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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
Where do common smut galls develop on the plant?
on ears, leaves, stalk, or tassels
26
When does Ustilago maydis (common smut) occur throughout the year?
At any time during the growing season
27
What conditions favor Ustilago maydis (common smut) development?
Hail, wind, insect, herbicide, or mechanical injury of young growing tissues Rainy wet weather Poor pollination Excessive nitrogen fertilizer
28
What fertilizer increases risk of Ustilago maydis (common smut)?
Nitrogen
29
List four disease management strategies for Ustilago maydis (common smut)
Resistant hybrids Crop rotation Proper soil fertility Limit plant damage
30
Is Goss's Wilt seedborne?
Yes
31
What type of organism causes goss's wilt?
bacteria
32
List four disease management strategies for Goss's wilt
Resistant hybrids Crop rotation Bury residue Limit plant damage
33
List two symptoms of Diplodia ear rot.
Infection begins at the base of the ear | The ear becomes bleached and brown
34
What pathogen causes diplodia ear rot?
Stenocarpella (Diplodia) maydis
35
What is Stenocarpella (Diplodia) maydis?
the pathogen that causes diplodia ear rot
36
When does diplodia ear rot occur?
after flowering
37
What conditions favor diplodia ear rot? (4)
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
What pathogen causes diplodia stalk rot?
Stenocarpella maydis (the same pathogen that causes diplodia ear rot)
39
When do Aspergillus ear diseases occur?
Anytime after the ear emerges, can also develop in post-harvest grain storage
40
What pathogen type is aspergillus?
fungus
41
Does aspergillus occur more in wet or dry years?
dry
42
Define aflatoxin
a toxin produced as a result of an infection of the developing corn grain by a fungus from the genus Aspergillus
43
What two species of Aspergillus produce aflatoxin in corn?
A. flavus | A. parasiticus
44
What is the most potent carcinogen?
Aflatoxins
45
What reduces the likelihood of aflatoxins?
reduce plant stress harvest corn early and dry quickly avoid damaged kernels store at 12% moisture
46
What percent moisture should corn be stored at?
12%
47
How many parts per billion (ppb) of aflatoxin are allowed for animal feed intended for immature animals, dairy animals, or unknown destinations?
20
48
What is the pathogen that causes common rust?
Puccinia sorghi
49
What is the pathogen that causes southern rust?
Puccinia polysora
50
What is Puccinia sorghi?
the pathogen that causes common rust
51
What is Puccinia polysora?
the pathogen that causes southern rust
52
Is common rust a warm or cool weather disease?
cool
53
Is southern rust a warm or cool weather disease?
warm
54
How does common rust enter the plant?
penetration via stomata on upper or lower leaf surface
55
Does the postule membrane of common rust break easily?
yes
56
Does the postule membrane of southern rust break easily?
no
57
How many days does it take to observe symptoms of common rust?
2-3 days
58
How many days does it take to observe symptoms of southern rust?
6-7 days
59
Does common rust infect both sides of the leaf?
Yes
60
When does rupture of the postules occur in the development of common rust?
Early
61
How many spore types are present in the complete life cycle of common rust?
5 spore types
62
Do all spore stages of common rust occur in USA?
No
63
Do all spore stages of common rust occur in Mexico?
Yes
64
How many hosts does common rust need to complete its life cycle?
2
65
Does southern rust infect both sides of the leaf?
Yes, but mostly on the upper leaf surface
66
What is the easiest way to distinguish common rust and southern rust?
Common rust infects both sides of the leaves, | Southern rust infects mostly the upper leaf surface
67
List two methods of controlling rust diseases
Plant resistant hybrids | Fungicide applications
68
Which fungicide is recommended for treatment of rust diseases after they occur?
triazole

Diseases of Crops (11 decks)

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