When it come to incorporate large , full - incarnate flowering shrubs for privacy and delineation of spaces in a landscape , one popular choice is the rhododendron . Landscape designers and home gardeners plant rhododendron in hedge arrangements or as support - alone specimens for the splashes of color that their bound bloom and dark unripened foliage add to their landscape . These flowering dish belong to the Ericaceae , heath , family and are sometimes affected with brown situation on their leaves . Knowing what causes brown spots and sympathize how to prevent and treat them may store your rhododendron from irreversible damage .

Fungal Causes

Fungi from the Phytophthora , Cercospora , Colletotrichum , Pestalotiopsis and other genera are known to cause brownish spots on the leave of rhododendron . transmission ordinarily occurs in the springtime , but may not be to the full manifested until the winter or the next spring .

Phytophthora Dieback Disease

brownish spot on rhododendrons are commonly because of the Phytophthora dieback fungus genus , which has several species that affect the foliage of rhododendron plant . These fungi assail the shrub ’s new ontogenesis , its leave and stems . The septic share are intrude on with browned spots that thrive and overspread from the leaves and to the stems to taint the established rhododendron leaf . As stated by R.K Jones and D.M. Benson , plant pathologists at North Carolina State University , infected leaves will have a " water - soaked " appearance ; then they will become dried out and strike off of the shrub .

Environmental Causes

Brown smudge on rhododendron folio may not be a sign of disease . rhododendron can be affected by a consideration call " physiological leaf spot . " This condition is make by poor root wellness , unlawful irrigation as in over- or under - watering , drought and extreme heat photograph .

Management

At the first sign of chocolate-brown spots , whether do by an transmission or a physiological problem , remove the moved leaves before the spots spread beyond the initial site to the residue of the works . Properly dispose of the infected plant life parts far away from rhododendron bush . Do not let the leaves come down to the ground to taint the soil . Apply fungicides specifically formulated for dark-brown spots on rhododendrons to assist kill the fungus and forbid its bedspread .

Prevention

kick upstairs healthy growth of your rhododendron may prevent brown spot contagion . This includes balancing the stain consideration at the proper pH mountain chain and bestow fertiliser , mulch and adequate tearing . implant your rhododendrons in a location where they receive good sunlight . Prune your rhododendron in the evenfall or recent winter / early spring before the flower bloom to upgrade fair to middling breeze circulation through the shrub to keep their farewell and bloom dry and aerated , consort to Daniel H. Gillman , plant diagnostician of the University of Massachusetts Extension landscape , nursery and urban forestry program .

References

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