Plant diseases

By Christopher Rupp

BLACKLEG

• Blackleg is caused by a bacteria with many strains which also infect stored potatoes, carrots, bulbs, and damaged tissue causing Soft rot by dissolving the cell walls.

• prevelant during periods of increased temperature and humidity.

• There is no treatment so prevention is the only measure that can be taken.

http://www.dgsgardening.btinternet.co.uk/blackleg.htm

Blackleg continued- prevention

• Use certified 'seed' potatoes which should be free of the disease.

• If infection occurs remove all affected stems and tubers - including the original 'seed' tuber which is most likely the source.

• Space well when planting to improve air flow which discourages the disease.

• Store at low temperatures, eg. in clamps outside. • If storing indoors use crates or stout cardboard boxes

which can be regularly inspected.

BLACKSPOT

• fungus spreads by means of asexual spores (conidia) produced by the growing spots throughout the summer

• Chemical control must start in early the year as the leaf buds start to swell and become vulnerable to spores being splashed up from debris and stem lesions.

http://www.dgsgardening.btinternet.co.uk/blackspot.htm

Box Blights

• there are two organisms which cause Blight in the Genus Buxus; both are fungal and they can occur together

• Volutella has been around for many years. It is caused by Volutella buxi resulting in browning of the leaves and dieback of branches leaving bare patches in hedges and topiary specimens

• It spreads in wet humid conditions

http://www.dgsgardening.btinternet.co.uk/boxblight.htm

continued

• The other Box Blight is more serious, has only been recognized in the British Isles since the mid 1990s, but is causing great concern

• The fungus Cylindrocladium buxicola produces symptoms similar to Volutella with defoliated plants

• The disease requires moist conditions to thrive - the asexual spores die in dry conditions. Viable spores have been found in decomposing leaves after nearly a year, so any debris should be burnt if possible - never add to the compost heap.

Brown rot

• Brown rot is caused by the bacterium Ralstonia solanacearum

• It prefers warm temperate regions, so it infests potato crops in the UK.

• The symptoms are wilting of the aerial parts of the plant after it has attacked the vascular bundles in the stem.

• vascular areas are also present in the tubers and it is here that the disease is most noticeable. A brown ring is found if the tuber is cut in half; as the disease progresses the ring rots away completely, and a pale ooze may emerge from the "eyes" and heel of the tuber.

http://www.dgsgardening.btinternet.co.uk/brownrot.htm

Brown rot continued

• infection is carried in seed potatoes and in water

• contaminated potato waste should never be dumped where crops are to be grown or added to compost heaps. Any affected tubers left behind after gathering (groundkeepers) can carry it over to following seasons

Bud blast

• fungal disease which can have a devastating effect on the blossom of Rhododendrons and Azaleas

• It is associated with infestations of the Rhododendron Leafhopper which acts as a vector.

• The infection may enter via the wounds made as they feed or when the females insert their eggs into the tissues of the plant.

• the only treatment is removal of affected buds as soon as possible

http://www.dgsgardening.btinternet.co.uk/budblast.htm

FUNGAL CANKER

• A fungus which infects the branches of fruit trees causing sunken areas in the bark and these develop into distorted areas which may girdle the branch, eventually killing it. Any shoots which grow are weak, and may break in the wind.

http://www.dgsgardening.btinternet.co.uk/cankerapp.htm

CHOCOLATE SPOT

• A fungal disease which attacks Broad Beans and looks like the leaves have been dusted with chocolate powder.

• It is favored by acidic growing conditions, lush growth and damp spring weather. Winter-sown crops are more susceptible

http://www.dgsgardening.btinternet.co.uk/chocolate.htm

CLUB ROOT

• The roots become stubby and swollen and can develop wet rot.

• This greatly reduces the function of the roots causing the leaves to become yellow and a severe stunting of growth

http://www.dgsgardening.btinternet.co.uk/clubroot.htm

CORAL SPOT

• this fungal disease will migrate to living tissue after entering via pruning snags and frost damaged twigs

• Usually found on dead wood• Small, pinky-orange or coral coloured pustules

will be seen on the bark and these contain the spores

http://www.dgsgardening.btinternet.co.uk/coralspt.htm

Entomosporium Leaf Spot

• disease affects woody members of the Rosaceae Family but for gardeners it is most notable with the Photinias

• It attacks mainly fresh growth in the spring and autumn when the warm moist conditions it favours are present - temperatures above 14.5°C, 58°F. Small, bright red spots appear on the upper and lower surfaces of the leaf

http://www.dgsgardening.btinternet.co.uk/entomosporium_spot.htm

HONEY FUNGUS

• usually top of the list of diseases which concern gardeners as it can cause dramatic damage if it affects a much-loved tree or shrub which may have been an important feature.

• The name derives from the honey color of the mushroom-like fruiting bodies.

http://www.dgsgardening.btinternet.co.uk/honey.htm

POTATO SCAB

• An infection on the skin of the potato• Raised scab-like patches grow and can split

the surface. • The flesh of the potato is not usually affected

and after cooking the scab pulls away with the skin.

http://www.dgsgardening.btinternet.co.uk/potatoscab.htm

POWDERY MILDEW

• A fungus which appears as a dry powdery bloom on the upper sides of leaves, usually in hot dry conditions

http://www.dgsgardening.btinternet.co.uk/mildewpowdery.htm

botrytis

• Gray mold can be a problem in greenhouses when humidity is high and temperatures are moderate

• first symptom is usually a water-soaked spot. The tissue later becomes soft and watery. The affected parts of the plant wilt and collapse. If the humidity remains high, a grayish-brown coating or web of mycelium (fungus threads) and spores develops over the surface of the collapsed tissue.

http://gardening.wsu.edu/library/vege002/vege002.htm

Damping off

• variety of fungal problems that lead to sudden seedling death.

• The pathogens attack the tender stems and roots of the seedlings. Some seedlings look pinched at the base of the stem, others flop over, and some wither away entirely. Once the process is underway, it’s hard to save even a few of your plants. Prevention is the best cure.

http://davesgarden.com/guides/articles/view/277/

phytopthora

• leaves of plants affected by Phytophthora rot appear drought stressed.

• Trees or plants often wilt and die rapidly with the first warm weather of the season.

• Leaves may turn dull green, yellow, or in some cases red or purplish

http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn74133.html

Cedar apple rust

• fungal disease• Symptoms often include swollen growths or

woody galls on branches or shoots

http://plantclinic.cornell.edu/FactSheets/cedar-applerust/cedar-applerust.htm