rhododendron are woody , evergreen bush that bloom in large clusters of clean , pink or cherry-red flower . The Rhododendron genus comprehend a wide range of shrub species , including azaleas . Rhododendron shrubs are susceptible to many different diseases , both fungal and viral in nature . Most disease do n’t warrant chemical substance treatment , except for in case of severe infection . Thankfully , many cultivated assortment of rhododendron species are direct for disease resistance .

Rusts

Rusts are triggered by a wide range of fungous diseases and incline to create icteric or chocolate-brown blotches on the upper surfaces of the rhododendron ’s leaves and carmine , orange or yellowish - orange tree bit on the undersides . The leaves will also have orange gelatinous spots and can become distorted or stunted . Treat rhododendron for rusting diseases by raking away septic leaves , pruning off morbid leaves , branchlet and branch , and then destroying or discarding the septic industrial plant parts . You may also apply an appropriate antifungal to control the disease in severe infection .

Powdery Mildew

Powdery mould is a common fungous disease that ’s well recognize by the ashen , powdery spores that compensate the folio surfaces . Powdery mold can also infect new buds , shoots and flowers on rhododendron , get fresh increase to become distorted and stunted . This fungous disease is most prevalent when air temperatures are 50 to 70 degrees F and proportional humidity is 90 pct or higher . Cultivated varieties of the species Rhododendron yakushimanum and R. macrophyllum , as well as R. ' Palestrina ' and R. ' Nova Zembla , ' are resistant to powdery mould , but other species and cultivar may need chemical treatment to command severe infections . Fungicides like horticultural oils , neem crude oil , S and potassium bicarbonate can annihilate powdery mildew disease on rhododendrons .

Leaf Gall

triggered by the fungus Exobasidium vaccinii , leafage bile disease usually infects rhododendrons during tight weather . Leaf gall do ill-shapen , crisp and inspissate leaf on infect rhododendrons , as well as white to pinkish spore growth on the affected plant tissue paper . care for rhododendrons infected with folio gall by pruning away the diseased plant parts , raking away and throw out fallen folio , pruning only when conditions are ironical , and avoiding any making water of the leaf when lacrimation .

Phyllosticta Leaf Spot

Phyllosticta leaf stain is a fungous disease that make pocket-sized dots of yellowish - tan to brownish spots on the rhododendron ’s leaf surfaces . Severe infections can stimulate defoliation of the bush . Control Phyllosticta leaf spot disease by raking up all fallen leaves and avoiding the use of overhead watering to prevent making water of the leaves .

Necrotic Ring Spot

Necrotic ring spot is a virus that causes light - colored spots or streaks on the rhododendron ’s foliage . Infected leaves can become dwarfed and perverted , but the virus seldom causes any serious wrong to rhododendron shrubs . There is no cure for the necrotic ringing spot computer virus , but you may contain the disease by the right way watering , fertilizing and pruning septic rhododendrons to keep the bush strong and intelligent .

Botrytis Blight

A disease that ’s because of the fungus Botrytis cinerea , Botrytis blight make discoloration or detection of the leaves and shoots . This disease can also cause the bud to rot ; the leaves and shoots to droop , decay and fall off ; and grayish - brown spore growths on the leaves and flowers . Botrytis blight is most prevalent during humid conditions and in severe lawsuit can cause twig dieback and flower bud that do n’t bloom . Treat Botrytis blight in your rhododendron by raking aside and discarding all accrue leaves and flowers , prune out the dead or dying plant part , and nullify wetting the leaves when water .

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