It's time again to answer a few questions from readers and help solve some problems that you and many others might be seeing in gardens this time of year.
Q: The leaves on my aspen trees developed some dark-brown spots a few weeks ago. The spots are getting larger, and the leaves are now dark and shriveled. What should I do?
A: This disease is a caused by a fungus and is more severe when we have wet weather.
The disease is aspen leaf spot. When the leaves stay wet from excess rain or sprinkling, the fungus develops and infects the plant.
What is confusing to most gardeners is that the symptoms show on the leaves much later in the year. After the symptoms show on the leaves, it is too late to do anything about the infection.
Keep the sprinklers from hitting the leaves to prevent further fungus or further spreading. If the disease is very serious or the trees are in a very visible area, spray the trees every two weeks in the spring with a fungicide.
Start when the buds break and continue spraying until the weather becomes hot and dry.
Q: Earlier this season, my apricots were covered with purple spots. Now my peaches are covered with spots that are oozing bits of gum. What is wrong with my fruit this year?
A: The fruit is affected by the fungal disease coryneum blight.
The disease also causes stone-fruit leaves to develop purplish spots that turn brown and drop out of the leaf. This gives the disease another name of shot-hole blight, because they look like they have been peppered with buckshot.
Some years the disease is more serious than others. This year's wet June has enhanced the problem. Once the disease develops, it is too late to control it. Make plans to spray the trees in the fall with copper, daconil or another registered fungicide.
Q: Many of my tomatoes have a dark-brown, leathery spot on the bottom of the fruit. How do I control the problem?
A: This problem is blossom end rot. This problem is not caused by a disease organism or an insect, but it is a physiological problem caused by an internal calcium imbalance in the plant.
If your soil was deficient in calcium, you would add more — but that isn't the problem in Utah.
Most soils, unless you have pure sand, are limestone-based, meaning they have excessive amounts of calcium carbonate.
For us, it is largely an issue of managing irrigation. Keep the soil on the tomatoes moist. If the soil is too wet or too dry, the tomatoes will have more serious problems. In most cases, the first tomatoes on the plant are the ones that have the worst problems.
Cut away the affected area and use the rest of the tomato. While the disease is most frequently seen on tomatoes, it also shows on peppers, squash, watermelons and other vine crops.
Q: What can I do to control the myriad wasps that are attacking my peaches, grapes raspberries and other fruits?
They seem to be everywhere and have even stung me. I have hung up traps, but they are not working.
A: According to Diane Alston, entomologist at Utah State University Extension, the problem is that we are dealing with a different pest than we have previously had in Utah.
"The most likely reason is that the trap you are using is not attractive to the target wasp species. Since the invasion of the European paper wasp to Utah less than 10 years ago, this species has become a prominent nuisance and fruit-eating pest for growers and home gardeners.
Alston explained that the wasp traps sold in garden centers contains heptyl butyrate, a chemical that attracts yellow jacket wasps, not the European paper wasps.
European paper wasps have narrow waists and more black than yellow on their abdomens. They build upside-down umbrella-shaped paper nests on the underside of roofs or overhangs.
Peter Landolt, an entomologist with the U.S. Department of Agriculture's Agriculture Research Service in Wapato, Wash., developed a homemade trap to attract European paper wasps using fruit juice as bait.
That way, you can reduce the damage that these wasps are doing to your plants.
If you would like pictures and directions on how to build and bait these traps from pop bottles, log onto Alston's article at utahpests.usu.edu/files/uploads/UtahPests-Newsletter-summer09.pdf
Do you have a question for Larry Sagers? If so, send an e-mail to email@example.com. Questions may be answered in a future column.
Larry A. Sagers is a horticulture specialist for the Utah State University Extension Service at Thanksgiving Point.
Thanksgiving Point is offering Fabulous Fall Color in the Landscape, Sept. 1, 8, and 15, 2-4:30 p.m.; and Spectacular Spring Flower Bed Design, Sept. 1, 8, and 15, 10 a.m.-12:30 p.m. or 6-8:30 p.m. Cost is $40 per class. Call 801-768-7443 to register. For more information, log on to www.thanksgivingpoint.com. A 15 percent discount is available to those who register for both of the classes.
The second annual Utah Green Festival is Sept. 12, 9 a.m.-5 p.m., at the Jordan Valley Water Conservancy District's Conservation Garden Park, 8215 S. 1300 West, West Jordan. The free event will feature informational classes, experts and vendors on conserving energy. For more information log on to www.conservationgardenpark.org or call 1-877-728-3420.
Joy Bossi, KNRS' "Joy in the Garden," will discuss water-wise ideas during a walking tour on Sept. 10, 6-8 p.m., at the Jordan Valley Water Conservancy District, 8215 S. 1300 West, West Jordan. For more information, log on to www.conservationgardenpark.org or call 1-877-728-3420.