Phythophthora diseases of soybean, caused by Phytophthora sojae, are present wherever soybeans are grown in Nebraska. The pathogen survives primarily as  resting  spores in the soil or in association with infested crop debris. Symptoms associated with Phytophthora sojae, infections include seed rots, pre- and post-emergence dampin goff of seedlings and stem rot of plants at various growth stages. Knowledge of the races present in the state and how varieties with different resistance genes have performed in a grower\u27s field is critical to variety selection for maximum profitability

Christensen, Jane A.

Giesler, Loren J.

Zwiener, Christopher M.

English

Phytophthora diseases of soybean, present wherever soybeans are grown, is outlined in this NebFact

DigitalCommons@University of Nebraska

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 2002 NF518 Management of Phytophthora Diseases of Soybeans Loren J. Giesler University of Nebraska-Lincoln, lgiesler1@unl.edu Jane A. Christensen Christopher M. Zwiener Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Giesler, Loren J.; Christensen, Jane A.; and Zwiener, Christopher M., "NF518 Management of Phytophthora Diseases of Soybeans" (2002). Historical Materials from University of Nebraska-Lincoln Extension. 94. https://digitalcommons.unl.edu/extensionhist/94 This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. C-10NF518Management of Phytophthora Diseasesof SoybeansLoren J. Giesler, Extension Plant PathologistJane A. Christensen, Research Technologist, Plant PathologyChristopher M. Zwiener, Student Assistant, Plant PathologyPhytophthora diseases of soybean, caused byPhytophthora sojae, are present wherever soybeans aregrown in Nebraska. The pathogen survives primarily as “resting” spores in the soil or in association withinfested crop debris. Symptoms associated withPhytophthora sojae infections include seed rots, pre-and post-emergence damping off of seedlings and stemrot of plants at various growth stages. Disease develop-ment is most rapid at soil temperatures above 60oFwith high soil moisture. This disease is most commonin low-lying areas of a field, in poorly drained or com-pacted soils, and in soils with high clay content. It alsomay occur on well-drained hillsides during growingseasons with excessive moisture availability. Currently55 races of the pathogen have been identified. In 2000,Phytophthora sojae race surveys for soybean wereinitiated with funding from the Nebraska Soybean Board.As a result of ongoing survey efforts, races 1, 3, 4, 25,and 28 have been recovered from soybean fields inNebraska. Previous surveys were conducted in easternNebraska in 1980 and 1981 and resulted in recovery ofraces 1, 3, 9, 14, 18, and 23.Once P. sojae is established in a field, it cannot beeradicated. The disease must be “managed” with the useof seed treatment fungicides and resistant varieties.Knowledge of the races present in the state and howvarieties with different resistance genes have performedin a grower’s field is critical to variety selection formaximum profitability.Seed TreatmentSeed treatment fungicides can be used for manage-ment of early season seed rot and damping off causedby Phytophthora sojae. The compounds labeled forcontrol are metalaxyl and mefenoxam. Mefenoxam isone of the chemical compounds which has been isolatedfrom metalaxyl. A list of products containing these com-pounds and their recommended rate of application isprovided in Table I. In general, all varieties of soybeangrown in problem fields should be treated since condi-tions favoring Phytophthora sojae also favor Pythiumspp., which commonly cause seedling problems inNebraska.Financial resources for the Nebraska SoybeanDisease Surveys cited in this publication wereprovided by the Nebraska Soybean Board.File under: PLANT DISEASESC-10, Field CropsIssued April 2002Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Countiesand the United States Department of Agriculture.University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies of the University of Nebraska–Lincolnand the United States Department of Agriculture.© 2005, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.Table I. Seed treatment fungicides1 labeled for Phythophthora sojae control on soybean.2Application rate forPhytophthoraProduct Name Common Name control ManufacturerAllegiance LS Metalaxyl 1.2-2.4 fl. oz./100 lbs. seed GustafsonAllegiance FL Metalaxyl 0.75-1.5 fl. oz./100 lbs. seed GustafsonAllegiance Dry Metalaxyl 1.5-2.0 oz/100 lbs. seed Trace Chemicals LLCApron FL Metalaxyl 0.75-1.5 fl. oz./100 lbs seed GustafsonApron Flowable Mefenoxam 0.82-1.64 fl. oz./100 lbs. seed Wilber-EllisApron Maxx RTA3 Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed SyngentaApron Maxx RTA+ Moly3 Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed SyngentaApron TL Metalaxyl 2.0-4.0 fl. oz./100 lbs. seed Wilber-EllisApron XL LS Metalaxyl 0.16-0.64 fl. oz./100 lbs. seed SyngentaSystem 3 Pentachloronitrobenzene 4-6 oz/bu Helena(PCNB), Metalaxyl, andBacillus subtilits GBO3Warden RTA Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed Agriliance LLC1Product list is intended for information purposes only. No criticism is intended for products not listed nor endorsement for products listed. Always readand follow label directions when applying any pesticide.2Application rates on the high end of the labeled amount are generally necessary for adequate Phytophthora sojae control.3In fields with a history of high phytophthora pressure, the label recommends using Apron Maxx RTA or Apron Maxx RTA + Moly at the recommendedrate of 5.0 fl. oz./100 lbs. seed in combination with Apron XL LS at a rate of 0.16-0.48 fl. oz./100 lbs. seed.Genetic ResistanceUse of resistant varieties is the most effective means ofmanaging phytophthora diseases in soybean. Genetic resis-tance in the host is expressed in terms of Rps (Resistance toPhytophthora sojae) genes. The genes are denoted as Rps 1a,1b, 1c, 1d, 1k, 3, 6, and 7. The pathogen exists in races thatinteract with these genes. A race is identified by its interactionwith the eight known Rps genes. In a resistant reaction, theplant survives when infection occurs; susceptible varieties arekilled when infection occurs (Table II).Table II. A list of the races of Phytophthora sojae identifiedin Nebraska over the last 20 years and the Rps genereaction to these races.Race Rps Resistance Genes1-a 1-b 1-c 1-d 1-k 3 6 7  1 R R R R R R R s  3 s R R R R R R s  4 s R s R R R R s  9 s R R R R R s s14 R R s R R R R s18 R R s R R R R R23 s s R R R R s s25 s s s R s R R s28 s s R R s R R ss = susceptible or plant killed R = resistant or plant not killedSoybean varieties are marketed on the basis of theirgenetic make-up in relation to the predominate Phytoph-thora sojae races in a given area. The predominant races inNebraska are 1 and 3. The most widely available resistancegenes in the Midwest are 1-c and 1-k, commonly referredto as c or k in seed company literature. Gene 1-c protects againstraces 1, 3, 9, 23, and 28, where gene 1-k protects against races1, 3, 4, 9, 14, 18, and 23. Gene 3 is the onlygene that protects against all known races that occur inNebraska. Currently 40 percent of the maturity group 2 and63 percent of the group 3 soybean varieties marketed inNebraska contain some resistance to Phytophthora sojae.Resistance within these maturity groups is listed below.Maturity Percent Nebraska Marketed VarietiesGroup With Rps Gene Resistance1-a 1-b 1-c 1-d 1-k 3 6 7 1k/1aGroup 2 5 0 20 0 72 1.5 0 0 1.5Group 3 9 0 34 0 54 3 0 0 0Growers should consult local seed company represen-tatives to request varieties with different Rps genes thanmarketed in a specific area.

NF518 Management of Phytophthora Diseases of Soybeans

UNL | Libraries

University of Nebraska - Lincoln 
DigitalCommons@University of Nebraska - Lincoln 
Historical Materials from University of 
Nebraska-Lincoln Extension Extension 
2002 
NF02-518 Management of Phytophthora Diseases of Soybeans 
Loren J. Giesler 
University of Nebraska - Lincoln, lgiesler1@unl.edu 
Jane A. Christensen 
University of Nebraska - Lincoln 
Christopher M. Zwiener 
University of Nebraska - Lincoln 
Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist 
 Part of the Agriculture Commons, and the Curriculum and Instruction Commons 
Giesler, Loren J.; Christensen, Jane A.; and Zwiener, Christopher M., "NF02-518 Management of 
Phytophthora Diseases of Soybeans" (2002). Historical Materials from University of Nebraska-Lincoln 
Extension. 1969. 
https://digitalcommons.unl.edu/extensionhist/1969 
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - 
Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an 
authorized administrator of DigitalCommons@University of Nebraska - Lincoln. 
NebFact
Published by Cooperative Extension, Institute of Agriculture and Natural Resources,
University of Nebraska-Lincoln
C-10
NF02-518
Management of Phytophthora Diseases 
of Soybeans
Loren J. Giesler, Extension Plant Pathologist
Jane A. Christensen, Research Technologist, Plant Pathology
Christopher M. Zwiener, Student Assistant, Plant Pathology
Phytophthora diseases of soybean, caused by 
Phytophthora sojae, are present wherever soybeans are 
grown in Nebraska. The pathogen survives primarily 
 as “resting” spores in the soil or in association with 
infested crop debris. Symptoms associated with 
Phytophthora sojae infections include seed rots, pre- 
and post-emergence damping off of seedlings and stem 
rot of plants at various growth stages. Disease develop- 
ment is most rapid at soil temperatures above 60oF 
with high soil moisture. This disease is most common 
in low-lying areas of a field, in poorly drained or com- 
pacted soils, and in soils with high clay content. It also 
may occur on well-drained hillsides during growing 
seasons with excessive moisture availability. Currently 
55 races of the pathogen have been identified. In 2000, 
Phytophthora sojae race surveys for soybean were 
initiated with funding from the Nebraska Soybean Board. 
As a result of ongoing survey efforts, races 1, 3, 4, 25, 
and 28 have been recovered from soybean fields in Nebraska. 
Previous surveys were conducted in eastern Nebraska in 
1980 and 1981 and resulted in recovery of races 1, 3, 9, 
14, 18, and 23.
Once P. sojae is established in a field, it cannot be 
eradicated. The disease must be “managed” with the use 
of seed treatment fungicides and resistant varieties. 
Knowledge of the races present in the state and how 
varieties with different resistance genes have performed 
in a grower’s field is critical to variety selection for 
maximum profitability.
Seed Treatment
Seed treatment fungicides can be used for manage- 
ment of early season seed rot and damping off caused 
by Phytophthora sojae. The compounds labeled for 
control are metalaxyl and mefenoxam. Mefenoxam is 
one of the chemical compounds which has been isolated 
from metalaxyl. A list of products containing these com- 
pounds and their recommended rate of application is 
provided in Table I. In general, all varieties of soybean 
grown in problem fields should be treated since condi- 
tions favoring Phytophthora sojae also favor Pythium 
spp., which commonly cause seedling problems in 
Nebraska.
Financial resources for the Nebraska Soybean 
Disease Surveys cited in this publication were 
provided by the Nebraska Soybean Board.
File under: PLANT DISEASES
C-10, Field Crops
Issued April 2002
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture.
Elbert C. Dickey, Dean and Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.
University of Nebraska Cooperative Extension educational programs abide with the non-discrimination policies of the University of Nebraska-Lincoln
and the United States Department of Agriculture.
Table I.  Seed treatment fungicides1 labeled for Phythophthora sojae control on soybean.2
  Application rate for
  Phytophthora
Product Name Common Name control Manufacturer
Allegiance LS Metalaxyl 1.2-2.4 fl. oz./100 lbs. seed Gustafson
Allegiance FL Metalaxyl 0.75-1.5 fl. oz./100 lbs. seed Gustafson
Allegiance Dry Metalaxyl 1.5-2.0 oz/100 lbs. seed Trace Chemicals LLC
Apron FL Metalaxyl 0.75-1.5 fl. oz./100 lbs seed Gustafson
Apron Flowable Mefenoxam 0.82-1.64 fl. oz./100 lbs. seed Wilber-Ellis
Apron Maxx RTA3 Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed Syngenta
Apron Maxx RTA
+ Moly3  Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed Syngenta
Apron TL Metalaxyl 2.0-4.0 fl. oz./100 lbs. seed Wilber-Ellis
Apron XL LS Metalaxyl 0.16-0.64 fl. oz./100 lbs. seed Syngenta
System 3 Pentachloronitrobenzene 4-6 oz/bu Helena
 (PCNB), Metalaxyl, and
 Bacillus subtilits GBO3
Warden RTA Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed Agriliance LLC
1Product list is intended for information purposes only. No criticism is intended for products not listed nor endorsement for products listed. Always read and follow 
label directions when applying any pesticide.
2Application rates on the high end of the labeled amount are generally necessary for adequate Phytophthora sojae control.
3In fields with a history of high phytophthora pressure, the label recommends using Apron Maxx RTA or Apron Maxx RTA + Moly at the recommended rate of 5.0 
fl. oz./100 lbs. seed in combination with Apron XL LS at a rate of 0.16-0.48 fl. oz./100 lbs. seed.
Genetic Resistance
Use of resistant varieties is the most effective means of 
managing phytophthora diseases in soybean. Genetic resis-
tance in the host is expressed in terms of Rps (Resistance to 
Phytophthora sojae) genes. The genes are denoted as Rps 1a, 
1b, 1c, 1d, 1k, 3, 6, and 7. The pathogen exists in races that 
interact with these genes. A race is identified by its interaction 
with the eight known Rps genes. In a resistant reaction, the 
plant survives when infection occurs; susceptible varieties 
are killed when infection occurs (Table II).
Table II. A list of the races of Phytophthora sojae identified 
in Nebraska over the last 20 years and the Rps 
gene reaction to these races.
 Race Rps Resistance Genes
  1-a 1-b 1-c 1-d 1-k 3 6 7
   1 R R R R R R R s
   3 s R R R R R R s
   4 s R s R R R R s
   9 s R R R R R s s
 14 R R s R R R R s
 18 R R s R R R R R
 23 s s R R R R s s
 25 s s s R s R R s
 28 s s R R s R R s
s = susceptible or plant killed R = resistant or plant not killed
Soybean varieties are marketed on the basis of their 
genetic make-up in relation to the predominate Phytoph- 
thora sojae races in a given area. The predominant races in 
Nebraska are 1 and 3. The most widely available resistance 
genes in the Midwest are 1-c and 1-k, commonly referred 
to as c or k in seed company literature. Gene 1-c protects 
against races 1, 3, 9, 23, and 28, where gene 1-k protects 
against races 1, 3, 4, 9, 14, 18, and 23. Gene 3 is the only 
gene that protects against all known races that occur in 
Nebraska. Currently 40 percent of the maturity group 2 and 
63 percent of the group 3 soybean varieties marketed in 
Nebraska contain some resistance to Phytophthora sojae. 
Resistance within these maturity groups is listed below.
Maturity Percent Nebraska Marketed Varieties 
Group With Rps Gene Resistance
 1-a 1-b 1-c 1-d 1-k 3 6 7 1k/1a
Group 2 5 0 20 0 72 1.5 0 0 1.5
Group 3 9 0 34 0 54 3 0 0 0
Growers should consult local seed company represen-
tatives to request varieties with different Rps genes than 
marketed in a specific area.


NF02-518 Management of Phytophthora Diseases of Soybeans

University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Historical Materials from University of Nebraska-Lincoln Extension Extension 2002 NF02-518 Management of Phytophthora Diseases of Soybeans Loren J. Giesler University of Nebraska - Lincoln, lgiesler1@unl.edu Jane A. Christensen University of Nebraska - Lincoln Christopher M. Zwiener University of Nebraska - Lincoln Follow this and additional works at: https://digitalcommons.unl.edu/extensionhist  Part of the Agriculture Commons, and the Curriculum and Instruction Commons Giesler, Loren J.; Christensen, Jane A.; and Zwiener, Christopher M., "NF02-518 Management of Phytophthora Diseases of Soybeans" (2002). Historical Materials from University of Nebraska-Lincoln Extension. 1969. https://digitalcommons.unl.edu/extensionhist/1969 This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. NebFactPublished by Cooperative Extension, Institute of Agriculture and Natural Resources,University of Nebraska-LincolnC-10NF02-518Management of Phytophthora Diseases of SoybeansLoren J. Giesler, Extension Plant PathologistJane A. Christensen, Research Technologist, Plant PathologyChristopher M. Zwiener, Student Assistant, Plant PathologyPhytophthora diseases of soybean, caused by Phytophthora sojae, are present wherever soybeans are grown in Nebraska. The pathogen survives primarily  as “resting” spores in the soil or in association with infested crop debris. Symptoms associated with Phytophthora sojae infections include seed rots, pre- and post-emergence damping off of seedlings and stem rot of plants at various growth stages. Disease develop- ment is most rapid at soil temperatures above 60oF with high soil moisture. This disease is most common in low-lying areas of a field, in poorly drained or com- pacted soils, and in soils with high clay content. It also may occur on well-drained hillsides during growing seasons with excessive moisture availability. Currently 55 races of the pathogen have been identified. In 2000, Phytophthora sojae race surveys for soybean were initiated with funding from the Nebraska Soybean Board. As a result of ongoing survey efforts, races 1, 3, 4, 25, and 28 have been recovered from soybean fields in Nebraska. Previous surveys were conducted in eastern Nebraska in 1980 and 1981 and resulted in recovery of races 1, 3, 9, 14, 18, and 23.Once P. sojae is established in a field, it cannot be eradicated. The disease must be “managed” with the use of seed treatment fungicides and resistant varieties. Knowledge of the races present in the state and how varieties with different resistance genes have performed in a grower’s field is critical to variety selection for maximum profitability.Seed TreatmentSeed treatment fungicides can be used for manage- ment of early season seed rot and damping off caused by Phytophthora sojae. The compounds labeled for control are metalaxyl and mefenoxam. Mefenoxam is one of the chemical compounds which has been isolated from metalaxyl. A list of products containing these com- pounds and their recommended rate of application is provided in Table I. In general, all varieties of soybean grown in problem fields should be treated since condi- tions favoring Phytophthora sojae also favor Pythium spp., which commonly cause seedling problems in Nebraska.Financial resources for the Nebraska Soybean Disease Surveys cited in this publication were provided by the Nebraska Soybean Board.File under: PLANT DISEASESC-10, Field CropsIssued April 2002Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture.Elbert C. Dickey, Dean and Director of Cooperative Extension, University of Nebraska, Institute of Agriculture and Natural Resources.University of Nebraska Cooperative Extension educational programs abide with the non-discrimination policies of the University of Nebraska-Lincolnand the United States Department of Agriculture.Table I.  Seed treatment fungicides1 labeled for Phythophthora sojae control on soybean.2  Application rate for  PhytophthoraProduct Name Common Name control ManufacturerAllegiance LS Metalaxyl 1.2-2.4 fl. oz./100 lbs. seed GustafsonAllegiance FL Metalaxyl 0.75-1.5 fl. oz./100 lbs. seed GustafsonAllegiance Dry Metalaxyl 1.5-2.0 oz/100 lbs. seed Trace Chemicals LLCApron FL Metalaxyl 0.75-1.5 fl. oz./100 lbs seed GustafsonApron Flowable Mefenoxam 0.82-1.64 fl. oz./100 lbs. seed Wilber-EllisApron Maxx RTA3 Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed SyngentaApron Maxx RTA+ Moly3  Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed SyngentaApron TL Metalaxyl 2.0-4.0 fl. oz./100 lbs. seed Wilber-EllisApron XL LS Metalaxyl 0.16-0.64 fl. oz./100 lbs. seed SyngentaSystem 3 Pentachloronitrobenzene 4-6 oz/bu Helena (PCNB), Metalaxyl, and Bacillus subtilits GBO3Warden RTA Mefenoxam and Fludioxonil 5.0 fl. oz./100 lbs. seed Agriliance LLC1Product list is intended for information purposes only. No criticism is intended for products not listed nor endorsement for products listed. Always read and follow label directions when applying any pesticide.2Application rates on the high end of the labeled amount are generally necessary for adequate Phytophthora sojae control.3In fields with a history of high phytophthora pressure, the label recommends using Apron Maxx RTA or Apron Maxx RTA + Moly at the recommended rate of 5.0 fl. oz./100 lbs. seed in combination with Apron XL LS at a rate of 0.16-0.48 fl. oz./100 lbs. seed.Genetic ResistanceUse of resistant varieties is the most effective means of managing phytophthora diseases in soybean. Genetic resis-tance in the host is expressed in terms of Rps (Resistance to Phytophthora sojae) genes. The genes are denoted as Rps 1a, 1b, 1c, 1d, 1k, 3, 6, and 7. The pathogen exists in races that interact with these genes. A race is identified by its interaction with the eight known Rps genes. In a resistant reaction, the plant survives when infection occurs; susceptible varieties are killed when infection occurs (Table II).Table II. A list of the races of Phytophthora sojae identified in Nebraska over the last 20 years and the Rps gene reaction to these races. Race Rps Resistance Genes  1-a 1-b 1-c 1-d 1-k 3 6 7   1 R R R R R R R s   3 s R R R R R R s   4 s R s R R R R s   9 s R R R R R s s 14 R R s R R R R s 18 R R s R R R R R 23 s s R R R R s s 25 s s s R s R R s 28 s s R R s R R ss = susceptible or plant killed R = resistant or plant not killedSoybean varieties are marketed on the basis of their genetic make-up in relation to the predominate Phytoph- thora sojae races in a given area. The predominant races in Nebraska are 1 and 3. The most widely available resistance genes in the Midwest are 1-c and 1-k, commonly referred to as c or k in seed company literature. Gene 1-c protects against races 1, 3, 9, 23, and 28, where gene 1-k protects against races 1, 3, 4, 9, 14, 18, and 23. Gene 3 is the only gene that protects against all known races that occur in Nebraska. Currently 40 percent of the maturity group 2 and 63 percent of the group 3 soybean varieties marketed in Nebraska contain some resistance to Phytophthora sojae. Resistance within these maturity groups is listed below.Maturity Percent Nebraska Marketed Varieties Group With Rps Gene Resistance 1-a 1-b 1-c 1-d 1-k 3 6 7 1k/1aGroup 2 5 0 20 0 72 1.5 0 0 1.5Group 3 9 0 34 0 54 3 0 0 0Growers should consult local seed company represen-tatives to request varieties with different Rps genes than marketed in a specific area.

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NF02-518 Management of Phytophthora Diseases of Soybeans

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