Quick Facts...
- Sugar beets are an important cash crop in northeastern Colorado with
approximately 30,000 acres planted and 650,000 tons harvested in 2003.
- Fusarium yellows, also known as Fusarium wilt, is a fungal disease
(caused by Fusarium oxysporum Schlechtend.:Fr.) with presumed
host-specific strains that attack sugar beet (F. o. f. sp. betae)
or dry bean (F. o. f. sp. phaseoli).
- Fusarium wilt losses in dry bean fields can vary from a trace to more
than 30 percent crop loss; in addition seed size can be reduced 10 percent
to 15 percent.
The Central High Plains (Colorado, Nebraska and Wyoming) is among the
largest producer of dry edible beans and sugar beets in the United States.
Sugar beets are an important cash crop in northeastern Colorado with approximately
30,000 acres planted and 650,000 tons harvested in 2003. Approximately
250,000 acres of dry bean market types (pinto, great northern, light red
kidney) also are planted annually with a farm gate value that varies between
$75 and $150 million. With both sugar and dry bean processing plants in
Greeley and Fort Morgan, production is centered in northeast Colorado
counties. Many growers in this area grow both sugar beets and dry beans
in rotation, which may accentuate problems with soil-borne pathogens that
attack both crops.
Fusarium yellows, also known as Fusarium wilt, is a fungal
disease (caused by Fusarium oxysporum Schlechtend.:Fr.) with presumed
host-specific strains that attack sugar beet (F. o. f. sp. betae)
or dry bean (F. o. f. sp. phaseoli). Severely infected plants become
yellowed, wilted and die prematurely, which may cause yield reduction
or total crop loss. Because sugar beets and dry edible beans are commonly
grown in a short rotation of less than four years in the Central High
Plains, incidence and variability of the pathogens may have increased
in recent years. Problems may also have been aggravated by the regional
drought impact during 2001 to 2006. Fusarium wilt losses in dry bean fields
can vary from a trace to more than 30 percent crop loss; in addition seed
size can be reduced 10 percent to 15 percent. Reports from Wyoming indicate
that the disease has been found in more than 30 percent of sugar beet
fields with significant reduction in yield in various counties.
Problem and Cooperative Project
Because yield losses due to this disease vary from year
to year and are not easily measured, there has been little effort to develop
resistant sugar beet hybrids. Colorado State University personnel have
been incorporating disease resistance to local strains of the bean pathogen
into pinto bean varieties in recent years. Nonetheless, Fusarium yellows
continues to be a serious problem for growers throughout the Central Great
Plains, such as the Fort Morgan to Sedgwick area of Colorado. Additionally,
it is difficult to identify the different species of Fusarium using a
microscope and other laboratory procedures and impossible to determine
whether they are sugar beet or dry bean types without a greenhouse test
on the plants. Screening for Fusarium yellows requires precise and laborious
laboratory conditions to identify isolates and races of Fusarium oxysporum.
Evaluations are not always repeatable or accurate, even with replication;
however, recently, methods based on new biotechnologies have been used
to “fingerprint” isolates.
In 1997, a multi-disciplinary and multi-agency team of
scientists and industry collaborators joined to: 1) define the extent
of the disease in sugar beet and dry bean production areas, 2) collect
samples of diseased plants, 3) isolate and purify cultures of the pathogen,
4) conduct laboratory tests to study cultural and molecular variability,
5) initiate greenhouse studies to verify pathogenicity of fungal cultures
on diverse hosts and germplasm, and (6) develop tools based on new biotechnologies
to identify different isolates of the fungus. The ultimate goals of this
project are to provide updated disease management educational materials
for integrated pest management technology transfer and to identify resistant
parents that can be most effectively utilized by researchers involved
with germplasm improvement programs at Colorado State University and the
USDA.
Pathogen Survival and Variability
|
Figure 1: Sugar beet plant wilting caused by Fusarium Wilt
(photo by E.G. Ruppel, USDA ARS-retired).
|
The pathogen is a soil-borne fungus that survives as microscopic
spores (chlamydospores) which germinate and infect the sugar beet or bean
root under favorable conditions. The fungus invades water-conducting tissues
of the root and grows upward into leaf petioles and stems of sugar beet
and/or bean plants. Optimum conditions for infection are a temperature
of 80 degrees Farenheit or greater, combined with other stress factors
such as herbicide, fertilizer, salinity damage to roots, soil compaction,
moisture extremes, and poor water drainage.
Recent tests with a large collection of fungal isolates
from Colorado and Nebraska, detected a great deal of variability (low
to high) in the ability to cause disease within fungal isolates recovered
from sugar beet and dry bean plants. An isolate originally recovered from
an infected dry bean plant more than 10 years ago in Colorado has caused
serious disease symptoms to stressed sugar beet seedlings in a greenhouse
test, suggesting that some isolates of Fusarium may have a broader host
range than expected. This variability is being studied with various tools
in the laboratory, including molecular markers developed in this project.
Disease Symptoms
|
Figure 2: Sugar beet plant yellowing caused by Fusarium Wilt (photo
by E.G. Ruppel, USDA ARS-retired).
|
Symptoms of Fusarium yellows of sugar beet include wilting
of the foliage, yellowing between the veins in the leaves (interveinal
chlorosis), and a darkening of the rings in the taproot. Plants can be
affected at any stage from seedling until harvest; the majority of plant
death appears to occur when plants are in the seedling stage to the four-leaf
stage of growth. Dead plants are light brown and many remain visible until
harvest. Although diseased plants may be scattered throughout the field,
most occur in localized areas. Plants that were infected when young usually
are stunted and show severe symptoms of interveinal chlorosis and marginal
leaf browning. Plants infected later in the season will be larger in size
and usually show mild symptoms, consisting only of minor interveinal chlorosis.
When plants are removed and roots sliced in cross section, many show a
yellow-brown to gray discoloration of the water-conducting, vascular tissues.
|
Figure 3: Sugar beet vascular discoloration caused by Fusarium Wilt
(photo by E.G. Ruppel, USDA ARS-retired).
|
Above ground symptoms on dry bean appear on lower leaves
that exhibit yellowing and wilting, which become more pronounced and progress
upward into younger leaves. Stunting is evident, especially if plant infection
and stress occurred during the seedling and vegetative stages. The margins
of infected leaves turn tan to brown, and diseased plants become progressively
more yellow. Severely infected plants exhibit permanent wilting and premature
defoliation. Vascular discoloration on the main stem is the diagnostic
symptom usually evident after the initial appearance of foliar symptoms.
The reddish-brown vascular discoloration of root, stem, and petiole tissue
of infected plants will vary considerably in intensity, depending on variety
reaction, severity of infection, and environmental conditions.
Bean Disease Management
- Plant certified seed of Fusarium wilt-tolerant or resistant varieties
, if available.
Figure 4: Soil compaction aggravates Fusarium Wilt of
bean (photo by H. F. Schwartz, CSU). |
- Treat seed or furrow with recommended fungicides to delay initial
infection of seedlings by Fusarium and other soil-borne pathogens, including
Pythium and Rhizoctonia.
- Don’t follow dry beans with sugar beets; rotate for three to
five years with non-host crops such as corn, wheat, barley or alfalfa.
- Good weed management is important to reduce populations of other potential
hosts such as pigweed (susceptible to sugar beet strains of Fusarium).
- Plant when the surface 2 to 6-inch soil temperature is warm (above
60 F) for rapid germination of seed to promote rapid emergence and good
root vigor.
- Chiseling (sub-soiling) 10 to 20 inches deep between crop rows reduces
soil compaction and promotes water movement and root penetration.
- Manage irrigation to eliminate moisture stress to the developing plant,
but avoid excess water, which may deprive roots of oxygen.
- Space plants at recommended distances with crop rows to reduce plant
competition for water and nutrients, without sacrificing ground cover
and yield potential of the crop.
Figure 5: Fusarium Wilt discoloration of bean plant stem
(photo by H. F. Schwartz, CSU). |
- Till soil up around the base of infected bean plants to enhance lateral
root development above infected portions of the hypocotyl.
Sugar Beet Disease Management
- Plant certified seed of Fusarium wilt-tolerant or resistant varieties,
if available.
- Treat seed or furrow with recommended fungicides to delay initial
infection of seedlings by Fusarium and other soil-borne pathogens including
Pythium and Rhizoctonia.
- Don’t follow sugar beet with dry bean; rotate for three to five
years with non-host crops such as corn, wheat, barley or alfalfa.
- Good weed management is important to reduce populations of other potential
hosts such as pigweed (susceptible to sugar beet strains of Fusarium).
- Plant when the surface 2 to 6-inch soil temperature is cool (less
than 60 F) for rapid germination of seed to promote rapid emergence
and good root vigor.
Figure 6: Fusarium Wilt yellowing and wilting of bean (photo by
H. F. Schwartz, CSU). |
- Chiseling (sub-soiling) 10 to 20 inches deep between crop rows reduces
soil compaction, and promotes water movement and root penetration.
- Manage irrigation to eliminate moisture stress to the developing plant,
but avoid excess water, which may deprive roots of oxygen.
- Space plants at recommended distances with crop rows to reduce plant
competition for water and nutrients, without sacrificing ground cover
and yield potential of the crop.
- Be careful during tillage operations to avoid movement of soil (contaminated
with other pathogens such as Rhizoctonia solani) into susceptible crown
tissues.
- Properly dispose of sugar beet tare soil to avoid introduction of
the Fusarium pathogen (or new races) into the field.
References
- Franc, G. D., Harveson, R. M., Kerr, E. D., and Jacobsen, B. J. 2001.
Fusarium Root Rot. Pp. 146, in Sugarbeet Production Guide. Coop. Ext.
Reg. Bull. EC01-156, Univ. of Nebraska, Lincoln, NE.
- Gray, F. A. and Gerik, J. S. 1998. Biology and Management of Sugar Beet
Diseases in the Big Horn and Wind River Basins of Wyoming. Pp. 8-10, in
Ext. Bull. B-1063, Univ. of Wyoming Coop. Ext. Service, Laramie, WY.
- Schwartz, H. F., and Yuen, G. 2005. Fusarium Yellows. P. 15, in Compendium
of Bean Diseases 2nd Ed., APS Press, St. Paul, MN.
- Schwartz, H. F., Brick, M. A., Harveson, R. M., and Franc, G. D. 2004.
Fusarium Wilt. P. 115, in Dry Bean Production & Pest Management. Coop.
Ext. Reg. Bull. 562A, Colorado State University, Fort Collins, CO.
- Whitney, E. D. and Duffus, J. E. 1986. Fusarium Yellows. P. 18 in, Compendium
of Beet Diseases and Insects. APS Press, St. Paul, MN.
|
