December 16, 2004 at 7:18 a.m.
Broom rust on balsam fir is a fungal disease that occurs on the branches of most native fir. The main characteristics include a multiple of upright branches with thick, shortened needles. This growth can reach several feet in diameter and is called a witch's broom. The always popular balsam fir Christmas tree is a common host of broom rust. Even though fir broom rust can cause loss of tree quality, it is rarely considered a major threat to Christmas trees.
Fir broom rust, like most rust diseases, requires two hosts to complete its life cycle. The alternate host, chickweed, is infected in summer by spores which are produced on the needles of fir. After the infection of the chickweed leaves, the fungus produces two types of spores that reinforce the original host. The following spring the spores infect the fir needles, causing the witch's broom.
To manage fir broom rust, prune and destroy all brooms. This disrupts the disease cycle. Also, remove all chickweed plants by burning, mowing or applying herbicide to the plants.
Brown spot is a fungal disease that commonly infects Scots pine, another popular Christmas tree. This disease is a serious threat to Christmas trees because it causes browning of the needles and premature needle loss. Although brown spot rarely kills Christmas trees, severe infections render the Christmas trees unsaleable.
Brown spot usually occurs near the base of the tree where moisture levels are the highest. Individual reddish-brown, circular spots with a yellow halo begin to appear on the needles in late summer. As the spots enlarge and the fungus continues to grow, they girdle the needle, killing it. As the needle dies, it turns yellow and then brown from the tip inward. Brown needles are most frequently seen from August through October. When the needles have died, the fungus forms black structures. They are visible from the needles during wet periods. Spores released infest new growth and the cycle repeats itself.
To manage brown spot, try to maintain tree health by properly watering, fertilizing, and mulching. If infections are severe, fungicides such as chorothalonil may be needed. In Christmas plantations, remove and destroy severely infected trees and Scots pine trees along windbreaks.
Your indoor gift may include a poinsettia, which may also have disease problems. Poinsettia, like all other plants is susceptible to root rot. A number of different fungi are known to cause root rot of poinsettia. These fungi survive and live in the soil and are stimulated by wet conditions.
Poinsettias infected by root rot fungi may begin to show symptoms of poor growth, drought stress, yellowing leaves near the base of the plant, or leaf drop. It is important to check soil moisture before watering plants, so that you do not mistake root rot symptoms with poor growth or drought stress and over-watered plants.
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