Insects develop from the eggs and excrete onto the upper surface of leaves below, creating sooty mould, a fungus which develops over the winter months especially under greenhouse conditions. Rabbit populations go up and down depending upon myxomatosis, but they can eat the young foliage on evergreen azaleas and dwarf rhododendrons when there is little else for them to eat. Bark split occurs when the stem is full of sap and freezes hard, expanding to crack open the bark, like water in bottle. We are confident that our plants leave here inoculated against vine weevil damage. Shelter susceptible plants from drying winds, either with other plantings or by planting near structures. It is spread by leaf hoppers (see 4.2.5) which are a pale green insect that appears between June and September. Millais Nurseries. Bud blast is reduced when leaf hoppers are reduced, though recent research is challenging this link. All plants can take a year to settle into a new garden, but some of our choice varieties are not stocked by Garden Centres because they do not bud up and flower at a young age. Chlorosis of the leaf can also be caused by poor conditions such as drainage problems, soil pH or drought, so check these first. These insects do not cause any damage whilst feeding, but the trouble comes in the autumn when they lay their eggs in next year’s flower buds. It is these grubs which feed on the tasty soft roots of rhododendrons, and they can eat all the bark away from the main stem just at or below compost level. The white grubs pupate into adults during warm spring weather and the life-cycle starts again. Please refer to the RHS website for the most up to date list of chemicals available. Spores can be spread to healthy plants by insects or by air. This is usually a sign of lack of iron. This is a fungal disease which disfigures the leaves of evergreen azaleas and is spread by airborne spores. Early autumn frosts can mark tender ‘second flush’ leaves which have not toughened up in time for the winter. Alternatively use a chemical vine-weevil killer drenched into the MOIST root-ball to kill grubs in the soil from September to May. However, sometimes the leaves show that they are not as healthy as they should be, and hopefully this section will enable you to make corrections. This is especially a problem after rainfall or irrigation. The disease can also be prevented by ensuring good air movement, better spacing, removing overhanging branches, and not planting in still, humid corners of the garden. Caterpillars can feed on rhododendrons, sometimes dropping off overhanging trees onto the foliage, where they make notches on leaves which can resemble vine weevil damage. Provide adequate soil moisture by irrigation where dry soil is a problem. Azalea (Rhododendron spp. In all cases, the damage is purely cosmetic, and it will not harm the plant. Use a good organic or chemical insect spray after the flowering season. Deciduous azaleas with R. occidentale parentage can be prone to powdery mildew in early September. Microclimates can be improved with a tree canopy. For further details and an up to date list of chemical controls, please refer to the RHS website: https://www.rhs.org.uk/advice/profile?pid=253. In this regard, why are the leaves on my rhododendron turning brown? However, caterpillar notchings are more gentle and not as jagged, and sometimes even in the middle of the leaf. A number of rare species that we grow are shy flowering types, especially those of the taliensia subsection which are real collector’s plants not available elsewhere. For further advice, please refer to up to date recommendations from the RHS: www.rhs.org.uk/advice/profile?PID=234. But frost can damage just some of the ‘pips’ within a flower, so that it opens with a reduced number of corollas in spring. See 4.2.1 Vine Weevil. Adults, cast skins, and brown excrement can be found on the undersides of affected leaves. Rhododendron lace bug is closely related to the better known Pieris lace bug. Your soil may be natural limey, or you may have a pocket of lime leaching out of a wall. If your Rhododendron isn't flowering and you can see some black buds, this could be either frost (see 4.1.5) or bud blast. For further details and an up to date list of chemical controls, please refer to the RHS website: https://www.rhs.org.uk/advice/profile?PID=663. It marks rhododendron leaves with unsightly pock-marked yellowish spotting on the upper surface during the summer. Many are cosmetic, and whilst they may be unsightly, they cause little long-term damage. Water stress can occur under both extremes of flooded, overly-saturated soils or under drought conditions when too little water is present.