Ash whitefly usually controlled by natural predator

Q: I have two ash trees in my yard. There's one healthy looking tree in the rock yard on one side of my driveway and on the other side there's a larger ash tree on my small grass lawn. The larger one on the lawn seems to be suffering from aphids. The leaves began to curl just as they bloomed this spring and over the summer it seems to have affected 80 percent of the tree. It has not looked healthy all summer.

A: This is most likely ash whitefly, if it persisted during the summer months. Normally this insect disappears in our climate after a season or two. There is a natural predator that helps to control their levels as well.

They are very difficult to control and you will have to use some hard pesticides for any measure of success. The product will have to have a label that lists ash trees or at least ornamental trees and should list ash whitefly or at least insects or whiteflies on the label to be used legally and if you want any measure of control. The best time for a foliar spray would be in the early months of summer when the population is starting to develop.

But as I said, this pest has been in the valley for at least 15 years now and has not shown any signs of developing into a big problem. I would try to let it run its course over the next season or two, or apply an approved insecticide to the foliage in late spring and early summer.

Q: I am apparently "stuck" with powdery mildew disease, or something like it, on my yellow rose vines. I water them using overhead sprays for my lawn. Can my vines die from this disease? I spray for disease control every three weeks, but if I quit spraying them, will they die on me?

A: For diseases to occur they must have the disease organism present, an appropriate host, which in your case is your Lady Banks roses, and the right environment or weather conditions.

It is not just simply a matter of weather conditions but also the microclimate where your roses are grown. As long as this microclimate exists for your roses and weather conditions prevail you will always have problems with them growing there.

The two problems that make things worse are the overhead water falling on the foliage and the lack of air movement around the foliage.

You have choices. Try to change the microenvironment by keeping the foliage dry and pruning the roses so they have better air circulation, move the roses to a new location, alter the environment in some way or continue spraying.

Powdery mildew does have the potential to severely damage your roses but it probably not kill them in our climate. The amount of damage and where it occurs will most likely be the foliage that has poor circulation and repeated applications of sprinkled water.

I guess you can weigh what is more important to you. Would you like to continue to make spray applications and spend your time and money there or make other alterations in your landscape design to minimize your labor and costs?

Q: What can I grow this fall in my backyard besides salad mix. I had very good results last year. I had fresh organic salad mix for months.

A: Much of the fall garden depends upon current temperatures and the length of time it takes to mature certain crops. Easiest right now are things like radishes, which can be sown every week to 10 days throughout most of the winter for successive crops of radishes.

I would hurry and get in some beets, carrots and arugula. And you might try green beans and snow peas. Plant your garlic now, along with spinach, kale, Swiss chard, kohlrabi and other primarily spring crops grown in more northern parts of the country.

Q: I have a large date palm in my backyard. I wrote to you about it before regarding this problem, but now it seems to be getting worse. About 3 feet below the green limbs, the stubs from the cut off limbs seem to be swelling out, but you can actually grab them and remove them very easily. Do you have any ideas on what can be causing this to the tree? I have another palm this same size and the limb stubs on that tree are tight and completely intact.

A: I do not believe that this is a cause for concern. These stubs are the bases of the fronds that are attached to the trunk of the palm tree.

Fronds are removed when they appear to be dying or when they are dead, leaving the dead stubs, as you call them, on the trunk. The still-attached stubs are subject to decay and eventual separation from the trunk.

The stubs are not part of the trunk nor are they a part of the integrity of the trunk. These stubs are simply dropping away from the trunk as they decay over time . They do not all separate from the trunk because they are not all decaying and separating at the same time.

I hope this helps reduce some of your worries. Unfortunately, the trunk will not look as pretty as these stubs separate from the trunk.

Q: I've attached a couple of pictures of our poor pineapple guava plant. It did well until this year, but for some reason it is dying. The leaves are turning brown and dropping even though it gets plenty of water. It sits on the north side of a wall and next to the house, so it does get reflective heat. It has been fertilized and I have found no bugs or fungus. Can you shed any light on what is killing it?

A: It appears that it does not get enough water in combination with poor soils. Pineapple guava likes to have a soil higher in organic matter than a soil covered in rock can provide.

I know you think it has plenty of water but I would be giving this plant about 5-10 gallons of water three times a week in midsummer and about the same amount per application now but twice per week.

Rock mulches tend to allow the soil to mineralize (deplete the soil of organic matter and nutrients) about three to five years after planting and applying rock mulch. I think you will see a dramatic improvement in the plant if you pull back the rock mulch about 3 feet from the tree trunk, put about 2 inches of compost around the base, cover that open spot with 4 inches of wood mulch and water with larger volumes.

Q: I have attached a picture of my beautiful Canary palm that hangs over our pool and creates the wonderful ambiance seen from our living room. Unfortunately, the roots are moving the block wall and it has to be removed. Can you please suggest something that will fill in this space and possibly hang over the pool a bit, and that has a small root system and minimal droppings?

A: Here is a list of poolside plants written by Lucy Bradley, formally with the University of Arizona cooperative extension. It is an extensive list. I Googled it for you.

You will have to determine which of these plants you like and secondly if it will survive with our winter temperatures compared to Phoenix.

I don't like to recommend plants because I do not know what is available locally. I could be sending you on wild goose chase looking for plants. It is best for you to find out what is available locally and then use the list at this website: http://ag.arizona.edu/pubs/garden/az/1058.html.

Q: My mimosa tree seems to continue to have problems. I have found a large white worm under the bark at limb joints. The surrounding limb area is soft and punky. I am not sure how to treat this. I have attached pictures of the tree. The tree is great in the spring but yellows as the temperature rises. It seems to be just this one limb. Would it be wise to remove the limb and reshape the tree?

A: I can't see the worm but my guess is that it is not a borer or other damaging insect to a living tree. It is possible it could be existing on some dead debris in the tree but not causing damage.

The usual problem is a disease that causes these trees to die at an early age. The disease invades the tree through the roots and plugs some of the water-carrying vessels causing limb dieback. I am guessing this is what your tree has.

There is no cure except replacement. These are short-lived trees here and in many places. That is why you don't see very many large, old ones here.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at morrisr@unce.unr.edu.