The symptoms, factors favoring infection, prediction and control measures for Cercospora leaf spot of sugar beet is described in this 2007 NebGuide

Harveson, R. M.

English

DigitalCommons@University of Nebraska

University of Nebraska - LincolnDigitalCommons@University of Nebraska - LincolnHistorical Materials from University of Nebraska-Lincoln Extension Extension2007G07-1753 Cercospora Leaf Spot of Sugar BeetR. M. HarvesonUniversity of Nebraska-Lincoln, rharveson2@unl.eduFollow this and additional works at: http://digitalcommons.unl.edu/extensionhistPart of the Curriculum and Instruction CommonsThis Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted forinclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University ofNebraska - Lincoln.Harveson, R. M., "G07-1753 Cercospora Leaf Spot of Sugar Beet" (2007). Historical Materials from University of Nebraska-LincolnExtension. 2811.http://digitalcommons.unl.edu/extensionhist/2811G1753Cercospora Leaf Spot of Sugar BeetRobert M. Harveson, Extension Plant PathologistThe symptoms, factors favoring infection, predic-tion and control measures for Cercospora leaf spot of sugar beet is described in this NebGuide.IntroductionCercospora leaf spot (CLS) is the most serious and de-structive foliar disease of sugar beet in the Central High Plains of western Nebraska, northeastern Colorado and southeastern Wyoming. This disease is caused by the airborne fungus Cercospora beticola. CLS has a long history and has played a shaping role in sugar beet cultivation throughout the central and eastern production areas of the United States. Years ago this disease became a major limiting factor in early Nebraska production areas, and was a primary reason for the shift of sugar beet production from eastern portions of the state to the west in the 1960s. The disease was of minor importance in western Nebraska until the mid-1980s, when it began to cause significant yield and sugar reductions throughout the North Platte River Valley.Losses due to this disease can approach 40 percent, and are represented by both root tonnage and sugar percentage in roots. Beets with low sugar levels do not store well, and losses in storage result from increased storage decay. Profit-able yields are additionally reduced due to greater levels of impurities in roots and increased sugar loss to molasses during processing. Signs and Symptoms Individual leaf spots initially occur on older leaves and then progress to younger leaves. Individual lesions are approxi-mately one-eighth inch in diameter with ash-colored centers and purple to brown borders, and are circular to oval shaped (Figure 1A). Cercospora leaf spot is distinguished from other leaf diseases (Alternaria, Phoma and bacterial leaf spots) by their smaller size and shape (Figure 2), and the presence of black spore-bearing structures, called pseudostromata, that form in the center of the lesions (Figure 3). These structures are easily seen as black dots with the aid of a hand lens (10X magnification) (Figure 4). During periods of high humidity the black dots will be covered with colorless fuzzy masses of spores resembling cobwebs (Figure 5), which serve as the source for secondary infections within fields that season. As disease progresses, heavily infected leaves initially turn yellow (Figure 6). Individual spots may coalesce and form larger areas of dead tissue (Figure 1B), causing severely infected leaves to wither and die (Figure 7). Severely diseased plants can be viewed at a distance when dead or dying leaves appear above the canopy, giving a burned or scorched appear-ance (Figure 8). Disease often is unevenly distributed in fields usually being more severe in protected areas adjacent to windbreaks formed by trees or taller crops, or other areas that may result in higher levels of humidity.Conditions Favoring Cercospora  Leaf SpotThe development of disease is highly dependent upon the presence of suscep-tible cultivars, adequate inoculum and environmental conditions characterized by periods of high humidity or leaf wetness periods longer than 11 hours and warm temperatures (>60oF). Since leaf wetness is not routinely measured, relative humid-ity above 90 percent humidity can be used as a substitute. All of these factors must be present simultaneously for disease to begin and progress. For example, if a susceptible cultivar and adequate inoculum are present, but temperatures are too cold or warm or no Figure 1A-B. Individual ash-colored circular lesions with dark brown borders (A).  Advance infec-tion with coalescing of individual lesions (B).Figure 2. Comparison of symptoms among several common foliar dis-eases of sugar beets. From left to right: Cercospora, Alternaria, Phoma and bacterial leaf spots.Figure 3. Microscopic side view of pseudostromata (spore-bearing structures) with spores attached (left) and empty (right).Figure 4. Macroscopic view of pseudostromata within lesion centers. Figure 5. Microscopic top view of pseudostromata without spores (left) and with spores (“cobwebs”).moisture is on leaf surfaces, then infection cannot occur.Generally, temperatures at night in western Nebraska are near the lower limits favoring disease development, but leaf wetness does occur (particularly with sprinkler irrigation). Very little infection will occur below 60oF or during periods of less than 11 hours of leaf wetness. Greater spore germination and leaf infection generally occurs when night temperatures exceed 60oF and day temperatures are between 80o and 90oF.Initial inoculum potential depends on the survival of the fungus spores and spore-bearing structures (psuedostromata) from the previous year’s infected crop residue. Plants related to sugar beets such as weeds (lamb’s quarters and pigweed), and vegetable crops (chard, spinach, table beets) also may be a source of inoculum for infection in sugar beet. New spores produced under humid conditions on surviving pseudostromata can be carried by wind or splashing water to infect adjacent leaves and plants. Under favorable conditions in mid-summer, inoculum levels continue to increase and the life cycle of the disease may be completed within 10 days. Whenever leaf spots are observed, infection has taken place sometime in the previous 7-10 days, thus total infection present during favorable conditions is greater than what would be visible for up to 7 days. Predicting Cercospora Leaf SpotBecause of the strict environmental conditions needed for infection to occur, the disease is well suited to prediction of time periods when outbreaks would most likely be favorable. The prediction system is an estimate of the potential for disease development based on the relative humidity and temperature measured within fields. This system was developed in the late 1980s by UNL scientists, Albert Weiss and Eric Kerr, and still is being used today at the Panhandle Research and Extension Center. Over the last eight years the forecasting system has been a collaborative effort between UNL, Western Sugar Cooperative agriculturalists and independent consultants. It has utilized up to 14 sites per season located in Nebraska, Colorado, Wyoming and Montana. Results are then collated by the plant pathology program in Scottsbluff and disseminated to more than 40 sources, including consultants, researchers and media (Web, print, television and radio). This system assumes that a susceptible host and sufficient inoculum are present. Based on hours of leaf wetness or high relative humidity (>90 percent) and temperature during this period, a daily infection value (DIV) is determined (Table I). If the two-day sum of the DIVs is seven or greater, there is a strong potential for infection and further disease develop-ment. If the sum is less than six, there is little likelihood of infection. The following example will illustrate how to use the Table I information. Assume that on Day 1 there were 13 hours of leaf wetness and the mean temperature during this period was 63oF. On Day 2, there were 15 hours of leaf wetness with a mean temperature of 65oF. The DIV for Day (Figure 9). Some of the most susceptible cultivars may have high yield potential in the absence of leaf spot, but fungicidal applications will be necessary for satisfactory yields when disease becomes severe.• Fungicidal sprays may be necessary in fields where inoculum has carried over from the previous year, sus-ceptible cultivars are grown, or environmental conditions are favorable for infection. The first symptoms of CLS in western Nebraska usually are observed in mid- to late July or early August. Since infections may already be established before symptoms appear, it is important to monitor environmental conditions daily for detecting favorable periods of infection after symptoms become apparent. Fungicides should then be applied after favor-able conditions occur to prohibit rapid disease progress in these situations.• Many different fungicides are registered for management of CLS. The most commonly used products for CLS management are listed in Table II. The majority of these fungicides are systemic in plants, and thus provide lon-ger periods of protection than the protectant fungicides. Triphenyltin hydroxide is the protectant fungicide that is used to the greatest extent. Mancozeb, and other dithio-carbamates are also examples of protectant fungicides, but rarely are used today in sugar beet production for CLS management.Figure 6. Cercospora-infected leaves. Leaf at left is beginning to yellow and die.Figure 7. Severe infection with multiple leaves completely dead and covered with masses of coalesced lesions. New growth emerg-ing is unaffected.Figure 8. Severe infection from a distance, giving plants the appearance of being burned.Figure 9. Benefits of genetic resistance to the pathogen after a severe CLS epidemic. Plants at left are susceptible and those at right are tolerant.1 was three while on Day 2 it was four. The sum of these two days was seven, resulting in conditions that would favor infection. If no symptoms were observed on leaves, then the DIV sum indicates that careful scouting is advised; if symptoms were present, a fungicide application would be warranted. If on Day 3, there were 12 hours of leaf wetness and the temperature during this period was 62oF, then the DIV sum for Days and 2 and 3 is 4+0=4, and no action would be necessary.Disease Management • Cultivation and rotation can reduce levels of overwinter-ing inoculum and at least a three-year rotation is needed to reduce quantities of infested residue from a severely diseased crop. Tillage reduces inoculum levels by burying sugar beet residue, which encourages tissue decomposi-tion, and reduces spore dispersal into a new crop. To minimize chances of spore dispersal into new crops, susceptible sugar beet cultivars should not be planted within 100 yards of last year’s severely infected crop.• Using leaf spot-tolerant cultivars can significantly reduce disease severity and yield losses. Many new resistant cultivars are continually being developed that also are regionally adapted and contain multiple disease resistant packages. Resistant cultivars allow disease progress to develop more slowly, even under favorable conditions Table I. Daily infection values based on number of hours of high relative humidity (> 90 percent) or leaf wetness and concurrent average temperature during this period. Hours       Daily infection values 24 1 2 4 5 5 6 6 6 6 6 6 6 23 1 2 3 4 5 6 6 6 6 6 6 6 22 1 1 3 4 5 6 6 6 6 6 6 6 21 0 1 2 4 4 5 5 5 5 5 6 6 20 0 1 2 3 4 5 5 5 5 5 5 5 19 0 0 1 3 4 5 5 5 5 5 5 5 18 0 0 1 2 3 4 4 4 4 4 4 5 17 0 0 1 2 3 4 4 4 4 4 4 4 16 0 0 0 2 3 4 4 4 4 4 4 4 15 0 0 0 1 3 4 4 4 4 4 4 4 14 0 0 0 1 3 3 3 3 3 3 3 4 13 0 0 0 0 3 3 3 3 3 3 3 3 12 0 0 0 0 2 3 3 3 3 3 3 3 11 0 0 0 0 2 3 3 3 3 3 3 3 10 0 0 0 0 2 2 2 2 2 2 2 3   9 0 0 0 0 2 2 2 2 2 2 2 2   8 0 0 0 0 1 2 2 2 2 2 2 2   7 0 0 0 0 1 2 2 2 2 2 2 2   6 0 0 0 0 0 1 1 1 1 1 1 1   5 0 0 0 0 0 1 1 1 1 1 1 1   4 0 0 0 0 0 1 1 1 1 1 1 1   3 0 0 0 0 0 0 0 0 0 0 0 1   2 0 0 0 0 0 0 0 0 0 0 0 0  59 60 61 62 63 64 65 66 67 68 69 70 Average temperature (oF) during periods of leaf wetness or high relative humidityTable II. Common fungicides registered for Cercospora leaf spot management in sugar beetsProduct Fungicide Fungicide Class Pre-harvest interval (days)Dithane Mancozeb Ethylenebisdithiocarbamate (EBDC) 14SuperTin 80WP Triphenyltin hydroxide Organometalic 21Headline Pyraclostrobin Strobilurin   7Topsin M Thiophanate methyl Benzamidazol 21Eminent Tetraconazole Triazol-sterol inhibiting 14• The greatest disadvantage of the systemic fungicides is that strains of the pathogen have developed resistance to them, particularly those in the benzamidazole class such as thiophanate methyl (Topsin M). Other commonly used systemic fungicides include Eminent, Headline and Flint. The most important aspect to remember when using these products is to rotate fungicides with differing modes of action to avoid development of resistance in the pathogen. For example, a first application of Headline (strobilurin class) or Eminent (triazol class) should be followed by Super Tin. If a third application is needed, use either Headline of Eminent, whichever one was not used in the first application. • Best results for managing this disease in this region are achieved by integrating fungicide applications based on the Cercospora Alert system with the use of resistant cultivars and prudent cultural practices such as rotation and cultivation to reduce levels of infested residue.Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln cooperating with the Counties and the United States Department of Agriculture.University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policiesof the University of Nebraska–Lincoln and the United States Department of Agriculture.© 2007, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.AcknowledgmentThe author would like to recognize the work and contri-butions of the previous UNL authors of this publication, Eric D. Kerr, former Extension Plant Pathologist; and Albert Weiss, Extension Agricultural Climatologist.Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by University of Nebraska–Lincoln Extension is implied for those mentioned.UNL Extension publications are available online at http://extension.unl.edu/publications.Index: Plant DiseasesSugar BeetIssued August 2007

G07-1753 Cercospora Leaf Spot of Sugar Beet

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University of Nebraska - Lincoln
DigitalCommons@University of Nebraska - Lincoln
Historical Materials from University of Nebraska-
Lincoln Extension Extension
2007
G07-1753 Cercospora Leaf Spot of Sugar Beet
R. M. Harveson
University of Nebraska-Lincoln, rharveson2@unl.edu
Follow this and additional works at: http://digitalcommons.unl.edu/extensionhist
Part of the Curriculum and Instruction Commons
This Article is brought to you for free and open access by the Extension at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for
inclusion in Historical Materials from University of Nebraska-Lincoln Extension by an authorized administrator of DigitalCommons@University of
Nebraska - Lincoln.
Harveson, R. M., "G07-1753 Cercospora Leaf Spot of Sugar Beet" (2007). Historical Materials from University of Nebraska-Lincoln
Extension. 2811.
http://digitalcommons.unl.edu/extensionhist/2811
G1753
Cercospora Leaf Spot of Sugar Beet
Robert M. Harveson, Extension Plant Pathologist
The symptoms, factors favoring infection, predic-
tion and control measures for Cercospora leaf spot of 
sugar beet is described in this NebGuide.
Introduction
Cercospora leaf spot (CLS) is the most serious and de-
structive foliar disease of sugar beet in the Central High Plains 
of western Nebraska, northeastern Colorado and southeastern 
Wyoming. This disease is caused by the airborne fungus 
Cercospora beticola. CLS has a long history and has played 
a shaping role in sugar beet cultivation throughout the central 
and eastern production areas of the United States. Years ago 
this disease became a major limiting factor in early Nebraska 
production areas, and was a primary reason for the shift of 
sugar beet production from eastern portions of the state to 
the west in the 1960s. The disease was of minor importance 
in western Nebraska until the mid-1980s, when it began to 
cause significant yield and sugar reductions throughout the 
North Platte River Valley.
Losses due to this disease can approach 40 percent, and 
are represented by both root tonnage and sugar percentage 
in roots. Beets with low sugar levels do not store well, and 
losses in storage result from increased storage decay. Profit-
able yields are additionally reduced due to greater levels 
of impurities in roots and increased sugar loss to molasses 
during processing. 
Signs and Symptoms 
Individual leaf spots initially occur on older leaves and 
then progress to younger leaves. Individual lesions are approxi-
mately one-eighth inch in diameter with ash-colored centers 
and purple to brown borders, and are circular to oval shaped 
(Figure 1A). Cercospora leaf spot is distinguished from other 
leaf diseases (Alternaria, Phoma and bacterial leaf spots) by 
their smaller size and shape (Figure 2), and the presence of 
black spore-bearing structures, called pseudostromata, that 
form in the center of the lesions (Figure 3). These structures 
are easily seen as black dots with the aid of a hand lens (10X 
magnification) (Figure 4). During periods of high humidity 
the black dots will be covered with colorless fuzzy masses 
of spores resembling cobwebs (Figure 5), which serve as the 
source for secondary infections within fields that season. 
As disease progresses, heavily infected leaves initially 
turn yellow (Figure 6). Individual spots may coalesce and 
form larger areas of dead tissue (Figure 1B), causing severely 
infected leaves to wither and die (Figure 7). Severely diseased 
plants can be viewed at a distance when dead or dying leaves 
appear above the canopy, giving a burned or scorched appear-
ance (Figure 8). Disease often is unevenly distributed in fields 
usually being more severe in protected areas 
adjacent to windbreaks formed by trees or 
taller crops, or other areas that may result 
in higher levels of humidity.
Conditions Favoring Cercospora  
Leaf Spot
The development of disease is highly 
dependent upon the presence of suscep-
tible cultivars, adequate inoculum and 
environmental conditions characterized by 
periods of high humidity or leaf wetness 
periods longer than 11 hours and warm 
temperatures (>60oF). Since leaf wetness 
is not routinely measured, relative humid-
ity above 90 percent humidity can be used 
as a substitute. All of these factors must be 
present simultaneously for disease to begin 
and progress. For example, if a susceptible 
cultivar and adequate inoculum are present, 
but temperatures are too cold or warm or no 
Figure 1A-B. Individual ash-colored circular lesions with dark brown borders (A).  Advance infec-
tion with coalescing of individual lesions (B).
Figure 2. Comparison of symptoms among several common foliar dis-
eases of sugar beets. From left to right: Cercospora, Alternaria, 
Phoma and bacterial leaf spots.
Figure 3. Microscopic side view of pseudostromata (spore-bearing 
structures) with spores attached (left) and empty (right).
Figure 4. Macroscopic view of pseudostromata within lesion centers. Figure 5. Microscopic top view of pseudostromata without spores (left) 
and with spores (“cobwebs”).
moisture is on leaf surfaces, then infection cannot occur.
Generally, temperatures at night in western Nebraska are 
near the lower limits favoring disease development, but leaf 
wetness does occur (particularly with sprinkler irrigation). Very 
little infection will occur below 60oF or during periods of less 
than 11 hours of leaf wetness. Greater spore germination and 
leaf infection generally occurs when night temperatures exceed 
60oF and day temperatures are between 80o and 90oF.
Initial inoculum potential depends on the survival of the 
fungus spores and spore-bearing structures (psuedostromata) 
from the previous year’s infected crop residue. Plants related 
to sugar beets such as weeds (lamb’s quarters and pigweed), 
and vegetable crops (chard, spinach, table beets) also may be 
a source of inoculum for infection in sugar beet. New spores 
produced under humid conditions on surviving pseudostromata 
can be carried by wind or splashing water to infect adjacent 
leaves and plants. Under favorable conditions in mid-summer, 
inoculum levels continue to increase and the life cycle of the 
disease may be completed within 10 days. Whenever leaf spots 
are observed, infection has taken place sometime in the previous 
7-10 days, thus total infection present during favorable conditions 
is greater than what would be visible for up to 7 days.
 
Predicting Cercospora Leaf Spot
Because of the strict environmental conditions needed for 
infection to occur, the disease is well suited to prediction of 
time periods when outbreaks would most likely be favorable. 
The prediction system is an estimate of the potential for disease 
development based on the relative humidity and temperature 
measured within fields. This system was developed in the late 
1980s by UNL scientists, Albert Weiss and Eric Kerr, and still 
is being used today at the Panhandle Research and Extension 
Center. Over the last eight years the forecasting system has 
been a collaborative effort between UNL, Western Sugar 
Cooperative agriculturalists and independent consultants. It 
has utilized up to 14 sites per season located in Nebraska, 
Colorado, Wyoming and Montana. Results are then collated by 
the plant pathology program in Scottsbluff and disseminated 
to more than 40 sources, including consultants, researchers 
and media (Web, print, television and radio). 
This system assumes that a susceptible host and sufficient 
inoculum are present. Based on hours of leaf wetness or high 
relative humidity (>90 percent) and temperature during this 
period, a daily infection value (DIV) is determined (Table I). 
If the two-day sum of the DIVs is seven or greater, there is 
a strong potential for infection and further disease develop-
ment. If the sum is less than six, there is little likelihood of 
infection. 
The following example will illustrate how to use the 
Table I information. Assume that on Day 1 there were 13 
hours of leaf wetness and the mean temperature during this 
period was 63oF. On Day 2, there were 15 hours of leaf 
wetness with a mean temperature of 65oF. The DIV for Day 
(Figure 9). Some of the most susceptible cultivars may 
have high yield potential in the absence of leaf spot, but 
fungicidal applications will be necessary for satisfactory 
yields when disease becomes severe.
• Fungicidal sprays may be necessary in fields where 
inoculum has carried over from the previous year, sus-
ceptible cultivars are grown, or environmental conditions 
are favorable for infection. The first symptoms of CLS 
in western Nebraska usually are observed in mid- to late 
July or early August. Since infections may already be 
established before symptoms appear, it is important to 
monitor environmental conditions daily for detecting 
favorable periods of infection after symptoms become 
apparent. Fungicides should then be applied after favor-
able conditions occur to prohibit rapid disease progress 
in these situations.
• Many different fungicides are registered for management 
of CLS. The most commonly used products for CLS 
management are listed in Table II. The majority of these 
fungicides are systemic in plants, and thus provide lon-
ger periods of protection than the protectant fungicides. 
Triphenyltin hydroxide is the protectant fungicide that is 
used to the greatest extent. Mancozeb, and other dithio-
carbamates are also examples of protectant fungicides, 
but rarely are used today in sugar beet production for 
CLS management.
Figure 6. Cercospora-infected leaves. Leaf at left is beginning to yellow 
and die.
Figure 7. Severe infection with multiple leaves completely dead and 
covered with masses of coalesced lesions. New growth emerg-
ing is unaffected.
Figure 8. Severe infection from a distance, giving plants the appearance 
of being burned.
Figure 9. Benefits of genetic resistance to the pathogen after a severe 
CLS epidemic. Plants at left are susceptible and those at right 
are tolerant.
1 was three while on Day 2 it was four. The sum of these 
two days was seven, resulting in conditions that would favor 
infection. If no symptoms were observed on leaves, then the 
DIV sum indicates that careful scouting is advised; if symptoms 
were present, a fungicide application would be warranted. If on 
Day 3, there were 12 hours of leaf wetness and the temperature 
during this period was 62oF, then the DIV sum for Days and 2 
and 3 is 4+0=4, and no action would be necessary.
Disease Management 
• Cultivation and rotation can reduce levels of overwinter-
ing inoculum and at least a three-year rotation is needed 
to reduce quantities of infested residue from a severely 
diseased crop. Tillage reduces inoculum levels by burying 
sugar beet residue, which encourages tissue decomposi-
tion, and reduces spore dispersal into a new crop. To 
minimize chances of spore dispersal into new crops, 
susceptible sugar beet cultivars should not be planted 
within 100 yards of last year’s severely infected crop.
• Using leaf spot-tolerant cultivars can significantly reduce 
disease severity and yield losses. Many new resistant 
cultivars are continually being developed that also are 
regionally adapted and contain multiple disease resistant 
packages. Resistant cultivars allow disease progress to 
develop more slowly, even under favorable conditions 
Table I. Daily infection values based on number of hours of high relative humidity (> 90 percent) or leaf wetness and concurrent average temperature 
during this period.
 Hours       Daily infection values
 24 1 2 4 5 5 6 6 6 6 6 6 6
 23 1 2 3 4 5 6 6 6 6 6 6 6
 22 1 1 3 4 5 6 6 6 6 6 6 6
 21 0 1 2 4 4 5 5 5 5 5 6 6
 20 0 1 2 3 4 5 5 5 5 5 5 5
 19 0 0 1 3 4 5 5 5 5 5 5 5
 18 0 0 1 2 3 4 4 4 4 4 4 5
 17 0 0 1 2 3 4 4 4 4 4 4 4
 16 0 0 0 2 3 4 4 4 4 4 4 4
 15 0 0 0 1 3 4 4 4 4 4 4 4
 14 0 0 0 1 3 3 3 3 3 3 3 4
 13 0 0 0 0 3 3 3 3 3 3 3 3
 12 0 0 0 0 2 3 3 3 3 3 3 3
 11 0 0 0 0 2 3 3 3 3 3 3 3
 10 0 0 0 0 2 2 2 2 2 2 2 3
   9 0 0 0 0 2 2 2 2 2 2 2 2
   8 0 0 0 0 1 2 2 2 2 2 2 2
   7 0 0 0 0 1 2 2 2 2 2 2 2
   6 0 0 0 0 0 1 1 1 1 1 1 1
   5 0 0 0 0 0 1 1 1 1 1 1 1
   4 0 0 0 0 0 1 1 1 1 1 1 1
   3 0 0 0 0 0 0 0 0 0 0 0 1
   2 0 0 0 0 0 0 0 0 0 0 0 0
  59 60 61 62 63 64 65 66 67 68 69 70
 Average temperature (oF) during periods of leaf wetness or high relative humidity
Table II. Common fungicides registered for Cercospora leaf spot management in sugar beets
Product Fungicide Fungicide Class Pre-harvest interval (days)
Dithane Mancozeb Ethylenebisdithiocarbamate (EBDC) 14
SuperTin 80WP Triphenyltin hydroxide Organometalic 21
Headline Pyraclostrobin Strobilurin   7
Topsin M Thiophanate methyl Benzamidazol 21
Eminent Tetraconazole Triazol-sterol inhibiting 14
• The greatest disadvantage of the systemic fungicides is 
that strains of the pathogen have developed resistance to 
them, particularly those in the benzamidazole class such 
as thiophanate methyl (Topsin M). Other commonly used 
systemic fungicides include Eminent, Headline and Flint. 
The most important aspect to remember when using these 
products is to rotate fungicides with differing modes of 
action to avoid development of resistance in the pathogen. 
For example, a first application of Headline (strobilurin 
class) or Eminent (triazol class) should be followed by 
Super Tin. If a third application is needed, use either 
Headline of Eminent, whichever one was not used in the 
first application. 
• Best results for managing this disease in this region are 
achieved by integrating fungicide applications based on 
the Cercospora Alert system with the use of resistant 
cultivars and prudent cultural practices such as rotation 
and cultivation to reduce levels of infested residue.
Extension is a Division of the Institute of Agriculture and Natural Resources at the University of Nebraska–Lincoln 
cooperating with the Counties and the United States Department of Agriculture.
University of Nebraska–Lincoln Extension educational programs abide with the nondiscrimination policies
of the University of Nebraska–Lincoln and the United States Department of Agriculture.
© 2007, The Board of Regents of the University of Nebraska on behalf of the University of Nebraska–Lincoln Extension.  All rights reserved.
Acknowledgment
The author would like to recognize the work and contri-
butions of the previous UNL authors of this publication, Eric 
D. Kerr, former Extension Plant Pathologist; and Albert Weiss, 
Extension Agricultural Climatologist.
Reference to commercial products or trade names 
is made with the understanding that no discrimination 
is intended of those not mentioned and no endorsement 
by University of Nebraska–Lincoln Extension is implied 
for those mentioned.
UNL Extension publications are available online 
at http://extension.unl.edu/publications.
Index: Plant Diseases
Sugar Beet
Issued August 2007


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G07-1753 Cercospora Leaf Spot of Sugar Beet

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