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Weeping willow is a magnet for bugs and blight

Q: Two years ago, I planted a potentilla in a sunny spot. It did great for two years. This spring, I noticed, to my astonishment, that something had chewed every branch down to the ground! There is a thin branch sticking straight up out of the center of the plant.

It has a few pitiful new leaves growing on it. We live in a well-established suburb with a tall fence around the entire backyard, so this could not have been done by deer. What on earth could have done this? Can I anticipate new growth? How can I prevent it from happening again?

A: Look around your yard for evidence of cottontail activity. Rabbits will do the same thing to a shrub that deer will. Cut it down to the crown. If the plant went into the winter in a healthy, robust state, chances are very good it will recover this growing season, so be patient.

Before snowy weather arrives next fall, put up an exclusion fence (chicken or rabbit wire) around it or put your faith in one of the many rabbit repellents on the market. Trust me that the exclusion fence will work better.

Q: We have a very pretty willow tree in our front yard. It was planted right next to a pond that we have now filled in and made into a rock garden. I know it is a willow, but I don't know what kind. It has small, golden green leaves that hang down to the ground like a weeping willow. Until last summer, it seemed fine.

Now we have noticed that some of the branches are black and dying. We cut and pruned them away. What is happening? Some of the lower branches (thicker ones close to the trunk) seemed to be twisting around each other.

A: The tree sounds like a typical weeping willow, which is one of the more common trees seen throughout American landscapes in the north. Unfortunately for this beautiful tree, there are hordes of pathogens and insects that adopt it to live and multiply in. Some of them are bacterial twig blight, crown gall, black canker, rust, tar spot, aphids, willow galls and willow scurfy scale.

The species is a living lab for plant pathologists, entomologists and horticulturists to study. All of this doesn't help you solve the problem you are observing, so I suggest that you contact a local International Society of Arboretum certified arborist to inspect the tree to get the disease or diseases identified. The arborist can give you proper recommendations to control any further spread of the problem.

Q: I have a flowering crab apple tree. My neighbor noticed a large, hairy larva sack on one of the branches. I cut off the branch and got rid of the sack. Any idea what it was? I was very hasty in throwing it away. I should have taken a closer look.

A: That probably was a collection of tent caterpillars that are voracious foliage feeders. You did the right "organic" thing by doing what you did and likely got them all. Check the tree in the next couple of days to make sure there are no stragglers still feeding.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail