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Diseases of Crops > Corn Diseases > Flashcards

Corn Diseases Flashcards

1
Q

What is the causal agent of Northern corn leaf blight?

A

Exserohilum turcicum (a fungus)

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2
Q

What is Exserohilum turcicum?

A

The causal agent of northern corn leaf blight

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3
Q

Describe the shape of the northern corn leaf blight legions

A

The legions are elongated, can cross the veins on leaves, 1 to 6 inches in length and cigar-shaped

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4
Q

What legion will always be present with northern corn leaf blight?

A

The cigar-shaped legion

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5
Q

List four disease management strategies for northern corn leaf blight

A

Resistant hybrids
Crop rotation
Tillage
Fungicides

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6
Q

What is the causal agent of southern corn leaf blight?

A

Cochliobolus heterostrophus (a fungus)

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7
Q

What is Cochliobolus heterostrophus?

A

The causal agent of southern corn leaf blight

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8
Q

What is a symptom of southern corn leaf blight?

A

Legions are elongated, tan, between veins on leaves

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9
Q

When does southern corn leaf blight occur?

A

From mid-whorl up to maturity

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10
Q

What conditions favor southern corn leaf blight?

A

Warm temps 70-90
Wet Conditions
Monocrops
Reduced tillage or no till

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11
Q

List four disease management strategies for southern corn leaf blight

A

Resistant hybrids
Crop rotation
Tillage
Fungicides

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12
Q

When does gray leaf spot occur?

A

at any time during the growing season

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13
Q

What conditions favor gray leaf spot?

A

continuous corn with stubble in the field
warm and humid weather
wet plants for at least 11-13 hours

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14
Q

List four disease management strategies for gray leaf spot

A

Resistant hybrids
Crop rotation
Tillage
Fungicides

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15
Q

When does purple leaf sheath occur?

A

During reproductive growth stages after tasseling

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16
Q

What conditions favor purple leaf sheath occurance?

A

Warm and humid weather

Pivot irrigation

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17
Q

What is the alternative name for purple leaf sheath?

A

Yeast spot

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18
Q

What is Ustilago maydis?

A

Common smut

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19
Q

What is the causal agent of common smut?

A

Ustilago maydis (a fungus)

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20
Q

Where does Ustilago maydis (common smut) overwinter?

A

in crop debris or soil (teliospores)

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21
Q

Where can Ustilago maydis (common smut) be found?

A

everywhere corn is grown

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22
Q

How does Ustilago maydis (common smut) enter the plant?

A

penetration through wounds

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23
Q

What is the main symptom of Ustilago maydis (common smut)?

A

Smut galls - on ears, leaves, stalk, or tassels

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24
Q

Is Ustilago maydis (common smut) edible?

A

Yes, it is a delicacy in Mexico.

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25
Q

Where do common smut galls develop on the plant?

A

on ears, leaves, stalk, or tassels

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26
Q

When does Ustilago maydis (common smut) occur throughout the year?

A

At any time during the growing season

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27
Q

What conditions favor Ustilago maydis (common smut) development?

A

Hail, wind, insect, herbicide, or mechanical injury of young growing tissues
Rainy wet weather
Poor pollination
Excessive nitrogen fertilizer

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28
Q

What fertilizer increases risk of Ustilago maydis (common smut)?

A

Nitrogen

29
Q

List four disease management strategies for Ustilago maydis (common smut)

A

Resistant hybrids
Crop rotation
Proper soil fertility
Limit plant damage

30
Q

Is Goss’s Wilt seedborne?

A

Yes

31
Q

What type of organism causes goss’s wilt?

A

bacteria

32
Q

List four disease management strategies for Goss’s wilt

A

Resistant hybrids
Crop rotation
Bury residue
Limit plant damage

33
Q

List two symptoms of Diplodia ear rot.

A

Infection begins at the base of the ear

The ear becomes bleached and brown

34
Q

What pathogen causes diplodia ear rot?

A

Stenocarpella (Diplodia) maydis

35
Q

What is Stenocarpella (Diplodia) maydis?

A

the pathogen that causes diplodia ear rot

36
Q

When does diplodia ear rot occur?

A

after flowering

37
Q

What conditions favor diplodia ear rot? (4)

A

Ears are most vulnerable for three weeks after silking
Warm and wet weather after silking
Limit plant damage from birds and insects
Continuous corn

38
Q

What pathogen causes diplodia stalk rot?

A

Stenocarpella maydis (the same pathogen that causes diplodia ear rot)

39
Q

When do Aspergillus ear diseases occur?

A

Anytime after the ear emerges, can also develop in post-harvest grain storage

40
Q

What pathogen type is aspergillus?

A

fungus

41
Q

Does aspergillus occur more in wet or dry years?

A

dry

42
Q

Define aflatoxin

A

a toxin produced as a result of an infection of the developing corn grain by a fungus from the genus Aspergillus

43
Q

What two species of Aspergillus produce aflatoxin in corn?

A

A. flavus

A. parasiticus

44
Q

What is the most potent carcinogen?

A

Aflatoxins

45
Q

What reduces the likelihood of aflatoxins?

A

reduce plant stress
harvest corn early and dry quickly
avoid damaged kernels
store at 12% moisture

46
Q

What percent moisture should corn be stored at?

A

12%

47
Q

How many parts per billion (ppb) of aflatoxin are allowed for animal feed intended for immature animals, dairy animals, or unknown destinations?

A

20

48
Q

What is the pathogen that causes common rust?

A

Puccinia sorghi

49
Q

What is the pathogen that causes southern rust?

A

Puccinia polysora

50
Q

What is Puccinia sorghi?

A

the pathogen that causes common rust

51
Q

What is Puccinia polysora?

A

the pathogen that causes southern rust

52
Q

Is common rust a warm or cool weather disease?

A

cool

53
Q

Is southern rust a warm or cool weather disease?

A

warm

54
Q

How does common rust enter the plant?

A

penetration via stomata on upper or lower leaf surface

55
Q

Does the postule membrane of common rust break easily?

A

yes

56
Q

Does the postule membrane of southern rust break easily?

A

no

57
Q

How many days does it take to observe symptoms of common rust?

A

2-3 days

58
Q

How many days does it take to observe symptoms of southern rust?

A

6-7 days

59
Q

Does common rust infect both sides of the leaf?

A

Yes

60
Q

When does rupture of the postules occur in the development of common rust?

A

Early

61
Q

How many spore types are present in the complete life cycle of common rust?

A

5 spore types

62
Q

Do all spore stages of common rust occur in USA?

A

No

63
Q

Do all spore stages of common rust occur in Mexico?

A

Yes

64
Q

How many hosts does common rust need to complete its life cycle?

A

2

65
Q

Does southern rust infect both sides of the leaf?

A

Yes, but mostly on the upper leaf surface

66
Q

What is the easiest way to distinguish common rust and southern rust?

A

Common rust infects both sides of the leaves,

Southern rust infects mostly the upper leaf surface

67
Q

List two methods of controlling rust diseases

A

Plant resistant hybrids

Fungicide applications

68
Q

Which fungicide is recommended for treatment of rust diseases after they occur?

A

triazole

Diseases of Crops (11 decks)

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