Root Diseases and Disorders
Phytophthora Root Rot
Pythium
Fusarium
Rhizoctonia
Cylindrocarpon
Rust Spot (Abiotic)
New Crop Development Specialist

Crop Update:

Root Diseases and Disorders
As ginseng gardens age, a variety of foliar symptoms are beginning to emerge. These are often related to root disease or abiotic disorders. They are emerging now because gardens are beginning to dry out, temperatures are beginning to warm, and the tops are fully mature. The stress of root loss due to disease can result in wilting, especially during the day, and varying types of discolouration. Phytophthora, Cylindrocarpon, and Pythium are the most common root diseases being found at this time. Because of the extended period of foliar Phytophthora this spring along with repeated rains, Phytophthora rotted roots may not be showing up only in the low and wet areas. Once foliar Phytophthora has gone through a ginseng garden, spores that are produced on the leaves can be washed into the root zone during rainfalls and infect roots in all areas of a ginseng garden. It is important at this time to pay close attention to any weakened, stunted or discoloured tops and to dig up affected plants and examine the roots. Proper identification of the cause of root diseases and disorders is important to prevent further spread, or prevent similar problems in the future. However, proper identification of some of these diseases can be difficult without laboratory examination of the roots. Consult Publication 610 for cultural or chemical control options. 

Six of the most common diseases and disorders that will be encountered are:

Phytophthora Root Rot

•         Where to Look
–        Low areas
–        Beside trenches
–        In areas with foliar Phytophthora

•         What to Look for
–        Patches of dying/variable plants
–        Discoloured roots with a cheesy texture and sour odour (Figure 1)

Figure 1. Phytophthora root rot. Note the cheesy texture throughout the root.

Pythium

•         Where to Look
–        Throughout gardens

•         What to Look for
–        Soft, brown, swollen root tips (Figure 2)
–        Proliferation of fibre roots
–        Softer root rot than Phytophthora

Figure 2. Pythium damage to a ginseng root. Note the swollen root tips.

Fusarium

•         Where to Look
–        Throughout gardens

•         What to Look for
–        Shrivelled tan lesion below the straw
–        Leaves with reddish borders
–        Tops may wilt or droop just below junction of leaves
–        Pliable, wrinkled roots (Figure 3)

Note: Fusarium can also be a cause of rusty root, and symptoms can look very similar to those caused by weaker strains of Cylindrocarpon and abiotic rust spot. The cause of rusty root and rust spot lesions cannot be identified visually.

Figure 3. Fusarium affected roots are wrinkled and pliable.

Rhizoctonia

•         Where to Look
–        Especially in seedling and 2-year gardens
–        On the crown and buds of the root

•         What to Look for
–        Ginseng dying back in patches
–        Rusty lesions on crown (Figure 4)

Figure 4. Rust-coloured Rhizoctonia lesions on a crown.

Cylindrocarpon

•         Where to Look
–        Throughout gardens

•         What to Look for
–        Patches of dying plants
–        Roots completely rotted leaving only a shell (Figure 5)
–        Rusty lesions on roots

Note: Cylindrocarpon can cause a range of symptoms from disappearing root rot to a superficial rusty root. Symptoms, especially when they are less severe, can look similar to rusty root caused by Fusarium and abiotic rust spot. 

Figure 5. Cylindrocarpon rot on a ginseng root. 

Rust Spot (Abiotic)

•         Where to Look
–        Throughout gardens

•         What to Look for
–        Discoloured, stunted, or wilted tops
–        Whole root or patches of root with rust-coloured spots that can be 
          scraped off leaving healthy tissue beneath (Figure 6)

Note: There are many potential causes of abiotic rust spot including excess nitrogen/manure, heat or cold stress, boron toxicity, and the reduced form of iron in wet soils. Paying close attention to the location of rust spot in the garden can give clues to the potential causes. Abiotic rust spot can be easily confused with rusty root diseases caused by fungi. 

Figure 6. Abiotic rust on a ginseng root. 

New Crop Development Specialist
Evan Elford has recently been hired as OMAFRA’s New Crop Development Specialist. Evan will be based at the Simcoe Office and is available to answer your questions on new and alternative crops in Ontario. Evan can be reached by phone at 519-426-4509 or be email at evan.elford@ontario.ca. 

Questions about ginseng can be directed to Sean Westerveld, OMAFRA’s Ginseng and Medicinal Herbs Specialist at 519-426-4323; E-mail: sean.westerveld@ontario.ca.