When fall arrives in the Sarnia Lambton area, it is normal to see yellowing and browning in the needles of juniper, pine, cedar and spruce trees. Typically discolouration will affect needles which are older and closer to the trunk of the tree. This discolouration can begin as early as August and continue until the ground is frozen. The needles of the tree will usually begin to drop in fall and can continue into the winter months.
The amount of shedding can be increased if the tree is placed under stress due to insects, mites, drought or flooding. Every tree varies in the growth and shedding of needles, spruce trees can keep their needles for several years while conifers do not keep their growth on their branches. The reason evergreens are bare of needles towards the centre of the trunk is because the needles it drops are not replaced.
Other Potential Causes of Discolouration
Winter Stress – The effects of winter stress are most noticeable during spring. A common cause is over fertilization in the late summer and fall that promotes succulent growth that does not have sufficient time to fully mature before the onset of winter.
Mites and Insect Attacks – Mites and insect attacks can also cause unnatural browning and yellowing throughout the growing season.
Needle cast fungi – In severe cases, needle cast fungi can not only cause yellowing and browning in the needles of spruce and pine trees but can also leave the tree sparse of needles to the point it can not longer produce enough food and slowly dies. Needle cast fungi needs to be treated as soon as it appears in the growth of new needles furthest away from the trunk.<
Fruiting bodies – Fruiting bodies appears as small, black ovals that may be seen in the straw-coloured areas of infected needles. The infection is spread through spores produced by the fruiting bodies. Professional identification of the fungus is necessary to make sure chemical treatment is applied before the spores are released. A method of non-chemical based control is to rake up and destroy all the needles the tree sheds.