"Soybean cyst nematode (SCN) is a plant nematode. Nematodes are microscopic roundworms, and plant nematodes feed on plant parts. Many different kinds of nematodes exist, and their common names often reflect their most important host."--First page.Terry L. Niblack (Department of Plant Pathology), and George S. Smith (Integrated Pest Management, College of Agriculture)Revised 2/90/10

Niblack, Terry L.

Smith, George S.

English

University of Missouri: MOspace

i. = n 0 u II II "' ,la; r, " J"7 E ~ ~,ltB· :-r!J. bl~;l1fB· ~1'4 ~ 11 ~ ~ l-, la..,= .  B ~·  L...., L...J" L...J l~. !":J□--. t...; '=•~" □ ,~~ □- r::::::ll~ • ~ .. • • I( = 1 I • =: [JJ .. .. -(l. ll ~bifl:j" f :_. I =t~::.□·~ • ~ '.·-= .... I~ " ~:-::..a =-r!.!l =; _::'..J u ~zrrb, ·11111. Ili c ,I ~ iii a= I Ji! 111 , rlli- 1 [VJ, ~ ... 1 -1!: •HJ r,-1 1;i, Urr~ B_; =:LI.~a. all . • r., _ll• lia: I=! II [J lJ u u u ll u II u u I •• I Answers to the most asked questions about Soybean cyst nematode Terry L. Niblack, Department of Plant Pathology and George S. Smith, Integrated Pest Management, College of Agriculture Cost of printing paid for in part by the Missouri Soybean Merchandising Council What is soybean cyst nematode? Soybean cyst nematode (SCN) is a plant nematode. Nematodes are microscopic roundworms, and plant nematodes feed on plant parts. Many different kinds of plant nematodes exist, and their common names often reflect their most important host. So, although SCN can attack other plants, soybean is its most economically important host. SCN is called a cyst nematode because the females (Fig. 1) become egg-filled cysts at maturity. Other cyst nematodes, such as sugar beet cyst nematode and clover cyst nematode, are also common in the Midwest. SCN was first identified in the U.S. in 1954 and in the Missouri Bootheel in 1956. By 1990, SCN was found in 70 Missouri counties (see map on back). It is found in most major soybean growing regions in the world. How does SCN infect soybeans? SCN survives in soil as eggs in protective cysts (Fig. 2). Cysts may persist in soil for many years, even in the absence of soybeans. The eggs hatch whenever condi-tions are favorable for soybean growth and when soy-beans or another suitable host are present (see Table 1). The hatched juvenile, or larva, is the infective stage, and can move through soil. Using their stylets, or Fig. 2a. Above, eggs containing juveniles from a ruptured SCN cyst (magnified 600 times). Note the stylet (black arrow) in the head of the folded-up juvenile. Fig. 1. Female soybean cyst nematodes (white arrows) and nitrogen-fixing nodules (black arrows) on a soybean root from a field-grown plant. spears, the juveniles penetrate and move within roots until they establish feeding sites. Once feeding sites are established, the juveniles swell and molt several times as they develop into adults (Fig. 3). Males recover their vermiform (worm-like) shape and leave the roots upon maturity. They don't feed, but move through soil to find mates. The lemon-shaped females remain attached to roots and are incapable of moving. They produce 200 to 500 eggs Fig. 2b. Infective cyst juvenile after hatching. Cyst juveniles are about 1/64 inch long. Photo courtesy of R.S. Hussey (University of Georgia). _A,,-,----~ $1.00 11!!:JJi PRINTED WITH G4450 ~ SOYINK II II Archiveversion - chck for updatesand turn from white to yellow to brown as they mature into cysts (Fig. 4). Under optimum conditions, the entire life cycle can be completed in less than 30 days, so there is the potential for several generations in one growing sea-son. Life cycles are overlapping, however, and the pro-cesses of hatching, infection, and egg production con-tinue throughout the growing season. Fig. 3. SCN juveniles within soybean roots, stained pink for observation in the laboratory. Different degrees of swelling correspond to different stages of development. Fig. 4. SCN females at various stages of maturity. Gelatinous masses are produced by the white females and contain eggs. Fig. 5. Reduction in root growth caused by SCN and soybean-infecting fungi. All plants are infected with SCN, but the plants on the left have also been damaged by Rhizoctonia and Macrophomina (charcoal rot fungus). How does SCN spread? Anything that moves soil will move SCN: wind, water, migratory birds, and most important, humans. SCN can easily be transported from one field to anoth-er in soil, on machinery, or in soil in improperly cleaned seed lots. The nematodes can move only rela-tively short distances under their own power. How does SCN damage soybeans? SCN females maintain feeding sites in soybean roots, where they remain attached throughout their lives. Low SCN infection rates may cause little or no plant damage, or even may stimulate plant growth. But if plants are stressed by some other factor, or if SCN infection is high, plant growth is disrupted. The nematodes compete with normal plant organs (leaves, pods, and seed) for nutrients. Nodulation by nitrogen-fixing bacteria, or their nitrogen-fixing ability, may be reduced (Fig. 5). Root growth is reduced by SCN, and may be further reduced by root-rotting organisms (Figs. 5,6). Yield reductions caused by SCN can be 100 percent in areas within a field, and up to 75 percent averaged over a whole field. Typical losses are 15 to 30 percent. What are the symptoms of SCN? There are no specific symptoms of SCN presence in soybeans! The disease was first called "yellow dwarf" because heavy infestations cause yellowing and stunt-ing (Fig. 7). But, there may be no symptoms at all (Fig. 8), or strong symptoms of other plant stresses, such as a nutrient deficiency (Fig. 9). Proper field fertility can increase yields, but will not control SCN. Often, white to yellow SCN females can be observed on plant roots, if they are carefully dug. But the females can easily be missed, and brown cysts can't be seen against the background of soil. The only way to get an accurate diagnosis is with a soil sample. Fig. 6. Williams 82, in the tour rows on the left, has resistance to some races of Phytophthora, a root-rotting fungus, but has been killed by the fungus in this SCN-infested field. Williams 82 has no resistance to SCN. Fayette, in the four rows on the right, has no resistance to the fungus, but does have resistance to SCN. Photo courtesy of D.C. Norton (Iowa State University). G4450 How do you sample for SCN? Sampling is recommended for suspected infesta-tions, areas where SCN-resistant soybeans have been grown, and prior to planting a susceptible soybean cul-tivar in a rotation. You may sample at any time, but SCN densities are highest August through October. A sample should usually not represent more than 10 acres, but it isn't necessary to sample a whole farm. SCN is spread so easily that if a farm has one infested field, an SCN management program should be consid-ered for the whole farm. The following technique will give you an estimate Fig. 7. Stunting and yellowing caused by SCN. Apparently healthy plants in the foreground are also heavily infected. Fig. 8. Williams 82 and Fayette, growing side by side on a SCN-infested field, appear to be doing equally well. At harvest, however, Williams 82 (with no resistance to SCN) yielded 24 bushels per acre less than Fayette (a SCN-resistant soybean). Photo courtesy of David Quarles and Zane Helsel (University of Missouri-Columbia). Fig. 9. "Hot spots," areas within a field where SCN densities are highest, may also show severe symptoms of another stress, in th is case, potassium deficiency. of the average number of nematodes in a field: •Collect small amounts of soil with a shovel or soil probe in the recommended pattern (Fig. 10). Don't just sample "hot spots" where damage is obvious in a field! Doing so will result in an inaccurate estimate of your SCN population. •Sample to a depth of 6 to 8 inches and combine all the collected soil in a bucket. • Mix the soil thoroughly, and remove a subsample of 1 pint to 1 quart depending on the test desired (see the Nematode Sample Submission Form for a list of tests available). • Place the subsample in a plastic bag, seal the bag and write your name and a field number on the bag with a permanent marker. • Fill out a Nematode Sample Submission Form (MP 655), available from your local extension office, and submit the sample and form to the address on the form. What are races of SCN? SCN races are field populations that can reproduce on a certain standard set of soybean lines. They occur because the resistance to SCN that is bred into soybean cultivars is not complete. That is, even on the most resistant cultivars, a few SCN females will be able to mature. Offspring of these few females will then have an increased ability to parasitize the "resistant" host. After a few generations, the field's SCN population may be a race different from the original. There are 16 possible races based on the standard laboratory test. The most common is Race 3, especially in fields where resistant soybeans have never been Fig. 10. A zig-zag sampling pattern is recommended for a 10-acre field. G4450 grown. It is possible to test a field for race determina-tion, but this is usually not necessary unless you have observed damage on resistant soybeans and cannot rotate to a nonhost crop on that field. Be aware, how-ever, that the SCN race in a field can change within a single season. What are the other hosts (and nonhosts) for SCN? Nonhost crops generally recommended in rotation schemes for SCN management include grasses, such as corn, wheat, oats, sorghum, or forage grasses. Red clover is a poor host, but white, crimson, and other clovers are very good hosts. Other fair to good hosts for SCN in the Midwest are listed in Table 1. How do you reduce losses to SCN? Once SCN infests a field, there is no way to eradi-cate it. Once an SCN infestation has been confirmed by soil test, begin planning to manage the pest regardless of the infestation level. SCN persists for many years even if soybeans are not grown, but SCN can be man-aged to minimize losses. The best way to minimize SCN damage is to use crop rotation with SCN-resistant soybeans. Table 1. Hosts (crops and weeds) and nonhosts for the soybean cyst nematode in Missouri. Hosts Crop plants beans (green, bush, kidney, lima, etc.) birdsfoot trefoil clovers (crimson, scarlet, alsike) cowpea crownvetch lespedeza lupines, white pea soybeans sweet clover vetch (common, hairy) Weeds chickweed, (common, mousear, sicklepod, coffeeweed) common mullein henbit hop clovers mil kvetch pigweed, winged pokeweed purslane spotted geranium vetch (American, Carolina, wood) Nonhost crops alfalfa canola corn cotton forage grasses melons oats peanuts red clover rice rye sorghum (milo) tobacco wheat This list is not complete, but includes some of the better known hosts and nonhosts for SCN. The "Nonhost" list includes some poor hosts. Rotation. A minimum four-year rotation is recom-mended. See Table 1 for a list of host and nonhost crops. Year 1: Nonhost crop Year 2: Resistant soybean cultivar Year 3: Nonhost crop Year 4: Susceptible soybean cultivar Have a SCN egg count done at the end of Year 3 to determine whether a susceptible soybean may be grown. The susceptible cultivar is included because growing resistant cultivars continuously may cause development of races to which there is no good resis-tance (see section on races, above). If SCN densities are still high, then a nonhost or a resistant cultivar other than the one grown in Year 2 might be chosen. Another soil sample should be tested for SCN before a suscepti-ble cultivar is planted. Nematicides. Nematicides are labelled for SCN control in soybeans, although they are generally not economical. Check labelling and recommended rates carefully. More information is available from chemical company representatives. Cultural practices. Any practice that reduces crop stress will help alleviate SCN damage. These include controlling weeds, maintaining proper soil pH, fertiliz-ing to soil test recommendations, and irrigating. To slow SCN spread, clean tillage equipment after use in an infested field . Combine infested fields last, when they are dry. Purchase seed from sources with reliable spirals so that seedlots are free from soil peds (SCN is not seedbome). Distribution of Soybean Cyst Nematode in Missouri 1956-1966 ~ 1966-1976 !1Dl f\_)l University \..;I Extension ■ Issued in furtherance of Cooperative Extension Work Acts of May 8 and June 30, 1914 In cooperation with the United States Department of Agriculture. Gail L. Imig, Director, Cooperative UNIVERSrTY OF MISSOURI LINCOLN UNIVERSrTY Extension Service, University of Missouri and Lincoln University, Columbia, Missouri 65211. ■ An equal opportunity Institution. G4450 Revised 2/90/1 OM 

Soybean cyst nematode

https://mospace.umsystem.edu/xmlui/bitstream/10355/72849/1/g4450-1990.pdf

Soybean cyst nematode

Abstract

Similar works

Full text

Available Versions

University of Missouri: MOspace