Tree Health Update – Winter 2022 – Sioux Falls

Here we are in early February and its 50 degrees in Sioux Falls and as brown as a paper bag outside. I’ll admit, it is certainly comfortable be outside in weather like this. But for our trees and other plants, it is not ideal.

We need moisture.

We could use some snow, and a lot of it! I know its a pain to deal with, but a large reason why our conifers (evergreens) and other trees are struggling around the region, has a lot to do with the fact that we have seen many mild winters recently. Especially winters with little to no snow (or at least no snow until later in winter).

Snow acts as a great insulator along with recharging soil moisture levels as it melts. The roots of trees benefit from that insulation during the severe cold snaps. Cold hardiness for most plants relates to the threshold of how cold the soil and roots can handle, not the air temperature (although that does play a factor). Additionally, the soil temperatures fluctuate a lot more during warm stretches with no snow, causing it to dry out. This can kill sensitive roots or lead to stress when the ground thaws come spring.

What I’m seeing.

Death and damage to spruce and pine trees is still the most common thing I’m coming across. The stress caused by excessive rains in 2019, followed by drought starting in mid summer 2020 and continuing now through the winter, is creating pest and disease conditions we normally don’t have to deal with.

Last season was the first time that I have seen large amounts of spruce tree tops dying from engraver (ips) beetles. These are native species of beetles that can pile on to a sick spruce or pine tree and cause major damage. The most obvious sign is the dead top of a spruce tree.

In years past, it was not recommended to preventatively spray for engraver beetles because populations were low and the death to the top of a spruce trees was very low risk. However, this year, it is my recommendation that if you have spruce trees of value that you have them sprayed this spring to protect them from the high amounts of insect pressure that is out there.

What to expect this year?

Unfortunately, more and more trees will be getting sicker and showing signs of the drought stresses. Trees are very slow motion plants when comparing how we live day to day. It can take up to 3 years before a tree would show signs of stress from something like a drought. It all depends on how healthy the trees were going into the stress event.

We can expect more trees to show signs of the drought stress (especially conifers). I anticipate a lot more spruce to decline and succumb to the drought within this year. Those that do make it, will have a good chance of being attacked by Valsa Canker(formerly Cytospora) and engraver beetles. The impact of the drought may be seen in faster growing deciduous trees too. Trees like silver maple, may end up with die-back in the upper canopy if they didn’t get enough water last summer.

What to do?

There isn’t anything we can do about the weather. But we can water (correctly) and provide mulch. And those two things are usually the largest limiting factors to tree health in our region. Lastly, for the valuable spruce, again I do recommend considering spraying them this spring to protect from engraver beetles.

Watering

Watering your trees when it’s dry is very important. But care must be taken to water with intent and so it is available for the trees. Also, be sure to not overwater. More often in not in the urban areas of Sioux Falls, I run across over-watered trees than under-watered.

When thinking about watering, think of the soil like a sponge. You want the sponge to be wet enough that you could wring water out of it if you picked it up. But not so wet that water runs out of it if left on the counter or picked up. The best way to get that sponge to hold as much water as it can, is not to dump all the water on it at once, but to apply it slowly. In other words, water your trees with drip irrigation, a soaker hose, or a tree watering bag.

Lastly, water only once or twice a month. Again, overwatering in our soils is very common.

Mulching

Mulching the critical root zone (area under the canopy) is the other part to watering where the trees will benefit. Grass will outcompete a tree for water and nutrients. The difference between a tree that performs well and a tree that struggles is often the difference between good mulching and reducing turf competition.

There should be 2-4 inches of mulch on the ground, evenly spread out, going from an inch from the trunk out to the drip line of a tree (edge of the canopy). If you don’t want to lose that much lawn, at least go out 2-3 feet radius from the trunk (5-6 foot diameter circle).

I like a shredded hardwood mulch. For spruce and pine trees, the mulching should go out past the drip line. Any less and the trees WILL struggle as they get older. Lastly, no weed barrier or anything like that should be between the mulch and soil. The weed barrier fabrics negate the benefits of the mulch (you may as well have grass).

Closing

Thank you for reading! Having healthy trees in South Dakota can be a challenge. Especially when the climate favors grass and is as erratic as it has been the past number of years. But it is not impossible, it just takes a little more effort and care than other parts of the country. If you have questions on the care of your trees, you can find more resources on my website. Or can reach me via email: sam@aspenarbo.com or call/text 605.759.6020