Spray insecticide on prickly pear if used as ornamental

Q: I appear to have a massive infestation of white, cottony cochineal scale on my prickly pear cactus. I can usually get most of it off by hosing, but much of it is hard to reach. Beyond hosing, what insecticide or other kind of solutions do you recommend? Permanent, if possible!

A: Yes, this infestation is quite common on cacti in general and prickly pear in particular. It can be hosed off the pads with a strong stream of water, but it reinfests the pads very quickly and in full force in a week or two.

When I am growing prickly pear as a food, I am more concerned with insecticides and getting them into the food we eat, but if they are grown only as an ornamental plant and not used for food, then I feel better about using something stronger than water, soap and water sprays.

The problem with a strong stream of water is that the force from this water is not enough to knock the insect off of the pad, only the white, fluffy coating surrounding the insect. So it is a short time before the insect regrows this protective cover and the unsightly mass of cotton is back again.

Knocking the fluffy covering off first with a strong stream of water will make these insects more susceptible to an insecticide spray. Most of the common insecticides will work after that; malathion, pyrethrins, just about any common insecticide will work after the fluffy covering has been removed.

This does not mean they won’t be back. They will. But it will take longer for them to get established on the plant again.

Q: My apricots were doing very well as they have for the past several years. After thinning a large crop this year, they were growing well and appeared to be getting ready to pick when I opened the cots, I found the insides to be rotting. I’ve tried to do a little research without success.

A: This may be ripe fruit rot, sometimes called brown fruit rot. It can happen if there is rain near the time of harvest. We get other diseases on fruit as well if there are rainy periods at different stages of fruit development.

By the way, apricots usually do not need to be thinned. You don’t get much of an advantage in size when you thin as you would with peaches or plums.

There is not much you can do except hope that rain does not occur at that time again. Information from universities such as the University of California recommend fungicide applications earlier in the season to prevent it. But we have such a little chance of rain here it doesn’t make any sense to make these applications. Just figure this year you had some losses that come along very infrequently.

Q: Our dwarf Meyer lemon tree blooms extensively each year; many small lemons appear, but as soon as they reach the size of a small pea, they turn brown and drop off. A friend living nearby reports the same results. Any suggestions on what causes this?

A: Meyer lemon does very well in our climate if it avoids winter damage, and many people are successful in producing fruit here. It may flower but not produce any fruit for a couple of years after planting them in the ground. If this is the case, the flower may form a small fruit and it drops from the tree. This is simply because the tree is not old and big enough to keep the fruit but aborts them instead.

The second reason is irregular watering. The tree must receive watering regularly so the soil does not become excessively dry and then wet. Dry soils will cause the tree to drop its fruit. They are more difficult to irrigate when grown in containers in our climate. I find it is best to use an inexpensive soil moisture meter such as you use for houseplants to judge when to irrigate next.

The third reason may be the trees are watered with shallow irrigations and not deep, infrequent irrigations. Water them with a large enough volume to wet the soil to a depth of 12 to 18 inches each time you irrigate. Hold off on watering until the soil begins to dry and then irrigate again. In the spring, this would be applying water twice a week until it starts to warm up in May. This may change to three times a week in midsummer.

Q: Our year-old cactus had gorgeous yellow blooms this spring, but this week it bloomed again! What gives? I thought “one and done” with cactus? Also should it have the smallest drip head available and only one of them?

A: Flowering can happen over a long period of time and different cacti flower at different times. It also is possible flowering was triggered by our extended cool wet weather in the spring, which was unusual.

Cacti are not all the same regarding watering. It depends on the cactus and where it came from. Some cacti can go long periods of time between irrigations. Others should be watered more often. None of them should be watered daily. You might want to consider not using drip irrigation but just water them with a hose periodically.

Cacti can store water inside of them that they use when water is not available. Most of them are shallow rooted and take up water quickly after a rain or irrigation. You may see them swell after a rain or an irrigation.

When they don’t receive water for a week or two, you will see them become smaller in diameter as they use this stored water up. Two things cacti require: soils that drain in a matter of hours and infrequent watering.

I would not water them more often than once every one or two weeks. Some of the native cacti from the deserts of the Southwest should be watered every three to four weeks at the most.

Watch your cactus and look for shrinkage as it uses its internal water. This is a good indicator that you should water it and let it “plump up” again. Fertilize it once a year in the spring.

Q: This is my first Las Vegas summer. Is there a trick to keeping geraniums in this heat? They were beautiful when purchased. I water daily or every other day. They are on the edge of a covered patio, getting some shade but burning up.

A: Geraniums are cool-weather plants and do not like our summer heat, low humidity, poor soils and poor water quality. They do best in the fall, winter and spring months.

Otherwise keep them in an eastern exposure with filtered light after about 9 a.m. and no afternoon sun.

They will grow best in containers with a good bagged soil mix rather than planting them directly in our desert soils. The soil should be high in compost. Cover the soil with a wood chip or shredded wood mulch to keep the soil cool and moist.

Q: I have several chinaberry trees on my property. Most of them are full of leaves and looking very healthy. I have one that is struggling and I am not sure why. Any suggestions?

A: Chinaberry is a tough tree that can take a lot of abuse. But I have seen it not do well when water is limited.

Take a close look at what is supplying the water and see if this is the problem. One method is to put a hose on it and give it 20 or 30 extra gallons once a week for three or four weeks and see if you see a change.

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.