Cool, rainy weather perfect condition for fireblight disease

Cool, rainy weather when pear and apple are in bloom is perfect weather for fireblight disease. Fireblight is a very aggressive and dangerous plant disease that shows up as new infections in about May in Asian pear, European pear such as Bartlett and some apples. It can be a major problem on quince too.

But the disease problem, although unseen, can start now. The point of entry for this disease into susceptible plants are the open flowers and fresh pruning cuts.

Open flowers and fresh pruning cuts provide “fresh wounds” or points for this disease to enter the plant. Wind and rain are the usual culprits that spread the disease from plant to plant, but even honeybees can be responsible.

If this disease is seen early enough, usually in late April or May, it can be eliminated easily with a few snips of a sanitized hand pruner, eliminating the infection. But the hand pruner must be disinfected between each cut on the tree, or the disease can be spread on the hand pruners through each cut.

There is some disagreement about what to use to disinfect hand pruners, but chlorine bleach seems to be the favorite among orchardists. Heat from the open flame of a cigarette lighter also seems to work. Some people suggest alcohol, and others suggest household cleaners such as Pine-Sol.

Plants that were infected in previous years will show evidence of this disease when new growth occurs in the next couple of weeks. As the name suggests, this damage resembles the black from fire damage. This can be confusing because any damage to pear leaves can turn black. If you are unsure, send me a picture.

We have had a surge in this bacterial disease over the past few gardening seasons because of our cool wet springs. I will post more pictures of this disease from past years on my internet blog, Xtremehorticulture of the Desert.

Q: I find it impossible to purchase a bag of potting or garden soil that does not contain gnats. This has been a problem with different brands, from local nurseries and home stores. How does one avoid this problem?

A: Fungus gnats (small flies coming from potting soil) are a very common contaminant in potting soils because many are not heat-treated to kill them. Raw components are simply mixed together and not composted when it is finished. You will find this problem in nearly all bags of potting soils from expensive mixes to less expensive mixes.

The best way is to raise the temperature of the potting soil to at least 140 F for 30 minutes and kill the gnats. Put the potting soil in a clear plastic bag, moisten it slightly if it is dry, and let it cook in the sun for a few days near a south-facing wall in full sun. Turn it over and try to bake both sides as thoroughly as possible.

Another method is to put the potting soil in the oven and set the temperatures as low as possible, making sure it hits at least 140 degrees thoroughly for 30 minutes. You don’t want the temperature much above 180 F because it can harm the organic content of the soil.

Q: I was overrun with Mexican primrose but have completed all my weeding. I am thinking about putting wood chips around my roses to keep the weeds from returning. Is this a good mulch for the roses? Or might it attract ants or insects I don’t want?

A: Mexican primrose is very difficult to get rid of once it gets established. Many weed killers won’t touch it. An effective control technique is to keep removing the top of the plant as soon as it pops up. It takes lots of repetition and plenty of diligence, but it works.

Remove the tops by cutting them back with a hoe. Some weed-control chemicals burn it back and are essentially chemical hoers. The basic idea is to let the plant invest its energy into growing new, young tops and then remove the tops after they get only a couple of inches tall. This constant removal of the tops exhausts the energy supply stored in the roots, and the plant eventually stops producing.

Wood chips are a great mulch for roses, combined with an application of compost on the soil surface underneath the wood chips. In my experience, the wood chips are no worse than rock mulch or gravel applied to the soil surface regarding attracting insects.

Insects like to hang out in irrigation boxes where there is water. Spraying the inside of the irrigation boxes with an appropriate pesticide every couple of months usually takes care of this problem.

Q: I have a 4-year-old schefflera houseplant about 5 feet tall. New leaves grow only from the very tip, leaving a long ugly stem with nothing coming from it. Can I cut the plant to about 2-3 feet tall and have the same plant grow in the pot? Can I root the stem I cut off and start another plant?

A: Yes, you can. This technique is used by greenhouse growers to produce this plant in mass numbers for commercial sale. You will have a new plant in the same container and two to three new plants made of cuttings from the same plant. Here’s how.

Cut the stem with sanitized hand pruners. Where you make this cut on the stem is critical to success, so do the following carefully.

Along the stem, you will see depressed light colored areas in a spiral along the stem. These light-colored areas look similar to the eyes of a potato. These areas on the stem are called nodes.

The nodes are areas of high activity for the plant, capable of making new leaves and stems or roots depending on how these nodes are manipulated. When these nodes are in the light, they make new stems and leaves. When these nodes kept dark and moist, they make roots. When cutting the stem for the first time it is important to make the top cut ¼ inch above a node exactly where you want new growth to occur.

Removing the top of the plant with a single cut is enough to cause this node to sprout a new stem and leaves. Make this cut at a location where you want new growth to begin. I suggest making the cut at about 12 to 18 inches above the top of the container.

Now you have a container with an ugly stem sticking up from it with no leaves. The separated stem has no roots and a bunch of growth at the top of it. Remove this growth by cutting ¼ inch above a node close to the growth. The top growth can be thrown away.

Cut the stem into sections that have three to four nodes per section. The top cut will be ¼ inch above a node. The bottom cut will be ¼ inch below a node. Following these instructions are important because any residual part of the stem between the cuts will die.

Prepare a new container and fresh potting soil after cutting the stem into pieces. Create a hole in the soil by pushing it into the potting soil so that two nodes are below the soil and one to two nodes are above the soil.

Pull this stem out of the soil and apply powdered rooting hormone to the bottom cut. Carefully place these pieces back into the moist potting soil without rubbing off the rooting hormone and press the soil shut with your fingers.

Place these potted cuttings out of sunlight until new growth appears. After new growth appears, put them back into a lighted area.

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

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