Not knowing what sort of "cedar hedge" to which you are referring makes it difficult to make a recommendation. In the west, cypress tip moth sometimes infests cypress (Cupressus and Cupressocyparis) and false cypress (Chamaecyparis); those are also sometimes called cedars. In the east, cedar often refers to Juniperus (red cedar), Thuja or Chamaecyparis (white cedar); all are subject to bagworm infestations and various tip-miners. In the west, timely shearing is the most effective way to control cypress tip moth, and this may also be a tactic in other parts of North America. In many cases, infestations occur because there are few natural enemies about to reduce pest levels. Sometimes, pests are attracted to plants that are already weakened by stress. Healthy plants and diverse plantings, together with a reduction in pesticide use, will over time, increase beneficial organisms which will in turn reduce pest levels. Spraying to reduce pests generally affects beneficials to a greater degree than the actual target pest. This is because pest species often have a greater capacity to rebound -- they often reproduce faster, have a greater tolerance for pesticide residues and have a greater capacity to become resistant to pesticides. In the United States, one of the best sources of advice is your county, state or local agricultural university extension service. See, for example, the following links: University of Missouri-Columbia University of Massachussets Kansas State Research and Extension
Cedar hedge moths - part 2 Sorry I was missing some pieces of information. I live in South Surrey BC and have the type of cedar hedge that is common to this area but I dont know exactly what kind it is. It is what you see and get in the nurserys for cedar hedges, a tall slim tree about 4-6 feet. Ours are now about 10 feet, over a period of 10 years growth. We have white moths and have received two different pieces of advice on how to to eliminate them. One source said to spray now. The second source said to spray in the spring when the caterpillars have hatched. The advice from the second source seemed more credable when he explained the life cycle of the Moth.
I would say it is probably cypress tip moth that is the insect in question. For control you can spray Malathion or Sevin in late April as the larvae emerge from the cocoon (spraying prior to that is pointless as they are in the cocoon), and when eggs hatch in mid-June and again in early July. This information is quoted from the Nursery and Landscape pest management and production guide, page 218, 2002 edition.
If the plants are Thuja species -- either eastern white cedar (T. occidentalis) cultivars 'Smaragd' or 'Fastigiata' ("Pyramidalis" as its known in the trade) or the western red cedar (T. plicata) cultivar 'Excelsa' the problem is doubtfully cypress tip moth, as that pest prefers Junipers and true cypress hosts in the Vancouver area. However, even if the plants were to be attacked by this pest, the application of pesticides is wrong-headed. At this time of year, the cypress tip miner is safely protected by a thick layer of plant tissue. Most pesticides will not penetrate the tissue to where the pests are overwintering and will merely run off. Those pesticides that have systemic activity (are translocated in the tissue) are generally considerably more toxic and pose a significant hazard to people, pets and other organisms. Cypress tip moth mines only the tips of the branches and can easily be controlled by a light shearing in August in this area. Imagine how many other organisms (including beneficials) are sacrificed by such misguided pesticide applications.
