A Greener View by Jeff Rugg

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.

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.

Q: The stem of one of my coleus plants turned black and the leaves above that point wilted and died. Part of the plant is still green and alive. There are a lot of different kinds of coleus plants in pots on my patio and I don't want to lose them or the other potted plants.

What could cause this and what do I do to stop it from spreading?

A: There are numerous fungal and bacteria diseases that get into plant stems. It is probably one of the Phytophthora fungal disease organisms. Sanitation is key here. Remove the whole plant and all the soil around the roots and dispose of it. Spray the trowel, if you used one, with a bleach spray or other sanitizer. If you used a pruner or scissors to cut out the dead and dying stems, sanitize them between every cut so you don't spread the disease agent to healthy plants. Watch your other plants and if any show signs of wilting or black stems, remove them quickly.

The disease organism could have gotten in through the roots that may have begun rotting from being damaged while being planted. It could have gotten into roots that died from under-watering or over-watering. Insects may have brought it in and might spread it to other plants.

No matter what it is or how it got there, sanitation is the key to stopping the spread.

Q: The ends of my Bradford pear tree branches are turning black. Is this a serious problem and can I just prune it out?

A: It sounds like the tree has a bacterial disease called Fire Blight. It looks like someone has taken a lighter to the end of the branch, scorching the leaves. Also, usually the end of the branch will bend down and look like a shepherd's crook. This disease affects the rose-family plants of roses, apples, pears, crabapples, pyracantha, serviceberry, spirea, raspberry, mountain ash, quince and cotoneaster, among others.

The bacteria survive the winter in cracks and damaged areas of the stems and branches. In the spring, sap and bacteria ooze out of the cracks. The ooze drips and splashes onto young succulent growth, infecting it. It is also transferred by bees and other insects that feed on the ooze before pollinating a flower.

The bacteria move from the flower into the stems, causing the black shepherd's hook appearance. The bacteria stay in the stem if the plant can wall off that area, or they move down into the trunk, where it can kill the whole plant if the plant doesn't stop them. New infections can occur anytime the stem is damaged by pruning, insects, hail or wind — especially if the weather is warm and humid.

Usually, the disease doesn't spread rapidly and the diseased branches should be removed in the winter when new infections won't start in the freshly cut ends. Make the cut at least a foot below the visible damaged tissue. Sterilize the pruning tool between every cut so you don't transfer the bacteria to new branches or new susceptible plants.

Pruning in the summer should only be done on plants that the disease appears to be spreading rapidly. Cut out as much of the diseased plant as possible, sterilizing the pruner as you go.

An antibacterial spray labeled for Fire Blight would need to be applied in the spring when plants are in bloom, long before symptoms appear. Don't fertilize these plants, as fast-growing succulent tissue seems to be easily infected.

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

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