Spruce bark beetles – a potential problem in your woodlot

Spruce bark beetles aren’t going to take out your prized peonies or decimate your potato crop but they can have devastating impacts on your property, and if you are managing a woodlot, could impact future harvests.

Spruce bark beetle adult. Adults are approximately 1/4inch long and reddish-brown to black. Photo by M. O’Donnell and A. Cline Wood Boring Beetle Families, USDA APHIS ITP, Bugwood.org

Spruce bark beetle adult. Adults are approximately 1/4inch long and reddish-brown to black. Photo by M. O’Donnell and A. Cline, Wood Boring Beetle Families, USDA APHIS ITP, Bugwood.org

Spruce bark beetles are small, cylindrical beetles that tunnel beneath the bark of spruce trees. Adult beetles bore through the bark, where they lay eggs and feed in the tissue responsible for transporting sugars produced in the needles down to the roots of the tree. Spruce bark beetles prefer to attack large, weakened or stressed trees. They are commonly attracted to areas of wind damage due to the large amounts of downed material that serves as a great host. In living, standing trees, damage from the spruce bark beetle cuts off the tree’s ability to feed itself and the tree dies.

As a native pest, spruce bark beetles are always present in the environment. They usually exist at low-level populations in downed and damaged material. Under the right conditions, however, spruce bark beetle populations can build up, resulting in outbreaks.

Spruce trees killed by spruce bark beetle. Photo by Daniel Miller, USDA Forest Service, Bugwood.org

Spruce trees killed by spruce bark beetle. Photo by Daniel Miller, USDA Forest Service, Bugwood.org

Signs and symptoms of spruce bark beetle infestation

Early evidence of an infestation can include:

Spruce bark beetle boring dust on bark. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

Spruce bark beetle boring dust on bark. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

 

Boring dust: This dust is the result of the beetles boring into the tree. This material is pushed or falls out of the entrance hole and collects around the bark or base of the tree.

 

Spruce bark beetle pitch tube. Photo by Darren Blackford, USDA Forest Service, Bugwood.org

Spruce bark beetle pitch tube. Photo by Darren Blackford, USDA Forest Service, Bugwood.org

Pitch tubes: Pitch tubes are the tree’s efforts to physically push the beetles out with excessive pitch. The tree pitch is often combined with the boring dust created by the beetles giving the tubes a reddish-brown color.

 

Woodpecker bark removal on a spruce bark beetle infested tree. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

Woodpecker bark removal on a spruce bark beetle infested tree. Photo by Edward H. Holsten, USDA Forest Service, Bugwood.org

Woodpecker activity: Woodpeckers are often attracted to trees infested with bark beetles and other wood-boring insects. Woodpeckers flake away bark to gain access to the beetles underneath. Flaked bark on the ground is usually observed in the winter and spring.

Sometimes this evidence is not visible or noticed. Trees that are heavily drought stressed may not produce pitch tubes and boring dust can be blown away in heavy winds. Leaf discoloration may be the first evidence of infestation that is noticed. Needles on trees infested by spruce bark beetles usually go from green to yellow to reddish brown. This may occur in a single growing season or may not happen until the following season. As a caution, leaf discoloration can be caused by several factors including insects, disease, and environmental stress. Change in needle color does not automatically indicate a spruce bark beetle infestation.

Management options

In woodlots and forests, the best way to manage spruce bark beetles, and other forest or tree health pests, is to manage for overall forest health.

  • Thin stands to reduce competition and encourage diversity of age classes.
  • Clean up debris after storm events.
  • Avoid unnecessary injury to trees.

Once a tree has been attacked by spruce bark beetles, there are few options available for that specific tree. Instead, measures should be taken to prevent the beetles spreading to nearby trees, including:

  • Remove the infested tree from the area.
  • Avoid cutting and injuring trees (including pruning) during the active adult flight period from May to July.
  • Water trees during excessive dry spells, if feasible.
  • Avoid stacking spruce firewood near live spruce trees.

For high-value landscape trees preventive sprays may be used to protect uninfested trees on your property.

  • Sprays should be done in spring before the adult flight period.
  • Treatments should be made to the trunk of the tree up to 25 feet.
  • Insecticides containing carabryl and pyrethroids are effective in killing adults as they attack trees.

Insecticides will not cure trees that are already attacked by spruce bark beetles and if timed or applied incorrectly will not prevent a tree from being attacked. Read and follow all label directions for any pesticide product, and observe all safety precautions. For more information on pesticides, contact your local Cooperative Extension Service office.

For more information about spruce bark beetles and how to manage them, check out these resources:

Spruce Bark Beetles: A guide to Tree Management Options for Home and Woodlot Owners for Southcentral and Interior Alaska.

The Spruce Beetle — Forest Insect and Disease Leaflet

Root maggots

Root maggots are one of the most dreaded insect pests in Alaska’s farms and gardens.

They are common pests of most crucifer crops, which include radishes, turnips, cabbage, kale and others. Certain species of root maggot are a problem for onions and other alliums. You may have noticed the maggots tunneling through your turnips when you were slicing veggies for a fresh salad, or maybe you noticed stunted cabbages with yellowing leaves. Or maybe you have been lucky to not have root maggots in your plots– yet!

Cabbage stunted from root maggot damage. Photo by Clemson University, bugwood.org

Cabbage stunted from root maggot damage. Photo by Clemson University, bugwood.org

Whether you have been battling root maggots for years or are new to the fight, there are ways to manage their damage.

To control root maggots, you must first understand their life cycle. It is the larval stage of a small, nondescript fly, about half the size of a housefly. The flies overwinter in the soil as pupae, with adults emerging in the spring as soil temperatures warm over the course of four to eight weeks.

Adult root maggot fly in the family Anthomyiidae. Photo by David Cappaert, bugwood.org

Adult root maggot fly in the family Anthomyiidae. Photo by David Cappaert, bugwood.org

After emerging, the adult flies mate and lay eggs to start the next generation. Eggs are laid at the base of host plants (i.e., your prized cabbage) or in the soil nearby. Once the eggs hatch, the larvae tunnel into the root tissue and feed, causing the damage that you see in your veggies.

There are several options to minimize the damage done, but it is important for home gardeners to know that there are no pesticides approved in Alaska to control root maggots in vegetable gardens. Commercial farms have pesticide options available and should contact their local Extension Agent for advice and recommendations.  

Keeping your garden clean is probably the most important thing you can do. This means cleaning up your crucifer crops and not leaving them in your garden beds, especially if they become infested with root maggots this season. As your crucifer crops stop producing, remove the whole plant, including the roots. If you have a hot compost pile include the debris – any larvae that may have been in the roots will not survive the composting process.

Row covers are another option to incorporate into your plan. Floating row covers can be used to blanket new crucifer seedlings and young transplants to prevent adult flies from laying eggs early in the summer. Floating row covers allow some light and water to pass through the fabric and have the added benefit of protecting against frosts.

Floating row cover used to protect from frosts and block root maggot adults from laying eggs on plants. Photo by gardenabby, Flickr.com

Floating row cover used to protect from frosts and block root maggot adults from laying eggs on plants. Photo by gardenabby, Flickr.com

Crop rotation should also be used, especially if you are planning to use a row cover. If you use a row cover in an area that had crucifers last year, you run the risk of trapping the emerging adults, where they can happily mate and lay eggs without ever leaving the protection of the cover. Just remember to plant crucifers where you were not growing crucifers last year.

Another idea: plant fast-growing radishes and turnips as an early crop to be harvested before adults lay eggs or as a late crop for a fall harvest.

If you find root maggots to be a substantial problem in your garden year after year, look into using more intensive techniques, such as beneficial nematodes or fall tillage. If you find only a small percentage of plants  affected by root maggots, consider yourself lucky and continue to use the practices described above to keep numbers low. And remember, a root maggot can easily be cut out of your radishes or turnips and the veggies will still taste excellent in your salad.

See the Alaska Cooperative Extension Service publication on root maggots for more information:  https://www.uaf.edu/wp-content/uploads/sites/637/ces/publications-db/catalog/anr/PMC-00330.pdf

Orange Hawkweed

Orange hawkweed, if you have it you’ll know it. This dainty little orange flowered plant is pound for pound one of the most aggressive invasive weeds in Alaska. Lawns, hayfields, pastures, and grassy meadows are are all taken over by orange hawkweed quickly and thoroughly.

Orange hawkweed infestation on Camp Island within the Kodiak National Wildlife Refuge.

Orange hawkweed infestation on Camp Island within the Kodiak National Wildlife Refuge.

How does hawkweed do it? First, hawkweed aggressively spreads with creeping roots, and stolons (above ground stems).  Second, seeds are wind dispersed, and viable even when they are not fertilized because of a characteristic known as apomixis. Finally, orange hawkweed is allelopathic, meaning it produces chemicals that work like herbicides stressing plants to the point that the competition for space is won by orange hawkweed.

Hawkweed has proven time and time again in Alaska, that if it can find a sunny spot it will dominate the vegetation. Reducing forage quantity and quality for farmers, aggressively out competing native vegetation, and forming monocultures in the process, orange hawkweed is a plant you want to get on top of before it is too late.    

Control of orange hawkweed is not simple or straightforward. Those roots that creep through the ground are composed of numerous fibrous segments that if split easily, and when left behind they form a new plant. When pulled or dug up hawkweed often comes back just as numerous as before you did anything. Killing the roots and doing as little soil disturbance as possible is key to managing orange hawkweed, and for all but the smallest of infestations this means using an appropriate herbicide.

Herbicide management of orange hawkweed is ideally done early in the season after it starts to grow, but before it is flowering. Later applications will show results, but are less effective in the long term. A surfactant (additive that breaks water viscosity) should be used with liquid herbicides because hawkweed is covered with small hairs that prevent herbicides from touching the leaf and stem tissue.  For more information on controlling orange hawkweed see our publication “Control of orange hawkweed’.

Orange hawkweed pub

Cover of the newest orange hawkweed control publication from the University of Alaska Cooperative Extension Service

Orange hawkweed is the only orange to red flowered sunflower family plant that has spread in Alaska. If you see orange hawkweed on public land use our mobile application “Alaska Weeds ID’ to report the location.  If you think you have orange hawkweed on your property you can use the “Alaska Weeds ID’ app to get identification help, and sending a report will get you in touch with an expert with the Cooperative Extension Service or a colleague that can provide you with advice on controlling it. Orange hawkweed has never been seen north of the Alaska Range, so if you spot it up there let us know.