Community Agriculture Alliance: To spray or not to spray


— The Colorado State Forest Service and the U.S. Forest Service held a joint press conference Monday to discuss the results of last year's aerial forest health survey. The big news continues to be the mountain pine beetle epidemic. An additional estimated half million acres of lodgepole pine were infested last year, bringing the total to more than a million acres affected in Colorado since 1996. The outlook is grim; most of the mature lodgepole pine in Colorado is likely to be affected before this epidemic is over.

Landowners with dead and infested trees face tough choices. Harvesting to mitigate fire danger and promote the growth of the next forest is generally recommended. There is little we can do to stop the current epidemic; there is a lot we can do to prevent the next one from being so bad. Managing the forest to create a healthy and sustainable forest for the future is well within our power, if we begin today. That said, it is still a difficult and daunting prospect to face the loss of all or most of your lodgepole pine if you're a landowner with a lodgepole pine forest.

The Colorado State Forest Service recommends preventative spraying for mountain pine beetle as a valid tool for landowners on a limited basis. Important landscape trees and trees in recreation areas often are selected for spraying. It is not practical and perhaps not desirable to spray the entire forest. Trees that are not healthy (broken or dead tops, poor crowns, diseased) are not good candidates to invest in spraying.

There are several formulations of sprays registered for use to prevent mountain pine beetle attacks. Of these, carbaryl has been in use the longest as a mountain pine beetle and spruce beetle preventive measure. If applied correctly and all spraying procedures are followed, there should be a very high rate of success with any of the chemicals listed below.

• Carbaryl (2 percent solution-Sevin XLR plus, Sevin SL)

• Permethrin (Astro, Dragnet)

• Bifenthrin (Onyx)

When these sprays are applied to healthy trees in late spring to early summer (preferably during May and not past July 1), they will deter attacking beetles. Preventive spraying is effective through one mountain pine beetle flight, which is one year. It is recommended that reapplication of the insecticide be done on a yearly basis until the beetle infestation has subsided. When that will occur is difficult to predict for our area, but it would probably be safe to think in terms of at least a five-year commitment in spraying.

Preventative spraying

Although most homeowners, landowners and business owners hire certified commercial applicators to spray their high-value trees, some may choose to spray their trees.

Private landowners spraying their own trees are not required to have an applicators license; however, safety and procedure training is highly recommended for do-it-yourself sprayers. Information can be found on the Colorado Department of Agriculture/DPI Web site:

Most garden-type sprayers provide protection up to about 15 feet high on the tree trunk, an area on which beetles are usually found. However, as concentrations of beetle population continue to increase, beetles have been found to attack higher in the tree, therefore it has become more important to also protect the upper trunks of the taller trees. In this case, it is recommended that you use a professional grade sprayer to ensure that the highest point possible on the tree is protected. These sprayers can cost a good deal of money, and you may want to consider bringing in a commercial applicator at this time.

Spraying failures

It is important to understand that whether you choose to spray your trees yourself or hire a commercial applicator, there will be some trees that were sprayed that might get attacked. Typically 2 percent to 5 percent of sprayed trees still get attacked. The following are possible factors that contribute to the failure of the spraying working on all trees:

1. Misidentification of healthy trees: Dry conditions and less vigorous trees contribute to not seeing the "classic" signs of infestation (i.e. pitch tubes). It is important when identifying a tree to be sprayed to check the entire circumference and up high on the bole of the tree for small entry holes and frass (fine sawdust) in the crevices of the bark and around the base of the tree.

2. Timing: Spray treatments applied after June may run the risk of a tree being hit by early emergence attacks. To ensure treating your high-value trees before the first flight, it is recommended to start your treatments in early to mid-May (as long as there is no snow impeding the spray at the base of the tree) and spraying no later than mid-June and the absolute latest to the end of June. Your greatest protection will be achieved the earlier you do your treatments.

3. Improper coverage: It's important to spray starting at the very bottom of the tree to as high as possible toward the crown (at least to a 5 inch diameter at the top) and to spray all the way around the circumference of the tree. Any strips or patches missed will create windows for bark beetles to attack.

4.) Environmental conditions: Significant moisture or rain within 2 hours of application may wash off the insecticide; spraying during very high temperatures may break down the chemical; windy conditions will cause the chemical to drift away from the tree being sprayed and affect the amount that is intended for application.

5.) Improper dosage: It's important as an applicator to make that the proper percentage of the active ingredient for bark beetles is mixed. A greater percentage is needed for mountain pine beetle, spruce beetles, etc., compared to other insects. Some commercial contracts require a sample of the spray mixture used on a particular day for analysis in the event of a major spray failure.

6.) Improper mixing: It is important to maintain continuous agitation during mixing and application to assure a uniform suspension.

7.) Improper volume: Lodgepole pine has "flakey" bark and may require more spray to cover the tree thoroughly.

8.) Formulation: As a homeowner, if you are planning to treat your trees without using a licensed applicator, make sure that the chemical has a legitimate label such as Carbaryl (Sevin) SL or XLR. Make sure the insecticide comes from a manufacturer that specializes in insecticides that are used for bark beetle prevention.

9.) Shelf life and storage: If stored correctly, Carbaryl should have a shelf life of 2 years after the manufacture date. Unused insecticide should be stored in its original container only, in cool, dry areas. Do not store in areas where temperatures frequently exceed 100 degrees Fahrenheit.

Be sure to read and follow the directions and cautions on the label of each product carefully before spraying your trees.

Remember that although some homeowners may want to try spraying their own trees, the most susceptible trees are usually too tall to be sprayed effectively without using high-powered and expensive equipment. It is recommended that a certified commercial applicator with training, personal protective equipment and a high-pressure sprayer perform the treatments on your high-value trees.

Again, for successful spraying treatments on your high-value trees all the factors listed above must be followed to ensure the highest percentage of success.

For more information about preventive spraying, call the State Forest Service at (970) 879-0475.


Use the comment form below to begin a discussion about this content.

Requires free registration

Posting comments requires a free account and verification.