Rhododendron Diseases: Fighting Diseased & Yellow Leaves

Rhododendrons are usually pretty to look at. However, you can find out here what to do about yellow leaves, black buds and signs of damage.

As easy to care for as they are in every other respect - the genus of Rhododendrons (rhododendron) is susceptible to fungal diseases and animal pathogens are also up to mischief in the evergreen foliage of the rhododendron. Below we list the most important pests and diseases and give tips on how best to deal with them.

Rhododendron: Yellow and brown leaves

The discoloration of the leaves usually has two causes: either the plant is malnourished or suffers from a lack of water or it has been attacked by a fungal disease. Depending on the cause, the yellow or brown lesions can vary. In order to do something about the discoloration, the source of the damage must first be identified. Here you will find a list of common fungal diseases of rhododendrons.

Common fungal diseases in rhododendrons

• characteristics: Mealy gray coating on leaves and sometimes stems
• reason: Occurs when there is a lack of ventilation and excessive humidity
• countermeasure: Generously cut back affected areas
• home remedies: Spray milk diluted with water (in the ratio 8:1) on the remaining shoots and leaves; rinse after 20 minutes and repeat 2-3 more times; the lecithin in milk kills fungal spores

leaf spot disease

• characteristics: Combines several clinical pictures; In general, leaf loss, growth inhibition and spots on the leaves occur
• reason: Leaf spots can be caused by various fungi (more than 20 species known), damp weather conditions promote infestation
• preventive measures: choose favorable locations; avoidance of overly shady locations; preventive use of fungicides

rust

• characteristics: Can be identified by yellow-orange spore deposits on the underside of leaves, is often confused with leaf spot diseases
• reason: fungal pathogen; occurs very rarely
• preventive measures: Optimal site selection and soil conditions; need-based fertilization; Keeping the leaves dry (when watering, for example) Use of pesticides is possible, but not necessary

Animal pests of rhododendrons

But not only fungal diseases can cause problems for your rhododendron. Animal pests can also lead to diseases of your rhododendron.

• characteristics: Adult animals feed on leaves; Larvae partially damage roots; the feeding marks are visually unattractive, but no danger to the plant
• reason: infestation by adults and larvae; widespread in German gardens
• combat: Pesticides are mostly not effective because animals keep themselves hidden; collect; reliable control by parasitic nematodes like ours Plantura HB nematodes between April and May; Lightly incorporate neempress cake into soil to repel larvae

rhododendron bug (Stephanitis rhododendri)

• characteristics: Pale yellow mottling on leaves, progressively becoming brown-black necrotic spots; the pests are easily recognizable on the underside of the leaf
• reason: Infestation by the bugs is favored by too sunny location and warm weather
• Preventive measure: Occasionally water with nettle manure; use soft water; loose and mulched soil
• The use of a pesticide is usually not necessary

• characteristics: sucks in buds; sucking damage only slight; the actual damage is caused by a fungus (Pycnostysanus azaleae); the females cut buds to lay eggs, the fungal spores penetrate through the wound, the buds turn black and die
• reason: infestation by adult animals and subsequent fungal disease; one of the most common pests on rhododendrons
• combat: Break out and dispose of affected buds (not on compost, but in household waste); yellow boards hang out to detect infestation, use insecticides against adult cicada

• characteristics: feeding on leaves; speckle-like symptoms on leaf surface; plant loses vitality; leaves die off; leaves sugary honeydew on leaves, providing breeding ground for fungi; then mostly black discoloration of the leaves
• reason: Infestation by adults and larvae
• countermeasure: Posting of yellow boards; Fight larvae with systemic pesticides, parasitic wasps

Yellow leaves due to improper care

If there is neither a pest infestation nor a disease, the rhododendron was cared for incorrectly. If the leaves of the evergreen shrub become increasingly chlorotic, this is usually due to a pH value that is too high or too low. Because if the pH value of the soil is not in the optimal range, the nutrients contained in the soil cannot be properly absorbed.

calcareous chlorosis

• characteristics: First the young leaves turn from yellow to brown, the leaf veins remain green; If no countermeasures are taken, growth disorders will occur
• reason: The soil pH is too high (over 5), so the iron in the soil cannot be absorbed, iron deficiency occurs, and later manganese and magnesium deficiency
• countermeasures: transplanting into lime-free soil; watering with soft rainwater; Fertilize with mulch, compost, or an iron-heavy fertilizer

nitrogen deficiency

• characteristics: The sheet yellows over a large area; the plant sprout only sparsely and only forms small leaves that fall off quickly
• reason: The supply of nitrogen is insufficient, too little or wrong fertilization
• countermeasures: Fertilize with mineral nitrogen fertilizer, this is available to the plant particularly quickly

Incorrect care not only affects the color of the leaves, but also the formation of flowers. So that your rhododendron can decorate your garden vitally, green and full of flowers, we have everything you need here Caring for rhododendrons compiled for you.