Lawn yellowing this time of year likely due to irrigation issue
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Question: Recently I have noticed brownish yellow patches in various parts of our lawns in our community. We have a sprinkle system, which operates once every 24 hours. Could lack of sufficient water cause this condition? I thought may be application of main nutrients could remedy the problem
Answer: At this time of year the usual problem is irrigation. However, we are right now entering our lawn grass disease problem time of year.
First of all, if we have a sudden rise in temperature the irrigation clocks are frequently behind the lawns' demand for water, particularly in those parts of the lawn that may be getting less water than the others. Walk into those areas and you can frequently feel under your shoes the difference between a spongy and moist area of grass and a hard and dry area.
If not, take a very long screwdriver or a piece of rebar and push it into the lawn in the green areas and in the brown areas. See if it pushes in with more difficulty in the brown areas. Moist soils are easier to push into than dry areas unless of course you hit rocks then you have to poke around for awhile to find a space not filled with rocks.
Yellowing, if it is caused by a lack of fertilizer, will usually not turn brown. It will just be an off-color, like a pea green rather than a dark green. If yellowing is from a lack of iron then the yellowing will be patchy rather than consistently yellow through the lawn.
One easy way to find out is make a fertilizer application and see what happens. If you make a liquid application and spray it on the results should be seen in 24 hours. With a dry fertilizer it may take a few days to see.
Q: Our privet trees, that look healthy, nice and green, but they shed lots of leaves. Is this normal?
A: If privets are planted in rock landscapes with drip irrigation they will frequently drop their leaves. They do not like their soil dry at all and privets drip-irrigated will struggle. They do best in a lawn that is well watered.
Q: I am writing regarding a problem I am having with the rabbits eating the verbena I just planted. Is there something I can put on the plants or around them to keep the rabbits away? I don't want to kill the rabbits I just want them to stop eating my verbena. This is the only plant I notice them eating.
A: There will not be much you can do except to put some fencing around the plants. I assume you are out in some recently developed area. As these areas become more developed you will see fewer rabbits and less damage.
Have you tried cacti with big thorns? They have pretty flowers. Of course I am joking a bit but cacti have thorns for a very good reason.
The Arizona Master Gardeners recommend some of the herbs when rabbits are a problem. Many herb plants have very attractive flowers and the rabbits don't like to eat them.
Consider rosemary, mint, sunflowers, thymes, vincas, pineapple sage, Russian sage, Mexican bush sage, scented geraniums, passion flower, California poppies, breadseed poppies, cilantro/coriander, dittany of Crete, Jerusalem artichoke, caper, scarlet flax, evening primrose, hollyhocks, lavenders, coreopsis, daturas, and basils. All of these herbs have beautiful flowers, and the rabbits don't eat them.
Q: My favorite rosebush has a white, milky substance on the leaves. What is it, and how can I get rid of it?
A: I had checked with you for the obvious answer which is powdery mildew and you confirmed that it was not powdery mildew as you knew this frequent disease of roses. Since it is not powdery mildew, then perhaps mealybugs might be contributing. Mealybugs are tough to control. You can use a systemic insecticide against both whiteflies and mealybugs. The insecticide is absorbed into the plant and works against the insects as they feed on the plant and does not wash off.
Another possibility (I am really stretching on this one) is honeydew from aphids along with mealybugs. They both produce honeydew which attracts ants. But for those of you not that familiar with powdery mildew on roses, read on.
Regarding the roses the most obvious explanation is powdery mildew, a fungus disease on many plants that appears as a white powder on the leaf surface. It usually spreads during more humid days in our climate, at lower temperatures of the spring and fall, but seldom is a big problem unless the plants are in some shady locations and a lack of air circulation.
Powdery mildew is spread by splashing water so make sure they are on drip irrigation, not on overhead irrigation that splashes water. There are some pictures included in the newsletter.
Some varieties are more susceptible to this disease than others. If this is a reoccurring disease every year you might want to either move the rose to another location, make sure it is on drip irrigation or select a more resistant variety and replace it. Rugosa roses are typically more resistant.
You can apply some materials to help stop the spread of the infection. Some nontoxic remedies according to the University of California IPM program include horticultural oils, Neem oil, jojoba oil, sulfur, potassium bicarbonate, bicarbonate of soda (baking soda), and the biological fungicides AQ10 and Serenade.
With the exception of the oils, these materials are primarily preventive, although potassium bicarbonate has some eradicant activity. Oils work best as eradicants but also have some protectant activity. Make sure oils are not applied when temperatures are above 90 F and never right after a sulfur application.
Q: Some of my oleanders have a lot of gold spots on the underside of the leaves. Should I be concerned? A: My first reaction is the yellow oleander aphid which we have here. If you have good eyes for close-up viewing, you should have seen the little yellow bugs (aphids) clustered on the stems of new growth where it is still soft and succulent. But if you need bifocals, and you weren't wearing them, it could appear as yellow spots.
The other possibility on the oleander is damage due to under watering which will appear as yellowing and eventually browning. If that is the case just increase the watering. Oleander is not a low-water-use plant to look good. Although it is very drought-tolerant it is a high-water-use plant and does very well under rather frequent deep irrigations much like any other nondesert shrub.
Q: The tender leaves of my basil are gnawed or with holes. I tried to spray water with soap but without result. I attempted to spray Sevin but I gave up. Can you help me?
A: It must be good basil. There as so many pests that like basil it is hard to narrow it down, but the chewing types can primarily include grasshoppers and larvae of moths and beetles. If they are larvae, I would try either of two products; Bt which is called Dipel or Thuricide or sprays that contain spinosad. Both of these types, Bt and spinosad, are organic methods. A general organic spray might include Neem. Check the label to make sure application to your plants is legal. Grasshopper control is good with Sevin but you must wait a certain number of days before you can use it. It is on the label.
Bob Morris is an associate professor with the University of Nevada Cooperative Extension.
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