Tuesday, January 23, 2018

Orchard Math

Orchard Math 101:
For Proper Spray Application

1.  Calculate GPA (gallons per acre) for the specific orchard. 

Begin with Tree Row Volume (TRV).  Refer to diagram on page 3.

TRV  =  Tree diameter (ft) x Tree height (ft) x 43,560
                                                      Row spacing (ft)

Use TRV to determine Gallons per Acre (GPA).  A dilute constant* should be selected:  0.5 for bare trees, 0.7 for sparse trees (minimum), or 1.0 for dense canopies (maximum).

GPA  =  TRV x (dilute constant*)
                                              1,000 cu ft

Proper GPA should give good coverage without over-dosing or under-dosing.  Refer to page 3 for recommended adjustments.

2.  Select appropriate nozzles to deliver proper gallonage. 

Convert GPA to Gallons per Minute (GPM).  Note:  For tractors without a speedometer, MPH calculation on page 3.

GPM  =  GPA x MPH x Row spacing (ft)

GPM is the total gallonage needed.  Now, divide by the number of nozzles.

GPM per Nozzle  =  _____GPM_____
                                                          Number of nozzles

Choose individual nozzles based on the GPM per Nozzle.  Know pump PSI (have a gauge).  Hollow cone nozzles are recommended for canopy sprays (airblast).  Hollow cone nozzles produce appropriate size droplets for canopy applications.  Flat fan nozzles are used for herbicides.  Ceramic nozzles are most resistant to abrasion and corrosion.  They are worth the extra cost.

See example Tee Jet selection guide below.

Check coverage and drift.  Calibrate sprayer.  Refer to recommended adjustments section below.

Check coverage, deposition, and drift.  Some recommendations include:

ü  Deposition should penetrate tree canopy but not blow through to the next row.
ü  Monitor deposition with water sensitive paper or photo paper, attach to poles in the center of tree row, stapled upward every 12 inches.  Also, use water sensitive paper in next row to monitor blow through and drift.
ü  Droplet size should be fine, but not aerosol.  If droplets are too big (>300µm), they will bounce from leaf surfaces.  If droplets are too small (<150 µm) they will drift without sticking.  Hollow core nozzles produce droplets within ideal range.
ü  Droplets density (droplets per cm2) should range from 20-30 droplets per cm2 for insecticides and 50-70 droplets per cm2 for fungicides.  There should not be streaks or overlapping spots.  Refer to label.  Sample data sheet from water sensitive paper attached (page 4-7).
ü  Adjust nozzle direction for best coverage.  Monitor by using poles with flagging (air direction) for even coverage.  70% of spray should cover the top half of the canopy.  30% of the spray should reach the lower half of the canopy.
ü  Calibrate sprayers annually by 1) confirming tractor speed (MPH), 2) calculating nozzle output (see page 1), and 3) checking nozzle outputs (see book Effective Orchard Spraying).  Error up to ±5%, adjust pump pressure or tractor speed.  Error over ±10%, replace nozzles.
ü  Most orchard pumps are too large for modern canopy architecture.  Ideal pressure is below 150 psi, but centrifugal pumps range from 150 to 200psi.  Diaphragm pumps have a wider range of adjustment, but they are more expensive.  It is critical to have a gauge to measure psi. Lower pressure by adjusting fan blade pitch, adjusting fan speed via PTO or separate pump.  Keep pressure as low as possible; high pressure creates horseshoe vortex and boundary layer.
ü  Adjust air volume via reducing intake (wooden donut) or reducing outlet (louvers) to eliminate blow through.
ü  Run a constant speed; faster travel speed causes turbulence.
ü  Calibrate nozzles and check for wear.  Change nozzles if ±10%.  Clean tank and nozzles often.
ü  Miles per hour (MPH) can be calculated by marking a 100 ft row, using a stopwatch to time the drive run, and then calculating    MPH  =  ­­­­___100 ft row x 60­­__
                                                     Seconds traveled x 88

Example:  from Syngenta website

Water-Sensitive Paper
What is water-sensitive paper?
Water-sensitive paper is a rigid paper with a specially coated, yellow surface which will be stained dark blue by aqueous droplets impinging on it. It has been developed for field use by Syngenta for the quick evaluation of LV sprays. For droplet assessment, aqueous sprays no longer need the addition of dye. Just place the papers in the target area before spraying. Following exposure to the spray the water-sensitive papers will be stained. Retrieve the papers as soon as they have become dry. Check the droplet pattern. For a quick estimate compare the exposed collectors with a known standard or count the droplets either using a hand lens or an automatic image analyzer.
Water-sensitive paper after exposure. (Courtesy Spraying Systems Co.)

Where to use it
Water-sensitive paper can be used for checking spray distribution, droplet density from aerial and ground spray applications and droplet sizing. 
Overdosing is a waste of product. With herbicides, it might result in crop damage and claims. With insecticides underdosing might not kill the pest. Calibrate the sprayer and check the spray pattern. Water-sensitive paper helps you to keep the environment clean.
Airblast sprayers in orchards: staple water-sensitive paper directly onto leaves at the periphery and inside the canopy at the top, in the center and lower part of the trees.

Number the collectors consecutively before placing them on the supports. This will help you to spot irregularities in your spray system when evaluating the exposed cards. 
The correct boom height can also be determined with water-sensitive paper. Insufficient overlapping of the spray pattern can be corrected by raising the boom. Excessive overlapping is leveled out by lowering the boom.

Visual assessment of droplet densities
Compare your spray samples with some known standard. The standard cards below and on the following page cover the range of acceptable droplet densities for coarse and medium LV spray. The droplet density in the target area should not be less than:

For routine checking of sprays you might also prepare your own standard cards by selecting spray cards with known droplet densities from previous spray operations.
Standard cards with a known droplet density per cm square
Computer-plotted standard cards displaying the expected number and sizes cards spraying at 3 different volume rates (20, 30, 40 l/ha) and using 3 different droplet spectra (VMD, 200, 300) assuming waters sprayed and the spread factor is two.

This handout was produced for the
 Kentucky Extension IPM Implementation Program, Fruit Crops Working Group
                By Nicole Gauthier, Extension Plant Pathologist and Ric Bessin, Extension Entomologist.

Assessing and Utilizing UK Extension Resources
Commercial Fruit Production

College of Agriculture publications website

Departmental sites (publications, fact sheets, videos)
                Ag Economics www.uky.edu/Ag/AgEcon/extension.php
                Biosystems Engineering (Ag Weather) http://weather.uky.edu
                Center for Crop Diversification http://www.uky.edu/ccd/                             
                Horticulture www.uky.edu/hort/documents-list-commercial-fruit-nut
                Forestry http://forestry.ca.uky.edu/wildlife
                Plant Pathology http://plantpathology.ca.uky.edu/extension/publications
                Plant and Soil Sciences https://pss.ca.uky.edu/extension15

                Fruit Facts http://www.uky.edu/hort/documents-list-fruit-facts
                KY Pest News https://kentuckypestnews.wordpress.com/

Email Alerts (listserv)
                Contact Chris Smigel csmigell@uky.edu
                 Separate list servs for apple, peach, grape, blueberry, strawberry, brambles

Apps and Models
                Ag Models (Ag Weather) http://weather.uky.edu/ky/agmodels.php
                Disease and Insect Models (mobile version) http://weather.uky.edu/dim.html    
                Scouting Guides (mobile version) http://applescout.ca.uky.edu/ and                                                             
Social Media
                Ag Weather  https://www.facebook.com/ukagweather/
                Diseases of Ornamentals, Fruit, and Hemp https://www.facebook.com/KYPlantDisease/
                Spotted Wind Drosophila in KY  https://www.facebook.com/SWDinKY/
                UK REC Hort https://www.facebook.com/Ukrec-Hort-Group-122095484516798/
                UK Robinson Center  https://www.facebook.com/ukrobinsoncenter/
                University of Kentucky Ag Programs  https://www.facebook.com/UKANR/
                Center for Crop Diversification  https://www.facebook.com/CenterforCropDiversification/
                UK Extension @UKExtension
                UK Ag Weather Center @UKAGweather
                Ky-Bugs @KyBugs
                Southern IPM Center @southernipm
                Nicole Ward Gauthier @Nicole_WardUK
Lab Services
                Plant Disease Diagnostic Laboratory (free) submit samples through county extension office
                Soil Testing (fees vary) submit through county extension office.  http://soils.rs.uky.edu/
                Food Systems http://www.uky.edu/fsic/services.php
County Agents

                UK Extension Service http://extension.ca.uky.edu/county 

Wednesday, December 7, 2016

Cold Temperatures Pose a Risk to Kentucky Strawberries

Chris Smigell, Extension Associate for Small Fruits/Vegetables, 
University of Kentucky  

A cold front forecast for Thursday night may bring temperatures down to 18-19 ºF for all of Kentucky.  Strawberry plants are not fully dormant by now, so it is important to have some frost protection in place.  

We recommend  applying straw over matted row strawberries when the air temperature first drops into the low 20ºs F.  Mulching actually has several benefits:

  • Protects the plant roots from frost heaving. Cycles of freeze and thaw, lift the soil and plants.  This can break roots off,  especially the very smallest root hairs, that are critical for nutrient uptake.  This reduces berry size and yields.
  • Protects the plant crowns from winter injury. Fully dormant buds in crowns are hardy down to about 10º F, but it takes several freezes and consistent cold to fully harden the plants.
  • Minimizes plant desiccation due to winter winds.
  • Minimizes risk of black root rot  

A standard  straw bale should cover about 50 square feet of bed. A 3-inch layer of straw on an acre requires 3 tons of straw.

Leaves are not recommended. They tend to mat down which  can cause rotting and limit light penetration in the spring.

Frost heaving is less common on coarsely-grained soils. Clay-based soils are finely grained.   Any practice that helps drain the soil, such as adding organic matter, trenching, or tiling, helps reduce the risk of heaving.

It can take temperatures much lower than 32  to freeze all of the water in soil, depending on soil type. Thus  even an inch of straw can help reduce the percentage of water frozen in a soil profile, and the less freezing, the less the amount of heave. The following article describes the frost heave process. 

Here's a guide to correctly applying mulch. (photos by John Strang)




Applying plastic mulch in plasticulture systems is a multi-person job, so line up a few helpers, and set out mulch and weights to hold down the sheets ahead of time. Rock bags tend to work better than sod staples or cinder blocks which can tear the fabric. Plasticulture growers that are using lighter weight covers (.5-.75 oz/square yard) could apply one layer now to help protect the plants and then follow up with a second application later in the month or early next year when the extended bitter cold temperatures usually begin.

"Why not just put down straw or apply row covers well ahead of any critically low temperatures?"   Covering plants too early (late October, early November) can prevent late plant growth on those sunny days when temperatures are in the higher 50's. Second, plants need to be in full dormancy once winter really sets in. It takes several freeze cycles and cold soil  to bring plants into full dormancy.  This process will be delayed by applying mulch or cover too soon.  Generally by late November, it is safe to do so. Plant color is another guideline - strawberry leaves should have a grey-green appearance, indicating onset of dormancy.

Tuesday, June 28, 2016

Using Resistant Cultivars to Manage Strawberry Diseases

From the Midwest Small Fruit Pest Management Handbook

In any IPM program, the use of resistant cultivars is an important consideration.  Many commercial cultivars have resistance and/ore tolerance to leaf spot, leaf scorch, red stele, and powdery mildew.  The more resistance within a program, the better.  Table 21 (page 27) lists ratings for disease resistance in several of the more commonly grown strawberry cultivars.


Thursday, May 5, 2016

Calibrate your sprayer now—Here is an easy way to do it 

From Erdal Ozkan, Professor and Extension Agricultural Engineer, The Ohio State University
Originally published as part of The Ohio State University Extension Vegetable and Fruit Newsletter Vol. 23 Number 3, May 3, 2016

Spraying season is just around the corner. Now is the time to pay attention to your sprayer. First, check all the components of the sprayer to make sure they are in working order. The next step in preparations for the season is to calibrate the sprayer. The only way you can achieve maximum accuracy from a sprayer is by calibrating it once before the spraying season starts, and recalibrating it frequently throughout the spraying season. While applying too little pesticide may result in ineffective pest control, too much pesticide wastes money, may damage the crop, and increases the potential risk of contaminating ground water and environment. The primary goal with calibration is to determine the actual rate of application in gallons per acre, then to make adjustments if the difference between the actual rate and the intended rate is greater or less than 5% of the intended rate. This is a recommended guideline by USEPA and USDA. Before starting calibration, make sure you have a good set of nozzles on the sprayer. Nozzles wear off through extended use, causing over application, or some nozzles may become plugged. Clean all the plugged nozzles. Check the output of all the nozzles for a given length of time at a given spray pressure. Compare output from each nozzle’s output with the expected output shown in the nozzle catalog for that nozzle at the same pressure. Replace the nozzles showing an output error of more than 10% of the output of the new nozzle. Once you do this, now you are ready to calibrate your sprayer. Calibrating a boom sprayer is not as difficult as it sounds. There are several ways to calibrate a sprayer. Regardless of which method you choose, only three things are needed: a timer (or watch or smart phone timer app) showing seconds, a measuring tape, and a jar graduated in ounces. Here, I will describe perhaps the easiest of all the methods to calibrate a sprayer.

Photo: Nicole Gauthier, University of Kentucky

To calibrate a boom sprayer for broadcast applications using this method, follow these steps:

1. Fill the sprayer tank (at least half full) with water.

2. Run the sprayer, inspect it for leaks, and make sure all vital parts function properly.

3. Measure the distance in inches between the nozzles.

4. Measure an appropriate travel distance in the field based on this nozzle spacing. The appropriate distances for different nozzle spacing is as follows: 408 ft. for a 10-inch spacing, 272 ft. for a 15-inch spacing, 204 ft. for 20-inch spacing, 136 ft. for a 30-inch spacing, and 102 ft. for a 40-inch spacing.

5. Drive through the measured distance in the field at your normal spraying speed, and record the travel time in seconds. Repeat this procedure and average the two measurements.

6. With the sprayer parked, run the sprayer at the same pressure level and catch the output from each nozzle in a measuring jar for the travel time required in step 5 above.

7. Calculate the average nozzle output by adding the individual outputs and then dividing by the number of nozzles tested. The final average nozzle output in ounces you get is equal to the application rate in gallons per acre. For example, if you catch 15 ounces from a set of nozzles, the actual application rate of the sprayer is equal to 15 gallons per acre.

8. Compare the actual application rate with the recommended or intended rate. If the actual rate is more than 5 percent higher or lower than the recommended or intended rate, you must make adjustments in either the spray pressure or the travel speed or in both. For example, to increase the flow rate you will need to either slow down, or increase the spray pressure. The opposite is true when you need to reduce the application rate. As you make these changes, stay within proper and safe operating condition of the sprayer. Remember increased pressure will result in increasing the number of small, drift-prone droplets.

9. Repeat steps 5-8 above until the recommended application error of +5% or less is achieved.

Tuesday, July 28, 2015

Consider Safety with Flooded Garden Produce

Consider Safety with Flooded Garden Produce

Updated by Connee Wheeler, Senior Extension Associate, University of Kentucky, 2015

It seems we have experienced flooding this summer that has impacted nearly every county in the state. These floods have raised questions on how to deal with vegetable gardens that have been covered with flood water.  The following information was gathered from the University of Kentucky’s Dr. Sandra Bastin, Extension Food and Nutrition Specialist; Dr. John Strang, UK Extension Fruit and Vegetable Specialist; and from University of Michigan Cooperative Extension.

The first consideration for the gardener would be the source of the flood waters. Rain water or water from a potable water source, or uncontaminated source does not carry the same potential hazards as water from a river, septic field or other potentially contaminated source.

Water from floods can be contaminated with sewage or industrial pollutants. Raw sewage contains bacteria that can cause illness if contaminated fruit or vegetables are eaten. Flood waters that cover roads, vehicles, dumps or pass by factories and other manufacturing and business sites can carry heavy metals and other industrial contaminants.

Flood water may be contaminated with sewage, animal waste, heavy metals, pathogenic microorganisms or other contaminants.  These contaminants are deposited not only on the surface of the flooded fruits and vegetables, but may move into plant tissues.  These contaminants can also be present and may persist in the soil after flooding.

The Food and Drug Administration considers these contaminated products “adulterated” and not fit for consumption.  Pooled or standing water after a rainfall that is not likely to be contaminated should not be considered flooding. 

If there’s a doubt then don’t eat!

The most conservative and safe answer to the question regarding consumption of vegetables that have been in a flooded location is, “DON’T.” If you have any doubts or concerns, it is best to discard the vegetables.  Washing sometimes cannot remove these harmful pathogens and contaminants from fresh produce.  It is always the best practice to be safe than sorry.

Fresh fruits and vegetables that have been partially or completely submerged in flood water or that might have come in contact with contaminated water are just not safe to consume.  There is a high health risk of developing disease from consuming these products.

This would include vegetables that are ready to eat in our gardens now.  Also any root crop such as radishes, onions, garlic, beets and/or carrots would be included.

Vegetables that are eaten as stems or leaves, such as asparagus, rhubarb, Swiss chard and herbs would also be considered unsafe if flooded.  Perennial vegetable plants, such as asparagus and rhubarb, can be kept for production next year.  Do not eat them this season, if they came in contact with flood waters.

Also included in the non-edible list are vegetables and fruits that have very tiny, undeveloped fruits already on the vine, such as peas, strawberries, and possibly tomatoes if you bought some plants very early that were started in a greenhouse. You should remove these tiny fruits and any flowers that are on the plants now and not allow them to develop to an edible stage.

Vegetables that result from flowers produced on growth that develops after flood waters subside may be OK to eat.  That could include plants that you may already have planted, but have yet to bloom and set fruit. However, there is some evidence that disease pathogens can be found in plant tissue when these come in contact with contaminated sources, such as in flood waters.

Wash and peel first

To increase the safety for consumption of any vegetables that were grown in or near a flooded garden site this season, wash them well and peel them, if possible. Cook the vegetables thoroughly before eating to increase the level of safety. This could include tomatoes, peppers, eggplants, sweet corn, squash, cucumbers and similar vegetables.

Examine produce from previously flooded gardens carefully before picking it. If it is soft or cracked, or has open fissures where contamination might have entered at any point in time, even after the flood event, throw it out. Produce from plants that survive flooding with water that was not contaminated should also be discarded if they are bruised, cracked, or otherwise blemished.

Contaminated plants and produce from gardens can be tilled under or composted, using good composting methods.  Be sure the compost pile is turned and proper temperatures are reached to kill any pathogens. Contact the Extension Office for additional composting information.

If your produce was in close proximity to a flooded area but did not come in contact with the flood water, prevent cross contamination by keeping harvesting or cleaning equipment and people away from the flooded area during growth and harvest.  Clean well any equipment and tools used in the flooded field. Workers should wear protective clothing such as rubber boots and rubber gloves when working in the field and with plants that may be contaminated. These items should be thoroughly scrubbed and cleaned after working. 

If an unplanted field has been partially or completely flooded, determine the source of flood water and determine whether there are significant threats to human health from potential contaminates in the water.  Allow soils to dry sufficiently and rework the soil, before planting crops.  Adding compost or other organic matter when tilling will be beneficial to the soil.  We are still early enough in the growing season that new vegetable plants can be planted and some crops can be grown for fall harvest.

Replanting a flooded garden

When planting new gardens that have been covered with considerable floodwater soils that have been covered with floodwaters should be tilled at least six inches deep after they have dried out before planting a new crop. Standard soil tests done through the Extension Office will not be able to tell you if there are contaminates in your soil. These tests are for plant nutrient levels only. 

Any gardens that were covered with contaminated flood waters can be assumed to be contaminated with harmful pathogens, so special testing for this is not necessary. With rain and sunshine, the levels of the pathogens will disperse. After the first good rain, research shows that the majority of harmful pathogens are removed from the surface.

Since there are many bacteria, good and bad, normally present in the soil, but need other factors for growth, this is adequate for human safety levels. If you are still concerned, use rubber gloves to garden with and wash all fruits and vegetables well before consuming.

Produce from flood-damaged gardens should not be sold, given away or consumed until the risk of contamination is gone.  Produce should also not be used for home canning, freezing or used with other food preservation methods.

As always, proper food handling methods in the kitchen are important for food safety.  They include, washing hands while preparing food, cleaning and disinfecting work surfaces, equipment and supplies, use potable water and “if in doubt, throw it out”.

Contact your local Extension Office for additional information and answers to other food and gardening questions.

Original Article Published: May 7, 2010 by Kim Coward (former Franklin County Extension Agent) in The State Journal of Frankfort, KY - http://m.state-journal.com/spectrum/2010/05/07/horticulture-news-my-garden-s-flooded-now-what-do-i-do

Thursday, June 5, 2014

Winter Injury to Trees and Shrubs

Winter Injury to Trees and Shrubs
William M. Fountain, PhD
Extension Professor of Arboriculture and Landscape Management


            The welcomed warming temperatures of spring and early summer are a relief from the cold winter temperatures of 2013-14.  The USDA Plant Hardiness Zone Map (PHZM) for Kentucky (http://planthardiness.ars.usda.gov/phzmweb/Images/72dpi/KY.jpg) places most of the state in zone 6 (–10° to 0°F).  The far western counties are in Zone 7a (0° to 5°F).  By this data, Kentucky was on average no colder than we have historically experienced.  The visible indication of dead plants and utility bills indicated that something was different.


            Temperatures associated with the PHZM are based on the 30 year average of the lowest winter temperature experienced in a region.  This is not the lowest temperatures experienced over the last 30 years, just the average.  The map does not indicate the duration of the cold, soil moisture, humidity, solar radiation, topography or wind.  If you look at the map for the entire country (http://planthardiness.ars.usda.gov/PHZMWeb/Maps.aspx) you will note that Kentucky shares Zone 6 with places that have dramatically different environments (e.g. Texas panhandle, coastal New England and the Alaskan panhandle).  While there are shortcomings to this mapping tool, it is still a valuable aid in making the decision of what to plant and where it should be located.


            The winter of 2013-14 did not reach the historical lows of approximately -20°F experienced in parts of Zone 6 Kentucky in recent decades.  The extensive damage now being observed in landscape plantings are the result of factors not recorded in the PHZM.  Our recent winter was different in many aspects. 


Duration of Cold

            Winter temperatures fell as would be expected in a normal winter.  In a continental climate like Kentucky’s you can expect wide swings in temperature throughout the winter months.  A few days after a cold front pushes through either a warm front from the south replaces it or clear skies following the cold front allow the sun to warm the air and ground.   What was different this year is that the temperatures stayed consistently low for extended periods.  This allowed the soil to freeze deeper and stems to remain frozen longer than in previous winters.


Wind, Humidity and Sun

            The majority of the water lost by plants is from their leaves.  Deciduous plants drop foliage in the fall to reduce their need for water.  Water loss continues through winter but at significantly lower rates.  The small amounts of water lost from dormant stems must be replaced to prevent damage.  Sometimes this is not possible if the soil or stems are frozen.


            The winter of 2013-14 had numerous days when the wind, coupled with low humidity (often below 20 percent) resulted in more water loss from foliage and twigs than the plant could absorb and transport through frozen stems.  When this occurred in the presence of bright winter sun the rate of transpiration (water loss from the plant) increased even higher.   With water in the soil and stems frozen, the pull of transpiration resulted in embolisms (air pockets) developing in xylem cells (conducting tubes that move water from the soil to the top of the plant).  Like the air pocket in a syphon, plants could not move water through these damaged xylem tubes.  This was compounded when frozen stems were physically shaken to remove ice and snow or bent by ice, snow and wind.  Bending frozen xylem cells can fracture the cell walls reducing the plants ability to conduct water and mineral elements.


What Has Happened?

            Many evergreen plants turned brown in late winter and early spring.  Many of these broadleaf evergreens are marginally hardy in our climate.  They are from milder climates where they retain evergreen foliage all year long.  Some of these species survived previous winters because of the milder than normal temperatures experienced.  Examples include:

            Monkey grass (Mondo japonica)

            Southern magnolia (Magnolia grandifolia)


            The southern magnolia is a good example of a species with a wide provenance.  Though they may look identical, southern magnolias originally from the upper parts of the south are more winter hardy than those that were originally from the deep south.  Some native species can be found from the Gulf Coast north into Canada.  Becasue they are the same species does not mean that all individuals in this group have the same genetic level of winter hardiness.  One severely damaged plant I encountered was an eastern red cedar (Juniperus virginiana), a common Kentucky native.  Only after asking the right questions did it come out that this individual had been transplanted from a native stand in south Georgia.


            The Japanese maple (Acer palmatum) is another species that frequently suffers the ill effects of our continental climate.  As the common name indicates this plant is native to Japan, a series of islands bathed in the warming currents flowing north from the equatorial Pacific.  The moderate climate of east Asian islands do not experience the wide swings in temperature common to Kentucky.  This is especially true for the late spring frosts and freezes.  After a brief warm spell our Japanese maples leaf out prematurely only to be damaged by a late spring frost.


            Other broadleaf evergreens may look green and healthy as the coldest of winter temperatures transition into the warmth of spring followed by the first hint of summer heat waves.  Unseen is significant damage to the xylem cells (long tubes that conduct water upward).  Up to this point the individual plant has been able to supply its foliage with sufficient water.  But, the limited amount of healthy conductive tissue has been working at maximum efficiency to supply the plant’s water needs.  With a few days of 80°F in early spring the ability of the plant to absorb and translocate water as rapidly as it is lost becomes a water deficit.  The result is leaf and stem death as if it were much hotter and dryer.  Examples of species where this has been common include:

            Boxwood (Buxus spp.)

            Japanese aucuba (Aucuba japonica)

            Laurel cherry (Prunus laurocerasus)


            Snow and ice are a common form of winter precipitation.  Many gardeners are afraid that the slight bending will result in stem breakage. If the xylem in a branch freezes and then bends  downward as a result of the ice or snow load, the ice crystals can result in the rupturing of the xylem cells.  This type of damage is made worse by strong wind or when the owner of the plant shakes the snow or ice off of the plant thinking that they are helping the plant.


            Sometimes provenance (where it originated) is the major issue for winter injury.  Other times it is the location, specifically failure to match the plant to its site.  In winter the sun is very low on the horizon.  Locating broadleaf evergreens on the north side of a structure will help to protect them from the warming rays of the sun.  These same plants also need to be protected from the drying effect of the wind.  Though we may have fond attachment to them, marginally hardy southern plants do not belong in most Kentucky landscapes.


Sunscald on Red Maple

            In late May or June, well after the cold winter months have passed from our minds we begin to see the development of another type of winter injury.  This problem is called sunscald.  It is not only disfiguring but often leads to a long, slow mortality spiral.  It usually appears only on the south or southwest side of trunks and only on recently planted trees.  The first indication is a small vertical crack in the bark.  These cracks often run from close to the soil line up to the lower branches.  As the crack opens the bark begins to peel back exposing the wood.  The damage that caused this injury occurred during winter when the cambium died.  As the bark peels back exposing the wood fungi attack the xylem and insects are attracted to the open wound.  It is common for 40% of the trunk’s circumference to be damaged by sunscald.  This is more than a disfiguring problem.  It results in the loss of conductive tissues essential for growth and development.  Trees can no longer move water and mineral elements from the roots to the foliage nor supply the roots with sugars and other organic chemicals necessary for growth.  At best, trees stressed by sunscald will reestablish more slowly and are more susceptible to diseases and insects.  While these trees may ultimately survive, replacement trees outgrow severely damaged trees.


            Sunscald is almost always limited to young, recently installed landscape trees.  It is not seen on mature trees or those in forests.  It is most common on species with thin bark than trees with thick or exfoliating bark.  Problematic species include: 

            Maple (Acer spp.)

            Linden (Tilia spp.)

            Pear (Pyrus calleryana)

            Crabapple (Malus spp.)

            Cherry, plum (Prunus spp.)              

            Willow (Salix spp.)


            The most common species associated with this problem is red maple (Acer rubrum).  This is in part because it is the most widely planted (over-used) species and because it is a floodplane species.  While this problem can develop on any tree, it is more problematic on species with high water demands.  Understanding the multiple causes of this problem is the solution to preventing it.  Installing trees with larger soil balls (containing more roots) and watering during the winter months helps prevent water deficiencies leading to sunscald.


            Though not seen until later in the growing season, this damage occurred during the colder parts of winter.  Though the air is well below freezing, the intense winter sun warms the thin bark and the cambium below it.  This is most likely to occur in late afternoon when the low angle of the sun results in sunlight hitting the trunk directly.  The intense sunlight causes the cambium cells to begin dividing.  As a cloud moves across the sun or the sun sets below the horizon, the trunk quickly returns to sub-freezing temperatures and the cambium freezes and dies.


            Sunscald can be prevented by shading the trunks of young, newly planted, thin-barked trees.  A double layer of plastic or fiberglass windowscreen is an easy and economical way to accomplish this.  Wrap the double layer of screen around the trunk.  Hold the two ends of screen and staple them together (not to the tree).  Leaving excess screen will prevent girdling damage to the tree.  Screen is better than plastic pipe or paper wraps sometimes sold for this purpose.  Windowscreen allows moisture to evaporate from the trunk.  This protective covering should be removed after the tree begins to become established, usually one or two years.  White latex paint diluted 50:50 with water is also effective but is messy, unsightly and remains for many years after it is needed.


Cold Damage to Roots

            The least hardy part of any plant is its root system.  Roots grow in the ground where the insulating effect of soil buffers the roots against extremes of heat and cold.  Plants growing in above ground containers and plants being transplanted (balled and burlapped, bare root or container grown plants) lack the temperature moderating protection of surrounding soil.  When roots are subjected to low temperatures they can be killed even though the above ground portions of the plant are hardy and remain alive.  As a rule of thumb, roots are two USDA Plant Hardiness Zones less hardy than the rating assigned to the above ground portions.  As spring growth begins the buds begin to pop open but fail to put out new foliage.  The green stems quickly turn brown, and die.  This occurs because the roots were killed killed by cold and were unable to absorb water essential for growth.


            Winter injury to landscape plants appears with multiple visual symptoms.  While these injuries are associated with low temperatures, injury is usually the result of a combination of different environmental and cultural conditions (low temperatures, duration of cold, lack of soil moisture, low humidity, wind and sun).  Healthy landscapes are not an accident.  It is important to always match the plant to the site conditions.  This helps ensure that your investment will have every opportunity to thrive and return aesthetic dividends for years.


Managing Winter Injury on Landscape Plants

            Rule number one in diagnosing winter injury and making recommendations is don’t be impatient.  If the foliage or the tips have been damaged but the stems and buds are still green, give the plant the opportunity to put out new growth.  Sheering dead foliage will immediately improve the appearance of the plant.  Pruning should not be done until after the chance of the last frost has passed. 


            Spring fertilization is not recommended, especially for plants suffering winter injury.  The addition of nitrogen can encourage more growth than the damaged stems can supply with water during the hot, dry summer months.  The addition of water during dry periods is more beneficial than the addition of fertilizer.  When necessary, fertilization of woody landscape plants should occur in late fall after leafdrop (e.g. Thanksgiving to Christmas).


            Broadleaf evergreens that are established and exposed to winter sun can be protected from the intensity of winter sun and wind.  Cover these plants with light-colored cloth or burlap prior to the onset of winter.  Spray moisture on the cloth prior to the onset of extremely windy sub-freezing temperatures.  Water frozen on the cloth will further reduce the effect of the wind.  The best long-term approach is to match the plant to the site.  This can involve using hardy needled evergreens where evergreens are desired and deciduous species that originated in our climatic zone. 


            Damage to plants will vary widely depending on exposure and location in the state.  The following tables will offer suggestions on degree of damage and cultural advice.  The degree of damage varies widely across the state and even locally depending on exposure, vigor of the plant and genetic adaptions.


Table 1.

Broadleaf evergreens
Abelia (Abelia x grandifolia)
Foliage burn and stem dieback, can be cut back almost to the ground (3 inch stubs).
Japanese aucuba (Aucuba japonica)
Severe foliage dieback and stem dieback.  This marginally hardy evergreen should only be grown in full winter shade.
Barberry (Berberis juliana)
Moderate foliage and twig death
Boxwood (Buxus spp.)
Foliage damage, can be sheered back
Camellia (Camellia japonica)
Foliage and twig death. Even the cold hardy cultivars are not reliably hardy.
Threadcypress, Chamaecyparis (Chamaecyparis spp.)
Moderate foliage damage variable by species and cultivar. These plants do not generally tolerate heavy sheering.
Bigleaf wintercreeper (Euonymus fortunei)
Foliage damage and twig dieback. This plant will rebound (unfortunately).
Japanese euonymus (Euonymus japonicus)
not reliably hardy, cut back to the ground
Spreading euonymus (Euonymus kiautschovicus)
not reliably hardy, cut back to the ground
Foster holly (Ilex x attenuata)
moderate foliage damaage with some twig death
Japanese holly (Ilex crenata)
variable by cultivar but moderate foliage damage
American holly (Ilex opaca)
slight to moderate foliage damage in sunny locations.  Hard sheering often does not regrow.
Blue holly (Ilex x meserveae)
numerous cultivars with slight to moderate damage.  Do not prune unless severely damaged
Privet, ligustrum (Ligustrum spp.)
Damage to foliage and stems.  Plants resprout from the base. (Note: this species is considered invasive and not recommended.)
Liriope, bigblue lilyturf (Liriope muscari)
Trim back dead foliage being careful not to damage the crowns.
Southern magnolia (Magnolia grandiflora)
Severe foliage to twig death.  Most cultivars are of southern provenance. Damaged plants will often produce sprouts on the trunk.
Oregon grapeholly, Mahonia holly (Mahonia bealei, M. aquifolium)
severe damage to death of the entire plant.  These species are marginally hardy and should only be grown in areas protected from wind and winter sun.
Nandina (Nandina domestica)
Severe damage with many plants killed to the ground or killed completely.  Cut dead canes back to 3-inch stubs.
Laurel cherry (Prunus laurocerasus)
Severe damage to foliage and stems.  Plants that have not been killed will sprout back from the base. Plants should be protected from wind and sun during severe winters.
Azalea, rhododendrons (Rhododendron spp.)
Damage is variable by species and location.  Damage is from slight foliar damage to complete death of the plant.  Protect evergreen forms from winter wind and sun.
Yew (Taxus x spp.)
Damage is variable depending on location and species. Sheering will remove dead foliage though most Taxus do not tolerate hard pruning.
Willowwood viburnum (Viburnum x rhytidophylloides ‘Willowwood’)
Foliage and twig death. Plants generally come back from the base.
Leatherleaf viburnum (Viburnum rhytidophyllum)
slightly less winter hardy than Willowwood


Table 2.

Marginally hardy deciduous species
Mimosa (Albizia julibrissin)
Killed to the ground.  Trees will sprout back as shrubby or multi-trunk forms. (Note: this species is considered invasive)
Orange-eye butterfly bush (Buddleia davidii)
Severe dieback to the ground. (Note: this species is often listed as invasive.)
European hornbeam (Carpinus betulus)
Dieback of stems; expect flatheaded borers
Border forsythia (Forsythia x intermedia)
Flower buds of less hardy cultivars are often killed by sub-zero temperatures
Crape myrtle (Lagerstroemia indica)
Many cultivars have been killed to the ground.  Cutting dead plants to the ground will generally result in regrowth from the base.  These plants will be shrubs or multi-trunk trees unless trained back to a single leader.
Knockout rose (Rosa x spp.)
Stem damage or killed to the ground.