Issue 8, June 19, 2017

Spruce Tip Dieback

The University of Illinois Plant Clinic has received a number of samples, emails, and calls about tip dieback on spruce this spring. This is not a common problem on spruce in Illinois, so I was excited to receive our first few samples to see what we could find on them.

After incubation, we were able to identify the fungal pathogen Sirococcus on some of the samples. According to the Plant Clinic Director Dr. Suzanne Bissonnette, this was a very common disease several decades ago but prevalence has been decreasing for quite some time. The most recent records of Sirococcus at the Plant Clinic are from 2014, when two samples were confirmed with the disease.

Sirococcus causes a shoot blight on various conifers, including pine, spruce, fir, and hemlock. Development of the disease is favored by cool, humid conditions. The pathogen infects succulent tissue, usually seedlings, young shoots, and current or last year's twigs. The needles begin to droop as small cankers form on the shoots, leading to a browning and withering of the shoot tip. The pathogen forms fruiting structures on twigs, but these may be difficult to see and may be confused with other harmless fungal structures. Microscopic examination is required to confirm the disease.

Management for Sirococcus blight consists of fungicide applications (containing azoxystrobin, chlorothalonil, or chlorothalonil + thiophanate-methyl active ingredients) in spring. Fungicides should be applied as soon as bud caps fall off the needles, and again when needles are fully elongated. These fungicides may not be available without an applicator's license. Mulching the base of the tree, fertilizing in spring before new growth expands, watering during periods of dryness during the growing season, and pruning out dead branches during dry weather is also recommended to reduce stress on conifers.

After incubation and examination, no pathogens or insects were found on some of the samples. We suspect that environmental stress may be playing a role as well. We've had several years of stressful conditions that are still affecting the overall health of many of our trees. We recommend following the steps listed above to reduce stress and keep trees healthy. (Diane Plewa)

Diane Plewa

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