Spruce is a common grown shelterbelt tree in Manitoba. They prefer acid soils, that are coarse textured with good drainage, have adequate water and sheltered from extreme weather conditions. If conditions are not ideal, the trees will begin to decline and become more susceptible to pests. If your trees are declining and you are considering using a fungicide/insecticide, read the label carefully to make sure the product is registered for use on the trees species and to control the pest identified. Spruce problems can be divided into three categories – Physiological, Disease and Insect.
Winter burn or evergreen browning – caused by excessive water loss from the needles. In late winter/early spring, they take on a reddish brown appearance toward their branch tips and/or on one side of the tree. The south and southwest side may be worse due to more exposure to sun at potentially wind. If conditions are highly favorable for winter burn, buds can also lose moisture and be killed.
Natural Needle Drop – late August or early September, coniferous trees will naturally shed their older needles (usually needles which are 3 or 4 years old or older). During this process, the innermost needles will turn to yellow or brown and drop off. Although this process takes place every year, in some years it becomes more pronounced due to environmental factors. Needle loss can appear to be very dramatic and is often mistaken for a disease or insect problem. Nothing can be done to prevent natural death of needles since they do have a finite life span. Good maintenance can minimize environmental stress.
Competition Stress – if spruce are planted too close to each other, trees can suffer from competition stress. This occurs when the feeder roots from two or more trees take available water and nutrients from the same soil area resulting in slightly stronger trees taking most, while the weaker trees, deprived of water and nutrients, grow poorly and may decline and die. If the branches of two trees are in contact or intertwining, competition stress could be occurring.
Branch Canker – characterized by browning and death of entire branches. Individual diseased branches can occur anywhere on the tree, although the disease may start on lower branches and move upward. White or grayish crusty or resinous patches appear at the canker site and can also occur on the trunk. Pitch may ooze from these cankers and drip onto lower branches. During wet weather, some cankers can produce spores that disseminate to cause new infections. Pruning out areas affected is the only means of control once the disease has been initiated. Prune when the weather is dry, with pruning tools sterilized between cuts with alcohol (isopropyl alcohol), or a household disinfectant such as Pinesol or Lysol and all diseased material should be removed or destroyed.
Needle Cast – characterised by irregular tan, yellow, red-orange, reddish brown or black spots, specks or bands being produced on the needles from previous seasons of growth. The fungi can infect the new growth from the current season, but do not usually show symptoms on those needles until the following season. Affected needles generally drop early. Twigs of infected trees may appear stunted and may dieback. To prevent spreading, the new needles should be protected by applying a copper fungicide containing copper oxychloride just as growth begins in spring. Repeat applications 3 or 4 times at 10 day intervals. If the planting is not too large, it would be helpful to rake up and remove fallen needles from under the trees to remove them as a source of reinfection. There are currently no fungicides available for home use but fungicides with commercial or agricultural registration are available. Consult with an arborist or tree care service for fungicide options.
Spider Mites – all evergreen trees have a resident population, but during hot dry spells populations can explode. Visual symptoms start as dingy yellow or dusty needles and progress to brown and dry, then needles drop. There may also be a fine webbing, between the needles. In severe or prolonged infestations, dust particles, shed needles and dead mites catch in the webbing giving the tree an unhealthy appearance. Damage to the tree is caused by both adults and nymphs sucking sap from the needles. Mites can be controlled by using any insecticide listing mites and spruce on the label, at a rate recommended on the label. Dormant oil sprays can also be used to control spider mites. See directions for use on the labels.
Spruce Needle Miner – webbing is produced and may contain dead needles and frass (droppings). Damage is done after tiny larvae hatch from eggs that have been laid along the sides of a needle and begin to chew a hole at the base of it. The insects feed on the needles and exit from the same hole in search of new needles. Full-grown larvae are green with a brown head and are about 6 mm long. The larvae remain active until October when they construct a cocoon inside a nest of dead needles and frass to overwinter. Adults emerge as small greyish brown moths that have a 12 mm wingspan. If a tree has a large number of needle miner nests it can appear quite unsightly, as airborne material such as dust and poplar cotton become easily caught in them. Heavy infestations can severely weaken the tree through loss of needles. Before bud break in spring, the nests can be washed away with a strong stream of water from a garden hose. The debris should then be gathered and destroyed. This may help to reduce the current year’s infestation.
White Pine Needle Scale – evident by tiny white flecks on the needles that resemble spots of paint. Each white scale contains a dead body of a female scale insect and her overwintering eggs. During the summer the crawlers moult to become adults after which they begin to secrete a white scale covering. Scale insect feeding damage causes large yellow areas on the needles that can coalesce if the population density becomes excessively high. Sustained heavy attack for 2 or more years can cause trees to lose most of their needles. Insecticides or dormant oil sprays listing spruce and scale insects on the label can be used for control. Follow label directions.
White Pine Weevils – weevils kill the top 2-3 years growth of their host trees. Damage very conspicuous, causing the terminal leader (very top of the tree) to wilt and take on a crook shape, turn brown and die. Located below the damaged area, there can be found small exit holes made by the emerging adult weevils. Adult weevils overwinter in the litter on the ground. There are no insecticides registered for control. Prune and burn infested leaders before mid-July to remove and kill the insects. Cut back all but one live lateral (side) shoot by at least half their lengths to maintain single-stem dominance. Avoid planting the highly susceptible Colorado blue spruce in areas where white pine weevils have previously caused damage.
Spruce Bud Scale – heavy infestations can result in twig and branch dieback. The presence of sooty mold on twigs, needles and branches may be the first clue to the presence of the insect. The sooty mold does not cause any damage to the tree but is unsightly and since it is highly visible is often mistaken for the cause of needle and twig dieback if these are occurring in association with the scale infestation. The female adult scales cluster along the stems of twigs. They closely resemble the buds of the spruce tree, lower branches on the trees are often the most heavily infested. Heavy scale infestations result in discoloration and loss of needles, twig dieback, dieback of lower branches and reduced tree vigour and growth. Infested trees are also reported to be more susceptible to winter injury. Any insecticide listing spruce and scale insects on the label can be applied to reduce damage from this insect. Follow label directions. Insecticides should be applied while the crawlers are still active.