2019’s top horticultural questions in Laramie County include trees and prairie
By Barb Gorges
The phone calls Catherine Wissner gets are a good snapshot of what is going on in Cheyenne yards. She is the University of Wyoming Extension horticulturist for Laramie County.
When gardeners or property owners notice something amiss with their crops, landscaping or houseplants that they can’t figure out, Catherine gets their calls and will often visit. I asked her what the most frequent topic was this summer.
Trees and fungus
“Trees,” she said. Mistreat a tomato plant and you don’t get tomatoes. Mistreat a tree and you lose a major financial investment when it either dies immediately, or lingers for years, looking stunted and unhealthy.
This year, we can blame the weather for a lot of tree problems, Catherine said. April through June we had nearly as much precipitation as our annual average, 12-15 inches. All that moisture aided the growth of fungus.
The most common was verticillium wilt. It’s in the soil and gets into trees, shrubs or other plants through the root system. Damaged roots are most susceptible. Sprays and injections don’t work on fungus.
The fungus moves from the roots through the tree’s vascular system (think sap instead of blood) and within a week of showing signs of stress, the tree is dead.
Some tree species or varieties are more resistant, Catherine said. You must do your homework when looking for a replacement tree. But don’t plant the new tree in the same place.
Another fungus affects oak leaves, leaving brown splotches. Just clean up the leaves when they fall off. Next year the trees may not be affected.
Pines can be attacked by a tip-boring insect—it bores into the tips of branches causing them to look lumpy. Because she values pollinator insects and birds, Catherine recommends pesticides as a last resort. In this case, without using a systemic pesticide like Safari, absorbed through the trunk or as a soil drench around the trunk, the tree will be lost.
Get Catherine’s advice before choosing a pesticide. Read the directions and avoid methods that could blow the toxins onto other vegetation and animals.
Trees and drought
July through most of September we had no rain to speak of. Trees depend a lot on the roots in the top 1 to 2 feet of soil—and out much further than the reach of their branches. Many of the trees planted in Cheyenne are not drought tolerant, including cottonwoods which in nature grow along streams.
This year, many people in my neighborhood seemed to be saving money by not watering their lawns during those droughty months. That’s fine if the grass only goes dormant. If it dies though, the noxious weeds will move in.
No lawn watering means trees that are not drought tolerant start losing leaves prematurely and become victims of stress and disease. Catherine pointed out that watering your mature spruce tree is cheaper than the $1500 it would cost to have it removed if it dies.
This fall, and warm winter days once a month, is the time to make it up to your trees. Water your whole lawn if you have mature trees.
Late fall and winter are also the best times for tree pruning.
The shortgrass prairie outside Cheyenne, Wyoming, doesn’t need mowing. Photo by Barb Gorges.
People moving to acreage and unfamiliar with the prairie are smart to contact Catherine for basic instruction.
The worst thing to do to the prairie is mow it. But do mow the patch of bluegrass lawn the kids play on and the firebreaks immediately around the house and along fence lines.
Unmown prairie benefits you and provides bird habitat–grassland birds nest on the ground. Grasses shade the ground and keep it cooler and they will trap snow, giving it a chance to melt and sink in. Cooler ground is less likely to burn.
Mowed prairies encourage warm-season grass species at the expense of cool-season species which keep the prairie cooler.
Don’t mow the thistles! It encourages rhizomes, underground stems, to spread and pop up more plants. Catherine said to spray the individual plants when they are blooming or after the first frost. Thistle is a tough, non-native invasive plant that requires tough measures.
Catherine makes yard calls for free or you can bring in a diseased twig (in a sealed plastic bag) to her. You can also email photos to her.
FREE TREE ADVICE
Laramie County Extension Office
Catherine Wissner, 307-633-4383, firstname.lastname@example.org.
Trees and all other plants.
Cheyenne Urban Forestry Division
Tree species recommendations, planting and maintenance instruction, city tree ordinances, certified arborist list.
Laramie County Conservation District
Clark Young and Dale Beranek, 307-772-2600.
Trees, especially windbreaks.