Palm trees look their best when pruned annually

Q: I am chairman of building and grounds at a church where we have palm trees that are about 40 feet tall. These trees have skirts of dead fronds below the green tops. Somebody told me if we wait long enough, these dead fronds will simply fall off and we won’t have to trim them. Is this true?

A: No, it is not true unless a very strong wind blows them off, and you are prepared to have them look “ratty” until the rest of them blow off. Normally they hang from the palm trees in a skirt that can be very attractive if left fully intact but can harbor birds and rodents. Dead fronds also can be a fire hazard.

At best, your church has the expense of removing dead and dying fronds every couple of years if it can tolerate some dead fronds in the canopy. Otherwise, pruning must be done annually if the trees are to look their best.

Another problem of many palms are the seeds they throw everywhere each year. Have palms pruned the same time they flower and the flowering spikes that produce seed can be removed at the same time. This eliminates the problem of palm seedlings growing everywhere.

Q: My roses did not do well this summer after a spectacular spring. Now there are black spots on the plant’s leaves. I was told this is black leaf disease. What should I do now? They also got that white fungus when we had all that rain.

A: Summers are our “winters” for roses here in Las Vegas. They don’t grow well during our very hot summer temperatures. They like the cooler spring and fall months and even the winter months if planted in warm, protected locations. They do wonderfully here for about eight months of the year.

We don’t usually get black spot disease on roses here because the climate is so dry. This disease is more common in humid climates.

This is a fungal disease and so watering roses with drip irrigation, not overhead spraying, usually corrects the problem as well as eliminating powdery mildew disease (the white fungus you mentioned on the leaves). It also helps if roses are grown in the sun, not shade, for six to eight hours every day. Morning sun is best.

Keeping roses healthy helps fight disease and damage from heat and sunlight. It also helps if air can move easily through their canopy which helps control leaf diseases like black spot and powdery mildew. Pruning roses lightly during summer months helps keep their canopy open.

Roses like compost applied beneath them to improve the soil and wood chips applied after that as a mulch. Apply compost around the base of roses in January and cover the soil with 3 to 4 inches of wood chips instead of bare soil or rock. This makes a huge difference in the performance of roses.

Compost also is a great fertilizer. This same 1-inch layer of compost applied in January also will fertilize them until about April. Use a follow-up rose food in late spring and again in the fall months.

If you are convinced this problem is black spot disease, then pick up a rose fungicide that states it controls black spot on roses and apply it according to the label. Repeat applications may be necessary to protect any new growth from getting this disease.

The white powdery fungus you saw was probably powdery mildew. This tells me your roses may be growing in some shade. Shade, and watering with overhead sprinklers, keeps the leaves wet, a perfect environment for powdery mildew. Splashing water from overhead irrigation sprinklers spreads the disease from leaf to leaf and plant to plant.

Prune out unhealthy growth now, getting rid of diseased plant parts, and leave four to eight healthy canes for further pruning this winter.

Q: I have a couple of fig trees that are 4 to 5 years old which have some problems. They produce a lot of fruit during the year, but the fruit gets about grape size, turns yellow and falls off. Both trees are watered twice a day during the summer. The soil appears to be moist every time I check.

A: I can see your fig trees are very nice looking from the picture you sent. However, the irrigated area under the tree, about 18 to 24 inches across, does not look big enough to support 4-year-old fig trees. I don’t think you can put enough water under the tree to keep this tree producing figs until they are mature.

I’m sure it’s quite confusing. You have a very nice-looking tree, you are watering every day, but the tree doesn’t produce any edible figs. So it can’t be a watering problem. Right?

Wrong. Even though you water every day, if not enough water is applied, the fruit may fail to develop even though the canopy looks great. Leaf and stem growth is greatest early in the year when temperatures are cooler. Fruit develops when temperatures get hot.

Watering daily may have nothing to do with the amount of water applied. Fig trees, or any plant for that matter, doesn’t care if it gets water every hour, every day or every week. The total amount of water applied must be enough to satisfy its needs.

Fig trees use a lot of water. The amount of water required in a week increases 500 percent from January to July. If you want fruit from these fig trees, then they must get enough water while the fruit is developing. If they don’t, the fig fruits will be small and/or drop from the tree.

Increase the size of the area where water is applied to at least 4 feet in diameter. Six feet in diameter is better. Add additional drip emitters so the tree gets more water each time you irrigate. Avoid increasing the number of minutes on your irrigation timer.

Trees do not like to be watered every day. Water fig trees three times a week in midsummer, but each time apply about 30 gallons. That is 90 gallons a week in midsummer. The tree should have enough drip emitters around it to wet the area in a 4- to 6-foot diameter under the tree.

The total amount of water delivered in a single application should be about 30 gallons. Put a 4-inch-deep layer of wood chips under the tree about 6 feet in diameter to help keep the soil moist between irrigations.

Please realize you can water every day and still not give plants enough water.

Q: Some kind of thrip-like bug has invaded my garden. My grape leaves are brown and drying up from these bugs. There are tiny black spots where they were. There’s so many of them I can hear them as I approach the plant. I applied Spinosad in September but it didn’t do anything. Now they’ve gotten into my peach tree.

A: The tiny black spots on grape leaves is fecal matter from leafhoppers, not thrips. Thrips are very common on grapes here that feed on plant juices from the leaves of grapes and other plants.

Leafhoppers start building their colonies in grapes around April. Once established, they will build huge colonies in the grapes and spread to other plants.

They are easy to get under control in April and May when they are young. They are extremely difficult to control without some heavy duty insecticides later in the season.

Spinosad, a natural insecticide spray, works great if applied early in the season, such as April and May. Later in the season, you will need to bring out some heavy duty artillery to get them under control.

I hate to recommend anything this late in the year because the insecticides needed are very heavy-duty. It is best if you can wait until next spring and begin treatment early with Spinosad or pyrethrin sprays.

Alternate Spinosad with insecticidal soap and neem oil. Make sure to spray the tops and bottoms of the leaves. If using Spinosad, two sprays about six weeks apart starting in late April will take care of them, the hornworms and the skeletonizers all at the same time.

Bob Morris is a horticulture expert living in Las Vegas and professor emeritus for the University of Nevada. Visit his blog at xtremehorticulture.blogspot.com. Send questions to Extremehort@aol.com.