|
Freeze Damage to Evergreens
|
|
|
|
Spruce trees showing likely freeze damage, new buds and growth may or may not be impacted depending upon the severity of the freeze (Photo Credit: Galen Wittrock)
|
|
|
NFS staff and other state agents have noticed an increase in the number of browning evergreen trees this spring/summer likely due to freeze related injury. Most of this may be from early fall freezes, where temperatures dropped into the single digits quickly and tree tissue had little time to prepare. In some cases it may also be from prolonged periods of freeze in the late spring. When this happens, the damage is not usually noticed until the late spring, when outer tips may turn brown or in more severe cases large parts of the tree.
The other damage that can occur from harsh winters is known as winter desiccation. This is when the tree is unable to get enough water during the winter and dries out from the harsh winter winds. While this can occur due to a root issue, a common cause is simply the tree not getting enough water during the fall.
In all cases the best thing to do is to keep the tree as healthy as possible with proper watering and mulching. Although we can’t control the weather, keeping a tree as healthy as possible will significantly improve its chances of tolerating or recovering from extreme weather events.
|
|
|
|
Cedar damaged by a freeze. Notice the browning on the outer more exposed tips of the tree. (Photo Credit: Shirley Ferguson)
|
|
|
|
Growing Degree Days as of the beginning of June using a base temperature of 50 degrees F and a single sine curve.
|
|
|
Degree days are significantly accumulating across the state enough to the point where several major pests such as EAB adults (450 -1500 GDD) and bagworms (600-900 GDD) will be starting to emerge. As we move into the summer, keep in mind that many insects also have upper temperature thresholds above which development cannot occur. Even though some of these are closer to 100 degrees F, we do eventually see a sort of capping off where GDD are no longer gaining as much momentum as they were in the spring.
|
|
|
While the causes of growth regulator like damage seen on trees is still debated, the effects are showing up once again on many different species in our urban and rural trees. Oak, redbud, Kentucky coffeetree and hackberry seem to be the most heavily damaged, but it has also been noticed on a number of other species. Common characteristics include puckering, curled edges, elongation, or complete curling of leaves. It is believed that this is the result of certain growth regulator herbicides volatizing into the air and settling back down during temperature inversions. While the long term impacts of this are unknown, it does seem to be becoming more widespread and is not abating.
|
|
|
Two Red Oak trees in Lincoln planted directly next to each other. One shows significant herbicide damage while the other only shows slight damage. The tree with heavy damage also had a girdling root or had been planted too deeply which is likely contributing to stress.
|
|
|
|
Emerald Ash Borer Adult Emergence
|
|
|
Unfortunately we have reached that time of year again when EAB adults will begin to emerge from infested wood. After feeding for about a week on ash leaves, they will mate and begin to lay eggs on the bark of ash trees to start the cycle over again. Adults are bullet shaped, about 5/8ths of an inch long, and usually have a green sometimes gold color, although most people are unlikely to see them in this form.
To slow the spread of the beetle, movement of infested material from now until fall should be limited, or chipped on site even in areas where EAB is already present.
Injections for EAB can be conducted now through the fall as long as water is moving through the tree, optimal timing is May through June. However, soil drenches with imidacloprid should not be done until next spring.
|
|
|
Damage to young trees from sunscald is an all too common occurrence in many communities. Thin barked or young trees are susceptible to this during the winter and may be even more so if improperly planted. Often this occurs on the Southwest side of the tree, where the sun warms the tissue enough to cause it to break dormancy. Once the sun sets however, temperatures plummet and the tissue freezes. Different protective measures such as shading the trunk or painting it white to reflect sunlight can be employed. Proper planting is also of paramount importance however, since healthy unstressed trees are less likely to suffer damage.
|
|
|
This series of trees are all red maple, presumably planted at the same time, in progression down the street from A to D. Notice the severe sunscald damage on B and D. These trees likely have issues such as being planted too deeply (B) or disturbance around the trunk (D) which has made them more susceptible to damage.
|
|
|
|
|
Most of the state showed below average temperatures for the month of April. This likely is related to hard freeze conditions experienced throughout the state that lead to some freeze damage on trees.
|
|
|
|
Drought conditions for Nebraska as of May 26th 2020. Some areas in the south and east showing abnormally dry conditions.
|
|
|
Fungal Disease Control for Conifers
|
|
|
The time for treating several fungal pathogens of conifers is quickly approaching.
- For needle casts of spruce, applications will need to be made 3-4 weeks after the application made earlier in May.
- Cedars and junipers experiencing cercospora will need to be sprayed in mid-June, and again in late July at a minimum.
- Dothistroma on pine trees will need to be sprayed again when the needles are fully grown (usually the second half of June).
- Brown spot treatments should be done in June on pine trees when needles are half grown.
Remember to always follow the label instructions when using fungicides.
|
|
|
|
Bags which contained females last year and now harbor eggs, are getting ready to hatch. Pulling of bags will no longer be an effective control measure until fall.
|
|
|
Be on the lookout the next few weeks for the emergence of bagworms. The pests will be hatching in the coming days and spreading out as new larvae take to the wind on threads of silk. Timing of sprays is critical as bagworms will become harder to treat as the season progresses, and heavily defoliated conifers may die. Many pesticides are labeled for use on bagworms, however products containing Bt or Spinosad are more environmentally friendly and will do less damage to non-target beneficial insects.
|
|
|
|
Newly emerged bagworms are extremely small and difficult to see. Shown here are newly hatched bagworms under 10x magnification on the tip of a cedar branch.
|
|
|
Compiled by David Olson, Forest Health Specialist
|
|
|
Like what you read? Were you expecting to see something different?
Help us make this newsletter better.
|
|
|
|
|
