Foliage Browned In Winter indicates Wind and Sunburn
Cherry laurel shrubs growing near the northern limits of their range are vulnerable to winter damage. Winter sun and wind sometimes burn and dry the broad leaves, giving them a scorched appearance. Erect a protective screen of burlap or spun agricultural fabric around shrubs that show this problem. Be sure to allow adequate air circulation around the shrub. Do not wrap it, do not use plastic.
Shrub Declines; Small Holes In Stems means Shothole Borer
Shothole borers are beetles that attack trees and shrubs that are weakened or diseased. They occur throughout the United States. They bore into stem bark, leaving holes the size of a pencil lead with telltale reddish sawdust outside on the bark. They proceed to bore longitudinal galleries within the stems in which they lay eggs. When the eggs hatch, the emerging larvae make more holes as they bore out. There may be 2 generations each season in the North, three in the South. Affected shrubs grow progressively weaker and more vulnerable to heat, drought, and disease. Prevent attacks by maintaining the vigor of the shrubs. Feed, water and prune as described above.
To control existing borers, thoroughly examine affected shrubs before the spring season arrives. Cut and burn any dying stems below the borer holes. In June, crush any visible eggs. During the summer season, check to see if fine boring dust is being pushed from small borer holes. Cut out holes with a sharp knife. If the tunnels are fairly straight, kill the borer larva by probing the tunnel with a flexible wire, or pull it out by means of a hooked wire to make certain it is destroyed. Nicotine sulfate kills borers. Dip a piece of cotton or soft cloth into a solution of 1 part nicotine sulfate to 4 parts water, and stuff it into the borer's hole or try injecting nicotine paste into the holes. Clean up all yard debris and burn all weeds, stems and plant remains likely to harbor over wintering eggs.
For more information see file on Dealing With Borers.
Small Bumps On Leaves And Twigs tells us there is Scale
Various types of scale insects sometimes form groups of small bumps or blister-like outgrowths on cherrylaurel stems and leaves. About 1/10 inch in diameter, these waxy shells protect the insect feeding beneath. Some are gray bumps that have a raised nipple in the center and are clustered in masses on stems where they join branches or close to growing tips. They cause leaves to turn yellow, and they often secrete honeydew, which covers leaves and encourages sooty mold. A major infestation can kill a shrub.
Handle mild scale infestations by simply scraping the telltale bumps off shrub surfaces with a fingernail or cotton swab dipped in rubbing alcohol. Heavy infestations require spraying. Use a mixture of alcohol and insecticidal soap every 3 days for 2 weeks. Add 1 tablespoon of alcohol to to a pint of ready to use commercial soap spray. A light horticultural oil sprayed on cherrylaurel shrubs while they are dormant in late winter or early spring will smother over wintering scale. Spray Sevin when the young larvae (or "crawlers") have hatched and before they start forming their new scales.
For more information see file on Controlling Scale.
Leaves Discolored shows Psyllids
Laurel psyllid and others suck plant sap, causing discoloration and distortion (cupping) of foliage. Adults, about 1/10 inch long, are commonly known as "jumping plant lice," resembling tiny cicadas, covered with whitish waxy filaments. Control them by spraying shrubs in early spring with light horticultural (not heavy dormant) oil to kill adults and eggs. Spray established pests with insecticidal soap every 3 to 5 days for two weeks.
Plant Weakens, Leaves Turn Yellow means Whiteflies
Adult whiteflies are clearly visible on cherry laurel leaf undersides. They are white winged, moth-like insects about the size of a pinhead. In their pupa stage they are greenish white and oval. Bump or brush branches of an infested shrub and they suddenly fly up, looking like flying dandruff. Whitefly causes yellowish mottling on the upper side of the leaves. Nymphs and adults suck juices from shrub leaves, buds, and stems. A sooty mold fungus sometimes develops on the honeydew secreted by immature insects. Spray visible flies with commercial insecticidal soap spray every 3 to 5 days for two weeks. If that doesn't work, try pyrethrum every 5 days for two weeks as a last resort.
For more information see file on Controlling Whiteflies.
Red Spots on Leaves, Holes there is Leaf Spot
Leaf spot fungi cause red spots on the leaves of cherry laurel shrubs about the time new leaves become full-sized. New spots continue to develop over the summer. They gradually merge and rot out, leaving holes in the foliage. Heavily infected leaves turn yellow or brown and fall prematurely. Cool, moist spring weather encourages this disease when new leaves are developing. It is sometimes a minor problem in cherry laurel. Shake out all fallen and diseased leaves from the shrub and destroy them. Remove all dead branches in the center of the shrub to allow better aeration. Mulching helps prevent the disease spores from splashing up from the ground and infecting plants. Leaf spot rarely is severe. However, if it causes a shrub to become unsightly, spray at weekly to 10-day intervals with sulfur or Bordeaux mixture or other copper fungicide, starting when the blossom petals fall.
For more information see file on Controlling Fungal Disease.