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GARDENING: Curing the bad bugs of summer

Curt Swift
CURT’S CORNER
Free Press Gardening Columnist
Peach tree borer larva in base of tree.
Courtesy photo |

If you have a peach, apricot, nectarine, plum or cherry tree, now is the time to be concerned about and treat for the crown borer (aka peachtree borer). The adult clear-wing moth lays eggs at the base of these trees at this time of year. When the eggs hatch, grub-like larvae emerge and eat their way into the base of the tree and feeds on the nutrient-rich cambium, killing the roots. Trees that turn yellow, or when leaves suddenly dry up and fruit turns into dried up mummies, the problem is more than likely due to crown borers.

Tree death can also be caused by Cytospora canker. Infections by this fungus is easily identified by the hard dark amber masses forming on the tree. These hard masses can develop anywhere from ground level to the tips of branches, wherever the fungus invades the tissue. Crown borers on the other hand cause a gummy amber ooze at or below ground at the base of the tree. The best way to check your trees for this borer is to touch any ground level ooze to determine it is gummy or hard. The amber mass initially resulting from Cytospora will be soft and sticky. The gummy mass resulting from the crown borer will have the consistency of cooked oatmeal. If it feels and looks like oatmeal, your tree has an infestation of crown borers.

Most growers will use a liquid insecticide containing permethrin or another pyrethroid, while others will use a systemic insecticide containing dinotefuran. Permethrin is applied as a drench, soaking the base of the tree. Permethrin is a contact insecticide and needs to come in contact with the insect before the insect will die. Once this borer is inside the tissue, protected by its layer of gummy sap mixed with sawdust and frass created by the boring activity of the insect, applying a contact insecticide will not kill it. For that reason, some growers will use a neonicitinoid called Safari or Zylam. These products contain the systemic dinotefuran. When sprayed on the trunk of the tree, this insecticide is absorbed and moves throughout the tree killing scale, aphids, crown borer larvae, twig borers and other insect pests. Dinotefuran is labeled for use on non-bearing fruit trees so if you lost your peaches, apricots, or sweet cherries to our spring frosts or are willing to remove any fruit remaining on the tree, this is the product you should use to clean up the insect pests on these trees.



If your fruit trees are used only as ornamental, dinotefuran would be a great product to apply. Never apply such a product to plants that are in bloom as the pollinators will pick up the insecticide and be killed. The only place in the valley I know that has dinotefuran is Ewing Irrigation and Landscape Supply on Interstate off 23 Road. The advantage to this product is it can be applied to the bark, foliage or soil. This product is pricey, but is the best product for use on scale insects at this time of year.

Paradichlorobenzene (PDB), found in some crystalline borer products and some moth flakes and moth balls, has been used for years to fumigate the base of the tree to kill this insect. A trench an inch deep is dug around the tree 2 to 3 inches out from the trunk. The trench is filled with PDB and then covered with soil. This product produces fumes that find their way through the gummy protective ooze to the borer causing its death. Care should be taken to ensure PDB is not be in direct contract with roots or trunk tissue or damage to the tree can occur.



Another product that can be used once the borer is protected under the bark is Millenium, a formulation containing the naturally occurring insect parasitic nematode, Steinernema carpocapsae and a symbiotic fungus. These nematodes are released at the base of the tree “in their infective juvenile stage to search out and enter insect pests. Once inside, the nematodes release symbiotic bacteria that quickly kill targeted insects.” If you are interested in this product, you will need to contact Becker-Underwood at 800-232-5907. Other products containing nematodes for this use are also available. Check with the CSU Extension office for additional suppliers.

A service I can provide is a thorough evaluation of your grounds to determine what you can do to identify and correct current problems and concerns and prevent future problems. I charge $75 per hour for my time. I follow up site visits with a detailed email or letter. Give me a call at 970-778-7866 if you want to schedule a visit.

Dr. Curtis E. Swift is a retired horticulture agent with the Colorado State University Extension. Reach him at Curtis.Swift@alumni.colostate.edu or 970-778-7866.


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