Sweetness of paddle-tail cactus attracts predators

Q: What causes scarring along the surface of my cactus pads?

A: The picture you sent looks like a paddle-tail cactus, aka Opuntia, but without spines. Mexican farmers living in Central America burn the spines off so that cattle can eat them. Many types of cacti have spines on the paddles to protect them from chewing-type predators like jackrabbits and desert cottontails or any predator that likes to eat them.

Peach fuzz does the same thing for peaches and nectarines. That’s why nectarines (fuzzless peaches) get more surface scarring than peaches. The paddles are sweet and provide energy to those that eat them.

I have measured the sugar content of an American agave in its core, and it has a Brix of 16 during the summer. To put it into perspective, ripe wine grapes full of sugar and ready for harvest will average in the mid-20s or higher. A fully ripe lemon ready to harvest will be above 10 on that same scale and an apricot 15. In the summer they can have quite a bit of sugar in them. That’s a lot of energy (sugar) for an insect pest.

But biting or chewing damage has a different look than the damage shown to me in your picture. When the paddles don’t have any protection then a number of pests eat them and can cause this type of scarring.

Looks like your Opuntia spp. cactus had some small critters like insects attacking it for food (energy). They burrowed or ate just under the skin. That’s what caused the problems you are seeing.

Q: I have noticed tall Washington palm trees, about 30 to 35 feet tall, the have shed 8 to 10 feet of their frond stubble, some much more. It is somewhat unsightly and clutters the landscape with trash. What makes this happen?

A: You are calling it a Washington palm and is probably a Washingtonia fan palm which is the genus of this palm. There are two types of Washingtonia palms: the Mexican fan palm and the California fan palm. Both rely on the wind (think corn or dates) for pollination. This becomes important later.

The Mexican fan palm is a skinny palm that is nearly naked along its stem. This is the palm we think of when we think of landscapes in southern California. Its trunk seldom is greater than 12 inches in diameter. The leaves or fronds usually separate from the trunk.

The California palm, in its truest sense, is fatter than the Mexican fan palm and retains its leaves (fronds) resulting in a skirt that hugs the stem. This skirt can end up as a habitat or hiding place for lots of critters including rats. It can also catch fire.

This is the palm we think of when we think of a desert oasis. Both have their pluses and minuses.

If they flower at the same time and are grown near each other they will easily hybridize or pollinate each other. The offspring of these two palms results in hybrids with a mixture of traits such as stem diameter and if it develops a skirt or not.

Most likely what you are seeing are primarily Mexican fan palms (Washingtonia robusta) that don’t hold on to their fronds when there are strong winds.

Q: I recently planted a mandarin orange tree and a donut peach. I’m not sure how much water they should be getting. Each tree has 3- to 2-gallon emitters. We currently have them 12 minutes a day for three days a week. Is that enough water? How much water are they supposed to be getting?

A: I don’t like to talk about minutes of water but rather gallons. As I frequently point out, I can drink lots of coffee in a few minutes. Other people sip the same amount of coffee in an hour.

Five gallons of water for a plant in a 5-gallon nursery container is plenty. By the same token, 15 gallons of water for a newly planted 15-gallon nursery plant is more than plenty.

To add more water as it gets bigger, add drip emitters if you want to keep the minutes the same. Space them 18 inches apart. Half the area under its canopy should be wet by drip emitters.

This time of year, the amount of water I am talking about is enough if applied twice a week. Applications once a week might even be enough if there is a 2-to-3-inch layer of wood chips on the soil surface and depending on the soil type. Applying water three times each week is relegated to the hottest of the months.

Always try to give tree roots a day to breathe if you have a chance. Water should wet the soil to a depth of 18 inches. Use a length of steel to judge the wetting depth.

It’s important to put a moat or donut around each tree to capture the applied water, particularly if there are fruit increasing in size, otherwise, it just goes everywhere.

Q: Seems like a couple of years ago you mentioned burning weeds with a torch if you had rock mulch. I had been using Roundup, but this spring I ordered the torch and attached it to a small propane tank. The propane tank was heavy with about 4 gallons in it, but the outcome was really smart. I took it over and treated the kids’ front yard as well. Now, two weeks later, we’ve got just a few weeds popping up which I pulled by hand.

A: I try to suggest using a fire weeder when possible because it minimizes the use of chemicals like Roundup. Roundup has its place. It is primarily a systemic grass killer, but it does leave a residue behind.

Roundup is not, of course, suitable for organic production. But a fire weeder is in most cases. Fire weeders are not systemic and should never be used near irrigation systems.

Fire weeders are oftentimes not permitted in urban settings. Check with the local fire marshal in your municipality to see if it is permitted.

Here are some precautions when using a fire weeder: Never use it on a windy day; know the combustibility of the weeds you want to control; don’t use near drip emitters; have a hose and water ready.

Q: I have an orange tree that has been in a pot for the past three years. This pot has large, drilled holes in the bottom. The orange tree has done well every year except this last year. The leaves mostly fell out, but some new ones are trying to grow behind the dead branch tips. I am now watering three times a week. Do you think I can repot the tree in a slightly bigger container with new potting soil or maybe just fertilize the tree with existing soil?

A: The orange tree will always do better after repotting it and changing the soil. Most repotting occurs in four or five years, but your container is pretty small so it might need it more often. Repotting is not just putting new soil into a larger container but includes pruning the roots and the top as well.

Your orange tree does not look like a dwarf type. It helps to know which orange this might be. Most oranges are not suitable for containers. They grow too large.

A dwarf orange is an exception. If it’s not a dwarf, then get it in the ground in a suitable location this year. You may need to protect it from the winter cold. Remember, Las Vegas is not known for its citrus groves.

From the pictures, the dieback looks like a lack of water or cold damage. Not disease. Otherwise, the new growth looks great.

I am not sure if the dieback (branch tips brown) was because of the cold or not. This is where a recording thermometer would help. If air temperatures dropped below freezing in the oranges spot, it’s possible. It depends on the type of orange, the temperature it got down to and for how long. In warmer climates it’s not a worry.

If using water coming from the Colorado River, make sure water comes out the bottom of the container. Salt can accumulate in the container quickly if not enough water is applied to leach it out the bottom.

Fertilizing fruit trees growing in the ground is only once or twice a year because of the soil volume. When growing in containers that all changes. I would fertilize your tree very lightly with every fourth application of water. If that is too much, then move it to every ten applications. With winter tender plants like citrus, stop using high nitrogen fertilizers (high first number) after the end of July.

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