Tony Bertauski: Fungus attacks popular red tips
Homeowners have favorite plants. At one time, it was red tips (Photinia x fraseri). Itís an evergreen and fast-growing shrub. The new flush of growth is bright red and thrives in a range of growing conditions. You could do almost anything to it, and it would just keep growing.
Eventually, something went wrong.
The culprit that put an end to rampant red tip plantings was a fungus that caused entomosporium leaf spot. Clearly, a scientist named the disease since most people canít remember or pronounce it. However, the fungus (Entomosporium maculatum) produces a spore shaped sort of like an insect, thus the name.
Leaf spot diseases are caused by a variety of pathogens, and most are harmless. Hydrangeas, dogwoods, sweetgums and crape myrtles are riddled this time of year with leaf spots caused by various fungi.
The hosts typically drop infected leaves earlier than normal without affecting its health. Most recommendations are to avoid treating the disease since the plants are about to naturally drop their leaves anyway.
If the spots are bothersome, the leaves can be removed from the area to reduce overwintering fungus, or preventive fungicide applications can be started next August (the timing depends on the disease and the host). Otherwise, the diseases arenít a problem.
However, entomosporium is different from most leaf spot diseases. First, itís host specific, primarily infecting red tips and Indian hawthorns. And second, it can kill the host.
On red tips, the disease appears as circular red spots. Maturing spots are gray in the center with a red border. The spots are more prolific on lower leaves because spores are spread via water, primarily splashing rain and irrigation.
Not all red tips have the disease. Some appear healthy and may even tolerate some level of infection and can do so for many years.
If you have red tips like this, avoid shearing during the spring when the disease is most active. Wounding opens avenues for spores to penetrate. It is preferable to prune during the winter. Remove any clippings or fallen leaves to avoid overwintering fungus.
Also, avoid wetting the leaves to reduce leaf moisture. Avoid fertilization that encourages new, susceptible growth. Red tips grow so fast they shouldnít need irrigation or fertilizer.
Red tips canít be replaced with red tips, nor should they. Garden centers stopped selling the shrubs because of the disease. Some avid gardeners propagate the shrub, but the disease will continue to be a problem.
There are numerous substitutes for red tip. Camellias are smaller and slower growing and flower in the winter. Tea olives get large and produce fragrant flowers throughout the winter. Cherry laurels and cleyera are good evergreen shrubs with waxy foliage. Viburnums are another hardy substitute.
But letís not forget Indian hawthorns. These foundation shrubs also are overused and will exhibit symptoms. While the disease is not as severe on Indian hawthorns as it is on red tips, it can cause significant problems under the right conditions.
Avoid unnecessarily wetting the foliage with irrigation and plant in full sun where leaves can dry. Avoid frequently shearing during the growing season that can open wounds for infection.
Unlike red tips, disease-resistant Indian hawthorns have been developed. In general, white flowering cultivars are more resistant than those with pink flowers. However, there are specific cultivars that have demonstrated good to excellent disease-resistance, such as Clara, Indian Princess, Georgia Petite, Georgia Charm and Snow White. When purchasing an Indian hawthorn, check the tag for disease resistance.
Since entomosporium is host specific, another approach to avoiding the disease is to substitute a different species. Consider planting dwarf hollies, rosemary, abelia, plum yew, or dwarf nandina.
Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback, email him at email@example.com.