Peach Tree Borers are a Problem Worth Facing

Southwest Yard & Garden by Dr. Marisa Thompson

 

Peaches harvested from a four-year old ‘Elberta’ peach tree in Las Cruces (photo credit: M. Thompson). 

Question:

I suspect that my peach tree died of borers a few years ago because when I took it out I found lesions way down low on the trunk, partially buried. I am finally ready to plant a tree and would like to plant a peach, but is it okay to plant in the same spot?

-        Wayne B., Los Lunas, NM            

Answer:

The greater peach tree borer (Synanthedon exitiosa) is known for causing oozing trunk wounds found at ground level or just below the soil line on stone fruit trees. The sap is often clear, but sawdust frass produced by the borer can be mixed in, giving it a darker color. Stone fruits are named for the pit, or “stone,” that encloses the seed; they include peaches, nectarines, plums, cherries, almonds, and others.

I’m focusing this column on the greater peach tree borer, but peach trees are susceptible to other pests as well as any damage to the thin bark tissue, all of which can cause a sappy glob to form. Damage from a weed whacker, for example, could create a gooey lesion down low on the trunk.

Besides a late freeze, the peach tree borer (also spelled peachtree borer) is the worst threat to stone fruits in New Mexico. Dr. Carol Sutherland, NMSU Extension Entomology Specialist and NMDA Entomologist, says peach tree owners need to be aware that “everybody will have peach tree borer sooner or later, and if you do nothing it will kill your tree.”

Plant stress can be an invitation to pests, which are more likely to attack when the immune systems are weak. Proper planting in an area that allows for a healthy root mass, combined with appropriate irrigation, sets the ideal situation for growing healthy, sustainable plants and protecting them from pests and disease. However, the peach tree borer is one pest that will attack perfectly healthy, non-stressed stone fruit trees.

So what should we do about it?

There are a limited number of insecticides available for control, but once the larvae get into the sapwood they are protected from most chemical treatments. See below for links to more information about insecticides. Always, always, always read the chemical label carefully before applying to plants in your garden and carefully follow directions!

Finding and either removing or killing the eggs is a good way to reduce the chance of infection. To do this, we need to know when and where eggs are laid and what they look like. Understanding the life cycle of any plant pest is key to controlling it. Female adult peach tree borer moths can lay up to 400 eggs on the bark and in trunk cracks down near the tree base of stone fruits, sometimes in the soil. Depending on where you are in New Mexico, this may occur from late June to September. Eggs are tiny (approximately 0.03 inch long), dark reddish-brown, hard, slightly flattened ovals. The photos of peach tree borer eggs look to me like miniscule watermelon seeds glued to the bark. The larvae hatch after only 7–10 days. Once you find the eggs, you can physically remove as many as possible. Larvae do not persist in the soil, so planting a peach tree in the same location where one was infested before will not be a problem.

Dr. Curtis Smith, retired NMSU Extension Horticulture Specialist, offers that “the borer may not completely girdle the tree, but may cause damage to the bark and cambium in a portion of the trunk. In such a case, with only one or a few borers active in the trunk, the top of the tree may die in sections, one branch at a time. A zone of dead bark will be found at the base of the tree, but the tree will not be completely girdled.” You may still be able to get a good load of fruit even after infestation, but management is still recommended.

If you do not see injury symptoms, one way to get ahead of eventual infestation is by trapping. You can monitor for the presence of adult peach tree borers by using strategically placed traps during the growing season. For links to more information on traps and the lures, visit the website listed above.

Peaches can be extremely rewarding to grow in New Mexico. Even with this pest pressure and other common problems, I still recommend growing them. Peach trees and other stone fruits are often called “short-lived trees.” But when I ask how long is short, the responses vary widely. Some say 20 years, some say 10—I’ve even heard 7 years for a peach tree lifespan. Because many of these trees grow so well and produce fruit quickly, you can enjoy huge crops on young trees.

Perhaps we should think of these short-lived fruit trees as “decadal” plants that live for approximately 10 years, and plan accordingly. Gardeners do not usually lament killing an annual plant, like tomato, at the end of its 1-year growing season. Staggering the planting of a few stone fruit trees over several years can help ensure that, by the time removal of older trees is necessary, a younger one will provide the peach fix.

So yes, go ahead and plant your new peach tree in the same place where your old tree died, and next year plant another.

WARNING: Each state has separate pesticide regulations. Be sure to check chemical labels for local application.

More information on preventative sprays and traps can be found at this Colorado State University Extension website: http://extension.colostate.edu/topic-areas/insects/peach-tree-borer-5-566/.

The following information is from Utah State University Extension (https://utahpests.usu.edu/ipm/agricultural/fruit/gptb):

"GENERAL MANAGEMENT

Protection of host trees from peachtree borer is the most critical during the first 3 to 5 years after planting.  There are few registered insecticides with adequate longevity to protect trunks from egg-laying and hatching larvae.  Mating disruption is the recommended control for commercial stone fruit orchards.  For orchards less than 1 acre, or for home yard trees, preventive trunk sprays is the primary control.

Insecticides:

Only a small number of products are registered for peachtree borer that have adequate longevity to protect trees from egg-laying and tunneling larvae for several weeks to a month. 

Cultural and Mechanical Controls:

• Select appropriate fruit tree species for the site to avoid stressed and unhealthy trees.
• Use good cultural practices (i.e., fertilization, irrigation, etc.) to maintain trees in a healthy and vigorous state.
• Paint trunks with a 1:1 dilution of white latex paint to water, or apply white tree wraps in the winter to prevent bark damage from sunscald.
• Do not leave wraps on trees during the summer.  This has been shown to increase borer attack.
• Avoid mechanical and rodent-caused injuries to trunks.
• Certain rootstocks have been found to result in fewer emerging adults.  ‘Siberian C’ peach rootstock had 40% fewer emerging adults than ‘Lovell’ rootstock in one study.
• Larvae inside trunks can be killed by inserting a wire into entry holes.  Kill larvae in the late summer and fall before they spend the winter and inflict their most extensive feeding damage the following spring.
• Keep the base of trees free of vegetation.  Heat and dryness reduce the survival of eggs and larvae."

This information about trapping peach tree borers is from the University of Kentucky Extension Department (https://entomology.ca.uky.edu/ef200).

"Pheromone Trapping

Pheromone trapping uses chemical lures to attract male moths. These lures are synthetic copies of the chemicals female moths use to attract the mates. Moth captures in pheromone traps alert growers to pest activity and aid timing of insecticide sprays. A trap consists of plastic top and bottom held together by a wire hanger with the lure placed inside. The inner surface of the bottom is coated with a sticky material to hold the insects once they land in the trap. Traps are hung in the tree at eye level, usually one for each ten acres of trees (minimum of two traps per orchard) in commercial orchards. For a list of source of the various types of pheromone traps, see ENT-54, Vendors of Microbial and Botanical Insecticides and Insect Monitoring Devices. 

Moth activity can occur anytime between mid June and early August. In order to detect the first activity, traps should be hung in tree well in advance of the anticipated flight. Usually this means hanging traps shortly after petal-fall. Trap lures need to be replaced once a month. Traps bottoms should be replaced when the stick surface becomes clogged with other debris. 

Proper identification of the moths captured in the trap is essential. There are many other moths which may wander into the trap, even other clear wing moths, such as the lilac borer or dogwood borer. Check the description of the male peachtree borers above. The lilac borer has red and black antennae, yellow and red legs, and the front wings are opaque black. The dogwood borer has thin yellow abdominal bars on the abdomen similar to the male peachtree borer, but the tips of the front wings have a broad black tips." 

Send gardening questions to Southwest Yard and Garden - Attn: Dr. Marisa Thompson at desertblooms@nmsu.edu, or at the NM Desert Blooms Facebook page (@NMDesertBlooms)

Please copy your County Extension Agent (http://aces.nmsu.edu/county/) and indicate your county of residence when you submit your question!

For more gardening information, visit the NMSU Extension Horticulture page at Desert Blooms (http://desertblooms.nmsu.edu/) and the NMSU Horticulture Publications page at http://aces.nmsu.edu/pubs/_h/.

Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, office: 505- 865-7340, ext. 113.