You usually have beautiful azaleas blooming on full, healthy bushes. However, now they are dying. What do you look for and how should you treat it? Azaleas tolerate dry conditions and a lot of sun; however, they can suffer from other problems. Soil, insects, diseases and climate conditions all play a role in how healthy your azaleas will be.
A deficiency of iron in the soil produces yellow leaves and large green veins. Perform a soil test for the soil pH. Use iron sulphate or sulfur to amend the soil for a pH balance of 4.5 to 6.0. For a soil low in calcium, sprinkle Epsom salts on the soil and work it into the top layer of the soil.
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Too much iron in the soil produces a pH balance above 6.5 and can damage plants that are too close to concrete foundations. Consider replanting the azaleas further away from concrete.
Look for sooty mold on leaves, white sacs in the forks of twigs, small dead twigs and yellowed leaves. This is an indication of scale. No treatment is necessary if the azaleas only have yellowed leaves as azaleas tolerate small populations of scale. Ladybird beetles in the garden area will control heavier infestations of scale without added treatment. However, if you prefer, spray the plant with horticultural oil, use the spray on dormant plants in the winter.
Wilted leaves and dying twigs indicate a rhododendron borer. Check if your azaleas have borers by pruning a branch that looks unhealthy, splitting the branch open lengthways and checking for larvae. Larvae are white with brown heads. The only remedy for a rhododendron borer is heavy pruning. This is not always effective. Applying beneficial nematodes may help by injecting the nematodes directly into the diseased branch; follow product directions.
Scattered dying branches indicate a fungus. If left untreated, the leaves wilt, turn brown and lay flat against the limb. This in turn, infects the limb, causing dieback. Treatment includes growing azaleas in partial shade as opposed to full sun, keeping dead twigs pruned regularly, and keeping the plant well watered during dry periods.
Petal blight only affects the flower petals of an azalea. The petals will look very wet in spots, which will grow and make the petal slimy. This disease is most noticeable in areas of the country that have high humidity. Applying a systemic fungicide only when new buds are just beginning to show color will control petal blight for four to six weeks.