How to Diagnose Diseases on Shrubs and Hedges
- 1). Check out the health of the shrubs and hedges. If they are declining in general, the problem may be root rot. Dig into the ground carefully around the roots to inspect them. Rotted, dead roots are a sure sign of too much water. Reduce watering to see if the shrubs get renewed health and vigor.
- 2). Notice leaves that are dropping to the ground too early and dead branches. These are indications of vascular wilts or Verticillium. The dying branches will have a black or brown ring within the vascular system. Apply a fungicide, following the manufacturer's instructions, to eliminate this fungal disease.
- 3). Identify fire blight if the leaves and shoots are red and look scorched. This affliction only affects the Rosaceae family, which includes your roses. Cut off diseased shoots and stems between late summer and winter. Destroy the wood to limit the spread.
- 4). Diagnose powdery mildew if there is a gray or white dust on the leaves. The fungus starts with small spots then spreads all over the leaves. Shrubs and hedges most susceptible are azalea, rose, lilac and rhododendron. Suppress the problem with the application of a sulfur-based fungicide. Get rid of the leaves that have fallen off.
- 5). Check out the roots, stems and crowns to see if there are rounded growths with a rough texture. This is crown gall. Prune the affected areas. Burn them to rid the shrub of the disease and disinfect the cuts.
- 6). Spot dead and diseased stems. If they have bulbous or gnarled growths, it's probably bacterial blight or bacterial canker. This is fairly common on shrubs and lilac bushes. Use a copper-based fungicide to treat it.
- 7). Know that spotty, dead leaves and twigs can indicate a foliar fungal disease. If twigs are dying back and there are cankers growing on the woody sections of the hedge, you need to treat them with a broad-spectrum fungicide. Get rid of fallen leaves to reduce spread.
- 8). Diagnose rose shrubs and rhododendrons with rose mosaic and rhododendron ringspot if their leaves have blotchy brown or yellow discolorations. These plants are likely to suffer when they are stressed, like following a drastic pruning or during a drought. Dig up the infected plant. There is no cure for shrub viruses.
- 9). Look for persistent canker growths or abnormal or diseased bark sections. These are fungal cankers. Trim the branches and twigs where they meet healthy wood. Apply a fungicide when new spores are being created.
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