Orange and avocado are the most sensible fruit trees to grow in a sub-tropical urban environment such as Los Angeles. Given plenty of sun, both are relatively pest-free trees and produce dependably once they have established themselves in your yard or garden. However, problems are sometimes encountered as the following letters demonstrate.
Q I have a navel orange tree that is about 30 years old. For the past two years, the tree has not produced as it once did. The fruit is very small, the size of a golf ball, where it was the size of a soft baseball. Also, the fruit is splitting and falling now. I have taken it to the nursery and they said “it’s either too much water or too little water or the weather was too hot when it was maturing.” So which is it? Can you help with this?
— Vicky Zenobio, Woodland Hills
A All citrus fruit are susceptible to splitting and navel oranges, within this group, are most susceptible of all. Fall is the season when splitting is most likely to occur. According to a University of California farm adviser report, hot weather — especially if accompanied by strong winds — often precedes splitting. If water is not sufficiently available to the tree, it will remove water from fruit and leaves, leading to softened fruit and cupped foliage. If water is then heavily applied, it will be taken up quickly by the fruit pulp which will expand rapidly, faster than the capacity of the peel to contain it, and so splitting will occur.
A 2- to 3-inch layer of mulch is the best preventive measure where splitting is concerned. Mulch will keep soil from drying out so that a slow and steady uptake of water can take place. This is particularly important where soil is sandy and easily prone to drying out or where dwarf, shallow-rooted citrus are concerned. Irregular fertilization can also contribute to split fruit so that slow-release fertilizers, which supply minerals over a period of several months, are recommended.
The fact that your fruit are small is of greater concern. Small fruit may be the result of mineral deficiency, especially zinc, so I would embark on a regular fertilization program with a product specially formulated for citrus to see if this will increase fruit size. Ideally, you would spray a liquid micro-nutrient formula that includes zinc on your foliage in spring, summer and fall. However, small fruit might also be the sign that your tree has mites or a virus. Hold a piece of white paper under foliage that is cupped or discolored and gently shake it. If you see small dots on the page that are moving about, you will know you have mites. You will either have to employ a miticide or locate predatory mites, courtesy of an insectary, if you wish to utilize biology to address this problem. Tristeza virus also leads to small fruit but, unfortunately, it has no cure. This virus is carried to citrus trees by aphids so planting drought tolerant sages (Salvia species) in the vicinity, which attract hummingbirds, is a recommended practice prior to planting citrus. Hummingbirds are ravenous insectivores and aphids are among their favorite treats.
Q I have some kind of disease on my ‘Holiday’ avocado tree. I’ve tried everything that I could find to get rid of it but it keeps coming back. I have three other new trees that haven’t been infected and I don’t want this to spread to them. Looking at the photos, do you have any idea of what it might be and, more importantly, do you know how to get rid of it?
— Larry Hanes, Pasadena
A It appears that you have Dothiorella canker. The bacteria that cause this disease are attracted to wounds and pruning cuts. Once the disease is observed, it is vital that any dead wood and leaves be pruned out and any fallen fruit be taken away since such wood, foliage and fruit could harbor the offending bacteria. As in the case of the citrus problems discussed above, stress is ultimately responsible for development of this disease. Proper irrigation and fertilization are the best means of prevention. Also, pruning and harvesting of your tree should be done when wood and soil are dry, and never following a rain, since wet conditions will encourage the disease to spread.
Q I have a large area behind my house that is a steep slope. Because of the potential fire problem every year, I cut down growth, which is mostly weeds, and spray herbicide. This keeps it clean until the next year, unless a good rain comes sooner, but it leaves the ground ugly with potential for erosion. I would like to do some simple landscaping and hardscaping but I’m concerned that whatever I do the weeds will reappear. Whatever I plant, it’s overwhelmed by weeds. I need advice.
— Jack Kulpa, Palos Verdes Peninsula
A I would recommend covering the slope with jute netting. Jute is a ropy material that will remind you of burlap. It is a fiber that is derived from an edible, tropical vegetable crop.
Once your slope is covered with jute netting — and make sure you get plenty of clamps or long u-nails to hold it in place — you simply pull apart openings in the cross-hatched jute where you want to plant. Jute netting does a pretty good job of keeping out weeds until ground covers can take over. When it comes to planting your ground covers, for quicker coverage, you will want to consider planting well-rooted quart (4 inch) or 1-gallon size plants, as opposed to rooted cuttings in dirt flats, which are slow to establish. One of my favorite ground covers for covering a slope, which grows in both sun and partial shade and is quite drought tolerant, is trailing rosemary (Rosmarinus officinalis prostratus).
For more information about area plants and gardens, go to Joshua Siskin’s website at www.thesmartergardener.com.. Send questions and photos to Joshua@perfectplants.com.
