Category Archives: Disease – Specialty Crop

Herbicide Damage

What is herbicide damage?  Herbicide damage is any adverse, undesired effect on a plant that is caused by exposure of that plant to a pesticide designed for weed control (i.e., a herbicide).  Any plant can be subject to this problem.
 

Squash leaf distorted due to exposure to a common lawn herbicide.
Squash leaf distorted due to exposure to a common lawn herbicide.

What does herbicide damage look like?  Symptoms of herbicide damage vary depending upon the plant affected and the herbicide used.  Common symptoms include stems that are flattened, or that twist or corkscrew.  Leaves may have abnormal shapes, sizes or textures.  In addition, leaves or leaf veins may yellow or redden.  In severe cases, plants may brown and die.  Some plants, such as tomatoes and grapes, are particularly susceptible to herbicide damage and can be used as indicators of unwanted herbicide exposure.
 
How does herbicide damage occur?  Herbicide damage results when an herbicide is misapplied.  Herbicides for control of broadleaf weeds are occasionally applied with fertilizers as part of a lawn care program.  If these products are applied too close to ornamentals or vegetables, or are applied when there is too much wind, then the herbicide can drift (move) from the area of application into an untreated area.  Often, drifting herbicides are difficult to detect by eye because they are extremely fine mists and can better be detected by smell.  Some herbicides readily produce vapors that can begin to drift several hours after application. 

How do I save a plant that has been damaged by herbicides?  Don’t panic!  There is nothing you can do after plants have been exposed.  However, most plants accidentally exposed to broadleaf herbicides applied with lawn fertilizers do not receive a high enough dose to kill them.  Young growth exposed to the herbicide will be distorted and discolored, but subsequent growth will be normal.

How do I avoid problems with herbicide damage in the future?  When using a lawn herbicide, follow the application directions exactly.  Don’t apply the product too close to, or in a manner that will cause exposure to, non-target ornamentals or vegetables.  To avoid drift, apply the herbicide when there is as little wind as possible (< 5 mph).  Apply the herbicide at low pressure to minimize production of fine mists.  Finally use amine forms rather than ester forms of herbicides as amine forms are less likely to produce vapors.

For more information on herbicide damage:  See UW-Extension Bulletin A3286 or contact your county Extension agent.

Rusty Root

What is rusty root?  Rusty root is slow-developing root rot of ginseng that typically attacks older ginseng plants (two-year-old ginseng or older).  While the disease can destroy the plant’s entire root system and kill the plant, often rusty root is more important because it leads to roots that are unmarketable due to low quality.

Rusty-brown, corky, dry tap-root decay typical of rusty root
Rusty-brown, corky, dry tap-root decay typical of rusty root

What does rusty root look like?  Ginseng plants with rusty root often do not exhibit aboveground symptoms of the disease, although foliage of infected plants can exhibit a red, orange or yellow discoloration.  Roots of infected plants are often only partially decayed.  Decayed areas are rusty-brown and remain firm with a dry, corky, but never mushy texture.  While rusty root can occur anywhere on a ginseng root, it often occurs at the tip of the root and progresses upward.

Where does rusty root come from?  The most commonly cited cause of rusty root is Cylindrocarpon destructans, a soil-borne fungus that appears to survive readily in soils where ginseng has been grown.  Other fungi, such as Fusarium spp. may also be involved.  In addition, some researchers suggest that a boron deficiency may also contribute to rusty root development.

How do I save ginseng with rusty root?  Once a ginseng plant has been affected by rusty root, little can be done.  There are currently no fungicide treatments available to control this disease.

How do I avoid problems with rusty root?  Avoidance of rusty root fungi is the only current means of disease control.  Select a site not previously used for ginseng production.  Be sure not to track soil or plant material from infested gardens into non-infested gardens.  Clean equipment, hand tools and footwear after working in infested gardens.  Use high-pressure water or a detergent solution to clean large equipment, and a 10% bleach solution or alcohol to clean hand tools and shoes.  Soil fumigation has been used by some growers to successfully manage rusty root, even in areas where ginseng has been produced in the past.  However, other growers have found this technique ineffective.

For more information on rusty root: Contact your county Extension agent.

Phytophthora Root Rot – Ginseng

What is Phytophthora root rot?  Phytophthora root rot is the most serious root disease of American ginseng (Panax quinquefolium) in Wisconsin.  Left untreated, this disease can totally destroy a ginseng crop during a typical three to four year production cycle.

Healthy (left) and Phytophthora cactorum-infected (right) ginseng roots.
Healthy (left) and Phytophthora cactorum-infected (right) ginseng roots.

What does Phytophthora root rot look like?  Ginseng plants with Phytophthora root rot show signs of wilting, often combined with a reddish discoloration in their foliage.  Roots of affected plants are tan and watery, and often disintegrate when handled.  Infected roots often also have a pungent, bitter, earthy odor. Where does Phytophthora root rot come from?  Phytophthora root rot is caused by Phytophthora cactorum, a common soil fungus.  This fungus is most active during wet periods, particularly during May and early June in Wisconsin.  However Phytophthora root rot can occur anytime during the growing season. How do I save ginseng with Phytophthora root rot?  Once a ginseng plant has been infected by Phytophthora cactorum, little can be done to save the plant.  If infected plants occur in patches, attempt to localize the area by carefully removing a 1 to 2 ft. wide swath of healthy plants, about 5 ft from the edges of the affected area. How do I avoid problems with Phytophthora root rot?  Site selection and maintenance are critical for control of this disease.  Select a site with topography and a soil type that ensures good drainage, and plan gardens so that older gardens DO NOT drain into younger gardens.  In wetter sites, dig trenches to drain standing water.  Also, DO NOT move soil or plant material from an infested garden into a non-infested garden.  Disinfect tools, boots and spray equipment with a 10% bleach or detergent solution when moving from garden to garden.  Fungicide treatments are also important for management of Phytophthora root rot.  A combination of Ridomil Gold GR and Aliette WDG provides the best control and should help prevent the development of fungicide-insensitive strains of Phytophthora cactorum. For more information on Phytophthora root rot: Contact your county Extension agent.

Mystery Seedling Disease

What is mystery seedling disease?  Mystery seedling disease (MSD) is a root disease that affects young (i.e., seedling) ginseng leading to plant death, or sparse, unthrifty stands.  MSD is similar to rusty root (see University of Wisconsin Garden Facts X1061) and may be a seedling phase of this disease.  Like rusty root, MSD is most important because it leads to roots that are unmarketable due to low quality.

Healthy ginseng seedlings (left) and those affected by MSD (right).
Healthy ginseng seedlings (left) and those affected by MSD (right).

What does mystery seedling disease look like?  Initial symptoms of MSD may simply be a lack of germination of ginseng seeds in seedling ginseng gardens.  Plants that do emerge often have foliage with a red tinge.  Roots of infected plants are often stunted and bulbous, with an intact crown and decayed taproot tip.  Older infected plants (e.g., two-year-olds) are typically severely stunted. Where does mystery seedling disease come from?  Current research indicates that several fungi (either alone or in combination) may be involved in MSD.  These include Septonema, Cylindrocarpon destructans, Rhizoctonia, Pythium and Fusarium.  Because of the similarity of MSD and rusty root, nutrient deficiencies (e.g., a boron deficiency) might also be involved in the disease.

How do I save ginseng with mystery seedling disease?  Once a ginseng plant has been affected by MSD, little can be done.  There are currently no fungicide treatments available to control this disease.

How do I avoid problems with mystery seedling disease?  Avoidance of MSD fungi is the only current means of disease control.  Select a site not previously used for ginseng production.  Be sure not to track soil or plant material from infested gardens into non-infested gardens.  Clean equipment, hand tools and footwear after working in infested gardens.  Use high-pressure water or a detergent solution to clean large equipment, and a 10% bleach solution or alcohol to clean hand tools and shoes.  Soil fumigation has been used by some growers to successfully manage MSD, even in areas where ginseng has been produced in the past.  However, other growers have found this technique ineffective.

For more information on mystery seedling disease: Contact your county Extension agent.

Foliar Phytophthora

What is foliar Phytophthora?  Foliar Phytophthora is the above ground phase of Phytophthora root rot (see University of Wisconsin Garden Facts XHT1018).  Left untreated, this disease, along with Phytophthora root rot, can destroy large sections of a ginseng garden.

Typical symptoms of foliar Phytophthora on a three-year-old ginseng leaf.
Typical symptoms of foliar Phytophthora on a three-year-old ginseng leaf.

What does foliar Phytophthora look like?  Watch for ginseng leaves with a papery, transparent appearance, the typical symptom of foliar Phytophthora.  Often papery leaf areas are separated from healthy tissue by watery, blackish-green tissue.  Infected leaves and stems disintegrate rapidly and often Phytophthora root rot follows as the pathogen moves from the leaves and stems into the roots.

Where does foliar Phytophthora come from?  Foliar Phytophthora is caused by Phytophthora cactorum, the same fungus that causes Phytophthora root rot.  This fungus is common in soil and can be splashed onto ginseng leaves during rains.  In Wisconsin, foliar Phytophthora is most common during May and early June.

How do I save ginseng with foliar Phytophthora?  Once Phytophthora cactorum infects the foliage of a ginseng plant, it often moves into the root system and little can be done to save the plant.  If infected plants occur in patches, attempt to localize the area by carefully removing a 1 to 2 ft. wide swath of healthy plants, about 5 ft. from the edges of the affected area.

How do I avoid problems with foliar Phytophthora?  Cultural methods that are useful for controlling Phytophthora root rot can also be useful for controlling foliar Phytophthora (see University of Wisconsin Garden Facts XHT1018).  Any activity that reduces soil moisture is important for control because Phytophthora cactorum tends to be less active in drier soils.  In addition, adequate mulching of ginseng beds is very important.  Mulch appears to provide a physical barrier that helps prevent splashing of the fungus from the soil onto leaves and stems.  Finally, during wet periods, fungicide treatments can be critical for management of foliar Phytophthora.  Alternating applications of Aliette WDG and Dithane DF (when available) provides the best control of this disease.

For more information on foliar Phytophthora:  Contact your county Extension agent.

Alternaria Leaf and Stem Blight – Ginseng Stem

What is Alternaria leaf and stem blight?  Alternaria leaf and stem blight is the most serious foliar disease of American ginseng (Panax quinquefolium) in Wisconsin.  Left untreated, this disease can totally defoliate a ginseng garden in a few weeks.

Alternaria stem blight on three-year-old ginseng.
Alternaria stem blight on three-year-old ginseng.

What does Alternaria leaf and stem blight look like?  Ginseng leaflets with leaf blight have irregularly-shaped necrotic (dead) areas, often surrounded by a yellow halo.  Necrotic areas expand to destroy the entire leaflet.  Ginseng stems with stem blight collapse and are brownish-orange, with a layer of black soot (spores of the causal fungus) that can be rubbed away.

Where does Alternaria leaf and stem blight come from?  Alternaria leaf and stem blight is caused by the fungus Alternaria panax.  This fungus first enters ginseng gardens as wind-borne spores.  Once in a garden, the fungus can survive in diseased ginseng debris, and there produce spores that cause new infections.  Warm, humid Wisconsin summers favor the development of this disease.

How do I save ginseng with Alternaria leaf and stem blight?  Preventative fungicide treatments are critical for control of leaf and stem blight.  If available and legal to use, Dithane DF is the preferred fungicide for Alternaria leaf and stem blight control.  Other, less effective fungicides such as a combination of Rovral and copper hydroxide, or Aliette may also be used.  Whenever possible, use these products in combination with Dithane DF.  Check with your county Extension agent about current product availability, as well as for information on appropriate rates, timings and methods of application.

How do I avoid problems with Alternaria leaf and stem blight in the future?  You can reduce the severity of Alternaria leaf and stem blight by reducing the humidity in your ginseng garden.  This can be accomplished by planting smaller gardens, orienting gardens in the direction of prevailing winds, planting less dense ginseng stands, using side and end curtains sparingly, and trenching to remove standing water.  In larger gardens, leaving 1 ft. gaps in the shade every 100 ft. will help increase airflow and reduce humidity.

For more information on Alternaria leaf and stem blight:  Contact your county Extension agent:

Alternaria Leaf and Stem Blight – Ginseng Leaf

What is Alternaria leaf and stem blight?  Alternaria leaf and stem blight is the most serious foliar disease of American ginseng (Panax quinquefolium) in Wisconsin.  Left untreated, this disease can totally defoliate a ginseng garden in a few weeks.

Alternaria leaf blight lesions on three-year-old ginseng leaves.
Alternaria leaf blight lesions on three-year-old ginseng leaves.

What does Alternaria leaf and stem blight look like?  Ginseng leaflets with leaf blight have irregularly-shaped necrotic (dead) areas, often surrounded by a yellow halo.  Necrotic areas expand to destroy the entire leaflet.  Ginseng stems with stem blight collapse and are brownish-orange, with a layer of black soot (spores of the causal fungus) that can be rubbed away.

Where does Alternaria leaf and stem blight come from?  Alternaria leaf and stem blight is caused by the fungus Alternaria panax.  This fungus first enters ginseng gardens as wind-borne spores.  Once in a garden, the fungus can survive in diseased ginseng debris, and there produce spores that cause new infections.  Warm, humid Wisconsin summers favor the development of this disease.

How do I save ginseng with Alternaria leaf and stem blight?  Preventative fungicide treatments are critical for control of leaf and stem blight.  If available and legal to use, Dithane DF is the preferred fungicide for Alternaria leaf and stem blight control.  Other, less effective fungicides such as a combination of Rovral and copper hydroxide, or Aliette may also be used.  Whenever possible, use these products in combination with Dithane DF.  Check with your county Extension agent about current product availability, as well as for information on appropriate rates, timings and methods of application.

How do I avoid problems with Alternaria leaf and stem blight in the future?  You can reduce the severity of Alternaria leaf and stem blight by reducing the humidity in your ginseng garden.  This can be accomplished by planting smaller gardens, orienting gardens in the direction of prevailing winds, planting less dense ginseng stands, using side and end curtains sparingly, and trenching to remove standing water.  In larger gardens, leaving 1 ft. gaps in the shade every 100 ft. will help increase airflow and reduce humidity.

For more information on Alternaria leaf and stem blight:  Contact your county Extension agent.