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Hort Update for Jan 20, 2015

turf damage
Damage caused by foot traffic on frozen turf.
In This Issue
Major Symptom:
1. Winter kill not as issue yet Snow and moisture provided by rainfall helped
2. Waterwise turf irrigation Make plans for improving irrigation efficiency
3. Young shade tree pruning Important time to develop good structure
4. Too early to prune tender shrubs and roses Wait until mid-April
5. Winter desiccation of broadleaf evergreens Brown leaf margins, or entire leaves, on broadleaf evergreens
6. Dormant oil applications Apply on mild days before plants begin to break dormancy
7. Wait to prune fruit trees Best done in February/March

1. Turf winter kill or injury

Thus far this winter, we have just enough snow and rainfall to help reduce winter dessication or cold temperature injury when compared to last winter. However, we are having a fairly open winter with little snow. Injury to turfgrass can still occur where there is little snow cover; or if temperatures warm and precipitation decreases. Desiccation injury is usually greatest on exposed or elevated areas where surface water runoff is great. It is also prevalent on poorly rooted turf that cannot take-up water from deeper in the soil profile. Winter watering is underway on most golf courses where it is feasible and professionals will need to continue monitoring turfgrass sites for dry conditions.

If winter irrigation is used, only water when the soil is not frozen and air temperatures are above 40 degrees F. Lightly irrigate high value turf on dry sunny days when the air temperature is well above freezing where feasible.  The goal is to rehydrate plant crowns (and lower leaves) back to a survivable level and restore soil moisture at the surface.  Avoid excessive quantities of water which may fill soil pores or runoff and present an icing hazard when cold temperatures return.  Also avoid trafficking high value turf areas as winter drought, like summer drought, increases the risk of traffic injury.  To prevent crown hydration injury, avoid watering before a sudden temperature drop is forecast, when the ground is frozen, or in low areas where water might collect and stand due to frozen soil or poor drainage.

Fighting Dessication: Should we water turf in winter?, Nebraska Extension


2. Waterwise turf irrigation

Urban lawn watering is the single largest water demand on many municipal systems during summer. Almost all turf areas could be watered less than they are currently, while still maintaining health and water-use efficiency. Now is the time to start planning ahead for summer irrigation.

Do not water your lawn next spring until the first signs of drought stress appear in the driest areas (footprinting or a bluish-gray coloring of the turf). When this occurs, manually turn on your irrigation system the next morning to wet to the depth of rooting, which may be 4 to 6" deep in the soil depending on the species, soil type etc. The amount of time it will take  to wet to this depth is dependent on sprinkler coverage and efficiency, soil type, volume, pressure, etc., so no recommendations can be made about how many minutes to water each lawn. After watering, do not water again until you see signs of drought stress and continue this process throughout the season.  You can also hand water dry spots instead of irrigating the entire lawn for a few dry areas.

Additionally, auditing your irrigation system for uniformity first thing in the spring and then watching it run throughout the summer will help minimize water waste. Replace broken or clogged sprinkler heads and adjust sprinklers to water the lawn, and not pavement.

Waterwise: Drought Effects on Turf in Landscapes, Nebraska Extension


3. Young shade tree pruning

Young shade tree pruning is best done during winter.  From about three years up to about 10 to 15 years after planting is an important time to prune for good form and structure. If a young tree was planted in the last two years, pruning is likely not needed. Check young trees for a double leader. Removing double leaders is about the only pruning that needs to be done in the first couple of years.

Don't be in a hurry to remove lower branches. Research has shown trees establish quicker and trunks increase in caliper faster if lower branches are left for a year or two. Lower branches provide photosynthetic tissue for food production trees need to recover from transplant shock. They are best removed before they are larger than one inch in diameter.

For trees planted three years ago, check for needed pruning. Gradually begin removing lower branches to eventually raise the height of the lowest branch for head clearance. Look for branches growing towards the trees center, crisscrossing and rubbing another branch or the trunk, or growing closely parallel to another branch. These are best removed.

If a branch growing towards the center or closely parallel to another is not rubbing and creating a wound, it can be left for a short time. Again, to provide photosynthetic tissue for young trees to become established. Don't forget to check the tree each winter to eventually remove these structural issues before they grow into a problem.

Avoid excessive pruning during one year. Removing too much tissue can stress a tree and/or lead to sucker growth. This is why it is best to monitor a young tree annually for pruning needs and to begin light pruning a few years after planting; continuing to do a little pruning each year as needed.

Pruning Trees, Nebraska Forest Service


4. Pruning tender plants

Wait until spring, typically about mid-April, to prune tender plants like roses and suffrutescent shrubs.  These types of shrubs retain a woody base from which new growth occurs each spring. Examples include Caryopteris (Blue False Spirea) and Buddleia (Butterfly bush). Wait until after these shrubs begin to grow before pruning them. This allows time to determine how far back the shrub has died that year and how much dead wood needs to be removed. Waiting also helps to avoid additional injury if pruning stimulates the plant to begin growth too early in spring.


5. Winter desiccation of broadleaf evergreens

Winter desiccation of broadleaf evergreens can be seen as dead, reddish-brown foliage or leaf margins on arborvitae, yew and broadleaf evergreens, such as holly and mahonia. The extent of the symptoms can vary from damage on one side of the plant, to one or two branches, to the whole plant. Injury is found on the outer portion of the branches and is often most severe on the side of the plant facing the wind or a source of radiated heat, such as a south or west-facing brick wall or street. Winter desiccation is a common type of winter injury that occurs when the amount of water lost by the foliage exceeds the amount picked up by the roots. Wind increases the amount of water lost through plant foliage, even in winter.  A lack of snow melt results in dry soil, which along with frozen soil, both result in an inability of plant roots to pick up enough water to meet plant needs.

No immediate action should be taken with broadleaf evergreen plants showing winter injury other than supplemental watering if conditions are dry. Plants with a small amount of leaf damage may still have live buds within the damaged branch sections. These buds will send out new growth and eventually fill in the damaged section in a few years. Evergreen shrubs, like holly and mahonia, may regenerate new leaves to replace the damaged foliage if injury was not severe enough to kill the underlying branches.

Winter Desiccation Injury of Trees and Shrubs, Oklahoma State University


6. Dormant oil sprays

Dormant oil sprays are applied to control insects and mites overwintering on trees and shrubs. They need to be applied during dormancy to prevent damaging plants. Dormant oils are best applied as late in winter as possible, when overwintering insects are at their weakest, but before plants begin to break dormancy. Pests controlled by oil sprays include scales, aphids, mites and some overwintering caterpillars and eggs. Air temperatures need to be at least 40 degrees before applying dormant oils, with applications made fairly early in the day. If the spray freezes before it dries, plants can be injured. Follow all label directions and thoroughly cover branches and twigs for effective control.


7. Wait to prune fruit trees until late February-March

The best time for pruning fruit trees for fruit production is in late winter, into early spring, depending on the weather. See the following publication for more information on fruit tree pruning.

Pruning Fruit Trees, University of Nebraska-Lincoln Extension