Weather, diseases causing brown spots in lawns

     By Bob Morris
     View columnist
      The following are typical issues our Master Gardeners deal with daily at the Nevada Cooperative Extension. If you have gardening questions, call the Master Gardeners' hot line at 257-5555 between 9 a.m. and 4 p.m. Monday through Friday. There is also a gardening Web site at http://www.intermind.net/mgarden/.
     
      This is the time of year when we have brown spots on lawns resulting from diseases. Let me explain why.
      For a plant disease to begin, three circumstances must coincide: the right plant, the right disease and the right environment.
      When the afternoons become cloudy and overcast due to our summer monsoons, the environment will be perfect for diseases in tall fescue lawns. However, the lawns most susceptible are those that have been over-fertilized.
      Over-fertilized lawns are weak and less likely to withstand attacks from disease. In the future, fertilize lawns only when color is beginning to fade. Secondly, use a high potassium fertilizer in April or May before hot weather hits.
      For now, if the lawn is diseased, lower the mowing height one notch; change the lawn watering to a different time of the day; and try to delay lawn watering until the sun is up or nearly up.
      If necessary, fungicides are available for these diseases at the nurseries and garden centers.
      Question: My mulberry tree has small leaves that are scorched and it's sparse.
      Answer: Frequently I have found mulberries with these symptoms infested with nematodes in the roots. They also will appear like this if they are underwatered.
      They require about the same amount of water, applied to the area under their canopy, as a tall fescue lawn. You can determine if there are nematodes in the roots of the mulberries by digging down into the root zone of the mulberry about 2 or 3 feet from the tree.
      Mulberry roots will be a characteristic yellowish-orange color. Look at roots that are about the same diameter as a soda straw or smaller. Roots infested with nematodes will have swollen knots along its length.
      There is nothing really that can be done to kill nematodes and not harm the tree. Keep the tree as healthy and as actively growing as possible. Make sure the tree is adequately fertilized and watered, and it will appear much more healthy.
      Q: My newly planted ocotillo is dying. What went wrong?
      A: This is a common question about ocotillo. They are dying all over town. In nearly every case they are over-watered or the soil does not drain properly.
      They cannot be put on the same irrigation line with other plants that require frequent waterings. The soil must have good drainage and drain freely. Drip emitters should not lie next to its base or crown.
      I wouldn't use an abundance of organic matter that is designed to hold water in the planting hole. Choose smaller ocotillo to plant over the larger ones. They will establish easier.
      These plants will root easily from a single cane, watered infrequently, in desert soils. They require only about 12 to 24 inches of water each year.
      Please, please, please don't cut off the tops of the canes. Remove a cane from the crown.
      Q: I planted cacti one month ago. How often do I water?
      A: I wasn't told if this was indoors or outdoors, but we'll assume it was outdoors. During establishment, I wouldn't water more than once per week in mid summer in sandy soils. They must have good drainage.
      Many cacti are opportunists when it comes to water. When they have water, they take full advantage of it. When they don't have it, they shut down. They are fascinating plants.
      To give one watering schedule for all cacti will offend many of the cacti lovers. To be fair, you should become familiar with these different plants and adapt your watering for each.
      These are plants that don't need to be on an irrigation system and are perfect for occasional waterings with a hose. Now I don't mean that they don't need supplemental water in our desert.
      That isn't true. We just don't get enough rain in Las Vegas. If this were Tucson or Phoenix we could slowly ease them off of extra water. Generally speaking, cacti grow when water is plentiful and don't if it's limited.
      Q: My fan palms that I planted eight months ago are showing almost no growth. What's going on?
      A: This is not a good sign. Eight months ago would have put its planting date during the winter months. The planting of palms should be avoided during the winter months.
      Nearly all other plants can be planted in the winter except bermudagrass, palms and many heat loving, desert plants. The possible problems? Palm bud rot.
      This is the most frequent reason we have for losing palms planted during the winter. The top turns brown and dies.
      The bud at the top can be pulled out fairly easily even when the leaves in the center are still somewhat green. Several pathogens can be responsible, ranging from a bacterium to a fungus. We don't have a good disease control recommendation.
      Other possibilities include underwatering, overwatering and poor drainage. Nematodes could also be a problem, but I'm assuming you bought this from a nursery or garden center and it should have been healthy coming from them.
      Q: My sago palm or cycad has yellow leaves. What could be the problem?
      A: The usual reasons for yellowing are planting in locations with too much direct sun, over-watering or poor drainage. They are tough plants.
      The sago palm, also called cycad, is a bit out of place in the desert. However, they will grow very well here if we are careful where they are planted, how they are planted and how they are maintained.
      They shouldn't be planted in full shade and they shouldn't be planted in hot locations in full sun. They prefer light shade or a few hours of direct sunlight in the morning or early afternoon.
      Avoid direct, late-afternoon sun next to hot walls. When they are planted, amend the soil heavily with organic matter, particularly those amendments that produce acid, such as peat moss or homemade, well-rotted compost if you have it.
      Use sulfur in the backfill along with a good starter fertilizer. Make sure that the irrigation system is watering the entire root zone when it's operating and that the planting hole is draining.
      It should be on an irrigation valve that is watering other plants that need frequent irrigations other than the lawn. Cycads do well in flowerbeds. Don't water from overhead if at all possible, or at least do it infrequently.
     
     Bob Morris is a horticulture specialist with Nevada Cooperative Extension.