There are 40 to 50 species of privets in the genius Ligustrum, a member of the olive family; they usually have oval leaves and sometimes blackberries and clusters of aromatic white flowers. Varieties are native to Asia, Australia, Europe and the Mediterranean. They are widely used for screens and hedges. Privet hedges grow well and are easy to care for. Their main diseases are wilt, honey fungus and spider mites.
If the leaves of your privet hedge curl, turn yellow or reddish and begin to die, your hedge might have wilt. Diagnosis is difficult because root rot and excessive soil moisture can cause the same symptoms. Wilt disease, a fungus, starts in the roots of privet and moves upward. As it does, the plant releases gums to fight the fungus and its vascular system becomes plugged. If you peel the bark away, you’ll see discoloration and a striping of the wood. The progression of wilt varies. Sometimes it disappears on its own. Other times it spreads. Dieback can occur over several years.
No fungicide will eradicate this fungus. Try to plant varieties of privet that are known to resist the fungus. If your plants show symptoms, water them and use fertilizer that is low in nitrogen and high in potassium. Sterilize the tools you use for pruning. Try to remove infected plants with the root balls intact and do not plant more privet in the same hole.
Honey fungus, or Armillaria, is a parasitic fungi that likes privet. It forms an edible yellow mushroom that can continue to thrive after it kills its host. The rizomorphs, clumps of long branching cells that the fungi uses to spread, grow along the ground causing root rot, among other problems. Leaves fail to appear in spring. Leafy branches die off. Strands that look like black boot laces appear around the tree and under the bark. Thin sheets of cream-colored fungi often grow at the base of the stem or under the bark. The fungus thrives close to the ground and can invade new roots or the root collar (where the root meets the ground).
Avoiding Honey Fungus
To discourage honey fungus, you should make sure that your soil drains well and use a clean, woody mulch. If your hedge is infected, dig up the plant and its roots and get rid of them. Get rid of all the plants on either side of your hedge.
If you see webbing in your privet hedge, your privet might be infected with spider mites. Spider mites are arachnids, relatives of daddy long legs, scorpions, spiders and ticks. They suck up sap from leaves of your privet hedge, discolor them, making them look gray or bronze. The leaves can drop off. A serious infestation can kill your hedge.
Eliminating Spider Mites
To kill spider mites, you can introduce natural predators including pirate bugs, thrip, and the Geocons, species of big-eyed bugs. The Stethorus species of lady beetle destroys spider mites. You can buy predatory mites online including Galendromus occidentalis, Mesoseiulus longipes, Neoseiulus californicus and Phytoseiulus perimilis. These mites need humidity and mainly are used to attack spider mites indoors. One reason for severe spider mite infestations is that the use of insecticides have killed their natural enemies. Pesticides that can control spider mites including those with the active ingredient of acephante, abamectin, bifenthrin, hexythiazox, spiromesifan or sulfur.