Spots on pluot fruit probably nutritional problem

Q: I purchased a Flavor Supreme bare root tree from the Horse Drive University Orchard in North Las Vegas six years ago. The pluots are hearty and taste good. I spray the tree with horticultural oil in January, apply iron EDDHA around the tree in early spring and add a shovelful of homemade compost made from organic vegetable scraps, garden and coffee grounds. The problem I had this year is that some fruits had black spots on them and some also have black spots inside the fruit. The leaves of the tree look fine except for some wind damage which is expected. I've looked online and the closest problem I can find is bacterial spot, but I'd appreciate your expert opinion.

A: I doubt it's a disease problem. When I grow fruit trees in the desert, I can count disease problems with less than five fingers. Thanks to our low desert humidity for that.

Flavor Supreme Pluot is an incredibly good variety, and it produced fruit about three out of five years when I had it at the North Las Vegas University Orchard. It's not a big producer, which is probably why it was never released. I agree that the fruit can be spectacular, but this particular variety can still be a light producer.

I had never had black spots on fruit before. This may be due to the sun (sunburn on the fruit) or, more likely, a nutritional issue. Sometimes a lack of calcium can cause nutritional problems that affect fruit quality and look similar on apples (bitter pit) and pears (corky spot) growing in calcium-rich western soils.

I know it sounds strange, but calcium is extracted quite heavily by certain fruit trees in our calcium-rich soils. Try an application of compost other than the one you produce around the tree. Many composts are also low in potassium, but often high in nitrogen and phosphorus.

Try applying a granular fertilizer to irrigated areas under the tree rich in calcium, magnesium, sulfur and potassium early next spring. If that doesn't work, you may need to send a soil sample for analysis to a certified agricultural soil testing lab (such as A and L in Modesto, CA) or do it yourself, but look specifically nutrient levels. It's probably not a pH (alkalinity) problem.

Q: The nursery told me that the two ornamental trees I purchased were male Chinese pistachios, so no berries. They were incorrect. This $1,000 tree turned out to be a female tree. It produced berries and I'm stuck with that. So I cut off all the smaller branches that had berries completely at the level of the larger branch. Now all the leaves are wilting and some have brown and yellow spots. Another Chinese pistachio planted within 10 feet of this tree, which I did not prune, is no problem. I was wondering if I was spreading a disease like verticillium wilt with the pruner.

If it turns out to be a calcium deficiency, let me know and I can tell you that we have fixed this problem. It may be necessary to spray the leaves.

A: Some trees only have male trees and female trees. This is how the sexes are separated in these trees. All types of pistachios are either male or female trees, similar to ash, African sumac, and mulberry.

Verticillium wilt can be spread with dirty pruning shears, but this disease is usually born in the soil. I guess if you dropped your pruner/lopper/saw on infested ground you could pick it up and infect the tree, but I think that's overkill.

I prune established pistachio trees (nut trees) without any disease issues. I've done this several times, and pruners and hand pruners weren't sanitized before pruning cuts. I don't see this disease problem happening with this tree by pruning.

I would rather suspect sunburn on young limbs followed by borer problems in early to mid summer. When the pistachio is young, it is more of a ruffled, open tree that fills out later.

Q: I have a row of waxleaf privet that I am trying to irrigate. I used to use wood chips around these plants, but I was afraid of smothering them. Currently I use two 4 gallon per hour drip emitters watering for an hour once a week. The tops are starting to wither and I wonder if it's a watering problem.

If there are signs of borer problems (bark loosening, sun damage to upper sides of limbs, open western or southern exposures to the sun), apply anti-borer insecticides (these contain imidacloprid in the active ingredients) by soil soaking. around the base of the tree and see if the tree recovers over the next two years.

A: Keep woodchips and woodchip mulch away from the trunk 6-12 inches and no daily watering. Leave this area bare and open to dry out the soil and mulch. The particular disease you fear will smother your plants is called crown rot or one of the so-called soil-borne diseases like Phytophthora.

Phytophthora crown rot or soil root rot will appear on many plants if soils are kept too moist. The heat only makes the problem worse.

Q: We have four fruit trees (one orange, one lime, and two types of lemon) in Sun City Summerlin. Shortly after they flower and start producing small fruits, the fruit falls from the tree. We don't know if this is the result of high winds, too much water or not enough water. Or maybe something else? We also fertilize regularly if that matters.

If you water your plants daily, the top layer of woodchip mulch may not be a great choice for your plants. Whenever possible, try to avoid daily waterings (with the exception of lawns, annuals, or raised beds) when woodchip mulch is used, as it holds the woodchip mulch on the surface and the ground below too moist. In some cases, daily sips of water can keep the soil too dry with difficulty managing irrigation.

A: Fruit trees need fertilizer once or twice a year, that's it - once as a half application when they start producing new growth and a second half application after harvest. The fertilizer is applied to the soil where the water is applied. If you only fertilize once, one full application in early spring to the soil is sufficient.

All fruit trees produce more fruit as they age. Some fruit trees do not start fruiting after 6 to 8 years of age, while others produce fruit sooner. Expect your fruit trees to produce more fruit as they grow and age. Much of the timing of fruit production depends on the variety of the type of fruit tree.

Fruit drop when young is quite common in all types of citrus fruits. When the trees are young, you see flowers with tiny fruits, and then the fruits fall from the tree. This is a natural thinning that occurs on young trees and is normal. It helps the tree balance the demands of a fruit load.

Fruit drop can occur for many different reasons: lack of pollination, too much fruit on the tree, too little or too much water, extremely high nitrogen fertilizer applications to name a few.

Q: Last year my roses were prolific and I had no problems. They were already there when I moved in two years ago and seemed to be thriving. I spray them regularly with Neem oil and Spinosad soap according to the instructions. This year, however, I've had myriad problems and reached the point where I don't know what to do. Do you have any suggestions for curing my plants?

What is not normal is for fruit to fall from larger, more mature trees when the tree has produced an abundance of fruit in previous years.

A: Roses are excellent mesic shrubs for our area and perform very well. Our desert climate reduces disease problems on roses but not necessarily insect problems. Insect problems I have seen on roses here include aphids and ants, cane borer, flower thrips and a few others.

Many of these insect problems require a harsh pesticide applied to the soil. You can try a spring application of a Rose insecticide that you can find at any store or nursery. Some come combined with a rose fertilizer. Most of them are systemic without the need to reapply for several months or not at all.

Bob Morris is a horticulture expert and professor emeritus at the University of Nevada, Las Vegas. Visit his blog at xtremehorticulture.blogspot.com. Send your questions to [email protected]