Question: I have something growing from my 10-year-old oleander that I’ve never seen before. It is a short, hard, and green mass that seems to be killing the branches it is on. Do you know what it is and what can be done about it?
Answer: Your oleander (Nerium oleander) is suffering from a gall disease caused by the bacterium Pseudomonas syringae savastanoi. The galls occur on twigs, branches, leaves, flowers and seedpods. Initially galls appear as small protuberances that subsequently develop into wart-like growths with roughened, fissured surfaces. Galls vary in size but average about a half an inch to 1 inch in diameter. Large galls are usually made up of several small galls that have grown together. Warm and wet weather is the perfect environment for growth and spread of this disease. For any disease, their success is based on the appropriate environment, a susceptible host (e.g., the oleander), and the presence of the pathogen, which is always around. Galls are the result of the growth and multiplication of the bacterium. The bacteria enter and infect oleanders through leaf and blossom scars, wounds produced by pruning, frost injury, and natural openings. Rain, sprinkler water and pruning tools can spread bacteria from diseased to healthy plants. When purchasing oleanders, examine them carefully to be sure they are free of galls. The vast majority of nursery stock is free from disease but prevention is always the most effective method of disease control.
For diseased oleanders, prune out infected plant parts and apply disinfection solution (a 10 percent solution of household bleach) to each cut surface. Always dip pruning tools in the disinfectant solution between cuts to reduce the possibility of spreading the bacteria. Pruning operations should be conducted during the dry seasons to avoid infection of wounds. Avoid sprinkler irrigation. Severe infection of large shrubs is difficult to control by selective pruning. If the entire shrub is cut down, the new succulent growth is extremely susceptible to infection. In certain situations, removal of the diseased plant and replanting may be the best method of control.
Question: This plant is growing in our yard in Oro Valley. (See photo above, right.) It is quite aggressive and I am concerned about it overrunning our yard. Our elevation is 3,000 feet.
Answer: The plant is called Coulter’s spiderling (Boerhavia coulteri) and it’s an annual in the four o’clock family (Nyctaginaceae). It can be easily found in washes and flat areas in the Sonoran Desert. It spreads like a groundcover, it produces spikes of tiny pink flowers, and it reproduces by seed. It’s native to the Southwest and found throughout most of the state. It is especially noticeable in summer in Southern Arizona. Some call it a weed and others call it a wildflower since it’s a native. It certainly grows like a weed so you have to decide if you like it enough to keep it or dislike it enough to pull it up before it produces seed. You can also use a weed wacker to knock it back or spray it with an herbicide when you first notice it emerging in the spring. Once the monsoon rains begin, this plant and many others grow very quickly and may overrun your yard if not managed.
Question: I have several euphorbia plants in my front yard in the Catalina Foothills. I had asked my gardener if an animal was resting on one of my large plants. He parted the euphorbia and there was this strange foam-like substance at the base. He had never seen this before. What is it and will it kill my plants? The daily monsoons have subsided a little and I wonder if it was related to this foam.
Answer: Euphorbia species have a milky white sap they exude when cut or broken. If something was lying on your plants, they may have broken some of the stems and caused the sap to flow near the base. The stems in your photo (above, left) appear to be damaged and browning, possibly from the breakage.
Question: My neighbor’s fig tree for years has attracted hundreds of fig beetles. It is quite the sight when they come out. I started my own fig tree this year. I sure hope the beetles don’t give me the same attention. I wonder if soaking the soil underneath the tree with Heterorhabditis bacteriophora would be helpful to lower the population. If so, what time of year is optimum?
Answer: Nematodes can be effective in the right situation and the Heterorhabditis bacteriophora species is known for its insect parasitizing behavior. Unfortunately, nematodes don’t do well in, sunlight, high heat, or low soil moisture. The optimum temperature is 68 to 86 degrees so applying them at night is important and the soil must be kept moist for two weeks after application. Also these beetles are known to lay eggs in soil with plenty of organic matter. Much of our desert soil lacks organic matter so we often find their beetle grubs in well-maintained vegetable gardens and compost piles rather than under the trees they use for food. If you wanted to experiment, the best time of year to apply nematodes is when the young larvae are developing in the soil. Once you see the adult activity stop, that means the eggs have been laid. A week or so later the young will hatch and begin to feed.
Question: I’ve read that you need to have new soil each year when you plant your annuals in pots; plus clean them. However my plants have done well up until this year after a couple two or three years in the same soil. I know that it’s time to replace and clean. However, my question is, is there any way to refresh this soil to make it usable or do you just have to discard. We don’t have a compost pile and live in a development that would not be easy to discard soil, as our yards are gravel.
Answer: Soil mixes for containers are reusable from year to year to some extent. Many mixes are soilless and have other materials that make them ideal for containers so that air and water can reach the roots. Eventually, these materials will break down and you will notice that they don’t drain as well. When that happens, you should discard the soil mix and refill the container with fresh mix.