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Managing Stewart’s wilt and common rust in sweet corn. Jerald K. Pataky Department of Crop Sciences Professor of Plant Pathology University of Illinois. j-pataky@uiuc.edu www.sweetcorn.uiuc.edu. Stewart’s wilt. Erwinia stewartii. Seedling wilt phase. Symptoms following leaf veins.

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slide1

Managing Stewart’s wilt and

common rust in sweet corn

Jerald K. Pataky

Department of Crop Sciences

Professor of Plant Pathology

University of Illinois

j-pataky@uiuc.edu

www.sweetcorn.uiuc.edu

slide2

Stewart’swilt

Erwinia stewartii

slide9

Two important generations

of 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)
slide10

Flea beetle winter survival

Average daily air temperature

Dec., Jan., Feb.

> 32 F survive*

27 - 32 F % survive*

< 27 F killed

*size of previous population

slide11

Ten Warmest Winters

since 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

slide14

Will flea beetles survive 2001/2002?

Average daily temperature

Dec Jan Dec Jan

Location01 0200 01

Janesville, WI31 28 12 21

Rockford, IL31 29 12 21

Mendota, IL32 2913 21

Urbana, IL35 34 17 26

Brownstown, IL37 35 21 29

Dixon Springs, IL41 38 28 34

slide15

Control Stewart’s wilt

  • resistant hybrids
  • control flea beetles
slide18

Resistance to Stewart’s wilt

  • flea beetle feeding wounds
  • limit movement of E. stewartii
slide19

moderately resistant

moderately susceptible

slide21

Informationon hybrid

reactionsto Stewart’s wilt

  • Midwestern Vegetable
  • Variety Trial Report
  • www.sweetcorn.uiuc.edu
  • extension publications
  • literature from seed companies
slide22

R

S

slide23

Effect of Stewart’s wilt

on sweet corn yield

  • growth stage
  • level of resistance
slide24

Stewart’s wilt and sweet corn yield

effect of growth stage at time of infection

Suparyono & Pataky, 1987

slide25

Stewart’s wilt and yield

effect of host reaction (resistant to susceptible)

Freeman & Pataky, 2000

slide26

Marketable ears and

incidence of systemic infection

slide27

Effects of Stewart’s wilt on yield

Growth stage

Hybrid 3- to 5- 5- to 7- 7- to 9-

reaction leaf leaf leaf

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
slide28

systemic infection

main stalk death

slide31

Stewart’s wilt and main stalk death

Main stalk Hybrid

Hybrid death (%) Rxn

Bold 10% MR

GH 2628 11% R/MR

Bonus 11% R

More 17% R/MR

GH 2757 30% MS

Empire 33% M/MS

Jubilee 60% S

July 1995, Manito, IL

slide32

Controlling flea beetles

Insecticides

  • seed treatments
  • in-furrow applications
  • foliar applications
slide33

Seed treatment

insecticides

60% to 80% control

of Stewart’s wilt

  • imidacloprid (Gaucho)
  • thiamethoxam (Adage/Cruiser)
  • TI-435 - clothianidin
slide34

Non-treated

Treated

Flea beetle

feeding wounds

slide39

treated

non-treated

slide40

Treated

Non-treated

slide42

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

slide43

Probability of 5% systemic infection

in central Illinois

Planted after 1 June 1998 to 2000

Hybrid reaction to Stewart’s wilt

Incidence of systemic infection

R

(1-2)

MR

(3-4)

M

(5-6)

MS

(7-8)

S

(9)

<5%

0.5

0.25

0.06

0

0

5-10%

0.31

0.31

0.19

0.13

0

>10%

0.19

0.44

0.75

0.87

1.0

1998 to 2000 represents worse case scenario

slide44

Common rust

Puccinia sorghi

slide46

Rust severity is affected by:

  • abundance of urediniospores
  • host growth stage
  • weather
  • host resistance
slide47

Urediniospores

Teliospores

slide50

Telia

Uredinia

slide52

Initial inoculum

(urediniospores)

does not overwinter

in the Corn Belt

slide53

Puccinia pathways

(urediniospores)

slide54

Secondary inoculum

(urediniospores)

comes from

infected corn

slide55

~ 5,000 urediniospores per pustule

200 urediniospores per day for ~ 4 wks

slide57

Rust severity is affected by:

  • abundance of urediniospores
  • host growth stage
  • weather
  • host resistance
slide58

Juvenile tissue is more susceptible

than adult-plant tissue

slide59

-

-

Epidermal Cell Differentiation in Juvenile and Adult Leaves

  • 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)

Adult

8

  • 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)

late juvenile

3

early juvenile

slide63

Rust severity is affected by:

  • abundance of urediniospores
  • host growth stage
  • weather
  • host resistance
slide64

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
slide65

Rust develops rapidly

on late-season crops

  • urediniospores are abundant
  • air is humid
  • low night temperature creates dew
slide67

Control common rust

  • plant resistant hybrids
  • apply fungicides
slide68

Rust resistance

  • general (partial) resistance
  • Rp-resistance
slide69

partial

resistance

susceptible

slide70

Informationon hybrid

reactionsto common rust

  • Midwestern Vegetable
  • Variety Trial Report
  • www.sweetcorn.uiuc.edu
  • extension publications
  • literature from companies
slide71

Probability* of severe rust

Rust severity %

and (estimatedReactions of sweet corn hybrids

yield reductions)**R MR M MS S

0-10% (3%) 0.63 0.26 0.11 0.11 0.11

10-20% (9%) 0.37 0.47 0.16 0.11 0

20-30% (15%) 00.26 0.63 0.26 0.16

30-40% (21%) 0 0 0.11 0.32 0.26

40-50% (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

slide72

Common rust on sweet corn

matures ~ August 5 in central Illinois

  • 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
slide73

Rp-resistance

Bands of chlorotic flecks

(qualitative reaction)

slide74

Single Rp genes

in the Rp1 region

Rp1-D

Rp-G

Rp1-E (Rp1-I, Rp1-K)

Rp1-M

Rp1-C (Rp1-N)

Rp1-A (Rp1-F)

slide76

Rp1D-resistant hybrid

Rock Falls, IL

September 1999

slide77

Rp1D-resistance

greenhouse

Sept. 1999

slide79

virulent

avirulent

slide80

Rp1-D resistance

Los Mochis, Mexico

March 2000

slide81

Future of Rp resistance

more confusing - variable

  • one Rp hybrid may be resistant
  • while another Rp hybrid may be
  • completely susceptible
  • different Rp genes
slide82

Future of Rp resistance

more confusing - variable

  • 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
slide83

Future of Rp resistance

more confusing - variable

  • an Rp hybrid may be resistant
  • at one location but susceptible
  • in another area
  • different isolates of rust
slide84

Future of Rp resistance

more confusing - variable

  • 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
slide85

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
slide86

Fungicides

  • EBDCs
  • TILT
  • strobilurins
  • (QUADRIS, F-500)
slide87

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)

slide88

Strobilurins

may change use of fungicides

on sweet corn

  • more efficacious
  • may have different thresholds ?
slide91

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

slide97

Sterling

Rust fungicide trial - 2001

slide98

Tentative conclusions

  • Thresholds for strobilurins
  • probably will be in the 5% to 15%
  • range
  • (compared to 1 to 2% for Tilt or EBDCs)
jerald pataky department of crop sciences university of illinois
Jerald Pataky

Department of Crop Sciences

University of Illinois

j-pataky@uiuc.edu

www.sweetcorn.uiuc.edu