After you spend considerable time and money buying and growing the flowers, it is disappointing to see them die prematurely or not bloom well because of diseases.
As a brief reminder, diseases are separated into two general categories. The first are the nonpathogenic or environmental diseases, which include extremes in temperatures, watering excesses or deficiencies, soil problems, nutrient deficiencies, mechanical damage or similar problems.
These diseases have no causal organism involved, so they cannot spread from plant to plant in other words, they are not contagious.
Pathogenic diseases have a contagious organism involved in their spread. These include fungi, bacteria, viruses, mycoplasmas, nematodes and even some parasitic seed plants.
While there many possible diseases that can occur in Utah, only a few are rampant. In most instances, problems are the result of environmental causes, so spraying has no effect. When you try to control pests, you must use very specific products. This means fungicides are needed for fungal diseases; bactericides for bacterial disease; and specific products for the other organisms.
Some problems are readily evident. Lack of water causes plants to wilt, as do excessively high temperatures. Various fungal and bacterial diseases, including verticillium and fusarium wilt, cause similar symptoms, so it is critical to identify the problem before starting any treatment.
Other diseases have complex reactions with the environment. For example, overwatering flowers keeps the roots from getting the needed oxygen so they grow poorly. But excess water also encourages the growth of fungi that attack the plants and kill them.
Several root-rot diseases attack flowers. Prevent problems by increasing soil drainage and watering only as needed. Preventing water molds and other fungi after plants are affected is almost impossible. Few fungicides are effective, and they are only available in commercial formulations.
Verticillium wilt affects more than 300 plant species. The soil-borne fungus enters the plant, usually through the roots, and plugs off the water-conducting tissues. The plant wilts and often dies. It usually appears with the hot weather. Since the fungus lasts for many years in the soil, using resistant plant varieties is the only practical control.
Iron chlorosis is one of the most frequently seen nonpathogenic diseases. The common symptom is that the leaves turn yellow and the veins stay bright green. It affects all types of flowers but is more serious on those that like acidic soils.
Utah soils usually have plenty of iron, but the high alkalinity and the high lime content of the soil make it unavailable. Overwatering also makes the problem worse, so improving drainage and watering correctly helps.
Treat the iron chlorosis with a chelated iron product. Chelating compounds are made from bark or other organic sources or synthetic organic molecules. The best is EDDHA, a synthetic chelate you buy as Sequestrene 138 and Millers Ferriplus iron.
It will work on flowers when the soil pH exceeds 7.5, while other chelates only work at lower pH levels.
Powdery mildew is a pathogenic disease. It is common on columbine, dahlia, delphinium, monarda, phlox and zinnia. It might not have hit your garden yet, but the disease occurs with a vengeance in late summer and early fall when nighttime temperatures drop.
Avoid planting susceptible flowers or use them in open areas where they are uncrowded and exposed to the sun. Avoid sprinkling the plants at night and avoid over fertilizing. Chemical controls are expensive and require frequent applications.
One final pathogen is dodder, a parasitic plant that attacks many flowers. It looks like a jumble of thick orange fishing line wrapped around the plants. Pick all orange string out of the beds and remove any plant to which it is attached. Fortunately, this strange looking problem is infrequent.
One of the best methods to control flower diseases is planting different kinds of flowers in the beds. The mixture of different flowers means they do not all show the same problems, and if susceptible flowers fade, the other stronger flowers can fill in and keep the beds looking good.Notice which flowers do best in your area. Pay attention to the sun exposure, the drainage and the wind conditions. Make some notes of the kinds and varieties of flowers in your beds. Take pictures throughout the season and analyze what grows well. You're the gardeners and you can make them better each season.
For more information on plant disease, log on to utahpests.usu.edu/ plantdiseases.
Red Butte Garden is offering a class on butterfly and hummingbird gardens, Saturday, 10 a.m.- noon. Regular garden admission applies; members get in free. No registration is required. For more information, log on to redbuttegarden.org.
Thanksgiving Point is offering a series of classes on flower bed design, Aug. 5, 12, 19 and 26, 2-4 p.m. or 6-8 p.m., and a series of classes on basic landscape design Aug. 5, 12, 19 and 26, 10 a.m.-noon. The cost of each series is $40. To register, call 768-4971 or log on to thanksgivingpoint.com.
Larry A. Sagers is the horticulture specialist, Utah State University Extension at Thanksgiving Point.