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Plant Health: Why do my Azaleas have brown spots on their leaves?

Have you been wondering why there are brown – grey spots on the top and underside of the Azalea leaves?©BMHPhotographyTheGardener’sNotebook2014Tetranychus urticae, commonly known as the two-spotted mite or red spider mite, is becoming a common pest in the home garden. Unfortunately, it has become a serious pest amongst many plant species, affecting a wide range of fruits, ornamental shrubs, vegetables, herbs and ornamental trees. But the main victim is Azaleas.
©BMHPhotographyTheGardener’sNotebook2014
T.urticae have strong piercing mouth parts which allow them to attack the plant’s individual cells. They produce a very fine webbing, resembling a web from a spider, on the foliage surface. Usually webbing will occur in the current feeding ‘grounds’ of affected plants. The two spotted mites are just visible to an unaided eye; usually if you look at the underside of a leaf you will see little brown/grey dots that move.

During winter months these mites will most likely congregate and feed in protected areas of a plant. For example, they will usually favour the underside of the foliage, bud/branch junctions, or even towards the base of a plant where they are protected from natural predators. As the weather gradually starts to get warmer and consistent in the spring months the mites will gradually work their way up, feeding on all areas of the plant. Unfortunately, T.urticae are more aggressive and are more damaging to a plant in the hotter weather of late spring and summer.©BMHPhotographyTheGardener’sNotebook2014Unfortunately, as T.urticae feed on their host plant, the upper leaf surface will gradually become mottled and start to discolour. In heavy infestations foliage will turn yellow and can become thin/brittle, like paper. Eventually these leaves will drop and shred from the plant.  If fruiting trees or shrubs are badly affected, it can be expected that the quality and quantity of future harvests will be poor, which is due to the weakened state of the plant.
©BMHPhotographyTheGardener’sNotebook2014
There are a few options in ways to try and maintain and control two spotted mite outbreaks in the garden. Because these mites do not like long periods of rain and moisture you can start treating your affected plants by watering them from above. But this is more effective when small outbreaks are occurring.  In the case of heavy infestations remove all the affected foliage and dispose of it in the bin (not in your compost!).  Also, consider doing a light prune, tip prune (5 – 10 cm), to encourage new growth. Otherwise another alternative is using pesticide sprays which is used to kill mites. But, depending on the state of the plant and the amount of infestation it is sometimes best to remove the whole plant and start a fresh.©BMHPhotographyTheGardener’sNotebook2014
By Bonnie-Marie Hibbs
©BMHPhotographyTheGardener’sNotebook2014

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