Fastidiously preserve blue spruces to stop a standard fungal illness from spreading

An outdated grouping of huge blue spruces in my entrance yard has been persevering with to say no in well being over the previous couple of years with decrease branches dying first after which progressing up the tree. What can I do to assist my timber?

— Sophia Desmond, Elgin

Your description signifies that your Colorado blue spruce (Picea pungens ‘Glauca’) is affected by cytospora canker. Cytospora canker is among the commonest fungal ailments of Colorado blue spruce. This illness is most extreme on Norway and Colorado spruce and is commonest on timber greater than 15 years outdated. Your timber are doubtless older than that if they’re massive timber which are greater than 20 ft tall.

Cytospora canker is characterised by the dying again of particular person branches, normally beginning with the oldest branches decrease on the tree. Because the illness progresses, increased branches will present injury. The lifeless brown needles might stay on the branches or fall off. Additionally, search for a tough, white residue on the decrease branches that resembles chook droppings. That is resin from contaminated branches increased on the tree dripping down. On these increased branches, you additionally might discover sunken, oozing cankers which are dripping the resin.

The fungus causes no drawback till the tree is pressured. That makes the illness extra prevalent on timber of low vigor, which will be brought on by low fertility, insect injury, shallow roots, drought, planting a tree in an improper web site or mechanical damage. Cytospora canker happens most frequently in timber which are drought-stressed. The spores of the fungus that causes cytospora canker are readily unfold by splashing water, birds, bugs, wind-driven rain and pruning. The fungus typically turns into established via wounds within the bark.

Bushes can stay a few years with cytospora canker, though it does make them a lot much less enticing because the illness progresses. Contaminated branches can’t be saved and needs to be pruned off. Do that when the climate is dry or when the tree is dormant in winter, so the fungus spores don’t unfold via dampness. Disinfect your pruner and noticed between cuts to cut back the prospect of spreading the illness. Lysol disinfectant works nicely for this. There are not any chemical controls for cytospora canker, so upkeep practices that scale back stress and enhance vigor are necessary. Forestall drought stress by supplying further water throughout dry climate.

The very best factor to do now could be present the tree with supplemental water for remainder of the season if circumstances proceed to be dry. Add 2 to three inches of mulch if there’s naked soil below the tree. Prune out contaminated branches this winter and fertilize the timber in spring. As soon as the lifeless branches are eliminated, you will want to determine if the timber are value holding. For those who preserve them, proceed the improved upkeep routine, together with watering, in future years.

For extra plant recommendation, contact the Plant Data Service on the Chicago Botanic Backyard at plantinfo@chicagobotanic.org. Tim Johnson is senior director of horticulture on the Chicago Botanic Backyard.