|By Dr. Larry Stein
Professor and Extension Horticulturist
So if you had to guess, what would you say is the average life span of a fruit tree in Texas – 5, 10, 15, 20, 30 years? I reckon if you got right down to it, most fruit trees last about 10 years in the landscape. However we have documented evidence of orchards still producing economic yields when they are 30 plus years old. Hence, the question, what do we do with old fruit trees? Or said another way, when do we decide to start over and stop “babying” those old, tired trees?
There are several reasons for the death of fruit trees, but the most common causes are scale, bacterial canker, peach tree borer, root rot, overproduction, and lack of care. There is no question that the number one killer of peach trees in Texas is scale. Scale literally sucks the life out of trees and in fact once a tree is severely infested, it is very hard, if not impossible, to revive. Hence, annual dormant oil applications are critical for the survival of fruit trees.
Bacterial canker is the second leading killer of fruit trees, especially Prunes sp., i.e. peaches, plums, and apricots. There is no cure for this bacterial problem once the trees are infected, so the goal is to maintain healthy trees. The more healthy the trees, the better they withstand the problem. The key is keeping the trees healthy with water, fertilizer and good weed control. The better you do these three, the less this potential killer will affect your trees. Still, even the best cared for trees will eventually succumb. Selective pruning of cankers can prolong the life, but eventually one must bite the bullet and start over.
Most folks would like to blame borers for the downfall of their trees. It is true that peach tree borer is again a major problem for Prunes sp., however many times other borer problems are secondary. If you have had trees die of peach tree borer in the past, you will have to spray to keep this pest in check. However, secondary borer problems can result from things which weaken the trees. What happens is the trees become sick and weak for whatever reason, which allows other borers an opportunity to get started in this weak wood on the tree. This secondary infection by the borers will usually finish the trees off.
Root rot, specifically cotton root rot, has been a huge problem in Texas for many years. Luckily this fungus does not occur everywhere, but where it does occur, there is nothing you can do to control the problem. Certain plants like Mexican plum and persimmon are less susceptible, but even these plants can succumb under high-pressure conditions. Maintaining good soil drainage and preventing tree over cropping can reduce the problem.
Another type of root rot that affects fruit trees is post oak root rot. This problem is associated with areas formerly inhabited by brush and trees, especially Post oak trees. Again there is no control for the problem.
Lastly we need to address your particular care or management program. Trees, even fruit trees, are particularly tough once established. A peach tree can endure an enormous amount of drought once established for several years and pears are well known for their hardiness. Still there are a few things we can do from a management standpoint that can reduce the amount of stress encountered by your trees. For one thing, there is only a limited amount of fruit a tree can hold without breaking down. Not only do branches break, but also the tree is pushed to the limit trying to fill out the huge amount of fruit on the tree. All food goes to this end and the result is limited stored food in the tree, which makes it vulnerable to cold damage. So crop load balance is one area of management that can help reduce tree stress. Ideally fruit should be thinned to one fruit for every 30 to 40 leaves on the tree. Of course, I realize you can’t control Mother Nature and the late freezes she sometimes throws our way which is why the fruit was limited in many parts of the state in 2003.
Other management aspects we have control over are food, drink and competition. Trees are just like us, they have to eat, they need water for the various physiological processes which occur in the cells and it is easier for one tree to grow in a small space than it is for 10. The most limiting factor to plant growth in Texas is nitrogen. Nitrogen is needed for strong shoot growth, and chlorophyll development, which is the backbone of photosynthesis or food manufacture. Contrary to some beliefs it does not matter where the tree acquires its nitrogen, i.e. either organic or inorganic sources. The key is that the tree has a sufficient amount to make 10 to 15 inches up to 2 feet of annual growth each year. If your trees are making this amount of growth under your current program, even if it means you are doing nothing at all, you are doing well. When your trees are not growing, have yellow leaves and look poorly, it is time to take action.
The factor which makes fertility work or not work, is water. In fact most nutrients move to the roots via this soil water rather than the roots moving to them. So if you have a nutrient deficiency and it is dry, it is a water or drought problem rather than the nutrient being absent. Most crop plants would like to have 1 inch of water per week. This may seem like a lot and of course trees survive on a lot less, so if nothing else a good soaking every three or four weeks would be most beneficial.
The management practice which is the most abused and neglected in the state of Texas, is weed control. What is really sad is that if folks did nothing but keep the weeds and grass away from a tree out to the drip line for the first five to six years of the life of the tree, the tree would do better than if they did one of the above things, but did not control weeds. Weeds are severe competitors for both water and nutrients.
So if you really want something to grow, control the weeds and grass around it. There are many good ways to control weeds: hoe, herbicides, mulch, weed barrier fabrics, and others. The key to weed control is to start when you plant the tree and continue to do so for the first five to six years. You can keep it up, if you like, for the life of the tree and the tree will do even better.
The last management practice which many folks grossly abuse is that of pruning. Pruning should only be done for a specific purpose. Good reasons to prune include: developing a strong tree framework for future production, removing dead or broken limbs, and/or thinning branches out to reduce potential crop load. This pruning should be performed right at or just before bud break. In this way the tree is in an active state of growth and the wounds will heal much faster. This will reduce the chance of bacterial pathogens entering the tree. So proper pruning will go a long way to maintaining tree health. Sometimes we prune too much which allows for intense sunlight to strike major scaffold limbs. This direct sunlight on previously shaded wood along with freeze damage can lead to sunscald or dead areas on the top of the scaffold limbs. This damage leads to dead and/or broken limbs. So many times we end with old trees, which only have one or two healthy and productive limbs.
Having said all of that brings us back to the original question, “What do we do with old fruit trees?” I hope you will agree that if one had managed the tree a bit, it would be more healthy and its life span would probably be longer.
Many of the things which we discussed will kill a tree outright, mainly scale and/or root rot. When that happens, we have no choice but to start over. However, many times we just lose a limb or two from borers, sunscald, or over cropping. So we prune these affected limbs off and eventually we end up with an old tree with maybe one or two productive limbs. Oftentimes we try to rejuvenate these trees, but in reality we need to take them out. There is no reason to “baby” a tree along which has no framework on which to produce a crop. In reality it would be best to take such trees out and start over with a young, healthy tree. Given the proper growing conditions, a young tree can grow 6 to 7 feet in one growing season. One can be back into production in a matter of months.
So the take home message from this article is to take trees out when their productive life has expired. Many have sentimental value, but are worthless as far as production goes. So if your quest is to produce fruit, you must bite the bullet and take trees out when they are no longer productive.
By the same token, do not give a tree too many second chances. If it fails to produce a quality product after four or five years, then it will probably never produce one and should be eliminated.
This may seem harsh but survival of the fittest is a must for commercial orchard folks and homeowners would be wise to follow their lead.