A GREENER VIEW: Black Knot Fungus and Mulch

Creators Syndicate | 5/28/2014, 7:45 a.m.
Q: I have a flowering cherry tree that has ugly "lumps" growing up the trunk and on the bigger branches, ...
Black Knot Disease Creators.com


Q: I have a flowering cherry tree that has ugly "lumps" growing up the trunk and on the bigger branches, the tree is around 20-feet tall. I have been told that these growths are harmless, which I find hard to believe. My question is: Will they kill my tree?

A: It sounds like the tree has a fungal disease called black knot. It is a fungal canker of apricots, cherries and plums. The cankers look like charcoal wrapped on the branch. They enlarge and kill the branch over two years. Whole trees die when the trunk is girdled or many branches are infected. The infected tree is weaker and may die of other causes.

Fungicide sprays can help stop new infections, but they do not cure old ones. It is probably too late to spray this year. The sprays are typically done as new growth comes out, and then again when the tree is flowering.

An infected branch can be pruned off if it is cut at least 8-10 inches closer to the trunk. During the first spring, the infected spot on the branch is very hard to find. It will swell and will be an olive green color. By fall, it will develop into the black knot that can be an inch to over a foot long. Pruning is often done in winter when the knots are more visible.

Q: I have a question on a pussy willow tree. When I bought it a few years ago, it was the weeping kind, with branches that drooped downwards and had catkins on it. Two years ago, I pruned it back, getting rid of all the dead stuff. I pruned it severely and cut all the branches off, leaving only about 2 feet of the main tree trunk. I figured it would grow back and be a weeping one again, but I've gotten a lot of healthy branches shooting off the side of the main trunk and they are all growing upwards. I have green leaves on them but no pussy willows. Did I ruin my tree? Will it go back to being a weeping one or will it stay an upright tree? Will I ever get the catkins back? That is why I bought it!

A: There are several kinds of weeping trees sold in stores that have branches that hang down from a single spot on a straight trunk several feet off the ground. I have seen weeping crabapples, cherries, mulberries, pussy willows, plums and others. They are all a combination of two different varieties of the tree species in question. The roots and tall straight section of trunk are one variety that does not weep. Grafted on to the top of the trunk is a different variety that has the weeping branches. You are allowed to prune the weeping branches back to the graft union (large lump) at the top of the tree trunk, but you cannot cut the graft union off the trunk. The shoots that remain on your tree should produce flowers at some point that will have the fuzzy flowers you want, but they won't be weeping. For a weeping tree, you will need to replace it.

I am sorry for the bad news, but if you have any more questions, let me know.

Q: How much mulch does it take to cover 100 square feet?

A: Let's assume you are going to cover the area 3 inches deep. Imagine a cube-shaped pile of mulch 3 feet tall, 3 feet wide and 3 feet long. That is a cubic yard of mulch. The base of the pile is 9 square feet, since it is 3 feet wide and 3 feet long.

Now imagine taking a layer off the top that is 3 inches thick. You can do this 12 times, since 3 feet tall is also 36 inches tall, and 36 divided by 3 is 12. There are 12 layers 3 inches thick and 9 square feet in size. So 2 times 9 square feet is 96 square feet. Therefore a cubic yard of mulch will cover almost 100 square feet of area 3 inches thick.

Email questions to Jeff Rugg at info@greenerview.com. To find out more about Jeff Rugg and read features by other Creators Syndicate writers and cartoonists, visit the Creators Syndicate website at www.creators.com.