Grapes Produce Shiny, Sticky Leaves When Infested with Mealybugs

Q. I discovered some white things on my grape leaves where it is connected to the branch of the trunk. The plant is only in its second year, bought from a local nursery last year. The leaves are green, but the vine does not grow. Please let me know what I should do.

A. The picture you sent was not clear. But what I could see looked like nothing I had seen here before on grapes. Grapes, both wine and table grapes, are being grown more and more in the Las Vegas Valley. It’s only a matter of time before pest problems in grape growing areas will become our problems as well. Some of these problems can devastate grapes.

            The first thing I noticed on the leaves of your grape plant were “shiny” leaves. The upper surface of the leaves was shiny and sticky to the touch. It was attracting ants and bees. This is from insects that entomologists call “piercing and sucking”. I pushed these leaves aside and found mealy bugs. This was a “new” insect for me on grapes growing in the Las Vegas Valley.

            Piercing and sucking insects (aphids are in this group) damage the plant to get at plant juices that are full of sugar. These insects feed and defecate a concentrated, sugary residue that lands on the leaves. This sugary stuff is what attracts the bees and ants.

            A control strategy, that doesn’t involve spraying chemicals on the plants, is controlling the ants. Ants like piercing and sucking insects because of the sugar. They will move young insects to uninfested locations to increase their supply of sugary “honeydew”. Controlling ants reduces the spread of these insects to new locations.

            Soap and water sprays applied directly to mealy bugs and other piercing sucking insects will kill them. There is no poisonous residue left behind so it should be repeated every three or four days until the problem is under control.

Mesquite Trees are Water Opportunists

Q. Do you have any ideas how to stop the flowers produced by mesquite trees? For the past two years mine seems to have gone crazy producing the little yellow flowers that create a constant scum of yellow on my pool all summer long. This mesquite has 1½ long spines on new growth together with the leaves.

Native mesquite in the Mojave Desert just outside of Las Vegas, Nevada. Restrained growth and flowering because of the 4 inches of rainfall the Mojave Desert gets each year.

A. The tree sounds like a native mesquite, perhaps the Honey Mesquite. This tree is native to our desert Southwest, a North American native plant.

            Production of fruit by olives and pods in mesquite, can be controlled by spraying the tree when flowers are open. The flowers must be present and open for the spray to cause the fruit to abort. So, timing of the spray is critical for success. Chemicals like Florel and Olive Stop are used. But sprays to prevent flowering are more difficult to find and apply.

            Under desert conditions of limited rain, flowers are produced only in the spring when temperatures warm up. If the soil has water in it, there will be lots of flowers. If the soil is dry, flowering is sparse. If this tree is watered freely then it is possible it can produce flowers, in waves, all summer long, with each flush of growth.

Mesquite make a good looking landscape tree if pruned and managed correctly. The density of shade has much to do with how much irrigation water it gets in the desert. Infrequent watering would produce filtered shade. Frequent watering produces dense shade. They would grow too fast if grown in wet climates.

            Desert plants, like this mesquite, are opportunists; they take advantage of water when it is present and restrict growth and flowering when water is not available. In other words, growth of all kinds including flowering is tied directly to irrigation.

Mesquite trees do not belong in lawns and they should not have flowers growing beneath them. They are prefect for desert environments.

            Manage its growth and flowering by managing its supply of water. Water less often but with lots of water when you do water. Give it water in the spring to so it can grow and flower and then restrict water the rest of its growing season.

            This restriction of water will curtail its growth and flowering to once a year. At least then the yellow scum needs to be cleaned out of your pool for only three or four weeks each year. 

Plumcots, Plums and Apricots Good Choices for the Desert

Q. I purchased a plumcot fruit tree years ago for my home in New Jersey. I got great tasting, sweet plumcots in early July every year. I never thought it could grow here. Yesterday, I was reading in the Real Estate Section that a house for sale had a plumcot on its grounds. Will they grow here or is it just that particular location?

A plumcot called 'Plum Parfait' producing fruit in the Eastern Mojave Desert. Below is 'Plum Parfait' tree, about six years old and pruned to 8 feet tall entering into fall color in mid October.

A. The plumcot is a man-made hybrid between a plum and apricot. Other hybrids between these two fruit trees, apriums and pluots, also exist. These types of hybrids don’t occur in nature and are not GMO’s but developed the old-fashioned way through plant breeding.

Floyd Zaiger in a propagation house at Zaiger Genetics, one of the plant breeding companies responsible for hybrids like plumcots, apriums and pluots.

            Our climate is a good climate for growing both plums and apricots as well as hybrids like plumcots. In fact, our desert climate is better for growing these types of fruit than the climate in New Jersey. Our intense sunlight and high temperatures help develop high sugar content and good flavor.

Aprium tart made from interspecific hybrid fruit, the aprium.

            Pick a location in the yard that has plenty of sun but away from walls that produce a lot of radiated heat or reflected light. Dig the planting hole plenty wide and mix a good quality compost with this soil when planting.

            Add water to the hole as you are planting to help settle the soil and stake the tree for the first growing season. Cover the soil with a four-inch layer of wood chips after planting. These “dissolve” into the soil where there is water and continue to improve it in the years to come.

Fig Leaves Showing Possible Disease Symptoms

Q. The leaves on my fig tree appear burned after this rain. I foliar sprayed it with Neem oil and soap and fish protein isolate, These trees were planted last fall and mulched with 1 foot of woodchips and looked amazing until now. They are watered three times each week in the summer.

A. The leaves do look like they are diseased. But I have a saying, “When the top looks bad, look at the ground.” First eliminate the easy problems before jumping to more difficult ones.

            I wonder if that 12 inches of surface mulch is rotting the trunk of the tree. It is easy to kill young trees if they sink, the bottom of the trunks buried in dirt, into the planting hole after planting. Or if woodchip mulch on the soil surface is piled against the trunk and kept wet.

            In both cases wet soil or wet mulch against the trunk can cause a disease called “collar rot”. The disease rots the trunk and “chokes” the top of the tree. When this happens, leaves look diseased or as if the plant isn’t getting enough water. This becomes very apparent during hot weather.

            Start on your knees and pull the mulch away from the trunk. Keep it there permanently, 6 to 12 inches away. Next, carefully remove the soil from around the trunk until you find tree roots coming from the trunk growing horizontally.

            If this small area of the trunk looks water soaked, there might be a problem. I will take a small penknife and cut away a narrow strip of the trunk that was buried in soil and mulch. The wood under the strip should be white or greenish white.

            If there is more than ½ inch of soil covering the trunk, or the trunk was buried in wet mulch, the tree may develop collar rot. All you can do is let the covered part of the trunk air dry and hope for the best.

            I have seen collar rot develop on the lower trunk young figs and pomegranate that are buried. Most figs and pomegranates are grown on their own roots. If the top of the tree dies, wait a couple of months and see if anything suckers from the roots or base of this tree. If it does, don’t replace the tree.

            These basal suckers will grow very rapidly into a new tree because the tree already has established roots. When one of the suckers is 12 inches tall, remove the others for a single trunk tree or select 3 to 5 for a multi-trunk tree.

            It’s possible these leaf problems are related to a leaf disease but I don't recognize it. Sometimes when dead areas develop from disease pathogens, the dead area of the is bordered by yellow. This yellowing is where the plant tissue is still dying. Sometimes this yellowing doesn't exist but only because the disease has stopped spreading.

            The humidity in Las Vegas is unusually high right now because of the so-called “summer monsoon” and rains. I expect diseases to pop up during this kind of weather. Having leaf diseases on fruit trees would not be uncommon during this time of year.

            Instead of spraying, driving using a passive approach towards controlling diseases. Remove extra leaves that might be blocking the movement of air and wind through the canopy. As you see leaf diseases, remove the infected leaves and dispose of them. The plant will grow new leaves in places where there is sunlight. Leaf diseases slow down or stop as the weather changes.

Leaf Miner Damage on Many Different Plants

Q. In my morning walk around the garden, I found this unusual pattern on the leaves of my Arabian Jasmine.  Do you have any thoughts on what might have caused this?

Serpentine leaf miner damage on Jasmine leaf.

A. This is one of the leaf miners. Because of its snakelike pattern of damage caused on the leaves, this particularly matter is called the "Serpentine" Leaf Miner. Leaf miners in general are the immature of moths or a flies but in this case of the Serpentine Leaf Miner the culprit is a fly. The fly's lifecycle has four stages; the adult fly with wings for finding a sex partner, the egg, maggot, pupa which finally turns into the adult again.

The serpentine leaf miner adult fly punctures the leaf surface. It inserts its eggs inside the leaf. This is a perfect warm and wet environment for the egg to hatch into a very tiny maggot. Food and moisture are all right there and protected from predators inside the leaf! This tiny maggot tunnels between the upper and lower surface of the leaf in this wet juicy nutrient rich layer where it feeds at the same time. 

Leaf miner attacking these leaves in Afghanistan

If you hold the leaf up to the light you will see that these serpentine patterns are tunnels, have nothing in them, but are surrounded by dark, green leaf tissue. The second thing you will see is that this serpentine tunnel gets wider along the feeding path and shows you the direction this maggot has moved inside the leaf; the tunnel is narrower when it is small and gets wider as it grows. At the end of this tunnel this maggot stops feeding and pupates into the adult fly and exits the leaf.

 

More leaf miner damage

To control this pastor not depends on the value of the damage it creates. Leaf miners also attack weekly green vegetables like lettuce and spinach. In cases like these, we don't want any damage or very little because we're going to eat these leaves. This insect is also causes damage to some fruit trees like citrus and ornamentals like roses, annual flowers and in your case Jasmine, where leaf damage can be tolerated more.

 

Leaf miner damage in citrus leaves

So the tolerant to damage of leafy greens is very low and start to control this pest in a variety of ways as soon as damage is seen. Control can be as simple as removing leaves as soon as you start seeing the damage. It takes a while for this past to create these tunnels so with a little bit of diligence, leaf removal works extremely well. Removing leaves as soon as you see damage reduces the level of adults and is very efficient at minimizing damage. When you remove the leaves, don't throw them on the ground but put them in the trash or destroy them immediately.

Heavy leaf miner damage. This damage is heavy enough that it might require spraying for prevention in the next planting.

You can spray the leaves with chemicals, and this is done frequently on leafy greens vegetables grown for commercial production to protect the crop, but if you don't need to spray then don't. Understand and live with the damage if it's minor and use leaf removal if it starts to get out of control.