We began the growing season with some evergreen trees and shrubs turning brown, and now appear to be ending the season with a little more evergreen browning.
In spring, most browning is due to winter drying. When needles turn brown during fall, it can be due to a number of different factors including natural needle drop, fungal disease, spruce mites or bagworms.
The only pest for which a control measure might be needed this late in the season is spruce mites; and then only if active mites can be found on spruce. Our recent rains likely knocked mites and their fine webbing out of spruce trees, which helps with control.
To check for mites, tap an affected branch over a white sheet of paper. Hold the paper still and watch the specks. If they begin to crawl around after a few seconds, mites may be present. Check a few more branches before deciding to control. Keep in mind fall rains will provide some control, as well.
When checking brown evergreens, especially spruce, arborvitae and junipers, look for bagworms. Their populations were high this year and we saw damage.
At this time of year, bagworms will appear as 2-inch-long, triangular-shaped bags covered with fragments of brown needles. The bags will be tightly attached to twigs.
Bagworms are now overwintering as eggs inside the bags and insecticides will not control them at this stage. For now, pick and destroy as many of the bags as feasible.
In mid- to late June of next year, an application of a chemical insecticide or the organic compound Bacillus thuringiensis can be applied to infested evergreens to control bagworms.
In some cases, needle browning during fall is not due to a pest but to natural needle drop, which is harmless. It occurs about every three to five years on most conifers and is as normal as shade trees dropping their leaves during fall.
Natural needle drop will appear as a sudden yellowing or browning of interior needles only, from the bottom to the top of the tree. In some cases, only 1- and 2-year-old needles will remain green. When discolored needles are touched, they are easily knocked out of the tree.
If needles on branch tips are brown and stunted, or brown needles along a branch are hanging straight down, this could be Diplodia tip blight. One way to confirm this disease is to look for black fungal specks on the bottom of pine cones.
If most of the browning is near the lower half of the tree and branches are affected from the inside out, this is likely Dothistroma needle blight. With this disease, infected needles turn brown from the tip of the needle down to a reddish band on the needle; and red or purple spots may be found on green needles.
Both of these pine blights can be controlled with the correct fungicide, Chlorothalonil or Bordeaux mixture, applied at the correct time next spring, usually in April and again in May.
If the evergreen is a Scotch pine and browning is progressing rapidly, this most likely is pine wilt and the Scotch pine is best removed during winter. White pines and Austrian pine are also affected by pine wilt.
And while we’ve had adequate rainfall, if the weather becomes warm and dry, water evergreens just enough to keep the soil moist about 8 inches deep up until the soil freezes. Be sure to avoid overwatering. This will help reduce winter drying and additional evergreen browning next spring.