For regions that can experience 2 infections per year the new growth will turn purplish brown and begin dropping from the tree by fall (University of Maryland Extension, (2021)) otherwise they discolour by spring. On a healthy needle you will see fine white lines, which are the stomata (the breathing pours). They may or may not have a tiny white cap on their tops, which is the plug from the stomata pores. They appear as dark, smooth, tiny little balls that are arranged in fine rows up and down the needles. The mature pycnidia are very tiny, but they are readily visible with the aid of a hand lense. The fruiting bodies of the fungus (pycnidia) will begin emerging through stomatal pores on these discoloured needles and release spores that can be splashed or blown to new foliage. ![]() By spring these infected needles die and usually turn a purplish-brown, although they may also appear to be brown, reddish brown or tan in colour. ![]() To the untrained eye this initial infection is difficult to detect. The first symptom of infection is a faint yellow band or mottling on infected needles along with small immature fruiting bodies. To positively identify Rhizosphaera and its species samples will need to be sent to a laboratory for microscopic evaluation, as other needle cast diseases or conditions appear very similar. The species Rhizosphaera kalkhoffii is the one most encountered on spruce, especially Colorado Blue Spruce. Rhizosphaera is comprised of several species and are known to infect various species of a variety of conifers including Spruce ( Picea), True Fir ( Abies), Douglas Fir ( Pseudotsuga), Pine ( Pinus), Cedar ( Cedrus), Hemlock ( Tsuga) (Hudelson B., (Revised: )) and larch ( Larix) (Brazee N.J., (Updated: April 2022)).
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