Plant Diseases

Meghan Danielson

Anthracnose• It is caused by certain fungi (usually

Colletotrichum or Gloeosporium) producing spores in tiny, sunken, saucer-shaped fruiting bodies

• Symptoms include sunken spots of various colours in leaves, stems, fruits, or flowers.

• dogwood anthracnose, was identified in North America. Unlike other forms of anthracnose, it thrives in cool climates

• Anthracnose can be avoided by destroying diseased parts, using disease-free seed and disease-resistant varieties, applying fungicides, and controlling insects and mites that spread anthracnose fungi from plant to plant.

Apple Scab• The infection cycle begins in the

springtime• 15 genes have been found in

apple cultivars that confer resistance against apple scab

• Apple scab is a disease to Malus trees, such as apple trees, caused by the ascomycete fungus Venturia inaequalis.

• Over the winter, V. inaequalis undergoes sexual reproduction in the leaf litter around the base of the tree.

Black Spot• Diplocarpon rosae is a fungus that

causes the rose disease black spot.

• Badly affected plants, however, will not show the circular patterning, as they combine to cause a large, black mass

• Upon infection, disease progresses from the lowest leaves upward, causing defoliation and black spots on leaves

• the fungus is most active at temperatures from 75 to 90°F.

Botrytis• a necrotrophic fungus that affects

many plant species• its most notable hosts may be wine

grapes.• The first, grey rot, is the result of

consistently wet or humid conditions, and typically results in the loss of the affected bunches. The second, noble rot, occurs when drier conditions follow wetter, and can result in distinctive sweet dessert wines

• The fungus is usually referred to by its anamorph (asexual form) name, because the sexual phase is rarely observed.

Canker• characterised by broadly similar

symptoms including the appearance of small areas of dead tissue, which grow slowly, often over a period of years

• Some are of only minor consequence, but others are ultimately lethal

• caused by a wide range of organisms, including fungi, bacteria, mycoplasmas and viruses.

• Canker can be spread by weather and animals

Cedar-Apple Rust• can defoliate trees and blemish

fruit making them unmarketable.

• requires two hosts, apple and eastern red cedar (Juniperus virginiana L.), to complete its life cycle.

• Before apple can be infected, adequate moisture must be present in a temperature range of 8-24 C (46-75 F) to allow for formation of basidiospores on cedar galls

Crown Gall

• a disease of roots and stems

• Galls vary considerably in size from 1/4 inch to a foot or more in diameter

• Crown gall is caused by the bacterium, Agrobacterium tumefaciens.

Fireblight• it can destroy an entire orchard in a

single growing season.• The causal pathogen is Erwinia

amylovora• The disease is believed to be indigenous

to North America, from where it spread to most of the rest of the world.

• insects, birds, rain and wind can transmit the bacterium to susceptible tissue.

• Injured tissue is also highly susceptible to infection

• Hailstorms can infect an entire orchard in a few minutes, and growers do not wait until symptoms appear, normally beginning control measures within a few hours

Powdery Mildew• It is one of the easier diseases to

spot, as its symptoms are quite distinctive.

• Infected plants display white powdery spots on the leaves and stems

• The lower leaves are the most affected, but the mildew can appear on any above-ground part of the plant.

• Powdery mildew grows well in environments with high humidity and moderate temperatures

Root Rot

• found in both indoor and outdoor plants

• Usually, this is a result of overwatering

• it is usually lethal and there is no effective treatment.

• Plants with root rot should be removed and destroyed.