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LI Landscape and Turf MainTenance www.landscapeirrigation.com Landscape and Irrigation March 2015 33 Pythium blight is all about stress. Requires long periods of leaf wetness. Good soil drainage and implementing sound irrigation prac- tices are crucial. Irrigate deeply and infrequently to wet the entire root zone. Repeat when the turf first starts to show signs of drought stress. Daily irrigation is unnecessary in most situations, and will only contribute to disease activity. Sites with a history of Pythium blight development should con- sider a preventive fungicide program applied when the weather conditions are conducive to the disease. If already treating for brown patch or large patch, don't necessar- ily need a special fungicide application just for Pythium blight. Certain QoI fungicides — such Heritage fungicide — pro- vide excellent control of Rhizoctonia diseases (brown patch, large patch) and also control Pythium blight. SprIng DeaD Spot A devastating disease of bermudagrass, and can also occur on zoysiagrasses. Disease can occur wherever these grasses grow, but is most se- vere in the northern parts of the transition zone. The pathogen, Opiosphaerella, weakens the turf and causes it to be more susceptible to freezing injury during winter dormancy. As a result, circular patches of infected turf fail to green up in the spring and are completely dead. Recovery from spring dead spot damage is very slow, some- times taking the entire growing season for the turf to spread back into the affected patches. Natural tendency is to apply extra fertilizer to stimulate recov- ery, but this is not recommended because it can fuel more aggres- sive disease activity. Instead, break up the mat of dead turf with regular aerification or spiking, apply fertilizer, and irrigate on a light and frequent basis to help the stolons root. Spring dead spot can be managed with fungicides, but must be applied preventively. Because spring dead spot attacks during the winter, a systemic fungicide must be applied in the fall to protect the plant during winter dormancy. The DMI fungicides, or DMI + QoI combination products (such as Headway fungicide), are the most effective options for spring dead spot control. Two or three applications prior to dormancy are typically rec- ommended depending on the severity of the disease. necrotIc rIng Spot Caused by the same pathogen that causes spring dead spot, but on Kentucky bluegrass the pathogen develops at a different time of year and induces different symptoms. This soil pathogen infects the roots and rhizomes when soil temperatures are between 60 and 75 degrees Fahrenheit. How- ever, above-ground symptoms do not appear until the majority of roots have been killed. Once the foliage begins to collapse, there is very little chance of recovery even with fungicide applications. Soil compaction and excessive thatch accumulation are two factors that commonly contribute to necrotic ring spot develop- ment. Kentucky bluegrass accumulates thatch very quickly, so annual vertical mowing or power raking is necessary to keep it in check. Hollow-tine aerification of high-traffic areas is also needed to manage soil compaction. Just like with spring dead spot, the DMI or DMI + QoI fungi- cides are most effective for necrotic ring spot control. Fall and spring applications on a 28-day interval when soil temperatures are between 60 and 75 degrees Fahrenheit will pro- tect the roots from infection. FaIry rIng Among the most complex and difficult-to-manage turfgrass diseases. Roughly 60 different fungi that have been shown to cause fairy ring in turf, and likely many more yet to be documented. All of these species vary in how they cause disease, when they are active, and which fungicides are most effective. Most fairy ring species do not infect the turf. Instead, they grow in the thatch and soil, using the organic matter as a food source. Fairy ring fungi indirectly cause symptoms on the turf by changing the chemical or physical properties of the soil. Example: fairy rings can cause a ring of greener, more quickly growing turf, sometimes called a Type II symptom, by releasing nitrogen into the soil profile. Rings of dead turf, sometimes called a Type I symptom, are the result of water-repellent substances that are the remnants of fairy ring growth. Fungicides can be effective on fairy ring, but they need to be ap- plied preventively, before the fairy ring symptoms are expressed. Fungicides will not rid the soil of excess nitrogen or re-wet the soil that has turned hydrophobic. QoI, DMI, and SDHI fungicides are among the most effective products, but remember that not all fairy ring fungi are sensi- tive to the same fungicides, so some trial-and-error is typically needed to determine which products are best. Article provided by Syngenta. Photo Provided by Syngenta