Soybean Nematode Management
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Soybean Nematode Management

   

Soybean Nematode Management 1

Jimmy R. Rich and Robert A. Kinloch2

Nematodes That Attack Soybean

Soybean is no longer an important agronomic crop in Florida, but the crop is very susceptible to many important plant-parasitic nematodes. Hence even minor production of soybean, even in its limited use as a forage crop, may increase nematode soil populations damaging to subsequent crops. Nematodes attacking soybean include all the root-knot (Meloidogyne spp.) nematode species that occur in Florida. In addition, reniform (Rotylenchulus reniformis) and sting (Belonolaimus longicaudatus) nematode populations are enhanced by soybean production. All of these nematodes can be limiting factors in the production of many crops in Florida. Soybean cyst nematode (Heterodera glycines), important in previous years, affects only soybean among the agronomic crops in Florida. This nematode has not been detected from Florida soils for many years since soybean production decline and much of the previous soybean acreage has shifted to production of cotton, a non-host of soybean cyst nematode.

Diagnosis

The presence or potential for nematode problems in soybean could be 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 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

Above-ground symptoms of nematodes attacking soybean are similar, resembling those caused by many other kinds of root injury, disease, or general nutrient deficiency. Irregular, oval shaped areas in the field may have plants that are stunted and yellowed. Near the end of the season, soybean plants may prematurely drop leaves. Frequently, lines of these damaged plants may stretch along rows following the direction of usual soil cultivation.
Figure 1. Stunted and yellowing plants in an oval pattern caused by root-knot nematodes.

Root Symptoms

All nematodes affecting soybean reduce feeder roots and produce root stunting. The nematodes differ in specific symptoms, and roots should be carefully dug with a shovel, not pulled, for close examination. Below-ground symptoms differ, depending on the nematodes causing them, but are not always distinct enough to use as a sole basis for diagnosis. Root-knot nematode infections cause the roots of soybean to swell into galls. These are generally not readily observable until the latter half of the soybean season. Root galling caused by nematodes on soybean may resemble Rhizobium nodules, and these can be confused when diagnosing a root-knot nematode problem. Rhizobium nodules on soybean roots grow on one side of the root, can be easily removed from the root and are a pink color inside. Root-knot nematode galls, on the other hand, grow around the small roots, are firmly attached, and are not pink on the inside. Soybean roots infected by the soybean cyst nematode usually have reduced Rhizobium nodulation and the roots are short, sparse, and dark in color. Small period-sized white dot-like cysts on the roots can be seen with very careful examination. These are the developing females of soybean cyst nematode. 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 cyst, reniform and sting nematodes on soybean.

Nematode Assays

Nematode problems of soybean can be determined only by nematode assay . Prior to taking samples, contact your county extension agent for information concerning available sampling tools, shipment bags and proper procedures for submitting samples. Be aware that soybean is such an excellent host for many important plant-parasitic nematodes that a field planted to this crop should be sampled before any cash crop is planted in the same site. Samples should not be taken when the soil is dusty dry or soggy wet. Two sampling strategies may be employed. A general survey should be performed immediately after soybean has been harvested. A soil core (1-inch wide by 8-10-inches deep) should be taken for every 1 acre in a 10-acre block containing a uniform soil type and cropping history. The cores should be thoroughly mixed and a 1-pint sample extracted and placed in a sealed plastic bag and kept cool (not frozen) before immediate shipment to an advisory laboratory. When possible, roots and root fragments should be included in soil sample.In a more definitive strategy where a nematode problem is suspected, several soil cores from within and immediately around a poor growth site should be taken while soybean is still growing. Include portions of damaged roots with the soil sample. These samples should be as described above.

Management

Nematode management depends on identifying and monitoring nematode populations to choose tactics for each field. It requires careful choice and integration of crop rotation, other cultural practices, resistant varieties, and nematicides.

Crop Rotation

Soybean is generally not a suitable rotational option for the nematode management of other crops. Soybean should not be planted either before or after cotton as both are hosts to important nematode pests including southern root-knot, reniform, and sting nematodes. The susceptibility of soybean to nematodes is so great that, even if planted as a forage, production of soybean for more than one consecutive season could subject a field to damaging levels of nematodes for subsequent crops. Unless a population of sting nematodes is recovered in a soil sample, a crop of soybean should be followed by a summer planting of a grass crop such as field corn, sorghum, or bahiagrass, etc. These crops are the most likely to reduce populations of root-knot and reniform nematodes.

Resistant Varieties

Considerable effort has been expended over the years to develop soybean varieties with resistance to soybean cyst and root-knot nematodes. Varieties listed in Table 1 have resistance to race 3 of the soybean cyst nematode in addition to resistance to at least one species of root-knot nematode. Resistant varieties should be the preference when planting soybean. However, the following cautionary information must be considered in reference to root-knot nematode resistant soybean varieties. Resistance in these varieties is considered 'quantitative' and is governed by a large unknown number of genes. Resistant varieties, therefore, may allow root-knot nematodes do survive and reproduce but at a lower level than susceptible varieties. This does not cause the resistance in a particular cultivar to fail but a considerable soil population of root-knot nematodes will remain following cultivation of a resistant soybean. Alternatively, soybean cyst resistance in soybean is considered 'qualitative.' Here resistance is conferred by a few dominant soybean genes. Compared to root-knot nematode, essentially no soybean cyst nematodes develop within a resistant cultivar. If soybean cyst resistant cultivars are monocultured for a few years, resistance breaking cyst nematodes will cause failure of that particular line of resistance. Soybean varieties or lines are no longer tested annually in Florida for nematode resistance traits. Other southeastern states, however, have active programs for screening soybean varieties and lines for nematode resistance. These should be consulted to determine variety resistance to the three root-knot nematodes (Javanese, peanut and southern) commonly found in Florida soybean fields. The University of Georgia has an internet site that provides such information. Go to: http://www.griffin.peachnet.edu/caes/soybeans/

Nematicides

Pesticides approved for nematode management of soybean are given in Table 1 . There is little or no justification for using nematicides on soybeans produced for forage. For market production, growers must carefully consider costs and commodity price expectations before choosing nematicides for nematode management in soybean. While Temik 15G is available for use on soybean, application of this nematicide is subject to several use restrictions:

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

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

Fields to be treated with Temik shall be so posted conspicuously at least 24 hours before application and for a minimum of 30 days afterwards.

Tables

Table 1. Nematicides that may be used for the management of nematodes on soybean.

Nematicide

Appplication1,2

Comment
Telone II
28-56 fl. oz. / 1000 ft. of row/outlet


Pesticide costs and commodity market expectations must be carefully considered before application of nematicides in soybean production.
Temik 15G


11-15 oz. / 1000 ft. or row


As above.
1Please consult labels for pesticide handling and use restrictions.

2Based on a 36 inch wide row spacing.

Footnotes

1. This document is Fact Sheet ENY-003 (NG018), one of a series of the Department of Entomology and Nemaatology, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Revised: December 2005. Please visit the EDIS Web site at http://edis.ifas.ufl.edu.

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

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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