The weather in March can be extremely variable. Very cold, wet weather can suddenly turn into warm and sunny weather. May of our cooler season pests become more active in March. Watch for eriophyid mites on hemlock and white pines. These extremely small, wedge-shaped mites are a translucent, straw, or orangey-yellow color. They can do considerable damage to the leaves of hemlock and pine. Hemlock leaves will turn yellow-green then olive green as the hemlock rust mite feeds. On white pine, especially dwarf cultivars, the pine sheath mite can be found at the base of the needle bundle. Pull the needles apart to find this very small mite. Needles will turn yellow then brown. For both hemlock and pine, heavy infestations will cause major needle drop. Tap a branch over a white sheet of paper. Check for this pest on the paper with a strong magnifying glass (20x). If present in large numbers, treat infected plants with a 2% horticultural spray.

    Another pest of hemlocks is woolly adelgids. These small, aphid-like insects are covered with a white "wool" which is quite visible. Look for little tufts of cotton on the base on individual needles. The adelgid feeds on the sap of the needle, causing it to turn grey or olive green, and then fall off. Heavy infestations over a few years can kill the tree. New juvenile adelgids, called crawlers, hatch in spring over a long period. Tap an infected branch over a sheet of white paper and with the aid of magnifying glass, check for this crawling stage. A 2% horticultural oil spray will control crawlers.

    Spruce spider mites also become active this month. They favor conifers: arborvitae, firs, spruce, junipers, and pines. They can be one of the most destructive pests of ornamental conifers. They feed on the underside of needles, causing the yellow, stippled appearance. On hemlock, spruce spider mites can cause the bottom half of needles to turn white. Silky webbing may be present, and needles eventually turn brown and fall off. Use a white sheet of paper and tap on a small branch. These mites will easily be spotted on the paper as red or blackish moving specks.