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Answer: Your tree is called African sumac (Rhus lancea) and it is a very common plant in our area. They can grow to a height and width of 30 to 40 feet. Once they become large trees, some people like them for the shade they provide. They are tough and do well with little care and may be used as street trees or in places where little else will grow well. Unfortunately, they are invasive and can spread easily in urban areas. Their seeds will grow wherever there is available water. As you know, persistence is required to keep them down once they start growing. Some people report allergies to the pollen so that is another concern. It’s hard to say no to a free tree but this is one that you might consider removing given the associated problems it brings.

Question: I’ve got a previously healthy stand of Mexican fence post cactus that has been infested with a white scale pest of some kind. Can you tell me what it is — and how I might get rid of it?

Answer:Your scale insect was identified as Diaspis echinocacti. They are found on a variety of cacti and other plants. The recommended management strategy for scale insects is a combination of integrated pest management tactics including natural enemies, physical removal, and applications of horticultural oil or insecticide. Because their outer covering protects scale insects, the ideal time to spray them is during the time in their life cycle when the young have recently emerged from their eggs and are crawling about unprotected. The timing is not always easy to determine but you have options to figure it out. Late winter is a good time to start watching. Carefully examine the infested plant to see if crawlers are present. A magnifying glass or loupe will come in handy when looking for these tiny insects. Alternatively, place double-sided tape around the cacti in affected areas of the plant when crawlers are expected. The tiny insect bodies get stuck in the adhesive. Once you see them you will have a general idea when they emerge. The next trick is to notice what else is happening nearby with your other plants. For example, what is recently blooming in your landscape? Year to year variation in insect development can be estimated by the use of phenology (the known influences of weather variations on plant and animal life cycles). By watching known phenological indicator plants you can accurately predict when particular scale insect eggs will hatch in your area in following years and thus you will be better prepared to manage the scale insects.

Question: We have a large ruby red grapefruit tree that is about 12 years old. We have always had nice crops of pink grapefruit until last year. Last year’s crop had smaller fruits and the flesh was yellow instead of pink. This year, the fruits look like they will be even smaller. We have consistently fertilized the tree three times a year, and it is on drip irrigation. The foliage is nice and dark green. What are we doing wrong?

Answer: Smaller fruit is often a symptom of insufficient irrigation. You said the tree is on a drip system but not how much water it is receiving. The recommendation for citrus trees is a deep soak to a depth of 36 inches every 7 to 10 days in the summer, every 10 to 14 days in the fall and spring, and 14 to 21 days in the winter. If you are already irrigating in this way, please let me know so we can puzzle it out further.

Question: Our olive tree was planted about three years ago and most recently has developed a growth on the trunk and throughout other areas of the tree. We are concerned that this might kill the tree and spread to other plants. Would appreciate your input on what growth might be and what we can do the properly treat it.

Answer: The growths you are seeing are called epicormic sprouts. These are often seen as a response to stress in a tree. In healthy trees, these buds remain dormant under the bark, held in check by growth regulators produced in the tree’s crown. If the crown has been damaged or pruned heavily, the tree may respond by producing these shoots to expand the amount of leaves for photosynthesis. Other causes may include a sudden change in environmental conditions and disease. If you want to remove these sprouts, it’s best not to remove them all at once, causing further stress, so remove no more than one-third at a time. The tree would likely produce more of them anyway. If you know of any changes in the tree or surrounding area, such as recent pruning or damage, that would help narrow down why the tree is responding in this way and possibly offer a way to mitigate a recurrence.