The nematode pests of cotton in Florida are the cotton root-knot nematode (Meloidogyne incognita race 3), the reniform nematode (Rotylenchulus reniformis), and the sting nematode (Belonolaimus longicaudatus). These nematodes annually cause major losses in Florida cotton production. In addition, they are important for increasing the incidence and severity of Fusarium wilt on cotton. Though root-knot nematodes may be found in all soils where cotton is grown, reniform nematodes are found mostly in fine-textured soil with less than 80 percent sand, and sting nematodes are essentially confined to soils with more than 80 percent sand. Root-knot nematodes are known to infest at least 60 percent of cotton fields in the Florida panhandle, and the incidence of reniform nematode is approximately 50 percent in the same area. The incidence of sting nematode is not clearly known but this nematode is more likely to be found with cotton when grown in the deep sandy soils of the Florida peninsula. Field infestations containing more than one of the problem nematodes, particularly root-knot and reniform nematodes, are common.

Diagnosis

The presence or potential for nematode problems in cotton is suggested by one or more of the following: 1) Cropping history of the field, e.g. two or more years production of cotton or equally nematode-susceptible crops; 2) Above-ground symptoms including off-color and/or stunted cotton in spots or large areas of a field; 3) Below-ground symptoms such as small knots on roots or stunted and swollen root tips.

Foliar Symptoms

General foliar symptoms of nematode damage may include areas or spots in the field where plant size is reduced. Height and size of the cotton are oftentimes reduced, and this is generally seen as irregular growth in oval patterns. Plants also prematurely wilt on hot days and sometimes take on a yellow cast. Heavily infested fields, particularly those with reniform nematodes, will show widespread irregular cotton plant growth. Severely damaged cotton plants often show nutrient deficiency symptoms which can complicate diagnosis.

Figure 1. Stunted cotton in a field infested with reniform nematodes.
Figure 2. Older cotton showing damage in an oval pattern in the field.

Root Symptoms

All nematodes affecting cotton reduce feeder roots and produce root stunting. The nematode species differ in specific symptoms with root-knot nematodes producing very small galls or knots on the roots. Roots should be carefully dug with a shovel and examined closely since galling on cotton is hard to see. Sting nematodes do not cause root galling but rather root tip swellings on the cotton. These nematodes stop root growth giving the appearance that roots have been cut off. Reniform nematodes are the most difficult to diagnose in the field. They only produce overall stunted root systems which show few feeder roots. A laboratory analysis is usually necessary to confirm reniform nematodes on cotton.

Figure 3. Root galling on cotton, these small galls on cotton roots result in considerable damage to cotton.

Nematode Assays

Nematode assays must be done to accurately determine that a nematode problem is present, which nematodes are present and their population levels. Soil samples are needed for reliable identification of the responsible nematode species. Only when sufficient numbers of the suspected nematode are extracted from soil samples can a nematode disease be diagnosed and appropriate management procedures implemented. Samples are best taken anytime between October, when problem sites are still apparent in the field, until March. Later as soil temperatures start to increase, nematode population densities start to decline in the absence of suitable host plants for the nematode. Prior to taking soil samples, contact your County Extension Agent for information concerning available sampling tools, shipment bags, and proper procedures for submitting samples.

Two nematode sampling strategies may be employed, one for current problem diagnosis or the other for predictive purposes. A general field survey should be taken every two to three years for predictive purposes. These nematode samples can be taken in conjunction with normal soil fertility samples, split and submitted to the appropriate laboratories. A soil core (1-inch wide by 8-10-inches deep) should be taken for each acre in a 10-acre block containing a uniform soil type. The cores should be thoroughly mixed and a one-pint sample placed in a sealed plastic bag for immediate shipment to an advisory laboratory. Where a nematode problem is suspected, several soil cores from within and immediately around a problem site should be taken while cotton is still growing. These samples should be as described above. Portions of cotton roots should be included in the sample. Irrespective of the sampling strategy employed, soil samples should not be taken when the soil is very dry or soggy wet. Also, do not allow samples to dry out or get too hot. If poor quality soil samples are received, accuracy of nematode recovery will be greatly affected.

Figure 4. Ten acre sampling patterns. Take 10 to 20 soil cores.

Management

Crop Rotation

Where practical, crop rotation is an excellent practice for managing nematode soil population densities. Rotations should include crops that are non-hosts or poor hosts of the problem nematode infesting the soil (Table 1 ). Identification of the nematode species is critical since it will dictate the choice of rotation crop and length of rotational interval required. As a general practice, two years rotation with a non-host crop is usually sufficient to reduce nematode populations to below damaging levels. Peanut, a non-host for the cotton root-knot and reniform nematode, is an excellent crop rotation choice. However, this rotation for only one year will not adequately reduce root-knot or reniform nematode damage for a following cotton crop. Crops in the grass family such as sorghum and some forage grasses are generally poor hosts of the cotton root-knot nematode and are non-hosts to the reniform nematode. The host status of corn and millet varies with the particular variety planted, and thus, they can not be directly recommended in a rotation system for the cotton root-knot nematode.

As indicted, peanut and all grass crops, including corn and millet, are non-hosts of the reniform nematode and are suitable for rotational management of this pest. However, depending on pre-determined soil population densities of the reniform nematode, taking cotton out of production for two or more years may be necessary to bring reniform nematode soil population densities below economic thresholds. Reniform nematode populations do not decline as rapidly as those of root-knot nematode in the absence of a host crop. Peanut, but not crops in the grass family, is also recommended for short-term rotations for managing sting nematode on cotton. Many varieties of soybean and some vegetable crops (tomatoes, southern peas) have been bred for resistance to the southern nematode. These varieties can be successfully used in rotation systems to manage root-knot nematodes in cotton.

Crop Destruction and Weed Management

Cotton roots may survive a long time after boll harvest. In years when there is a delay in the onset of cool fall soil temperatures (<59°F), nematodes can feed and reproduce on these and associated weed roots. This increases nematode soil population densities surviving through to the next planting season. Therefore, cotton stalks must be cut and soil must be tilled through the stubble zone immediately after harvest to destroy these breeding sites. When soils warm in the spring, weeds that are hosts to the problem nematodes may allow nematode soil population densities to increase prior to planting cotton. Consequently, use of winter cover crops is helpful to provide competition against spring weeds and also the cover crop planting process helps destroy those weeds growing in the fall. The cover crop must be a poor or non-host of the problem nematode. Winter cereals are most suitable for managing root-knot and reniform nematodes in this regard but are less effective for soils infested with sting nematode.

Use of crop rotation systems that include bahiagrass have been increasing, and this perennial grass is a non-host for nematodes affecting cotton. However, weeds must be managed in the bahiagrass or nematode populations will be maintained in such a system resulting in damage to the following cotton crop. A two-year bahiagrass rotation is sufficient to manage plant-parasitic nematodes in a future cotton crop providing broadleaf weeds are controlled early and regularly in the first year bahiagrass and this continued through the life of the rotation.

Resistance

There are no Florida-adapted cotton varieties with resistance to any of the three problem nematodes. However, since nematodes are aggravating factors in Fusarium wilt disease, only varieties with excellent Fusarium resistance should be grown in fields known to be infested with root-knot, reniform, or sting nematodes.

Nematicides

Three nematicides are approved for use in cotton production (Table 2 ). Before using nematicides growers should ascertain that problem nematodes are present to justify the expense of treatment. This can only be achieved by submission of soil samples. In University of Florida research, Telone II has shown relatively consistent efficacy for nematode management in cotton. This soil fumigant (1,3-D) is used to reduce initial nematode soil population densities prior to cotton planting. Application of the fumigant usually results in significant cotton yield responses in nematode-infested soils. Research over the last few years has shown an average increase of approximately 35 and 50 pounds of cotton lint per acre for each gallon of Telone II applied per acre to reniform and root-knot-infested soil, respectively. Telone II is applied with a single injection chisel to a depth of at least 12 inches beneath the row, seven to ten days prior to cotton planting. Deeper application is acceptable but Telone II should not be injected into clay subsoil. Applications shallower than 12 inches have sometimes led to poor nematode management. A range of rates from three to six gallons of Telone per acre is recommended. The three gallon rate is satisfactory for management of reniform and sting nematodes, but a minimum of four gallons per acre is necessary in root-knot nematode problem fields. Regardless of dosage rate, the fumigant should not be applied when the soil is dusty dry or wet. Sealing the chisel application slits immediately after application by bedding, press wheels, culti-packing, fluted coulters, or similar devices is necessary to prevent premature escape of the Telone II fumes.

The non-fumigant nematicides (Temik and Nemacur) are applied as 15 percent granular formulations incorporated into two or more inches of soil in a narrow band (four-six-inches-wide) immediately prior to or at-planting. There have been no University of Florida evaluations of Nemacur for management of cotton nematodes. Recent evaluations of Temik for management of root-knot and reniform nematodes have shown significant yield responses in only three out of eight tests. Though responses have varied widely over the years, evaluations of cotton yield responses to Temik applications in nematode-infested soil provide an average increase of ten pounds of cotton lint per acre for each pound of Temik 15G applied per acre. Application of Temik in cotton production is subject to several use restrictions:

In addition there are restrictions on planting any crops not listed on the Temik label in soil treated with Temik within ten months after the last application with the exceptions of:

The following are required by the Florida Department of Agriculture and Consumer services governing the use of Temik:

Tables

Table 1. Recommendations of crops for use in rotation to manage nematode pests of cotton.

Crop

Root-knot nematode

Meloidogyne incognita

Reniform nematode

Rotylenchulus reniformis

Sting nematode

Belonolaimus longicaudatus
Bahia grass


 Recommended
Recommended
Not suitable
Corn
Recommended1


 Recommended
Not suitable
Field pea
Not suitable2


 Not suitable
Not suitable
Millet
Recommended
Recommended
Not suitable
Peanut
Recommended
Recommended
Recommended
Snap bean
Not suitable2


 Not suitable
Not suitable
Soybean
Not suitable
Not suitable
Not suitable
Sorghum
Recommended
Recommended
Not suitable
Sudan grass
Recommended
Recommended
Not suitable
Tobacco
Not suitable2


 Not suitable
Recommended
Tomato
Not suitable2


 Not suitable
Not suitable
Watermelon
Not suitable
Not suitable
Not suitable
Winter oats
Recommended3


 Recommended3


 Not suitable
Winter rye
Recommended3


 Recommended3


 Not suitable
Winter wheat
Recommended3


 Recommended3


 Not suitable
1 Some corn varieties are known to be very susceptible to root-knot nematode.

2 Some varieties of these crops are resistant and may be suitable for rotation.

3 Recommentation is for management of weed hosts. Planting of winter crop will have little or no influence on nematode populations under subsequent cotton.

Table 2. Nematicides that may be used for the management of nematodes on cotton.

Nematicide

Rate

Application1
Telone II
9-12 gallons / acre
4-6 gallons / acre via single injection chisel 7-10 days before planting for root-knot nematodes (36-54 fl. oz. / 1000 ft. row at 3 ft. spacing).

3 gallons / acre via single injection chisel 7-10 days before planting for reniform or sting nematodes (27 fl. oz. / 1000 ft. row at 3 ft. spacing).

This is the primary recommended nematicide for use in severely nematode-infested cotton fields.
Temik 15G
3.5-10 pounds / acre
7 pounds / acre in a 4-6-inch band at planting for root-knot nematode. (8 oz. / 1000 ft. row at 3 ft. spacing).

5 pounds / acre in a 4-6-inch band at planting for reniform or sting nematode. (6 oz. / 1000 ft. row at 3 ft. spacing).

See text for restrictions governing use.
Nemacur 15G
6.5-9.8 pounds / acre
Insufficient data for recommendation.
1 Please consult labels for pesticide handling and use restrictions.

Footnotes

1. This document is ENY-004 (NG015), one of a series of the entomology & Nematology Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised: December 2005. For more publications related to agronomy/agriculture, please visit the EDIS Website at http://edis.ifas.ufl.edu/.

2. Jay, FL 32565 and Jimmy R. Rich, professor, North Florida REC, Institute of Food and Agricultural Sciences, University of Florida, Quincy, FL 32351 and Robert A. Kinloch, associate professor, Entomology and Nematology Department, West Florida REC, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.

U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.


Copyright Information

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