Nematoides Do Cisto Da Soja

7/27/2019 Nematoides Do Cisto Da Soja

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Soybean CySt nematode Field Guide

SoybeanCYSTNemaTode2n eitin

A reference for identifying,

scouting for and managingsoybean cyst nematode


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Soybean CySt nematode Field Guide

tableoF ContentS

Biology 3

Life cycle 4Symptoms 8Effects of drought 14

Scouting 15 Looking for SCN females 17

Collecting soil samples 19Soil sample results 26

SCN and soil factors 29Management 31 Nonhost crops 33

Controlling winter annual weeds 34Soil-applied nematicides 36Seed treatments 37SCN-resistant soybean varieties 38Integrated SCN management 48

Disease interactions 51 Sudden death syndrome 52

Brown stem rot 53The HG type test 55 Who needs an HG type test? 56

Conducting the HG type test 58

This publication is the result of a cooperativeeffort between the Iowa Soybean Association andthe College of Agriculture and Life Sciences andExtension and Outreach at Iowa State University

Note: Information in this guide may be specic toIowa Those from outside Iowa should check withtheir state extension service for local information

Soybean CySt nematode Field Guide2


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The SCN life cycle has three major stages: egg,

juvenile and adult. Juvenile worms hatch fromeggs and penetrate soybean roots. After enteringthe soybean root, juveniles move through theroot until they reach the vascular tissue, wherethey begin to feed. The juveniles inject secretionsthat modify root cells and convert them intofeeding sites. As the juvenile nematodes feed,

they swell. Female nematodes eventually becomeso large that they break through the root tissueand are exposed on the surface of the root. Malenematodes change back to worms as adults,migrate out of the root into the soil and mate withthe lemon-shaped adult females.

Diagram of the SCN life cycle.Note: All stages are not drawn to same scale.

liFe CyCle


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After male nematodes mate with and fertilizeadult females, SCN females produce 50 to 100eggs outside of the body, and then the femalebody lls internally with 200 or more eggs each.When the adult SCN female dies, the body walltoughens into a protective cyst around the eggs.Not all eggs produced by a female will hatch at

the same time, and eggs within a cyst can survivefor 10 or more years.

During a single growing season, there are severalSCN generations. In the summer, when soils arewarm, the SCN life cycle can be completed in 24

to 30 days.

SCN damages plants and reduces soybeanyield by:

Taking food from the soybean plant Stunting or dwarng roots

Disrupting root vascular tissue function

Reducing effectiveness and number ofnitrogen-xing nodules

Causing wound for other pathogens toenter roots


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Stages in the SCN Life Cycle

SCN eggs(each 1/200-inch long)

SCN juvenileentering thesoybean root(juvenile 1/50-inch long)

SCN juvenile(stained purple)developing insidesoybean root

SCN female (left)

and worm-shapedmale(female 1/32-inch long,male 1/16-inch long)

Adult SCN femalewith egg mass onsoybean root

Egg-lled SCN cyst


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Population dynamicsSCN egg population densities can increaserapidly when susceptible soybeans are grownbecause of the relatively short generation timeand the high reproductive capacity of SCN.In Iowa, it is almost certain that three SCN

generations occur per growing season and thepossibility exists for ve or more generations todevelop in very warm years.

Increase in SCN eggs per 100 cm3 soil on a susceptiblesoybean variety in one growing season in central Iowa.


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PlantHeight(in

)

Plnt Hight60

5040

30

20

10

0

4 6 8 10 12 14 16 18

Weeks after Planting

Resistant

Susceptible

The only unique sign of SCN infection is thepresence of adult females and cysts on thesoybean roots.

No obvious above-groundsymptoms

In many instances, SCN infection does not causeany above-ground symptoms, even when causingsignicant yield loss. The data in the followinggraphs are from an Iowa eld experiment inwhich a resistant and a susceptible soybeanvariety were grown in an SCN-infested eld.Plants were removed and measured every two

weeks throughout the growing season.

The heights of the two varieties were the sameduring the growing season (above) and leafweights were nearly identical until the last month

of the season (top graph next page).

SymptomS


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Yild(b

u/acr)

Resistnt Susceptible

Vriety

44.7

50.050

40

30

20

10

0

Yil

CanopyWeight(grams/m2)

L Wight700

600

500

400

300

200100

0

4 6 8 10 12 14 16 18

Weeks after Planting

Resistant

Susceptible

Despite no difference in heights and no differencein leaf weights until the last month of the growingseason, the resistant soybean variety yielded morethan ve bushels per acre or 10 percent more thanthe susceptible soybean variety (bottom graph).


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Below groundRoots infected with SCN are generally dwarfedor stunted and can have a decreased number ofnitrogen-xing nodules. SCN infections also maymake the roots more susceptible to attack by othersoil-borne plant pathogens. Roots infected with

SCN and other soil borne pathogens are generallydiscolored.

SCN-infected roots (right) are stunted, discolored andhave fewer nitrogen-xing nodules than uninfectedroots (left).


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Uneven plant height caused by SCN

Above groundSCN can cause several above-ground symptoms,such as stunting, yellowing and early maturationof the crop. However, above-ground symptomsof SCN are not unique. They often are mistakenfor symptoms of damage from soil compaction,

iron deciency chlorosis and other nutrientdeciencies, drought stress, herbicide injuryor other plant diseases. SCN injury oftenremains undetected for several years becausethe nondescript symptoms are attributed toother causes.


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Mid-season yellowing caused by SCN

Severe stunting and yellowing of leaf marginscaused by SCN


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Severe stunting and overall foliar yellowingcaused by SCN

Early senescence of soybeans due to SCN infection


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eFFeCtSoF drouGht

The severity of symptoms and yield loss causedby SCN is affected greatly by availability ofmoisture during the growing season. Above-ground symptoms of SCN damage can be quitesevere in dry years, but mild or nonexistent inyears with adequate or excess rainfall. SCNstunts the soybean roots, which is much more

harmful to the soybean plant in drought yearsthan in years of adequate or excess soil moistureas stunted roots explore less soil for water andminerals than normal-sized roots.

There are indications that SCN reproduction may

be greater in dry soil conditions than in wet soils.Hatched SCN juveniles enter soybean roots andset up permanent feeding sites, called syncytia,inside root tissue. The SCN juveniles possiblyestablish feeding sites deeper into the rootvascular tissue under dry soil conditions than wetconditions. And the nematode feeding sites maybe considerably more disruptive to root functionif they are located in the vascular tissue ratherthan in the outer cortex region of the roots. Also,SCN juveniles feeding in the vascular tissuemay have better nutrition than those feedingin the root cortex, possibly leading to greater

SCN reproduction.

Yield loss from SCN isconsiderably worse in drought

years. SCN reproduction may be

much greater under these severeconditions as well.


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Scouting

Scouting for SCN by checking soybean roots

or collecting soil samples is the rst step in

managing SCN.

Sco

uting


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lookinGForSCn FemaleS

The rst SCN females usually will appear onroots four to six weeks after planting. Femalesmay take longer to appear on roots if springweather is cool and/or wet.

The adult SCN females will appear as small,round objects on the younger roots. SCN females

are creamy white, but turn yellow to tan to brownover the course of several days.

Digging roots to look for SCN females is verysimple. Just dig dont pull. Pulling plants fromthe soil will strip the SCN females from the

young roots.

Once a clump of plants with roots and soil hasbeen removed through digging, carefully shakeor crumble off muchof the adhering soiland look closely on

ne roots for adultSCN females. As theseason progresses,dig deeper andfarther from thesoybean row to get to

young, healthy roots.

Adult SCN females on root


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Nitrgn-fxing nls

SCN lsAdult SCN femalesare about the size ofa period at the endof a sentence, andare much smallerand lighter coloredthan nitrogen-xing

nodules. Nitrogen-xing nodules arethe same color as theroots and will grow tobe much larger thanSCN females.


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ColleCtinG Soil SampleS

Exactly when and how to collect a soil sample forSCN analysis depends on your specic purpose.Soil samples can be collected to determine ifSCN is present in a eld or to determine if SCNis causing stunting and/or yellowing of a soybeancrop. You can also use soil sample results todetermine if your SCN management plan has

kept the SCN population in check.

SCN cysts are very small and are usuallyclustered in the soil, making soil sample resultsnotoriously variable.

With a typical 1-inch diameter soil probe, randomplacement of the probe into the soil can have atremendous effect on how many egg-lled SCNcysts are recovered, as illustrated below.

In the diagram above, soil probe A captures a clusterof seven SCN cysts (not drawn to scale) that maycontain 1,500 eggs. The placement of soil probe Bis only inch different from the placement of soil

probe A, and it misses the seven SCN cysts, resulting inup to 1,500 fewer eggs being present in the soil core.

a

sil prb tip

SCN cysts

sil prb tip

B

SCN cysts

ColleCtinG SampleS


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Soil must be collected from many differentplaces within the sampling area. Limit the arearepresented in a single soil sample, ideally, to nomore than 20 acres.

Use a soil probe or soil tube to collect cores.

Avoid collecting soil cores when the soil is

frozen or very wet.

Mix multiple soil cores very well beforeplacing mixed soil into a bag.

Keep soil samples at room temperature orcooler until shipped.

Send samples to a private soil testinglaboratory for analysis or send to:

Plant and Insect Diagnostic Clinic327 Bessey Hall, Iowa State UniversityAmes, IA 50011

Laboratories may report SCN sample resultsas the number of cysts, eggs or juveniles (referto pages 26-27) per 100, 250 or 500 cm3 ofsoil. When comparing SCN soil sample resultsfrom different laboratories, be sure the samevolumes of soil and the same SCN life stages are

compared. A result of 500 cysts per 100 cm3 is amuch greater SCN population density than 1,000eggs per 250 cm3 soil (each cyst may contain asmany as 200 more eggs; 250 cm3 is 2 timesmore soil than 100 cm3).


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Determining if SCN is presentin a feld:

Collect soil samples anytime (except whenthe soil is frozen or very wet).

The more soil collected and the smaller thearea sampled, the more accurate the results.

Soil cores should be collected from theupper eight inches of soil.

If corn or another nonhost crop was lastgrown in the eld, it doesnt matter if soilcores are collected from underneath the

previous crop rows or not. It is better to collect soil cores after a

previous corn crops rows have beendestroyed by tillage.

If soybeans were last grown in the eld,collect soil cores from under the old croprows if possible.


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If sampling conventionally (not gridsampling), collect 15 to 20 soil cores in azig-zag pattern from no larger than a 20-acreparcel of land.

If grid sampling, collect one or two soilcores from every grid cell sample and

combine cores from the number of cells thatrepresent approximately 20 acres.

The parcels of land represented by the soilcores need not be square or rectangular areas.Divide elds for sampling according to obviousagronomic features.


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Determining if SCN is responsiblefor stunting and/or yellowing:

Angle the soil probe underneath the row ofsoybeans into the root zone.

Soil cores should be collected from the uppereight inches of soil underneath the row.

Collect 15 to 20 soil cores from underneathstunted and/or yellow plants.

Collecting a soil core from under a soybean row

Multiple soil cores representing an areamust be mixed thoroughly.


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Assessing SCN population densitiesto monitor management:

Collect soil samples in the spring beforesoybeans are planted, or in the fall after theprevious crop has been harvested.

Take note of specic sampling details

to refer back to when samples are againcollected (areas sampled, numbers of cores,sampling time, before or after a soybeancrop, etc.).

The more soil collected and the smaller thearea sampled, the more accurate results you

can expect.

Soil cores should be collected from theupper eight inches of soil.

If corn or some other nonhost crop was lastgrown in the eld, it doesnt matter if soil

cores are collected in the previous crops row.

Sampling a harvestedsoybean eld for SCN

Soil cores should beeight inches deep.


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Multiple soil cores representing an area mustbe mixed thoroughly before lling a bag to

send to a processing laboratory.

It is better to collect soil cores after theprevious corn or other nonhost crops rowshave been destroyed by tillage.

If soybeans were last grown in the eld,collect soil cores from under the oldcrop rows.

If sampling conventionally (not gridsampling), collect 15 to 20 soil cores in azig-zag pattern from no larger than 20 acres.

If grid sampling, collect one or two soilcores from every grid cell sample andcombine cores from the number of cells that

represent approximately 20 acres.


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Cysts vs. eggsIt is important to know what life stage of SCNis reported when a soil sample is analyzed. TheIowa State University Plant and Insect DiagnosticClinic and most other soil test labs in Iowa countand report the number of SCN eggs. But some

labs report numbers of SCN cysts or juveniles inthe soil (page 27).

Cyst and egg counts generally correlate well,and cyst counts can be loosely converted to eggcounts by multiplying the cyst count by 125,which is the average number of eggs per cyst in

naturally infested eld soil. Juveniles typicallyare short lived, and their numbers are not asinformative as numbers of cysts or eggs.

Low vs. medium vs. high egg counts

Egg counts can vary greatly depending on theextraction procedure used by the laboratory.There are no industry standards for proceduresto extract SCN from soil samples. Comparingnumbers from samples processed by differentlaboratories is not recommended.

Also, the numbers of eggs considered to be low,medium or high depend on whether soybeans willbe grown as the next crop.

Soil Sample reSultS


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Life Stages of SCN Counted from Soil Samples

Stained SCN eggsSCN egg counts are animportant indicator of

the level of infestationAlmost all SCN eldresearch is based on

SCN egg counts

SCN juvenilesSCN juvenile countsuctuate greatly and are

not as informative as cystor egg counts

SCN cystsCysts are dead femalesfull of eggs Cyst countscorrelate well withegg counts


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For soil samples processed by the Iowa StateUniversity Plant and Insect Diagnostic Clinic:

If sybens re the next crp t be grwn

Lw = 1 2,000 eggs per 100 cm3 soil

mediu = 2,001 12,000 eggs per 100 cm3 soil

High = > 12,000 eggs per 100 cm3

soil

If sybens re NoT the next crp t be grwn

Lw = 1 4,000 eggs per 100 cm3 soil

mediu = 4,001 16,000 eggs per 100 cm3 soil

High = > 16,000 eggs per 100 cm3

soil

Warning: Fields may be infestedwith SCN even if soil sampleresults are zero.

Up to 25 percent of soil samples with egg countsof zero are infested with SCN. The reasons forthe false and misleading zero egg counts are:

Laboratory extraction procedures used toprocess samples do not recover 100 percentof the cysts and eggs present in the soil.

SCN cysts are very aggregated or clusteredthroughout a eld, and soil cores may nothave been collected from the spots in theeld where cysts were present.

If soil sample results are zero, follow-up soilsampling is recommended to check for SCNinfestations in future years.


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It is possible that many soil factors may affectSCN reproduction and soybean yield loss, butonly two soil factors are commonly associatedwith SCN damage and population densities soiltexture and soil pH.

SCN is capable of infesting soils of all textures,

but symptoms and yield loss generally are greaterin sandy soils than medium- and ne-texturedsoils. SCN-infected roots are stunted and lackne roots and, thus, can explore much less soilfor water and nutrients than healthy roots. Also,coarse-textured soils do not hold water and some

nutrients as well as medium- or ne-texturedsoils, and SCN seems to cause greater damageto plants stressed by other factors, such as lackof water and/or minerals. It is possible that SCNreproduces better in dry soils, such as during adrought (page14).

Soybean damage due to SCN isfrequently misdiagnosed. Reduceyour risk of loss by submitting soilsamples for diagnosis.

SCNand Soil FaCtorS


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In the mid 1990s, it was discovered that there is aconsistent relationship between SCN populationdensities and soil pH. Greater SCN populationdensities are consistently found in areas of eldswith higher pH. The relationship occurs over awide range of soil pH from pH 5.5 to 8.0. Itis not clear if SCN population densities would

decline if soil pH was lowered.

SCN egg population densities (per 100 cm3 soil, left) and soilpH (right) in 100 half-acre cells in a soybean eld in DallasCounty, Iowa. Note the consistent occurrence of higher SCNpopulation densities in cells with higher soil pH.

53 - 57

58 - 61

62 - 67

68 - 73

74 - 80

0

100 - 600

601 - 1400

1401 - 2300

2301 - 4100

4101 - 6600

6601 - 17600

Soil pHSCN eggpopulation densities

(per 100 cm3

soil)


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Soybeans can be produced protably

in SCN-infested elds with a tailored

management program.

m

anageent

ManageMent


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SCN cannot be eliminated from an infested eld

if soybeans are ever grown again. Once SCNis discovered, a management program should

be implemented immediately to minimize SCNreproduction and maximize crop yields. Thegoal of an SCN management plan is to maintain

protable soybean yields while keeping SCNpopulation densities at low to medium levels.

It is much easier to keep low SCNpopulation densities low than it isto drive high populations down.

SCN management can involve:

Growing nonhost crops

Controlling winter annual weeds

Applying nematicides to the soil

Using nematode-protectant seed treatments Growing SCN-resistant soybean varieties


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nonhoSt CropS

There are many crops on which SCN is unable tofeed. These are called nonhost crops. Without ahost crop, SCN cannot complete its life cycle andpopulation densities will decline. Thus, growingnonhost crops is one way to manage SCNpopulation densities.

Corn, oats, rye, wheat, sorghum and alfalfa arenonhost for SCN. Nematode numbers declinesimilarly when infested soils in Iowa are plantedwith corn, oats or alfalfa.

The greatest decrease in SCN population

densities will occur during the rst year a nonhostcrop is grown following soybeans. SCN densitieswill decline only slightly more if a secondnonhost crop is grown.

SCN juvenile (left)hatched from an

egg (right). Thejuvenile will starveif it does not feedupon a livinghost root.


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ControllinG WinterWeedS

The graph below illustrates how SCN populationdensities decline in three successive corn crops(red bars) following a soybean crop (gold bar)in Iowa.

Winter annual weeds

Common weeds that occur in Iowa corn andsoybean elds during the growing season are nothosts for SCN. However, the winter annual weedshenbit, eld pennycress and purple deadnettle

are moderate to good hosts for SCN. If thesewinter annual weeds are growing in SCN-infestedelds and soil temperatures are greater than 50F,SCN reproduction and increases in populationdensities can occur. SCN cannot develop in rootsbelow 50F.

end-o

f-sasonSCNnumbrs

(ggs/1

00cm3

soil)

syben 1st yer 2nd yer 3rd yer crn crn crn

Chnges in SCN ppultin densities verultiple yers f nnhst crp

18,000

12,000

10,000

9,450

20,000

16,000

12,000

8,000

4,000

0


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The SCN life cycle takes about 24 days tocomplete at ideal temperatures (76F) and cantake ve or more weeks at colder temperatures.There may be periods in the spring or fall whensoil temperatures are warm enough for SCNreproduction to occur on winter annual weeds.

Reprinted with permission from Winter Annual Weeds andSoybean Cyst Nematode Management, 2007, Purdue University

Field pennycress (left) and henbit (right)

JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Plantgrowth(%)

optil cnditinsfr SCN grwth

Winter annualweeds present

Winter annualweeds present

Soybeanspresent

Tieline f winter nnul weed nd sybengrwth nd SCN ctivity


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Soil-applied nematiCideS

There is at least one soil-applied nematicidelabeled for use against SCN, but this managementoption is not commonly used.

Nematicides generally do not give season-longcontrol. When applied to the soil at planting, theeffect of the nematicide may last long enough

to provide an economic yield benet. However,by the end of the growing season, SCN numbersmay be as high as, or higher than, they wereat planting.

Use of nematicides increases the cost of

production. Field-wide applications are oftenconsidered uneconomical, although an increasein yield of a few bushels per acre could offset thecost of the nematicide.

Unpredictable yield responses and inconsistentdecreases in SCN population densities are the

main reason why soil-applied nematicides are notmore commonly used.

In the future, site-specic application of soil-applied nematicides to manage SCN may makethis option more economical.


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Seed treatmentS

Protectant seed treatments are a new categoryof management products for SCN. Currently,products are available with active ingredientsor modes of action that include a bacterium(Votivo from Bayer CropScience), a bacterialfermentation compound (Avicta from SyngentaCorporation) and a protein that stimulates

natural plant defenses (N-Hibit from PlantHealth Care Inc.).

The products are on the seed when soybeansare planted, then move onto the developing rootsurface. Seed-applied products are described as

providing early season protection of soybeanroots, but protection from these products willdiminish over time during the growing seasonand nematode reproduction will resume later inthe season.

Using nematode-protectant seed treatmentsincreases the cost of production, and their valuedepends on the severity of yield loss caused bySCN, the effectiveness of the product used andthe value of the soybean crop. Consider thesefactors when deciding whether to use thesenematode management products.

Treated soybean seed


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SCn-reSiStant VarietieS

SCN-resistant soybean varieties pay dividendstwice rst, by producing good soybeanyields on SCN-infested elds and, second, bypreventing increases in SCN population densities.

Below are averages from SCN-resistant (redbars) and SCN-susceptible (gold bars) soybean

varieties at two locations in Iowa that illustratethe dual benets of resistance.

Greene C. mnre C.

Yild(bu/acr)

Resistnt

Susceptible60

5040

30

20

10

0

55.7

40.5

52.1

46.8

Greene C. mnre C.

Resistnt

Susceptible

21,000

18,000

15,000

12,000

9,000

6,000

3,000

0

2,460

19,594

1,762

11,444

e

nd-o

f-sasonSCNn

umbrs

(ggs/100cm3soil)


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Rsistnt

Sscptibl

How does SCN resistance work? SCN juvenilespenetrate the roots of SCN-resistant varieties, butare not able to feed in the roots. Subsequently,the SCN juveniles starve inside roots ofresistant varieties.

SCN juveniles after eight days in resistant (top panel)and susceptible soybean roots

Photos by Ben Matthews


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Note in the photos on the previous page howmuch larger the developing SCN juveniles are inthe susceptible roots (bottom panel) than in theresistant roots after eight days.

Different soybean breeding lines (called sourcesof resistance) have been used to develop SCN-

resistant varieties. Some breeding lines are calledplant introductions (abbreviated PI) and areassigned identifying numbers.

Sources of SCN resistance available to Iowagrowers include PI 88788, Peking and PI

437654, which is also referred to as Hartwigresistance or the branded CystX resistance.Each source of resistance has several genes thatprovide SCN resistance to the plant. Not all ofthe resistance genes from a source need to be ina soybean variety for the variety to be resistantto SCN. Soybean varieties with the same sourceof resistance will not necessarily have the samelevel of resistance to SCN.

Resistance to SCN in soybean varieties is not100 percent effective; a few SCN females willdevelop on roots of resistant varieties. Exactly

how many SCN females develop on a resistantsoybean variety depends on the resistance genesin the variety and also the genetic makeup of theSCN population in the eld.


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The HG type test (HG representsHeteroderaglycines, the scientic name for SCN) is designedto give practical information about how wellan SCN population in a eld can reproduce onthe various sources of SCN resistance (referto section labeled HG Type Test, page 55, formore information).

SCN-resistant soybean varieties paydividends twice good yields andcontrol of SCN population densities.

But not all SCN-resistant soybeanvarieties provide the same level ofnematode control, not even varietieswith the same source of resistance.

Rotate resistance

Recent survey results show that SCN populations(HG types, formerly called races) with greaterthan 10 percent reproduction on the commonlyused PI 88788 source of SCN resistance arewidespread in Iowa and other states. Some SCNpopulations have been found with reproductionexceeding 50 percent on PI 88788.


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To delay SCN populations developing theability to reproduce on SCN-resistant soybeanvarieties, producers should grow varieties withdifferent sources of resistance in different years.This is similar to using herbicides with differentmodes of action in different years to controlweeds and avoid the development of herbicide-

resistant weeds.

If it is not possible to obtain seed of an SCN-resistant variety with a source of SCN resistancedifferent from what had previously been used,rotate among different SCN-resistant varieties

with the common source of SCN resistance,PI 88788.

The Iowa Soybean Association provides soybeancheckoff funds to Iowa State University toannually evaluate SCN-resistant soybean varietiesthroughout the state. The yields and SCN controlprovided by hundreds of SCN-resistant soybeanvarieties are shown in reports available online atwww.isuscntrials.info.

Selecting an SCN-resistant variety

Choose a variety that yields well in various SCN-infested elds. Yield data from non-infested eldsare not useful for predicting yields of soybeanvarieties in SCN-infested elds.


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If possible, choose a soybean variety with asource of SCN resistance other than what hasbeen grown previously. Remember to chooseSCN-resistant varieties with other neededdefensive traits, such as tolerance to irondeciency chlorosis or resistance to sudden deathsyndrome or Phytophthora root rot.

Dont let SCN numbers creep up

Even the highest-yielding SCN-resistant soybeanvarieties can vary signicantly in the amount ofnematode control they provide.

In the graph below, the yields of the top threeSCN-resistant soybean varieties in a variety trialconducted in an SCN-infested eld were notsignicantly different.

60

50

40

30

20

10

0

Yild(bu/acr

)

Vriety Vriety Vrietya B C

48.8

51.3

49.3

SCN-rsistnt Sybn Vrity TrilNrth Cntrl Iw

Bst 3 Yiling Rnp RyVritis


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At harvest, there were signicant differences inSCN egg population densities in the soil amongthe three resistant varieties (below).

Soybean varieties labeled as resistant to SCNvary greatly in yield and in control of SCN.Both are determined by the genetics of thesoybean variety and also the genetics of the SCN

population in the eld. The results of an HGtype test indicate how well a population will becontrolled by the various sources of resistanceused to develop soybean varieties. There isno comprehensive testing of all SCN-resistantsoybean varieties to give an indication of those

with the most effective resistance.

Vriety Vriety Vrietya B C

8,000

6,000

4,000

2,000

0

5,800

1,513

1,913

SCN-rsistnt Sybn Vrity TrilNrth Cntrl Iw

Bst 3 Yiling Rnp RyVritis

end-o

f-sason

SCNnumbrs

(ggs/100

cm3

soil)


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Buildup of SCN reproductionon PI 88788

There are hundreds of SCN-resistant soybeanvarieties for Iowa. Almost all contain resistancegenes from the PI 88788 source of resistance.Repeated, widespread use of varieties with

PI 88788 SCN resistance has selected forSCN populations with increased or elevatedreproduction on PI 88788 resistance. More thanhalf of Iowas SCN populations now have greaterthan 10 percent reproduction on PI 88788, andsome have 40 to 50 percent reproduction on PI88788 (relative to 100 percent reproduction on asusceptible variety).

Despite increased SCN reproduction on thePI 88788 resistance, ISU research shows thatvarieties with PI 88788 SCN resistance oftenyield well (60 bushels per acre or more) and yield

better than varieties with Peking SCN resistancein elds with SCN populations with elevated(>10 percent) reproduction on PI 88788 andlow (


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The yields and SCN control provided byhundreds of SCN-resistant soybean varieties,most with PI 88788 SCN resistance, at varietytrials conducted throughout Iowa are availableonline at www.isuscntrials.info.

Adult SCN females on roots of an SCN-resistantsoybean variety


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Increased SCN reproduction(even up to 50 percent) onresistant varieties with PI 88788resistance does not necessarily

result in low yields or largeincreases in SCN populationdensities. Nonetheless, growsoybeans with Peking andother non-PI 88788 sources of

SCN resistance, if possible, tomaximize soybean yields in

SCN-infested elds long term.


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The most effective SCN management programintegrates as many different managementstrategies as possible to maintain high soybeanyields while preventing increases in SCNpopulation densities. It is much easier to keeplow SCN population densities low than to try todrive high numbers back down.

Such a management program usually includesscouting for early detection and growingnonhost crops in rotation with SCN-resistantsoybean varieties.

On the next page is a six-year crop rotationsequence recommended by Iowa State Universityfor elds with low or medium SCN populationdensities. The rotation begins with year one in theupper left of the diagram.

If SCN population densities are high, the rotation

sequence on the next page is not recommended.Instead, grow several years of corn or some othernonhost crop and collect soil samples every fallto assess the decline in SCN egg populationdensities. When numbers have decreased tomedium levels (page 28), the crop rotation

sequence on the next page can be started.

inteGrated SCn manaGement


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Crp rttin pln r flswith lw r i SCN

ppltin nsitis.

Nnhst crp(sch s crn,ts, ll)

Year 2

SCN-rsistntsybn irnt

r yr1

PI 88788SCN-rsistnt

sybn Six-YearCrop

RotationSequence



SCN-rsistntsybn irnt

r yr 1 n 3 rsscptibl sybn

Year 5

Year 1 Year 3

Year 4Year6


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tableoF ContentS

Growing soybean varieties with different sourcesof resistance will best discourage the buildup ofSCN populations with increased reproductionon resistant soybean varieties. But if varietieswith different sources of SCN resistance are notavailable, grow different SCN-resistant varietiesderived from the common source of SCN

resistance, PI 88788.

An integrated management program also includescontrol of winter annual weeds that can serve ashosts for SCN. Nematicides and seed treatmentsmay also be used during years that soybeans are

grown in SCN-infested elds.

Integrated SCN managementshould always include soilsampling to monitor SCN

population densities and growingnonhost crops and SCN-resistantsoybean varieties in a croprotation sequence.


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Infection of soybean plants by SCN

can increase diseases caused by other

pathogens living in the soil.

Interactions

DiSeaSeinteractionS


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Sudden death Syndrome

In addition to causing yield loss directly, SCNalso interacts with other pathogens, making otherdiseases worse.

Sudden death syndrome leaf symptoms

Sudden Death Syndrome

Sudden death syndrome (SDS) is a root-rottingsoybean disease caused by the soil-inhabitingfungusFusarium virguliforme. Soybeans infectedwith SCN develop symptoms of SDS earlierin the season than plants not infected with thenematode. Also, symptoms of SDS are moresevere in plants that are infected with SCN. Timeof symptom development and disease severity arethe two major factors that determine how muchsoybean yield loss is caused by SDS.


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broWn Stem rot

Brown stem rotBrown stem rot (BSR) of soybeans is a stem androot disease caused by the fungusPhialophoragregata, which lives in the soil. Soybean plantsinfected with SCN are infected earlier in theseason with the BSR fungus, and the BSR disease

is more severe in SCN-infected plants than plantsnot infected with the nematode. Even soybeanvarieties that have been bred to be resistant toBSR become infected and develop BSR when theplants are also infected with SCN.

Brown stem rot stem symptoms


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Infection of ve soybean varieties by the fungus thatcauses brown stem rot disease. Red bars are infection ofthe varieties with the BSR fungus alone and gold barsare infection of the varieties by the BSR fungus whenalso infected with SCN.

It is not known exactly how SCN makes SDS andBSR more severe.

Prcntstml

ngthcolonizd with BSR fungus

with BSR fungus + SCN

Sturdy BSR101 PI 84946-2 PI 437833 PI 437970

Syben Vriety r Breeding Line

(ll re resistnt t BSR except Sturdy)

100

80

60

40

20

0

57

100

91

0

32

83

3

57

60

0


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A greenhouse test, called the HG type test, can be

conducted to determine how well an SCN population

can reproduce on SCN resistance sources.

HGType

Test


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Who needSan hG type teSt?

The HG type test is a simplied replacement for

the SCN race system. To determine the HG typeof an SCN population, a greenhouse test must be

performed on the nematode population from soilcollected from an infested eld.

Results of the HG type test indicate how well anSCN population can reproduce on the different

sources of SCN resistance, such as PI 88788,used in soybean varieties.

Who needs an HG type test?

Soybean growers who have experienced subparyields from SCN-resistant soybean varieties

in SCN-infested elds should consider havingan HG type test performed. Also, if numerousSCN females are observed on roots of resistantsoybeans during the growing season (page 46),an HG type test might be warranted, and it might

be worthwhile to conduct an HG type test onSCN populations from SCN-infested elds in

which resistant soybean varieties were grownnumerous times in the past.

An HG type test might be neededif performance of SCN-resistant

varieties decreases noticeably.


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Collecting a sample fromHG type testing

As a general rule, collect at least two gallons ofsoil from an SCN-infested eld for an HG typetest. The soil must be from all areas of the eldin order for the test results to be meaningful. Soil

should be collected to a depth of eight inchesfrom 40 or more spots in a eld.

Getting an HG type test performed

The Iowa State University Plant and InsectDiagnostic Clinic conducts HG type tests. Mail

or deliver a two-gallon soil sample in a sealedplastic bag or bucket to:

Plant and Insect Diagnostic Clinic327 Bessey Hall, Iowa State UniversityAmes, IA 50011

It will take at least six to eight weeks forresults, depending on time of the year in whichthe test was requested. Call the Iowa StateUniversity Plant and Insect Diagnostic Clinic at515-294-0581 for current fees.


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ConduCtinGthe hG type teSt

Its not just about HG typeResults of HG type tests of SCN populationsfrom throughout Iowa reveal that manypopulations can reproduce at levels greater than10 percent on PI 88788, the source of resistanceused in almost all commercial SCN-resistant

varieties.

However, many SCN-resistant varieties with PI88788 resistance can yield very well in eldsinfested with SCN populations that have greaterthan 10 percent reproduction on PI 88788.See pages 45-46 for more information about

the buildup of SCN reproduction on resistantsoybean varieties.

Conducting the HG type test

To determine the HG type of an SCN population,SCN eggs are extracted from a two-gallon soilsample collected from a eld. The nematodepopulation is then grown on soybean linescalled HG type indicator lines under controlledgreenhouse conditions. The HG type indicatorlines are the soybean breeding lines that are thesources of SCN resistance in soybean varieties

(page 60).


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Soybean plants of HG type indicator lines growing in atemperature-controlled water bath in the greenhouse

After 30 days (enough time for SCN females todevelop), the numbers of SCN females on rootsof several replicate plants of the various HG typeindicator lines are counted, averaged and thencompared to the number of females that form ona standard susceptible soybean variety.

Adult SCN females

recovered from roots inan HG type test


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The HG type indicator lines on which there was10 percent or more of the number of the femalesthat developed on the susceptible variety arenoted, and index numbers of the indicator lineswith 10 percent or greater SCN reproductioncomprise the HG type designation.

HG typ inx nbr HG typ inictr lin

1 PI 548402 (Pking)

2 PI 88788

3 PI 90763

4 PI 4376545 PI 209332

6 PI 89772

7 PI 548316 (Cl)

An SCN population of HG type 1.3 indicatesthat the nematode population had 10 percentor more reproduction on Peking (indicator line#1) and PI 90763 (indicator line #3). So, ifpossible, SCN-resistant soybean varieties withresistance from Peking or PI 90763 should not

be grown in a eld infested with an HG type 1.3SCN population.

The HG type is 0 if there is not 10 percent ormore SCN reproduction on roots of any of theHG type indicator lines.


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Soybean CySt nematode Field Guide 61

Unless otherwise noted, the data in this eld guide are from

research conducted by Iowa State University personnel withnancial support from the soybean checkoff through theIowa Soybean Association and the North Central SoybeanResearch Program

The contribution of information about SCN reproductionon winter annual weeds by Earl Creech and Bill Johnson, PurdueUniversity, and the images of SCN juvenile development insusceptible and SCN-resistant soybean roots by Ben Matthews,USDA, are greatly appreciated

Also, thanks are expressed to John Allen (DuPont Pioneer),Jamal Faghihi (Purdue University), Don Hershman (Universityof Kentucky), Palle Pedersen (Syngenta Corporation), AlbertTenuta (Ontario Ministry of Agriculture, Food and Rural Affairs)and Daren Mueller and Adam Sisson (Iowa State University) fortheir thoughtful reviews of this eld guide and their many helpfulsuggestions

Written and edited by: Gregory L TylkaGraphic design by: Iowa Soybean Association

Photo, diagram and illustration copyrights:Iowa State University Gregory D Gebhart, Kristine Schaefer,Adam J Sisson, Gregory L TylkaPurdue University Earl CreechUSDA Ben Matthews

and justice for all

The US Department of Agriculture (USDA) prohibitsdiscrimination in all its programs and activities on the basis ofrace, color, national origin, age, disability, and where applicable,sex, marital status, familial status, parental status, religion, sexualorientation, genetic information, political beliefs, reprisal, orbecause all or part of an individuals income is derived from anypublic assistance program (Not all prohibited bases apply toall programs) Persons with disabilities who require alternativemeans for communication of program information (Braille,

large print, audiotape, etc) should contact USDAs TARGETCenter at 202-720-2600 (voice and TDD). To le a complaintof discrimination, write to USDA, Director, Ofce of Civil Rights,1400 Independence Avenue SW, Washington, DC 20250-9410, orcall 800-795-3272 (voice) or 202-720-6382 (TDD) USDA is anequal opportunity provider and employer

Cooperative Extension Service, Iowa State University ofScience and Technology, and the United States Depar tment ofAgriculture cooperating

aCknoWledGementS


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SoyBean cySt neMatoDe

FIeLd GuIdeA reference for identifying, scouting forand managing soybean cyst nematode

C i h 2012

Nematoides Do Cisto Da Soja

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