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notabotanist

Help! Large Azaleas appear sick....

notabotanist
17 years ago

I have 3 large azaleas in my backyard. They bloomed in spring of 2005, but did not bloom last spring. They appear to have set buds, but only generated new foliage, not flowers.

Now, the azeleas appear sick. The leaves are yellowing/discolored, and have brown spotting. Any ideas on what the problem could be?

The lot is wooded, but the plants receive some direct sun as well as filtered light. These are very mature plants (6' tall), so they have survived in this environment for a while (although I don't know when they were planted, I've been in the home since July 2005).

Is this disease? Pests? Poor nutrients? Poor soil pH? Thoughts? Remedies? Help!

Comments (2)

  • rhizo_1 (North AL) zone 7
    17 years ago
    last modified: 9 years ago

    You need to familiarize yourself with the azalea lacebug and the damage it causes. Your discription certainly fits. However, without a good picture, I'd only be guessing. So, I'll attach a picture for YOU!

    Lacebug would be my first guess. You should certainly take soil tests so that you have a notion of the pH of your new home. pH is important. You really can't address a supposed pH issue unless you know what you're working with.

    Back to the lacebug. You will find the critters, eggs, tar spots on the underside of the leaves, but the mottling and discoloration appears on the top.

    Here is a link that might be useful: {{gwi:400008}}

  • rhodyman
    17 years ago
    last modified: 9 years ago

    Yellowing of leaves surfaces, often with brownish burned areas, occurring on leaves that are more exposed to sun, is caused by more sun exposure than the plant is able to tolerate. Some varieties need shade, while all plants that have been protected from direct sun will be tender until hardened off by gradual exposure to sun light. Possible solutions are to give the plant more shade or move it to a more protected site.

    However, this doesn't explain why they don't bloom. There are two reasons rhododendrons don't bloom. One is they don't set flower buds and the other is the flower buds they do set don't survive until spring when they open. Here are some cuases:

    Failure to set flower buds may be a sign of too much health and vigor in a plant. One solution my be to prune the roots by cutting around the plant with a spade or moving the plant. This will check foliage growth and encourage production of flower buds. Application of nitrogen rich fertilizers are the main cause of vigor which suppresses flower bud production. Deadheading flowers as soon as they wilt can promote flower bud production. Too much shade, a cool wet summer, or inadequate phosphorus or potassium in the soil may also suppress flower bud production. There are a number of other reasons for a lack of flowers. The effect of each variable depends upon the variety of the plant. The effects include:

    * Pruning. The buds are formed in late summer and early fall so pruning then or later is not advisable since it will remove flower buds. New leaf buds will form in the spring, but new flower buds won't form until the next year.

    * Variety. Some plants will never bloom. Some rhododendrons that come from the seed of a hybrid plant will look good but will never produce flowers or will produce very poor flowers. To come true to the parent plant, a hybrid may be propagated by cuttings or tissue culture but not from seed. A good hybrid seedling only comes about once in a while. For that reason it is important to know that you are getting a good named variety or a good species.

    * Fertilizing. Nitrogen promotes leaf and branch growth and discourages flower bud production. It can also force late season growth that gets killed or stunted by frost damage. Phosphorus promotes flower bud production and hardiness. Potassium is necessary for well being.

    * Weather. Cold weather can kill flower buds. Usually you see the brown buds in the spring. Cold spells in the fall or spring can damage buds that are not hardened off. Bud blast (blooming in fall or winter) uses up good buds which are then not available at the normal blooming time.

    * Age. Most rhododendrons take 2 to 3 years to bloom from a rooted cutting unless forced. Some take longer and some bloom sooner. From seeds the plant may take 1 or 2 additional years.

    * Sun & Shade. Some rhododendrons need full sun to bloom and others can take fairly dense shade. In general, the more sun the more flower buds but also the greater exposure to damage from desiccation in summer or winter. More shade produces tall spindly foliage and less flowers.

    * Inspection. You can usually tell if the plant has ever bloomed. A rhododendron that has bloomed will have the seed pods on it unless it has been dead-headed. If dead-headed too late after blooming, new flower buds can be damaged.

    There are many other cultural variables that influence the plant's health and hence, its ability to produce flowers.

    Failure of flower buds to open could be due to a number of reasons. On a mature plant if they ever bloomed they will have a few of the seed pods still here and there. If you can't find any old seed pods, then they may have never bloomed. In any case, here are a few suggestions that may help:

    * Bud blast. Disease may attack the buds before they open. If it is a fungal infection, the dead bud will be covered with short hair-like structures.

    * Bud set. The buds could be foliage buds rather than flower buds. In this case check the previous section about flower buds not setting.

    * Fall Blooming. Some causes of fall blooming include a dry summer and moist fall and/or warmer climates including a warm fall. For some reason, fall blooming is more common in Georgia according to Dr. Sandra McDonald. Plants which are not sufficiently hardened off or are exposed to unseasonable warm spells can start bloom prematurely. These blooms are seldom satisfactory and many times get frozen before opening fully. In any case, the seasonal bloom is lost. Avoid application of nitrogen after late spring, but phosphorus and potassium may be applied throughout the growing season. Application of nitrogen too late in the season can hinder hardening off in the fall.

    * Low temperatures. The buds could be flower buds that froze. Early frosts are especially destructive. Plants harden off progressively in the fall. If a frost occurs before hardening is complete, the frost can kill flower buds. Late frosts in the spring after dormancy is broken is also a problem. This is especially true of early bloomers such as PJM that break dormancy very early. Cold climates may be too cold for many rhododendrons. Most rhododendrons have a low temperature at which the flower buds are damaged and will not produce flowers. It varies greatly from variety to variety and somewhat from season to season. Flower buds can also be damaged by cold, dry winds, particularly when warm winter weather is followed by a period of bitter cold.

    * Nutrients. Improper nutrients my be a problem that affects cold hardiness and flower bud set. A few things you can do are to fertilize with phosphorus (super-phosphate) per directions to increase hardiness and flower bud set. This can be done any time. Do not use nitrogen rich fertilizers as they may inhibit flower bud production and also reduce cold hardiness. Lawn fertilizers are notoriously high in nitrogen and should be kept away from flowering plants.

    * Acidity. Measure the pH and acidify if necessary. Flowers of sulfur (powdered sulfur) or iron sulfate are the best chemicals to use to increase the acidity [lower the pH]. Do not use aluminum sulfate since aluminum salts build up in the soil and eventually becomes toxic to many plants including rhododendrons and azaleas. If soil is too acid, the symptoms can be the same. Very acidic soil can prevent the roots from taking up nutrients. As many of my rhododendrons are planted in very acidic forest soil, an application of Dolomite and a light topdressing of mushroom manure in late spring is all they need. Sprinkle the lime on in late winter, very early spring. Don't overdo it - just a light sprinkle. If it is mid-spring, get the lime on right away so the rhododendron roots will be able to take up the soil nutrients in time for new growth. If you don't have rain, water it in well.

    * Protection. If the plants are wrapped in burlap during the winter, they may gain a few more degrees in hardiness.

    * Drought. When soil moisture is too low, the buds will not open. Watering will usually resolve this condition if detected soon enough. Also, summer drought with a moist fall can contribute to fall blooming.

    * Deer Damage. Deer and rabbits may eat many of the flower buds as they browse in the winter, particularly if the weather is harsh and other food is scarce.

    Here is a link that might be useful: How to grow rhododendrons and azaleas.