Rhododendrons diseases and pests

Phytophthora ramorum

Symptoms: wilting and drying up of buds, leaves, stems, necrosis on the leaves, branches and extension growth, wasting of bushes.

Protection: remove and destroy the contaminated plants in the Czech Republic quarantine body on the EPPO Alert List.

 

The coloration of leaves by algae

Symptoms: yellow to light green light removable coating on the upper side of leaves

Protection: not normally required, but if there is a very strong and permanent settlement of algae (assimilation effect) open the crop of plants to reduce humidity

 

Leaf spots resulting from the fungal infection on Azalea - Septoria azaleae

Symptoms: spots on leaves are usually limited by leaf veins, at first yellowish and reddish-yellow, after that dark brown to black, partly yellowish or reddish centre, starting from the edge or the tip of the leaf or alternatively on the blade, especially seen on the bottom of the leaves, spotted, black fruiting body in patches (Focus), wet with whitish clusters of spores

Protection: be careful when purchasing a plant with infected leaves, remove continuously contested leaves and ensure optimal growing conditions (often in the growing business)

 

Leaf spots caused by fungal infections in rhododendrons, species of the genus Phyllosticta, Cercoseptoria handelii, Glomerella cingulata

Symptoms: irregular, large, dark brown to ash-grey spots with partially dark and circular border, dark brown spots with dark edges, round or irregular, with dark brown spots sometimes with reddish border, on the upper side of grey hairs wet sponges, irregular, often large and dark brown spots.

Protection: remove infected leaves, examine the supply of nutrients

 

Verticillium alboatrum

Symptoms: pale-yellowish or dull-coloured leaves, wilted and dead shoots, a brown colour in the vascular

Protection: the selection of less susceptible varieties, plants with an infected foul trunk base and roots carefully dug out and removed.

 

Stephanitis spp.

Symptoms: pale green up to greensick mottling or blotches on the upper side of the leaves, later dark leaves, tarry leaves, brown-black droppings which dry out to crusty mass, on the underside of the leaves is up to 4 mm long, oblate insects with humped with parts extended neck shield and with transparent net-veined large wings, larvae up to 2 mm long, yellow and dark mottled

Protection: in early summer remove the contested leaves, on young bushes crush the infected leaves, by very strong presence treat the leaves chemically, in winter remove the end shoots with newly put eggs (the bottom of the middle leaf veins)

 

Otiorrhynchus sulcatus

Symptoms: pieces of leaves from the edge of curved or semi monthly nibbled by a black, coarse-grained topped 1 cm long beetle with a knurled nose which is incapable to fly and is also feeding on the bark and buds (at night) up to 1,2 cm long, white, fat and legless larvae with a brown head, damaging the roots by feeding.
Protection: collect insects and larvae regularly in the evenings at the base of the plants; biological control

 
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