University Of Minnesota Extension Ask Extension: Top 3 Topics For 2021

Press release from the University of Minnesota Extension:

August 26, 2021

Phones in our local extension offices were once again ringing off the hook this year. The unprecedented drought in Minnesota affected countless plants and landscapes. As a result, this growing season was very different from previous years.

After talking to other Extension educators who fielded yard and garden questions, three major themes emerged: tree issues, insect identification, and invasive species.

Sick maples and stressed evergreens

Maples and evergreens again had a rough year. For maples, the growing season started with many undergoing "masting." Masting means large amounts of seeds are produced by a tree. This requires that the maple invests much of its resources into its reproductive parts instead of leaves, often giving them a sparse canopy in the spring. While masting is thought to be a normal response for maples, it can sometimes suggest a stressful environment.

Other, more serious issues with maples included sunscald. Our multiple warm, sunny winters coupled with cold snaps caused many young, thin-barked maples to split. These splits can make them susceptible to fungal or insect attack. You can help avoid these wounds by wrapping your young maples during the wintertime. 

Trees planted too deeply often had the most severe sunscald symptoms. If your tree looks like a telephone pole then it is likely planted too deep. Always aim for a root flare to be visible when you plant your tree—ideally an inch above the ground. A root flare is the area where the trunk and roots meet.

Take a walk in the woods and see if your tree looks like its native cousins. You will notice the trees in the woods often have visible, wide root flares near the surface. The U.S. Forest Service Tree Owners Manual and Extension's  Planting and transplanting trees and shrubs are great guides to planting trees if you are curious.

The drought also hurt many young saplings, and even older trees that had been in the ground five years or longer. You can learn more about watering both young and established trees on our website. Also, watch this video on mulching to learn about one way to keep moisture in the soil.

Evergreens were also negatively affected by the extreme heat and dryness. To help prevent winter drying injury this coming year, continue properly watering your young evergreens, particularly any arborvitae. You can ease up in September to harden them off, but resume watering from October until hard freeze. 

While many fungal diseases did not like the dry conditions, a few still managed to cause issues. Diseases observed in southern Minnesota included diplodia shoot blight and dothistroma needle blight, which primarily affect pines. Spruce spider mites were also confirmed on a Norway spruce in Blue Earth County, but these pests did not cause serious damage. Colleagues in central Minnesota also found cases of needle cast disease and needle rust on spruce.

Insect identification

While I suspect the drought and heat may have made certain insects more common than previous years, I personally have never seen so many requests for insect identification. Many of these were not pests, thankfully. Quite a few calls involved wasps. As of this writing, the “murder hornet” that was all the rage last year still has not been observed in the Midwest or most of the U.S. Allof the photos we have seen so far are lookalikes, in particular cicada killers, elm sawflies, or great golden digger wasps.

If you have an unusual insect you wish to identify, consider contacting a Master Gardener via the Ask a Master Gardener service, visit the What insect is this? page, or reach out to your local UMN Extension for help. DO NOT contact the UMN Department of Entomology, as they do not accept photos or submissions of insects from the public. 

Certain apps such as iNaturalist are easy to use and fun, but unless human experts can confirm the insect, take what the computer guesses with a grain of salt. Another excellent website for ID help is BugGuide.Net, which has trained entomologists and an impressive amount of photos and information about insects. Be aware, however, that the site has strict rules for photo submission, so be sure to read them before posting any pictures.

Invasive species

Despite the optimism following the cold snap in February 2021, the spread of emerald ash borer continues in Minnesota, particularly in the southern part of the state. The Minnesota Department of Agriculture (MDA) has an excellent website that can help people make informed decisions about how to report and combat emerald ash borer. If you are wondering about treating your ash trees, I highly recommend the MDA’s Homeowners Guide to Insecticide Selection, Use, and Environment Protection publication.

For ash tree replacement, we recommend species according to your native tree community. Recommended trees for Minnesota includes lists of evergreen and deciduous species with information about the height, width, and other characteristics of each tree.

Consider planting a variety of trees instead of a single species to increase diversity and hopefully decrease pest and disease issues. Extension also has advice on finding a tree care professional.

Another invasive species found and spreading in Minnesota is the jumping worm. These animals can damage plants by how they change soil structure. While there is no effective treatment recommended yet, we urge gardeners and landscapers to be aware of this pest. The Minnesota Department of Natural Resources is an excellent source for additional pictures and jumping worm identification.

While we do not know what awaits us as the growing season continues, we can confidently say this is not just the year of drought, but the year of the tree and bug. The heat and dryness may be paradise for a few weeds and insects, but the majority of things in your yard could be stressed this year.

We urge you to closely observe your landscape during this droughty time, and to take action when needed—whether that is as simple as watering your newly planted tree to as serious as reporting an invasive species that is damaging to all of Minnesota.

This press release was produced by the University of Minnesota Extension. The views expressed here are the author’s own.