Managing Stewart’s wilt and common rust in sweet corn
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Transcript of Managing Stewart’s wilt and common rust in sweet corn
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Managing Stewart’s wilt and
common rust in sweet corn
Jerald K. Pataky Department of Crop Sciences Professor of Plant PathologyUniversity of Illinois
www.sweetcorn.uiuc.edu
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Stewart’s wiltErwinia stewartii
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Seedling wilt phase
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Symptoms following leaf veins
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Ooze test
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bacterial ooze
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Corn flea beetle
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Flea beetle feeding
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Two important generationsof flea beetles
• overwintering generation - peak numbers at first plantings
- decreases until ~ Memorial Day • second generation - peaks between June 20 to July 10 - size affected by weather ( larger when dry)
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Flea beetle winter survival
> 32 F survive*27 - 32 F % survive*< 27 F killed
Average daily air temperature Dec., Jan., Feb.
*size of previous population
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Ten Warmest Winterssince 1895
10. 1930-1931 36.2 9. 1952-1953 36.2 8. 1999-2000 36.2 7. 1908-1909 36.3 6. 1998-1999 36.4 5. 1953-1954 36.8 4. 1920-1921 36.9 3. 1997-1998 36.9 2. 1991-1992 37.9 1. 1931-1932 40.0
Laura Sweets, University of Missouri, Columbia
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Flea beetles and Stewart’s wiltAvg. temp (F) > 28
December, January & February
1995
1996
1994
1997
1999
19982000
1994-1998 Dekalb Genetics 1999-2001 University of Illinois
2001
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December 2000 16.7 F
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Dec Jan Dec JanLocation 01 02 00 01Janesville, WI 31 28 12 21 Rockford, IL 31 29 12 21Mendota, IL 32 29 13 21Urbana, IL 35 34 17 26Brownstown, IL 37 35 21 29Dixon Springs, IL 41 38 28 34
Will flea beetles survive 2001/2002? Average daily temperature
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Control Stewart’s wilt
• resistant hybrids
• control flea beetles
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susceptible moderate resistant
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Scale for rating Stewart’s wilt
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• flea beetle feeding wounds• limit movement of E. stewartii
Resistance to Stewart’s wilt
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moderately susceptible
moderately resistant
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susceptible
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Information on hybrid reactions to Stewart’s wilt
• Midwestern Vegetable Variety Trial Report
• www.sweetcorn.uiuc.edu
• extension publications
• literature from seed companies
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R
S
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Effect of Stewart’s wilton sweet corn yield
• growth stage • level of resistance
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Stewart’s wilt and sweet corn yieldeffect of growth stage at time of infection
Suparyono & Pataky, 1987
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Y = 80.9 + 13.7X - 2.9X2
r2
= 0.75
Stewart's wilt rating
2 3 4 5 6 7
Perc
ent yie
ld (
ea
r w
eig
ht)
0
20
40
60
80
100
120
20001999
Fig. 6. 1999 and 2000 combined regression, relationship between percent yield (ear weight)and Stewart's wilt rating
Stewart’s wilt and yield
effect of host reaction (resistant to susceptible) Freeman & Pataky, 2000
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Marketable ears and incidence of systemic infection
Y = 93.0 - 0.93X
r2 = 0.65
Systemically infected plants (%)
0 20 40 60 80 100
Pe
rce
nt
ma
rke
tab
le e
ars
0
20
40
60
80
100
120
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Effects of Stewart’s wilt on yield
Hybrid 3- to 5- 5- to 7- 7- to 9-reaction leaf leaf leaf
Growth stage
R 0% 0 % 0 %MR 0-30% 0 % 0 %MS 10-40% 0-20 % 0 %S 40-100% 15-35% 3-15%
• prior to 3-leaf stage -- main stalk death
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systemic infection main stalk death
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Growing point is killed
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Tillers from main stalk death
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Bold 10% MRGH 2628 11% R/MRBonus 11% RMore 17% R/MRGH 2757 30% MSEmpire 33% M/MSJubilee 60% S
Main stalk Hybrid Hybrid death (%) Rxn
Stewart’s wilt and main stalk death
July 1995, Manito, IL
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Controlling flea beetles
• seed treatments • in-furrow applications• foliar applications
Insecticides
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Seed treatment insecticides
• imidacloprid (Gaucho)• thiamethoxam (Adage/Cruiser)• TI-435 - clothianidin
60% to 80% control of Stewart’s wilt
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TreatedNon-treatedFlea beetle feeding wounds
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Urbana early trial (Planted: 27 April)
0
5
10
15
20
25
30
35
40
Check Adage 50
Adage100
Adage200
Adage250
Gaucho3.2
Gaucho4.8
Gaucho6.2
G2 4
G2 8
Inci
denc
e (%
) of
sys
tem
ic S
ewar
t's w
ilt
1 June
15 June
Stewart’s wilt control on Jubilee
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Manito early trial (Planted: 26 April)
0
5
10
15
20
25
30
Check Adage 50
Adage100
Adage200
Adage250
Gaucho3.2
Gaucho4.8
Gaucho6.2
G2 4
G2 8
Inci
denc
e (%
) of
sys
tem
ic S
ewar
t's w
ilt
2 June
22 June
Stewart’s wilt control on Jubilee
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Manito late trial (Planted: 22 June)
0
5
10
15
20
25
30
Check Adage 50
Adage100
Adage200
Adage250
Gaucho3.2
Gaucho4.8
Gaucho6.2
G2 4
G2 8
Inci
denc
e (%
) of
sys
tem
ic S
ewar
t's w
ilt
25 July
9 August
Stewart’s wilt control on Jubilee
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Urbana late trial (Planted: 19 June)
0
10
20
30
40
50
60
70
80
90
100
Check Adage 50
Adage100
Adage200
Adage250
Gaucho3.2
Gaucho4.8
Gaucho6.2
G2 4
G2 8
Inci
denc
e (%
) of
sys
tem
ic S
tew
art's
wilt
10 July
20 July
4 August
Stewart’s wilt control on Jubilee
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non-treated
treated
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Non-treated
Treated
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imidacloprid
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Economic value of seed treatment insecticides
Value = value of the crop ($/A) x incidence (%) x 0.7 (70% control)
Example: Crop value estimated at $800/A x 5% systemic infection (w/o control) x 0.7 (70% control) = $28 / A estimated value of seed treatment
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1.00.870.750.440.19>10%
00.130.190.310.315-10%
000.060.250.5<5%
S
(9)
MS
(7-8)
M
(5-6)
MR
(3-4)
R
(1-2)
Incidence of systemic infection
Hybrid reaction to Stewart’s wilt
Probability of 5% systemic infection in central Illinois
Planted after 1 June 1998 to 2000
1998 to 2000 represents worse case scenario
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Common rust
Puccinia sorghi
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Effect of rust on sweet corn yield
Y = 99.4 - 0.58 Xr = 0.81 n = 232
0
20
40
60
80
100
120
140
0 10 20 30 40 50 60 70
Rust severity (%) one week before harvest
Pe
rce
nt
ma
xim
um
yie
ld (
ea
r w
eig
ht)
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Rust severity is affected by:
• abundance of urediniospores
• host growth stage
• weather
• host resistance
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Urediniospores Teliospores
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Telia
Uredinia
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Initial inoculum (urediniospores)
does not overwinterin the Corn Belt
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Puccinia pathways (urediniospores)
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Secondary inoculum (urediniospores)
comes from infected corn
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~ 5,000 urediniospores per pustule200 urediniospores per day for ~ 4 wks
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50 pustules = 10,000 spores per day
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Rust severity is affected by:
• abundance of urediniospores
• host growth stage
• weather
• host resistance
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Juvenile tissue is more susceptible than adult-plant tissue
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Adult
late juvenile
early juvenile--
Adult Leaf Epidermal Traits
• bulliform cells, macrohairs, prickle hairs• alkane-rich shorter chain leaf waxes• neutral (purple) reaction with toluidine blue-O histochemical stain• highly-crenulated cell walls• rectangular cell shape (cross-section) • thick cuticle (~ 3 micron cross-section)
Juvenile Leaf Epidermal Traits
• crystalline waxes rich in primary alcohols• acidic (aqua) reaction with toluidine blue-O histochemical stain• weakly-crenulated cell walls• rounded cell shape (cross-section)• thin cuticle (~1 micron cross section)
3
8
Epidermal Cell Differentiation in Juvenile and Adult Leaves
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Whorls - primary site of infection
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Infection in the leaf whorl
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Rust severity is affected by:
• abundance of urediniospores
• host growth stage
• weather
• host resistance
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Moisture and temperature affect: • urediniospore germination• rate of infection• sporulation
• 6 hours of moisture• 60 to 75 F optimal• ~38 to 95 F minimum and maximum
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Rust develops rapidly on late-season crops
• urediniospores are abundant
• air is humid
• low night temperature creates dew
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Infection on wet leaf tissue (heavy dews)
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Control common rust
• plant resistant hybrids
• apply fungicides
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Rust resistance• general (partial) resistance • Rp-resistance
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partialresistance
susceptible
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Information on hybrid reactions to common rust
• Midwestern Vegetable Variety Trial Report
• www.sweetcorn.uiuc.edu
• extension publications • literature from companies
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Rust severity %and (estimated Reactions of sweet corn hybridsyield reductions)** R MR M MS S 0-10% (3%) 0.63 0.26 0.11 0.11 0.1110-20% (9%) 0.37 0.47 0.16 0.11 020-30% (15%) 0 0.26 0.63 0.26 0.1630-40% (21%) 0 0 0.11 0.32 0.2640-50% (27%) 0 0 0 0.21 0.32>50% (>30%) 0 0 0 0 0.16 * probability based on 18 years of evaluations in University of Illinois sweet corn hybrid disease nurseries
** yield loss estimated by multiplying rust severity by 0.06
Probability* of severe rust
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• MR - 75% chance of less than 20% rust • M to MS - ~75% chance of more than 20% rust • S - 75% chance of more than 30% rust
Common rust on sweet cornmatures ~ August 5 in central Illinois
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Rp-resistance
Bands of chlorotic flecks (qualitative reaction)
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Single Rp genes in the Rp1 region
Rp1-DRp-GRp1-E (Rp1-I, Rp1-K) Rp1-MRp1-C (Rp1-N)Rp1-A (Rp1-F)
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Susceptible Rp-resistant
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Rp1D-resistant hybrid
Rock Falls, IL September 1999
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Rp1D-resistancegreenhouse Sept. 1999
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avirulent
virulent
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Rp1-D resistance Los Mochis, Mexico
March 2000
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Future of Rp resistance
• one Rp hybrid may be resistant while another Rp hybrid may be completely susceptible • different Rp genes
more confusing - variable
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Future of Rp resistance
• one Rp hybrid may be slightly infected while another Rp hybrid may be severely infected • new race present and hybrids have different levels of partial resistance
more confusing - variable
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Future of Rp resistance
• an Rp hybrid may be resistant at one location but susceptible in another area • different isolates of rust
more confusing - variable
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Future of Rp resistance
• an Rp hybrid may be resistant at an early planting but susceptible at a later planting • a virulent isolates of rust is introduced during the season
more confusing - variable
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Know more about hybrid reactions to rust
• Rp-resistant hybrids• Rp gene• background reaction (R, MR, M, MS, S) • non-Rp hybrids• reaction (R, MR, M, MS, S)
• scout for rust• any pustules on Rp hybrids • thresholds on MR, M, MS, and S hybrids
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Fungicides• EBDCs
• TILT
• strobilurins (QUADRIS, F-500)
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Fungicides*• fungicides are preventative• fungicides ARE NOT curative
Rule of thumb: one or two early applications are superior to multiple late applications • juvenile tissue is more susceptible• infection occurs in the whorl • pustules on lower leaves = inocula for 2o infection (5,000 urediniospores per pustule)
* EBDCs, Tilt (1 to 2% action threshold)
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Strobilurins
may change use of fungicides on sweet corn
• more efficacious • may have different thresholds ?
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Rust & NLB - 'Florida XP-7' Leaf area necrotic (%) Rick Raid - UF-Belle Glade Planted: 17 Feb 1997
0
10
20
30
40
50
60
70
Non-treated
Manzate Tilt Folicur Quadris Tilt +Manzate
Folicur +Manzate
Quadris+Manzate
Quaddris+ Tilt
Lea
f ar
ea n
ecro
tic
(%)
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Common rust - 'Silver Queen' Leaf area infected (%)
Helene Dillard, NYAES- Geneva Planted: 21 June 2000
0
5
10
15
20
25
30
Non-treated Quadris 0.38 28 July 09 August
Quadris 0.77 28 July 09 August
Tilt 0.25 28 July 09 August
Quadris 0.38 09 August 21 August
Quadris 0.77 09 August 21 August
Tilt 0.25 09 August 21 August
Per
cen
t le
af a
rea
infe
cted
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Location: Urbana, IL - May 29, 2001
Hybrids: Snow White, Sterling
Compounds: Tilt, BASF F-500, Quadris (low, high rate)
Application: July 5 (2 to 4-leaf) 5% July 11 (4 to 6-leaf) 15%
July 17 (6 to 8-leaf) 30% July 24 (row tassel) 40%
21 treatments
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Rust fungicide trial - 2001
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Non-treated
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strobilurin-treated
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5.5
6
6.5
7
7.5
8
5% 15% 30% 40% Tilt weekly Check
Yie
ld (
ton
s/A
Tilt Strobilurin
Rust fungicide trial - 2001
Sterling
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• Thresholds for strobilurins probably will be in the 5% to 15% range (compared to 1 to 2% for Tilt or EBDCs)
Tentative conclusions
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