Cold damage, disease are hot topics

The weather for the past few weeks has been beautiful, with temperatures in the 70s.

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With this warm weather, the flowers are blooming, the trees are budding and putting on new leaves, and plants are starting to put on new growth.

The he temperature forecast for Tuesday night had everyone worried about cold damage to our plants, though. Most people still remember the temperature dropping to the low 20s in 2007. We were fortunate last week that the temperature stayed in the high 20s. At that temperature, most of our plants will be fine, but there are some plants that might be damaged.

Cold damage can occur on all parts of the plant, including leaves, fruit, stems, trunks and roots. Most people notice the damage done to the leaves, fruit or stems. These parts of the plant can turn black or brown and become mushy. The damage occurs on the plant when ice forms in the cells, then the cells expand, burst and die.

Another way that cold hurts plants is through desiccation, which is the loss of water in a plant. This occurs when we have cold conditions and wind. If there is not adequate soil moisture, the leaves will turn brown on the margins and the plant can defoliate.

Cold damage also can cause bark to split. This symptom doesn't show up until later in the year. The bark will loosen on the trunk and fall off. On shrubs, the bark will peel off the stem. This usually occurs 3 or 4 inches above ground level. I don't think that many of our plants were damaged by this latest cold snap, but there could be plants that suffered.

The next step is to wait, which can be hard for many gardeners. They feel they need to do something to help the plant. The best thing to do is give the plant time to recover to put on new buds and growth. Then, prune out parts of the plant that don't grow. Also, make sure that the plant doesn't go through any drought stress. Right now, we have plenty of soil moisture from recent rain. Delay fertilizing these plants until they have new growth on them and have recovered.

There are some more problems that I am seeing in lawns. Most problems are occurring in centipede and St. Augustine grasses. The first problem is caused by diseases such as large patch and take-all disease.

Rhizoctonia is the fungus that causes large patch. This fungus likes and needs nitrogen to reproduce. Applying the right amount of fertilizer at the right time can reduce the incidences of large patch.

Turf grass will lose a part of its root system each winter. This is why grasses are at their weakest when they are coming out of dormancy. Applying nitrogen fertilizer too soon can stress the grass, which makes it more susceptible to diseases.

Warm season grasses grow their best when soil temperatures reach 65 degrees. In our area, that typically occurs in late April or early May. This is the time to fertilize. This is especially true of centipede and St. Augustine grasses.

When these grasses are fertilized too early, they turn yellow from stress. The nitrogen in the fertilizer is causing more top growth than the root system can support. The grass becomes stressed, then large patch can start. If you apply more than one pound of actual nitrogen per 1,000 square feet, you are applying too much fertilizer.

Take-all is a disease that attacks grass in late October and early November. This fungus likes nitrogen as well. Therefore, make your last fertilization by late August.

The symptoms of take-all appear in the spring, but the fungus already has done its damage. To treat take-all, occasionally apply a fungicide the first and third weeks of October. The grass that is damaged by both large patch and take-all will grow back by midsummer.

The other problem that is hurting centipede is winter kill. I am seeing a large number of yards with winter kill or centipede decline.

Winter kill is caused by a combination of factors. The first is mowing height. Centipede should be mowed at 11/2 inches in height. Keeping centipede at 2 inches can increase the chances of winter kill. The stolons of the centipede are unable to root down, then the cold weather kills the stolons.

The second factor is over-fertilization. Over-fertilization will increase the amount of thatch in the grass. This can keep the stolons from rooting into the soil. To correct this problem, rake out the affected areas to allow sunlight to warm the soil. If the areas are large, install a few pieces of sod to help the grass fill in.

Reach Columbia County extension agent Charles Phillips at (706) 868-3413 or charlesp@uga.edu, or log on to www.ugaextension.com/columbia.