Once plant tissue is infected, it cannot be cured. One potential Rhododendron problem is that the leaves are turning yellow. Spraying leaves of plants with water and hand removal of egs on the plant may also help. Spray foliage in mid-June if there is fresh leaf damage and adults continue to be active. A grayish white, powdery coating or fuzzy white growth on upper or lower surfaces is Powdery Mildew. On the lower leaf surface are purple to brown, circular, diffuse feathery areas. Apply a fungicide to protect leaves before infection in the spring. Lacebugs A small brown insect with transparent wings sucks on the bottom of the leaf causing a mottled appearance on the top with yellowish, brownish or white spots. Sometimes, a sparse fungal growth is within the spots. Damage usually begins in early May on old leaves and later appears on new growth. Sometimes infected leaves become covered with white spots. Rhododendron Lace Bug (Stephanitis takeyai) Lace bug damage is indicated by stippling (very tiny spots) on leaves of plants growing on dry sites and those with low plant diversity. Rhododendron leaf spot. Phyllosticta leaf blotch is caused by several Phyllosticta species.. Host Plants – The rhododendron lace bug attacks over 120 types of rhododendrons, as well as mountain laurel and fetter-bush. Rhododendron Whiteflies, Dialeurodes chittendeni. By BBC Gardeners' World Magazine. If the infestation is severe, it can turn the entire leaf a pale, unhealthy white. Their feeding causes the white spots on the leaf tops. The lacebug nymphs infest the underside of rhododendron and azalea leaves. This is especially true with thin textured leaves. Leaf miners eat the chlorophyll causing the leaf to turn white and eventually brown. Friday, 15 March, 2019 at 3:00 pm . Epsom Salts* According to the American Rhododendron Society, if the plant has older leaves that have turned yellow between green veins, you likely have a Magnesium deficiency.Sprinkle some Epsom Salts* around the plant to correct the issue.. Iron Sulfate*. Control rhododendron leaf spot, with the advice from our guide. Here are some common pests affecting this shrub: Spider mites – Spider mites feed off of bud and leaf sap, leaving leaves yellow or bronzed. Or roots die and plants wilt without having leaf spots form. Cylindrocladium scoparium: Rake and destroy fallen leaves. Other symptoms on the upper leaf surface include large purple-brown spots, or purple-brown areas associated with veins, or purple ringspots, or occasionally green spots as the remainder of the leaf yellows. plants affected by it have leaves, buds, or stems that develop swollen, distorted growths in April or May. Leaf gall is a common springtime Rhododendron disease, but it is not particularly serious. Rhododendron Insect Problems. Plants die rapidly. Stems have brown spots on which white masses of spores later form. Overnight, flowers collapse into slimy mush. The most common hosts of Phyllosticta leaf blotch include witchhazel (Hamamaelis), hydrangea (Hydrangea), rhododendron/azalea (Rhododendron), holly/inkberry (Ilex), mountain laurel (Kalmia) and andromeda (Pieris).However, the fungus is able to infect a broad array of landscape trees and shrubs, mostly as a minor pathogen. The upper surfaces become mottled with white spots, and many times the leaves will dry and shrivel. If leaves are notched and the plant is wilting, examine the soil around for larvae. If the same symptom appears in new leaves, then it is likely … The underside will show a brownish residue. Control. Here is a link that might be useful: How to grow rhododendrons and azaleas. However, a garden sulfur fungicide sprayed on healthy plant leaves and blossoms will prevent the spread of the fungus onto them. Recognition and … Further treatments may be necessary based on monitoring. Of the few rhododendron insect problems that exist, most can be handled first through prevention or subsequent treatment with neem oil. Damage – Both the nymphs and adults prefer young leaves, which they damage by extracting the sap. Jan Feb Mar Apr May Jun … Black fecal spots will be present on the lower sides of stippled leaves. In humid conditions, this fungus peppers rhododendron blossoms with small white or brown spots. Cylindrocladium blight: Leaves turn brown to black and fall in 3 to 4 days. Hosts. A table displaying which months are best to sow, plant and harvest. This is caused by various species of the fungus Exobasidium.