Grape leaf eaters are really moths disguised as wasps
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If you are now having your grape leaves eaten up with the veins left behind, you have been hit by the grape leaf skeletonizer. If you are observant, this is the blue-black or iridescent flying insect that kind of resembles a black wasp. It is really a moth that uses that charade to confuse its enemies.
They lay their eggs on the underside of grape leaves in these yellow masses all in neat rows. They hatch into this larva, which is really a caterpillar, and march across the leaf, consuming its surface. If this insect larva falls on your skin, it will burn like a match head recently lit. Again, for protection against their enemies.
They are easy to control with a spray of the bacterial insecticide Bt, or spinosad. Follow label directions. They are both easy on the bees.
It is real close to the time of year when tall fescue gets a disease that causes brown patches. If you already have brown patches, it is probably related to your irrigation system. But this disease happens in late June and all of July. I would get a fungicide down on the grass that will control summer patch disease in the next week or two at the latest. That is good protection for about four to six weeks, and then you would make another application.
Question: After a canna has bloomed, what is the best way to cut off or break off the used bloom, and where on the stem should this cut be made? If I cut the whole stem off to the ground, I will also be cutting off leaves. Does it work if I just cut it back to the first leaf?
Answer: If you ever want to get me excited about a plant for our landscapes here, one of those plants is the canna lily. I will get to your question, but you first have to listen to a little spiel from me about cannas.
Cannas are some of the oldest garden plants used in the United States and they have dropped in appeal over the last few years, but are making a resurgence now. This is one of those plants that can be used in the high water use area of the yard in an oasis-type landscape. A select few of them can be used in water gardens.
To make a small tropical paradise in the desert in your yard in the entry or sitting area in the back, a combination of cannas, palms, ornamental gingers, bananas, asparagus fern and bird of paradise gives that lush tropical look. Canna flowers come in all colors except green, blue and black. The foliage looks like banana leaves, but comes in colors ranging from green, red, bronze, striped green and red, etc.
They come in four basic sizes -- pixie, dwarf, medium and tall (about 18 inches or up to 6 feet tall) -- so you must be careful when you buy them. Of course, the size differences can give you a sequence of blooms if planted in the same landscape.
There are two basic types -- one hybridized from plants native to the southeastern United States, called the orchid types; and those originally from the tropical parts of Central and South America, called the garden cannas). The flowers may be visited by hummingbirds and butterflies.
They will take direct sun as long as heat is not reflected from a hot wall except perhaps the white or off white flower types. These like some filtered sun. They do require lots of compost and organic mulch to do well in our soils.
The drawback to them is that they are not carefree. About every three years you have to dig them up, divide them and replant them in the fall, since they are planted from rhizomes like iris. They do occasionally get some caterpillars that may damage the leaves. They can be controlled easily with Bt or spinosad.
You would cut the flowers back about 6 inches below the spent flower. More flowers will come from the leaf stalk further down. In the late fall, cut the stems down to within about 1 inch of the ground and mulch. Leave young stems alone as they may flower for you in early next spring if they get through the winter undamaged.
Q: My favorite rosebush has a white, milky substance on the leaves. What is it, and how can I get rid of it?
A: 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 have 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.
I sent you pictures of the disease. Those readers getting my e-mail newsletter will get the pictures, as well.
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 horticultural 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 degrees Fahrenheit 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), 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 if you want it 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 non-desert shrub.
Q: My Martha Washingtons and snapdragons have really wilted in this heat. Perhaps I am watering too much or not enough. My schedule is four days a week and four minutes per hour for three hours each. I also fertilize these plants every six weeks with liquid fertilizer.
A: By Martha Washingtons, I assume you mean regal geraniums. Both of these plants are not a good choice for the summer months in our climate. Geraniums do well during the winter, spring and fall months.
As temperatures begin to warm, they might hang in there for a time on the east and north sides with lots of indirect light. They will need at least four hours a day of good light, good soil water drainage as their roots will rot out if they don't get it. This means really good soil preparation at the time of planting.
Mulch the soil to keep it moist, but don't over water. This is where it gets tricky for geraniums, finding the balance between enough and too much water, when they can require maybe up to half an inch of water each day. In a pot in the summer? Forget it.
Snapdragons are just a winter flower here. It is tough to make them work in the heat. If you have had luck in the summer with them here, you are a good gardener, very observant, with plenty of patience and time to commit to them. Now golden desert snapdragon, a desert native of the southwest, is a different story.
Bob Morris is a horticulture specialist with the University of Nevada Cooperative Extension.
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