As I have driven around Illinois this summer, I have noticed the poor condition of many of our spruces and pines in home landscapes, privacy plantings and windbreaks. While there can be a variety of factors responsible, in this article I want to touch on some abiotic and biotic factors to consider.
• The environment. As we all know, we have had extremes in weather the past several years. Very wet springs and early summers have been followed by hot and dry conditions in July, August and even September (especially 2017). The 2018 growing season was similar, but it brought more spotty late summer and early fall rains.
What does this have to do with the health of conifer trees? First, conifers do not like “wet feet.” Trees planted on heavy clay soils that are slow to drain (i.e., man-made berms) or are situated in low areas will suffer from excessive soil moisture and flooding. Saturated soils are hostile to root systems, leading to root rots and death of fine absorbing roots. The effects are similar to what probably went on during the 2012 drought, except then it was due to lack of soil moisture. Any time a tree’s root system is compromised or damaged, it is serious.
Second, Colorado blue spruce is used to moderate summer temperatures. Last year, we had lots of rain, and then it turned hot and dry from July into September. We have had a lot of hot weather in 2018, along with very dry spells. Stressors such as flooding and saturated soils followed by hot, dry weather really take a toll on tree root systems and their ability to take up water and nutrients, and to undergo photosynthesis. Trees under stress for whatever reason are more prone to insect attacks (i.e., bark beetles and wood-boring insects), needle cast diseases and cankers.
• Disease. Along with the environment, another potential stressor of Colorado blue spruce is Rhizosphaera needle cast. This fungal disease attacks the needles of Colorado blue, Norway and white spruce, as well as pines, and is associated with above-average precipitation and high relative humidity.
Faint yellow bands appear on infected needles four to 11 months after infection, followed by small, dark-brown or black spherical fruiting bodies (pycnidia) in spring. Heavily infected needles will have fine black lines on each side of the needle and from a distance will appear black or purplish. The disease typically occurs at the base of the tree canopy near the ground and then progresses upward and inward. Premature needle cast is the main problem, resulting in a thin canopy, branch dieback and an unsightly appearance. Dry springs and summers can help reduce disease incidence.
Management of fungal foliar diseases is always challenging. Nonchemical options include planting less-susceptible species, promoting good air circulation by using wider plant spacing, pruning lower branches (those touching the ground or losing leaves due to shade), minimizing vegetation from under the tree, and mulching. Trees that are in poor condition or dead should be removed, as they will provide sources of future fungal infections and insect breeding sites. Fungicidal sprays can be applied, but are required on a regular basis for the first two months after bud break.
A common spruce malady is Cytospora canker. This fungal canker attacks Colorado blue and Norway spruces. Symptoms include browning of needles and dying of lower branches, along with needle drop. The cankers are usually not clearly visible and may appear as amber, purplish-white or white patches of resin on the lower bark surfaces of affected branches. No fungicides are effective against cankers. Remove diseased branches and avoid wounding the bark, as this provides an entry point for the fungus. Avoid pruning during wet periods, and make sure to sanitize your pruning tools after each pruning cut.
Good plant health care practices — including proper plant selection and placement, mulching, fertilization and watering, drainage, and pruning — can help your trees stay healthy.
Miller is a horticulture professor at Joliet Junior College in Joliet, Ill., and a senior research scientist in entomology at The Morton Arboretum in Lisle, Ill. Email your tree questions to him at [email protected].