Mix with a wetting agent for best results to help the pesticie adhere to the leaf. Other synthetic pyrethroids include lambda-cyhalothrin Westland Resolva Pest Killer and cypermethrin e. Py Bug Killer. Petroleum oil has also been recommended. As the scale insects are on the underside of the leaf, it needs a particular approach,: You need a very high pressure sprayer which makes tiny droplets of spray and add a wetting agent.

You might need to spray twice in the season. At this point they are most vulnerable to insecticide. Old scales may remain on the plant for some time after the death of the insect. To check if treatment has worked, slide your thumb across a group of scales. If scales are dead, they will be hollow and the coverings will flake off easily.

Living scales will leave a colored, wet residue on your thumbnail. Hard pruning a badly infected camellia or rhododendron can be the best way to get rid of it. For a large garden with a bad outbreak I recommend a mixture of cutting back and burning and spraying. Get a contractor in to spray if you dont have access to a high pressure, small droplet commercial sprayer. As the insects are on the underside of the leaf, it needs a particular approach,: You need a very high pressure sprayer which makes tiny droplets of spray and add a wetting agent.

Aphids on rhododendrons Whitefly and greenfly can suddenly appear in large number on the underside of young leaves and on the stems, particularly in dry weather, sucking out the sap and causing puckered or wrinkled leaves. Pyrethroids: Deltamethrin e.

Westland Resolva Bug Killer cypermethrin e. Organics: Natural pyrethrum, Fatty acids, Plant oils. If you dislike using chemicals, soap concentrates can be used. It may take several doses to clear the infestation. With both chemicals and soap sprays, it is important to target the insects on the leaf undersides. This requires a fine spray to allow the water droplets to adhere.

There are also a number of biological controls which are most effective under glass. These include Aphidoletes midge and Aphideius predatory wasp. A serious problem in some areas. There are two different species of these sap-sucking insects, one which attacks rhododendrons and the other azaleas. Lace bug damage on leaves causes a greyish, or whitish leaf upper surface with a discolouring on the lower surface. The effect is most severe on plants grown in full sun and in shade it may not be a problem, where there are more lacebug predators to keep them under control.

This problem is becoming serious in parts of Germany and probably in adjacent countries. Frost Damage If buds are formed and then turn brown, cause is usually frost. To avoid frosted buds, protect opening buds with fleece or plant later flowering varieties such as deciduous azaleas. Flower buds do not form flower buds are fatter than growth buds which are usually more pointed. Some varieties, especially species, take many years to flower.

You may need to wait till plants are 10 years old for large leaved species for example. If planted in too much shade , will not flower well: best to move to sunnier spot. Fertiliser applied after late June encourages leaves, not flowers.

Stop feeding in June. Bud blast fungus: look for black bristles on the buds. It affects R. Can be severe in Germany and other countries.

Not much can be done about this. If it is very bad, consider destroying the worst affected plants. Large leaved species such as R. Sign Up. To view the Garden Centre Magazine click here Your Enquiry. Garden Centre Opening Times 9am-5pm 7 days a week Plants, gardening, foodhall, pets, birdcare, gifts, clothing and cards. Menu Contact Events Search. The most common pests, diseases and problems of Rhododendron and Azaleas. What's wrong with my Rhododendron?

Reasons include: because they are too wet, too dry, planted too deep, starved needing feeding , soil too alkaline, or so il is compacted: Why does my rhododendron with yellow or chlorotic leaves: This is a general sign of unhappiness and can have many causes: 1.

Rhododendron is starved. Apply fertiliser April-May to Late June. Why has my rhododendron got crinkly leaves? Caused by late Spring or early Autumn frosts When the new growth buds begin to elongate before unfurling, the tips of the new leaves can be puckered by frosts causing them to distort when they unfurl. Caused by Sap-suking insect aphids. For insects use a contact or systemic insecticide. The chemical we use is deltamethrin.

Systemic neonicotinoid insecticide acetamiprid Organic Sprays: fatty acids plant oils and extracts, natural pyrethrum. Why does my rhododendron not flower? Bud Blast fungus Bud blast fungus: look for black bristles on the buds. Why are my rhododendron leaves shredded or broken?

Wet soil or bark damage at the trunk may be clues of potential killers. Other symptoms like chewed leaves are not helpful — leaf-chewing insects rarely actually kill their hosts. Wood-boring beetles in larger trunks also tend to be secondary problems and may not have been the primary cause of death. Brown leaf tips: Usually this indicates the rhododendron has not been able to absorb enough water from the soil.

Normally it is from inadequate watering but sometimes a low-level root rot may be to blame if the soil is continually moist in warmer temperatures. A fungus may also be the cause. Leaf spots: Brown spots on the leaf are often caused by a fungal infection. There are many species of fungi that may attack rhododendrons. These spots are usually unsightly but not a major problem. Nonchemical-control strategies involve removing potentially infected leaf litter, pruning to improve air circulation and avoiding overhead irrigation that wets the leaves.

White leaves: New leaves that emerge white or rarely peach or light pink are infected with a fungus called Exobasidium. White leaves may show a powdery webbing underneath. The webbing is not from insects or spiders but rather the fungus itself. Infected shoots also tend to produce more frequent and more vertical branching than on uninfected shoots.

While infected plants may last indefinitely or only die after many years, reasonable control can be achieved by pruning out infected shoots as they appear. On azaleas, this same fungus produces distorted leaf galls rather than white leaves. White power: A white, powdery coating on the upper leaf surface is a fungus called powdery mildew. Some low-toxicity fungicides work very well against powdery mildews.

Sulfur or some formulations of insecticidal soaps work very well. Whatever you use, always follow the label instructions. Yellowish blotches: Yellow spots on the upper leaf surface, almost always associated with a purplish blotching on the underside, are another manifestation of powdery mildew.

Some rhododendrons, especially those with larger, evergreen leaves, do not develop the white powder when infected with powdery mildew.

This form of powdery mildew is not as easily controlled by the lower-toxicity fungicides. Luckily, this version is not as unsightly and is unlikely to cause significant harm to the plant. Orange spots: Tiny, orange dots underneath the leaf that look powdery, especially with a magnifying glass, are usually caused by rust fungi.

Most of the time, they are not a significant health problem for the rhododendron. In cases where the rust fungus is causing a decline usually yellowing or stunting , control with low-toxicity fungicides can be difficult because of the complex lifecycle of the rust fungi.

It is best to identify the rust species involved by bringing it to a Master Gardener clinic. From there, the sample may need to be forwarded to the Washington State University plant-diagnostic laboratory. With a B. He oversees irrigation, deals with pest and disease issues, and manages their compost program.

He lives in north Kitsap County with his family and various animals. Common rhododendron problems are listed below according to the symptom observed. Green veins with yellow space in between due to poor uptake of iron Yellow Leaves Yellowing leaves chlorosis on a rhododendron are not only a common symptom, almost every problem seems to result in some yellowing.

Wilting caused by low soil water Rhododendrons growing in excessively wet soils or plants that are just watered too much may also exhibit interveinal yellowing.

If the soil conditions in which they are grown are alkaline they will be unable to access certain nutrients such as iron when they need. The iron has to be absorbed easily and quickly so adding fertiliser heavy in iron is insufficient for these types of plants. Iron deficiencies are best cured by adding a seaweed and iron mixture to help restore the original foliage. Seaweed stimulates plant growth and the iron added to these products helps to give the rhododendrons the nutrients they need in the manner that they need it.

You should be using Rhododendron fertiliser on an annual basis which is a type of organic fertiliser that breaks down slowly, releasing the proper amount of nutrients at the proper times.

After flowering, you can give your plants additional fertilisers and it will help encourage vigorous growth and flowers the Following season. Having seaweed and sequestered iron additives mixed with regular fertiliser can help your Rhododendron foliage if you already have neutral or acidic soil. Adding the essential nutrients once the supply has been exhausted will correct just about any issue your Rhododendron is having which is the good news.

Issues with drainage can be tackled by transplantation as can issues with improper soil, you could also choose to improve the drainage by adding lots of organic matter and grit into the soil. Problems with nutrient absorption or hard water can be properly tackled by way of seaweed and iron mixtures as well as regular Rhododendron fertilisers. For healthy growth, place the plant under natural, dappled sunlight. Another significant cause for the Rhododendron plant leaves turning yellow is improper fertilization.

The yellow leaves may signal that the plant needs a more generous amount of nutrients. Another option is to use a diluted liquid fertilizer. Alternatively, your Rhododendron plant may develop yellow leaves when it cannot soak up the provided feed efficiently. When faced with such a difficulty, I apply fertilizer to the soil when it is moist; this ensures maximum absorption.

As much as you admire your Rhododendron plant, fertilizing it repeatedly can also lead to numerous problems, one of them being yellow leaves. The Rhododendron plant is a fairly large plant; however, feeding it over and over again is not a good idea. The Rhododendron plant may also form yellow leaves when an excessive amount of salts has accumulated in its system. While plant feed can be a significant source of salt buildup, chlorinated water falls right behind. To prevent salt buildup, avoid overfertilizing your Rhododendron plant and use room-temperature low-chlorine water only.

For fertilizing, use good-quality feed once a month only. To get rid of the salts in the water, fill up a bucket and let it sit overnight; the excess salts will settle at the bottom. The Rhododendrons are decently-sized plants with a moderate growth rate. Repotting it yearly is not essential; however, it usually needs repotting every two years.