Re: this is from the ASK US page, so please send me a CC
- Hi Sheri, [original emailed to Sheri]I will try to shed some light on each problem and deal with solutions in general.Gall: There are two types of gall, fungal and insect.
LacebugsFungal Gall or Exobasidium Leaf and Flower Gall, Exobasidium vaccinii: Exobasidium vaccinii is a very common fungal disease in the spring during wet, humid, cooler weather on azaleas and occasionally on rhododendrons. Some of the native azaleas are more susceptible than hybrid rhododendrons. In April and May leaves and buds of infected plants develop distorted growth. The fungus invades expanding leaf and flower buds causing these tissues to swell and become fleshy, bladder-like galls. Initially, the galls are pale green to pinkish. Eventually, they become covered with a whitish mold-like growth. Fungal spores are produced within the white growth and are spread by water-splashing or wind to other expanding leaf or flower buds, or they adhere to newly formed buds, over-winter, and infect these buds the following spring. Older leaves and flowers are immune to infection. As the galls age, they turn brown and hard. The disease does not cause significant damage to affected plants. It just looks unsightly. If only a few plants are affected, pick and destroy galls.Insect Gall or Gall Midge, Clinodiplosis rhododendri: Clinodiplosis rhododendri usually over-winters in the soil as a prepupa. Pupation occurs in spring, with the adult midge emerging just as the hosts begin vegetative growth. There may be two additional generations yearly corresponding with flushes of rhododendron growth. Eggs are laid in clusters on the undersurfaces of leaves that are emerging from buds. Larval feeding causes a downward and inward rolling of leaf margins. Larvae mature in about seven days, drop to the ground, burrow in and make a cocoon.
Petal BlightRhododendron Lace Bugs, Stephanitis rhododendri, and Azalea Lace Bugs, Stephanitis pyrioides: Adults are about 1/8-inch long. The body is pale yellow. The lacy wings (very distinctive) are held flat over the back and are transparent with two dark spots present. The nymphs are black, spiny and smaller than the adults. The eggs over-winter partially embedded in leaf tissue. The eggs hatch in May. The nymphs mature into adults in June and lay eggs during late June and July. The second generation of nymphs appears in August. The over-wintering eggs will be laid when these nymphs become adults. adults and nymphs feed on the undersides of leaves by piercing the leaves with their mouthparts and sucking the plant juices. This causes a mottled, silvery or white discoloration, known as stippling, on top of the leaf where the chlorophyll has been removed. The undersides of leaves are covered with dark brown to black, sticky spots of excrement. Plant rhododendrons and azaleas in partial shade to maximize the activities of beneficial insects.
Powdery MildewPetal Blight, Ovulinia azaleae: This fungal disease, caused by Ovulinia azaleae, primarily affects the flowers of azaleas, but mountain laurel and rhododendron flowers can also be infected. Indian and Kurume azaleas are especially susceptible. The disease starts on the flower petals as tiny, irregularly-shaped spots, giving a "freckled" appearance. On colored flowers the spots are white, and on white flowers the spots are brown. The spots quickly enlarge and become soft and watery. Flowers rot and stick to the leaves. Infection is easily spread from flower to flower by wind, rain and insects. The fungus survives the winter in the soil. The most important things that you can do to control this disease in the home landscape are to pick and destroy infected flowers and avoid overhead watering. This fungus survives in the soil, so it is important to replace the ground litter with uncontaminated mulches. Rake and remove flower debris from beneath plants and, if possible, remove old flowers still attached to plants. Apply new mulch around the base of plants to serve as a barrier to new infection. On large azalea plantings, where it is not practical to remove infected flowers, make weekly fungicide applications beginning just before bloom and continue until the last buds open.
Some general hints to avoid problems. Keep the plants healthy. Struggling plants are the most disease prone. Remove diseased material and destroy it (or put it in the garbage). Prune your plants so they get more open ventillation. Plants that are pruned like a hedge are the most disease prone. Old branches should be removed and the plants should be open enough for air to circulate. Place in partial shade so they don't stay moist too long and still have enough shade so the predators of pests can survive. If you wish to use chemicals, check with your county agent to see what is permitted and recommended in your area.Powdery Mildew, Microsphaera azaleae: Powdery mildew causes azalea and rhododendron leaves to discolor and become coated with a white powdery fungal growth. Control of the disease is difficult, especially in certain weather conditions that favor the disease, i.e. when it is warm and humid. Plants that are young or are growing in the shade are often most susceptible.This information came from my website at: http://rhodyman.net/rhodyho.phpSteve Henning, Zone 6, Reading, PA USA==============================Good day,First let me thank you for reading my email! My azaleas seems to have more than one disease.This happened before and I replaced all the ones that were diseased (my pink coral bellsare unaffected) but all the diseases are back!They have gall, lacebugs, petal blight and often powdery mildew although that seems okayright now.How do I treat all of that? I have seen fungicide reccomended, neem oil, insecticidal soap,but I dont know what to do first.ANY help you can provide is greatly appreciated!Thank you again,Sheri Williamson
- I planted an azalea 2 yrs ago and it died, so I bought another one last year and I thought it had died too but when I was about to dig it up I noticed little green leaves on the little stump (2-3"). It lost all of its branches last fall and the stump is the only thing that remains. This is what happened 2 yrs ago as well. Is it worth it to leave it be or should I dig it up because it has no chance. I live in eastern Iowa and we get cold winters, but it says that it can withstand them. I am confused if it is still thriving or on its way down.