By: Anthony C. Arnoldi, Board-Certified Master Arborist WI-0102B
Many spruce are deteriorating rapidly. Only a short drive around the neighborhood will reveal how prevalent the condition is. Their needles are browning on the inside portions of the branches, causing the trees to thin more and more.
The problem is a fungus that attacks the needles – Rhizosphaera Needlecast. Since so many spruce have become infected, it is imperative that it be mentioned again.
A two or three spray program of carefully selected fungicides is administered to the foliage in spring and summer to block the infection from the newly formed needles. The older needles are not protected by the fungicides and many will eventually fall as they are probably already infected. This fungicide protection must be repeated uninterrupted, usually over a 5 year period, so that enough needle growth is replaced to allow beauty and health to return. Because the bulk of the needles may already be infected when spraying is initially begun, the spruce may look worse before it gets better. Consistent care, however, is what wins. Patience is definitely needed, but is rewarded.
Another very important aspect to success in managing needlecast fungi is the need to avoid water stress. Infected needles take from four to seventeen months to finally fall off. Water stress shortens this time considerably.
Give supplemental water to these spruces. Watering has been sporadic if given at all. Also, many people in suburban areas rely on their wells to supply this water. The concern is constantly voiced that watering their trees will burn out their well or make it go dry, or that repeatedly dragging hoses and sprinklers is especially difficult for them. All of these are valid concerns.
Conserve the moisture that does fall or that can be given. Mulching spruce or increasing the size of the root area mulched will helpas will increasing mulch depth to a full 4 inches. (but be sure to avoid wetting the foliage, especially if watering in the evening, to avoid promoting fungal infection of the needles).
However, if more moisture is not forthcoming, increased spruce mortality will surely be the result. For those spruce already damaged by the effects of water stress, treatment to encourage the replacement of fine feeder roots will be necessary. This is because spruce with reduced feeder roots (lost from the dehydrating effects of dry soil) will struggle to pull in water even if rains return! Root zone injections of nutrients, root biostimulants or mycorrhizae may be prescribed. Call your professional Wachtel Certified Arborist for help in assessing your spruce’s situation.