Mint Diseases

Mint rust

Disease symptoms:

• Pale and distorted shoots in spring
• Dusty orange pustules on the stems and leaves.
• Pustule may change to dusty yellow or black in colour in later stage
• Large areas of leaf tissue die and plants may lose leaves

Survival and spread:

• When the orange spore pustules mature and break open in June or July, the spores are spread to other plants by the wind.
• The fungus enters the plant through the leaves lNewly infected plants seldom show symptoms until the following spring.

Favorable conditions:

• Dry weather with high relative humidity
• Pathogens overwinter on mint stubble & on wild mint.
• It spreads through propagation material and air

Verticillium wilt

Disease symptoms:

• Symptoms first appear in the foliage at the top of the plant.
• Symptomatic upper leaves are sickle-shaped and initially chlorotic or red, soon becoming necrotic.
• Premature defoliation and death of the plant can result.
• Vascular discoloration in stems and roots may be observed and diseased plants are often stunted.

Survival and spread:

• The transport of infected planting materials can transmit the pathogen to long distances.
• Spread of the pathogen occurs primarily by soil and movement of soil and water.

Favourable conditions:

• Verticillium wilt is favored by moist soils and a temperature range of 21-27° C.
• Micro-sclerotia are stimulated to germinate by root exudates of host plants

Anthracnose

Disease symptoms:

• Mint anthracnose, also known as "leopard spot".
• The fungus causes small, sunken brown spots to appear on the lower leaves and stems. These spots enlarge to form oval lesions with light gray centers and reddish-brown borders, and may unite.
• Mint anthracnose may cause defoliation and cankers, which may lead to splitting of the stem.
• Heavily-infected plants are weakened and oil yields are reduced.
• Anthracnose may become severe during wet seasons when the mint foliage is wet for long periods.

Survival and spread:

• Conidia are rain-splashed from overwintering infected plant in the spring and throughout the summer to new growth.

Favourable conditions:

• Infection requires three to twelve hours of wetness.

Powdery mildew

Disease symptoms:

• Powdery white patches are developed on the upper and lower surfaces of the leaves and stems.
• Under favourable conditions, the disease causes severe lossess. It also reduces the oil

Survival and spread:

• Resting spores is responsible for primary spread and airborne spores for secondary spread.

Favourable conditions:

• Disease becomes severe when weather is dry and air circulation is poor (warm and humid weather)

Black Stem Rot

Disease symptoms:

• Black stem rot is considered a moderate to serious problem in mint production.
• The fungus is most active during periods of cool and wet weather.
• Symptoms of infection include dark brown or black cankers on stems.
• Cankers may girdle the stem and cause plant parts above the infection to wilt and die.

Survival and spread:

• Pathogen survive in soil and on plant tissue for many years by producing small (1 to 3- mm diameter), irregular-shaped, brown to black sclerotia.

Favourable conditions:

Disease become more severe in soils that are moderately wet and a temperature range  of 15-25°C

Stem and stolon canker

Disease symptoms:

• Roots and stolon have brown or black progressively rotting areas. Plant stand may be greatly reduced.

Survival and spread:

• Pathogen survive on crop debris and in soil as black to brownish resting structures (sclerotia) or as resting fungal mycelium.

Favourable conditions:

• Warm soil with high humidity is favorable for disease development.
• Temperatures between 26-32°C, soil moisture between 30-60% and soil pH above 6.6 are conducive for disease development.

Septoria leaf spot

Disease symptom:

• Septoria leaf spots are dark brown/black, up to 3mm (⅛in) diameter and angular in shape (being constricted between leaf veins).
• Spores are sometimes visible within leaf spots on the underside of the leaf.

Survival and spread:

• The fungus survive in plant debris and on weeds .

Favourable conditions:

• Moist (more than 70% relative humidity) coupled with warm weather and intermittent rains favours disease development.

Disease cycles:

Mint rust

Verticillium wilt

Anthracnose

Stem and stolon canker

Powdery Mildew

Black Stem Rot

IPM for Mint

To know the IPM practices for Mint, click here.

Source: NIPHM; Directorate of Plant Protection, Quarantine & Storage