Originally Published In The Deseret News -- Wednesday, June 25, 1997
Borers Can Be At Fault - But So Can Mower, Fungus Or Even Improper Pruning. Larry Sagers Is A Horticulturist With The Utah State University Extension Service.
The scenario is all too common. You make a leisurely inspection of the backyard orchard and there they are. Tiny blobs of clear amber or brown ooze emerging as a plague to strike your trees. It's there, sliding down the trunks, erupting from the branches and oozing from the twigs. The mere sight of this ominous gunk is enough to panic even the most toughened and unsentimental gardener.
Take a few moments to gather your wits about you and get the facts straight. Diagnosing the problems takes a little investigation into what has happened to the tree and what the gumming really means. Gumming in and of itself is not a disease nor is the gum itself a problem. Gum is a symptom that may be roughly described as a plant protection or scab produced when the plant is injured. It may have many different causes, just as for us a runny nose can be prompted by allergies, colds or other problems.
Sleuthing out the problem is not always easy. The gum is obvious; the causes are not. The investigative process starts by narrowing down the field. To start you can rule out the apples and pears. The stone fruits are the victims here. Peaches, plums, apricots, nectarines and cherries will produce copious amounts of gum under the right or wrong situations, depending on your perspective.
Most gardeners automatically assume that the gum comes from borers. While borers are a common cause of gumming, they are not the only problem. Start by looking at where the damage occurs. There are several borers and they usually attack different sites on the tree. Mechanical damage is also a serious problem. Trunk damage often results in gumming and is a result of lawnmowers or string trimmers damaging the trunk. The bark does not have to be removed to be damaged. Scratch-ing cats, chewing dogs and destructive humans all add to the mechanical damage.
Several common diseases add to gumming problems. Cytospera is the most common fungus that attacks the stone fruits. While it does not directly create this symptom, the damage to wood results in excessive gumming. The affected plant parts will eventually die, so prune and remove them to prevent spreading the disease. While there is no cure for this disease, healthy plants can resist the problems. Besides pruning out damaged wood, keep the plants vigorous by applying adequate fertilizer and watering as needed.
Gum production is often obvious in the crotch areas of the branches. This results from winterkill. Narrow angles between the branches do not allow the wood to knit together properly. This means the tissues continue to grow late in the season to complete the process. This late wood does not acclimate and is killed even during relatively mild winters. The best control is proper pruning to develop wide branch angles that allow the wood to grow together.
Psuedomonous syringea is a bacterial disease that is almost certain to cause gumming. In fact, the common name of this disease is gummosis. With this disease, the gumming comes on all woody parts of the plant, including small twigs, large branches and trunks. When it first comes out it is clear and jellylike but it quickly hardens and turns dark. It is not a common disease in our area but does show up if we have extended periods of cool, wet weather. If you have been living underground for the past few months, we have had ideal weather for disease development. There are no controls for this disease now. In more humid areas, preventive copper fungicides are applied in the fall. Spraying now is of no value as the infection has already occurred.
Coryneum blight is a fungal disease that causes the death of many buds in the tops of the trees. This fungus also infects the plants in the fall. Preventive sprays are the same as those outlined for gummosis. As the infection progresses the buds start gumming and eventually die. The twigs beyond the dead buds are eventually killed.
Borers are a major cause of gumming. The two most common are referred to respectively as the greater peach tree borer and the lesser peach tree borer.
The lesser peach tree borer is also called the peach twig borer. The larvae often invade the base of the twig in the crotch and produce small amounts of gum in the tops of the tree. They also will attack and destroy the fruit. The preventives are applied as a delayed dormant spray in the spring with additional sprays on the first and 15th of June. The gumming produced by this borer is minor when compared to other borers.
The greater peach tree borer is usually called the peach tree borer or the trunk borer. These are the most destructive pests of stone fruits. Their feeding underneath the bark at the base of the tree is often fatal. Large balls of gum occur as a result of this feeding. Once you see the gum the damage has already occurred. Preventive treatments are essential to prevent serious problems.
Adult borers are clear-winged moths that resemble wasps. They are not usually visible unless you clearly observe the egg-laying sites. The timing is easiest to pinpoint by using pheromone traps that attract the males. The moths are flying now and laying their eggs at the base of the trees. They will hatch and start crawling around and then start burrowing into the bark. Once they get inside, they are difficult to control and have already started to damage the trunks.
The recommended control program is a spray of dursban applied to the trunk and allowed to puddle at the base. Timing is very important. Apply the first spray the first of July and a second one the first of August. Do not allow the spray to contact the fruit.
Gum is frustrating to discover on your trees. Remember it is only a symptom. The biggest challenge is to discover the real causes and then correct them. Hopefully this will allow you to grow high-quality, tasty fruit in your orchard without the frustration of oozing, dripping trees.
© 1998 Deseret News Publishing Co.