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Taking care of holes and thistles

June 19, 2009|By JEFF RUGG / Creators Syndicate

Q: We have found that one of our trees has lots of holes in the leaves. Is there something we can spray on the tree to stop the damage?

A: I get this type of question every year. I wish there were a simple spray that could fix plant problems. First, we need to know what caused the holes to form. They could be the result of environmental problems such as a frost months ago when the leaves were first forming or hail from a storm. They could be the result of some kind of insect that chews plant leaves, but unless it is still there, nothing sprayed on the tree will help it now. Holes can also be formed when dead tissue falls out of a leaf. Some diseases cause areas of a leaf to die and then when the environmental conditions change, the infection stops. The area that is dead may drop out of the leaf, leaving a hole.

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Secondly, if a spray is appropriate, we need to use it when it will be effective. The time to spray is often long past by the time the holes are noticed.

Plants of all kinds get damaged leaves every year. As long as it is just a few leaves, or just small areas on lots of leaves, the plant will do fine and nothing needs to be done. It is useless to spray pesticides unnecessarily for an unknown problem, a problem that is long gone or an environmental problem that no spray can ever help stop or prevent.

Q: I am having a problem with thistles in my flowerbeds. I can't seem to get rid of them. What is the best treatment?

A: The key to many weed problems is timing. Thistles are biennials. This means that during this spring, summer and fall, new plants will sprout from seeds. The rosette of leaves will grow a taproot to store energy over the winter. Next spring and summer, they will send up a flowering stalk that will send out tens of thousands of seeds. The plant will then die.

The most susceptible time to use a weed killer is when the plant is small, during its initial growth phase. Herbicides won't do much when it is dormant the first winter and are only partially effective the second year as it blooms.

Chopping the rosette off from the root will kill small plants without chemicals. Chopping it off when it is big is less effective, as the root might be big enough to send out some leaves and flowers. Chopping the flower stalk off prevents the seeds, and the plant might die without sending out any more flowers. Sometimes the flower stalk will need to be cut off a second time.

Preventing the flowers from producing seeds will reduce the number of plants in the future. As long as you cut off the flower stalk to prevent new seeds, you will win, as the second-year plant is going to die no matter what.

E-mail questions to Jeff Rugg, Kendall County unit educator, University of Illinois Extension at jrugg@uiuc.edu.

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