Institute of Ag Professionals Proceedings of the 2009 Crop Pest Management Shortcourse & Minnesota Crop Production Retailers Association Trade Show www.extension.umn.edu/agprofessionals Do not reproduce or redistribute without the written consent of author(s).
SOYBEAN AND CORN DISEASES KNOW THEM AND THEIR RISKS Dean Malvick Department of Plant Pathology University of Minnesota, St. Paul dmalvick@umn.edu
OUTLINE General Information Disease Risks for Corn and Soybean Disease Diagnosis
REVIEW OF CROP DISEASE PROBLEMS IN MINNESOTA IN 2009 Corn Stalk Rot Northern Corn Leaf Spot Goss s Wilt Eyespot Ear molds Soybean White Mold Brown Stem Rot Rhizoctonia Root Rot Pod and Stem Blight SCN
PUTTING IT ALL TOGETHER DISEASE DISEASE Poor weather DISEASE Planting YIELD Scouting Diagnosis Good variety Good growing conditions Importance in your situation Disease priorities for management Variety selection
THREE KEY FACTORS THAT AFFECT RISK OF CROP DISEASE SUSCEPTIBLE PLANT MANAGEMENT -tillage -planting date -seeding rates PATHOGEN PRESENCE -various fungi FAVORABLE ENVIRONMENT -Wet; cool, hot, dry
What are major disease risks in MN that can cause large (>25%) losses? Corn > stalk rot > Common rust? > Future - Gray leaf spot? Soybean > SDS > Phytophthora rot > White mold >Brown stem rot
CORN DISEASES Corn diseases throughout the season
CORN GROWTH STAGES Source of Figure University of Illinois Critical time for foliar disease : Tasseling +/- 2 wks Tasseling Silking
Corn Leaf Diseases Foliar/leaf diseases Anthracnose Common rust Eyespot Gray leaf spot Northern corn leaf blight Northern corn leaf spot Goss s Wilt
Corn Anthracnose Disease Cycle (Bergstrom and Nicholson, Plant Dis. 1999) ANTHRACNOSE Leaves and Stalks
ANTHRACNOSE RISK FACTORS Infested corn residue Cloudy, overcast weather corn is more resistant under high light intensity Extended periods of high humidity required for sporulation Rain: raindrops disperse spores (conidia) Warm temperatures (78 86F) Stress from other pests root lesion nematodes *severe infestations of European corn borer
GRAY LEAF SPOT Most serious leaf disease of corn in the U.S. Caused by the fungus Cercospora zeae-maydis Yield reductions up to 44% reported in the Midwest and 24 to 69% in Virginia
GLS RISK FACTORS Prolonged high humidity (>95%, >24 HR) Warm temperatures (70-85 F) Protected fields Large amounts of corn crop residue Late maturing hybrids Susceptible hybrids
COMMON RUST
COMMON RUST RISK FACTORS Favored by: Moderate temperatures (61-76F) High humidity (greater than 95%) Epidemics in southern U.S. and Mexico Inhibited by: High temperatures (over 85F) Usually develops in MN late in season
NORTHERN CORN LEAF BLIGHT 1 to 6 inch long cigar-shaped gray-green to tancolored lesions on the lower leaves. Symptoms on resistant cultivars: small chlorotic or necrotic spots
NORTHERN CORN LEAF BLIGHT RISK FACTORS Cool and wet weather Corn residue from previous crop on soil surface Susceptible hybrids
EYESPOT
EYESPOT RISK FACTORS Seed production fields with very susceptible inbreds. Cool and humid weather Corn-on-corn field with minimal tillage Hybrid susceptible to eyespot
GOSS S LEAF BLIGHT WESTERN MN 2009 Special thanks to the photographer
GOSS S LEAF BLIGHT RISK FACTORS Can cause leaf blight and seedling blight Corn debris from previous crop on soil surface Warm and wet weather Injury to leaves by wind-blow sand/soil Hail Infested seed
NORTHERN CORN LEAF SPOT Ohio State University Risk factors: Wet weather Infested crop residue on soil surface
ANTHRACNOSE: STALK ROT PHASE
GIBBERELLA STALK ROT Photos courtesy D. White
FUSARIUM STALK ROT
STALK ROTS RISK FACTORS Stress on the corn plant Stalk debris on soil surface or buried Corn on corn minimal rotation susceptible and high-yielding hybrids leaf disease and grasshopper damage high plant populations early maturation water stress high fertility, especially very high N low N, low K and low P
EAR ROTS AND MYCOTOXINS Diplodia Ear Rot D. maydis no toxins in US Giberella Ear Rot G. zeae zearalenone Penicillium Ear Rot ochratoxins Aspergillis Ear Rot (A. flavis) aflatoxin Fusarium Ear Rot (F. moniliforme, F. proliferatum, F. subglutinans) fumonisins
Fusarium ear rot >most severe when hot, dry weather occurs at or just after flowering. Aspergillis ear rot >favored by hot weather and low soil moisture
CLADOSPORIUM AND TRICHODERMA EAR ROTS COMMON IN MINNESOTA IN NOVEMBER 2009
FIELD GUIDE TO CORN DISEASES This Field Guide to Corn Diseases is an extensive guide to identification of common corn diseases in the United States. Disease identification and management will be aided with the brief descriptions and multiple color photographs for the 56 different diseases that are included in this guide. Can be orderd via the internet: shop.extension.umn.edu Or call: 1-800-876-8636
SOYBEAN DISEASES Soybean diseases throughout the season
What are major disease risks in MN that can cause major (>25%) losses? Soybean > SDS > Phytophthora rot > White mold >Brown stem rot > SCN?
D. Malvick University of Minnesota SOYBEAN GROWTH STAGES Critical time: Bloom through pod fill Source: University of Illinois Extension Source of Figure University of Illinois 3 developed trifoliates (leaf edges don t touch) Beginning bloom* Beginning pod* Beginning seed* * Found at one of upper 4 nodes on main stem
D. Malvick University of Minnesota YIELD LOSS FROM SOYBEAN DISEASES RESULTS FROM: Plant death Root and stem dysfunction Loss of leaves and leaf function Premature defoliation Increase in number of unfilled pods/plant Decrease in # of seeds/plant Decrease in seed weight Decrease in germination of seed
D. Malvick University of Minnesota STEM DISEASES LATE SEASON DISEASES Brown Stem Rot (BSR) White mold Stem canker Pod and stem blight Anthracnose
D. Malvick University of Minnesota BROWN STEM ROT (BSR) COMMON AND DAMAGING PROBLEM IN MANY AREAS IN MN IN 2008 AND 2009
D. Malvick University of Minnesota BSR: STEM BROWNING BUT NO FOLIAR SYMPTOMS
D. Malvick University of Minnesota EFFECTS OF BSR : PREMATURE DEFOLIATION Row with BSR
BROWN STEM ROT RISK FACTORS Cool temperatures (60-80 F) during pod fill - whereas, temperatures > 80F suppress symptoms. Leaf symptoms often most severe when: - wet soil near saturation at flowering/pod fill (R1-R6) & dry soil during maturation (R6-R8 stages) Short rotations Ineffective resistance Soybean cyst nematode ph <6.5
D. Malvick University of Minnesota WHITE MOLD IN SOUTHERN MN - 2008
WHITE MOLD RISK FACTORS HIGH MOISTURE DURING FLOWERING STAGES COOL TEMPERATURES DURING AND AFTER FLOWERING STAGES CROP ROTATON <3 YEARS OUT OF SOYBEAN OR OTHER HOST CROPS FIELD WITH HISTORY OF WHITE MOLD HIGH FERTILITY ESPECIALLY MANURE HIGH WEED POPULATION IN FIELD HIGH PLANT POPULATION HIGHLY SUSCEPTIBLE SOYBEAN VARIETY
STEM CANKER D. Malvick University of Minnesota
D. Malvick University of Minnesota ROOT DISEASES SDS Phytophthora rot Fusarium root rot Rhizoctonia root rot SCN
D. Malvick University of Minnesota SDS in southern Minnesota soybean field.
D. Malvick University of Minnesota SDS SYMPTOMS AT DIFFERENT STAGES OF DEVELOPMENT ON SOYBEAN LEAVES
BSR VS SUDDEN DEATH SYNDROME (SDS) SDS BSR No browning of pith in stems D. Malvick University of Minnesota
SDS RISK FACTORS Susceptible soybean varieties Early planting cool wet soil after planting Field history of SDS Compacted soil, poor drainage High SCN populations High yield environments Heavy rainfalls through June and to mid-july
PHYTOPHTHORA ROT OF SOYBEAN Phytophthora sojae Kills soybean plants at all growth stages. Outbreaks of Phytophthora Rot are generally associated with water-saturated soils Wrather, Univ. of Missouri
D. Malvick University of Minnesota PHYTOPHTHORA ROOT ROT RISK FACTORS Varieties without major resistance genes: Rps1K, Rps1c, Rps6, or Rps3 Varieties with low tolerance (partial resistance) Poor soil drainage Frequent rainfall in the first month after planting Warm wet soil for extended periods History of disease in field
RHIZOCTONIA ROOT ROT D. Malvick University of Minnesota
RHIZOCTONIA ROOT ROT RISK FACTORS Wet to moderately-wet soil Warm conditions Crop residue P and K deficiency ph unfavorable for soybean Physical damage to soybean plants
SOYBEAN DISEASES WEB SITE: WWW.EXTENSION.UMN.EDU/CROPDISEASES/SOYBEAN
www.extension.umn.edu/cropdiseases/soybean
DIAGNOSIS OF CORN AND SOYBEAN DISEASES Field Identification Laboratory Diagnosis
FIELD DISEASE IDENTIFICATION Symptoms - Lesions, Flecks, Streaks, Canker, Rots, Spots, etc... Signs - Spores, Ooze, Cysts, Particles, Mushrooms, etc. Field Patterns Time of appearance Field History
LABORATORY DIAGNOSIS Culturing Advanced Techniques One example is DNA analysis
SOYBEAN ROOTS AND STEMS CONTAIN MANY DIFFERENT KINDS OF FUNGI
DNA TEST TO CONFIRM SDS Plant With SDS Plant Without SDS We are using similar methods for BSR, Stem Canker, and Phytophthora
FINAL POINTS Disease is a significant factor in corn and soybean production Weather drives disease (and yield) One more diseases are favored by any weather conditions ranging from very hot and dry to very cool and wet. Scouting and disease identification in mid August can be very beneficial in managing corn and soybean diseases A proper diagnosis can be extremely valuable Common risk factors: wet weather in July, very dry weather in August, cool and wet May, poor drainage and compaction, no crop rotation, crop residue on soil surface