UMass Extension's
Landscape, Nursery and Urban Forestry Program
Tel. (413) 545-0895
Fax (413) 577-1620
Q. Recent hard frosts have injured leaves on many deciduous trees in landscapes and nurseries. Will these trees produce another set of leaves?
A. That depends upon how much of the developing leaf was injured. In many instances of spring frost injury, cells in parts of an emerging leaf may be killed, yet the surrounding undamaged cells will continue to develop. As the leaf continues to expand it will become distorted and appear as cupped, curled, or twisted. With further development, leaves may develop holes, but will persist. In other instances, a leaf may be so badly injured that the petiole will abscise. These leaves will drop from the tree. In this case, you can expect the tree to refoliate. The degree of foliar injury and the amount of frost-induced leaf abscission will vary within a single tree.
Q. What effect will this early spring drought have on the long term health of landscape plants?
A. It is too early to say with certainty what the effects will be. However, spring is a critical time for growth and development of plants. New growth in plants depends in part on newly divided cells being fully turgid to promote cell elongation, one of the stages in cell growth. On sites with the most severe water deficits, plant growth will be reduced. Leaves on affected plants may be smaller than normal. That can reduce the amount of photosynthate (sugars) produced and, in the long run, weaken plants, making them more susceptible to certain insect and disease problems. Spring is also an important time for development of root systems. The drought may mean plants such as turfgrass will have a diminished root system, making it more difficult for grass plants to tolerate normal summer heat and drought. In many areas, lawns have already begun to turn brown and go dormant. The potential for problems will certainly increase with each passing week without significant rainfall. Watering now is a must to reduce the physiological impact on plants. When watering, apply it deeply. With the ground as dry as it is, there is a tendency for water to run off surfaces rather than seep in. So attention must be paid to the watering process.
Ron Kujawski
UMass Extension Educator - Landscape, Nursery and Urban Forestry
The University of Massachusetts has released an alert on the 2001 spring drought and its effect on trees in New England. Following a winter that left a lot of plants suffering from winter kill, a late frost in May, we now have a spring drought that is creating serious challenges for woody vegetation. The National Weather Service predicts that the country will continue to have normal to above normal temperatures with normal to below normal rainfall. For many regions of New England this means a continuation of drought conditions, most of with no relief in sight!
The lack of rain and high temperatures this spring is creating hardships for trees and other vegetation. Water is required for all biological processes of plants, trees, and even people. When there is an adequate supply, water seeps down through the soil, gradually saturating each layer. Trees depend on water and moisture in the upper layers of soil usually the top 6 to 18 inches where the root system is located. Water that seeps beneath the upper layers eventually becomes available for use by people as well water. In severe drought conditions, more water is required to keep the upper layers of soil moist.
The first sign of water stress in large shade trees is a flagging, or wilting, of foliage. It can be difficult to notice. Next the leaves become “scorched” as they gradually curl, become dry at the edges, and begin to die. Eventually, trees will drop their leaves in an attempt to “save” themselves. It is important to remember that defoliated trees are weakened, but not dead. Many stressed trees are subject to attack by secondary organisms and proper arboricultural care will be required if these trees are to survive.
What can we do?
Apply 2 to 3 inches of mulch around trees. This conserves soil moisture and keeps soil temperature cool. Water trees in the evenings. Lower temperatures result in less evaporation and better conservation of water. This means more water for the trees!
Do a soil moisture test. Remove a small amount of soil near the roots of a tree and squeeze. If you can form a sticky ball, the soil is too wet. If it breaks like chalk, it is too dry. If the trees need watering, use proper watering techniques. Light sprinkling only settles the dust and evaporates quickly in the sun. Give the plants a weekly, deep soaking with a lawn sprinkler, allowing the water to seep at least 12 18 inches down. This helps the water to get below competitive grass roots, and reach the tree's deeper roots.
When irrigating, the amount of water should be based on the soil texture:
Sandy soil 1 inch of water is required to penetrate to 18 inches
Loam soil 2.5 inches of water is required to penetrate to 18 inches
Clay soil 4 inches of water is required to penetrate to 18 inches
In fact, if you water in too shallow a manner, the tree's roots could turn upward in a search for the lightly sprinkled water. When the soil then dries, the new, shallow roots will be killed more readily.
Overwatering can be just as bad as underwatering. Do not water if there has been adequate rainfall. Let the soil get somewhat dry between watering to avoid “drowning” your trees.
If most of your work is landscaping or turf and you are not a trained Arborist with the proper equipment then please subcontract out the tree work or consult with a Certified Arborist. It will be a lot safer and cost effective in the long run. For additional information on how to professionally maintain your clients trees contact the Massachusetts Arborist Association at (508) 6533320 or the National Arborist Association at (800) 7332622.
With some municipalities already implementing water bans you might want to obtain a copy of the newly released book Water Right: Conserving Our Water, Preserving Our Environment. This book is published by the Turf Producers Foundation. The 68 page booklet presents scientifically based information about the environmental, social and economic benefits of landscape water use compared to the small amount of water landscapes require. The booklet also addresses how landscapes can conserve and enhance water quality. Copies of the booklet can be obtained for $5.00 from the International Turf Producers Foundation, 1855A Hicks Rd., Rolling Meadows, IL 60008.
H. Dennis P. Ryan III, Arborist
UMass Dept. of Natural Resources Conservation
Water has become a critical problem for most Massachusetts communities. As the population and the amount of water used per person continues to increase and with a continuing deficiency in precipitation, the problem will become more acute. Many towns have already imposed restrictions on outdoor water use. Citizens should be aware of the seriousness of the situation and strive to conserve water at every opportunity. Here are some suggestions for making the most efficient use of limited water supplied.
Watering Lawns
1. Established lawn grasses are tough and resilient. Under drought conditions, permanent lawn grasses become dormant and turn brown much as in winter. With the arrival of fall rains, the plants become active and put forth new growth. If outdoor watering is limited to the extent that it is not possible to irrigate the lawn properly, it would be advisable not to water at all and to allow the lawn to go dormant.
2. Spring lawn seeding is not recommended. Fall seeding has always been considered the ideal lawn seeding time, and with a water shortage it becomes more desirable. Spring seedings require constant watering and are frequently overrun with weeds. Heat and dry weather increase the likelihood or failure of spring seedings. Weeds are not so serious in the fall; the weather is cooler, and rain is usually more abundantall factors favoring fall seeding.
If a spring seeding is necessary to cover up a bare lot, ryegrass may be seeded as a temporary lawn to be turned under in the fall prior to a permanent seeding.
3. If lawn watering is permitted, water thoroughly or not at all. Do not try to water the entire lawn lightly every day. Light watering encourages shallow rooting, making the lawn more susceptible to drought injury, and it encourages crabgrass. It is much better to water a portion of the lawn thoroughly once a week than to water the entire lawn lightly every day.
Lawns require an inch of water weekly for best growth, either from rain or irrigation or both. Inexpensive rain gauges may be purchased, or a coffee can be used to measure the amount of water applied. It takes about 625 gallons of water to apply an inch to 1,000 square feet of lawn area. The soil should be saturated with water to a depth of 3 to 4 inches.
In watering your lawn, do not apply water any faster than the soil will absorb it. Allowing the water to run off is wasteful. Use a sprinkler that applies a coarse spray. With a sprinkler that applies a fine mist, much of the water will be lost by evaporation before it hits the ground.
Good maintenance practices will promote vigorous lawn growth. A healthy lawn is better able to withstand and recover from drought conditions. Good maintenance includes liming and fertilizing regularly and proper watering and mowing. Mowing at 2 inches is recommended. It permits greater leaf growth, making for more vigorous grass; shades the soil surface; reduces evaporation; and suppresses crabgrass and other weeds.
Watering Trees, Shrubs and Flower Gardens
During dry seasons, watering is necessary to maintain healthy plants. Water is more important for new planting than for established ones.
Established trees and shrubs do not require as much water as new plantings, but during extended dry spells some watering may be necessary. Some principles of watering are as follows:
Watering with a hose and nozzle is not recommended. Merely syringing the plants and soil is of little value to the root system through which water is absorbed.
An open hose placed at the base of a tree with the water flowing slowly will provide needed water to the root zone. If the water is allowed to trickle into the soil gradually, it will seep down and saturate the area around the roots. Since the composition of soils varies, the rate of absorption will vary, but the water pressure should be as high as possible without surface runoff.
By saturating the soil around the plants, less frequent watering will be necessary. Each plant or bed should be saturated approximately once every two weeks or less depending on the weather.
New plantings will require more frequent watering than established plants. The same type of saturating should be exercised, but once a week may be necessary for new plants.
A ring of soil around newly planted trees and shrubs in the form of a saucer is recommended. This could be built from gravel or excess soil after planting. Fill the ring at each watering to allow gradual seepage into the soil. For the first month, water new plantings twice a week, then weekly for the rest of the season.
Mulching can help to reduce water loss. The use of mulch on new or established plantings is an excellent method of conserving water. Beds which are exposed to the sun and drying winds without cover will dry out rapidly. Trying to keep these areas moist by watering is not adequate, and a great deal of water is wasted.
Some of the more common materials used for mulching are peat moss, wood chips, straw, salt marsh hay, sawdust, pine needles, hay, leaf mold, compost, dried bark, leaves and many others. Much less water will be required to maintain vigorous plants with the use of a 2 inch mulch.
Overall Watering Program for Outdoor Plants. In trying to conserve water and to realize greatest benefit from water used, it is wise to set up a regularly scheduled program.
Do not try to water all planted areas at each watering.
Section off your areas, and concentrate on these areas individually for maximum benefit.
Saturate each area, and then allow to dry out before watering again.
Plan to use mulch around all planted areas to reduce water loss.
Do not allow plants to wilt before beginning a watering program.
Remembertwo hoses at low pressure without a nozzle is the best method of watering.
Over watering can be more harmful to plants than under watering. Roots need air as well as water. Do not keep soil saturated with water continuously.
From the fact sheet by Dominic A. Marini - UMass Extension Educator, retired
Drought causes primary and secondary physical damage as well as physiological changes in trees. The primary physical effect of drought or dry soil conditions is direct damage to the roots and root death. Non-woody feeder roots, usually located in the top 15 inches of soil, are particularly sensitive and are the first ones affected. When these roots dry, shrivel, and become nonfunctional, a water deficit develops since the roots cannot provide water to the top of the plant. In addition, many metabolic changes occur which substantially alter the physiology of drought-stressed trees. Among these are changes in hormone levels and other physiological factors (e.g., factors that influence the number of leaf initials in buds for the next year or that are responsible for the closing of stomates).
Effects of drought are particularly severe on seedlings or new transplants because their roots occupy the uppermost layers of soil where the most rapid drying occurs. In addition, recent transplants typically lose feeder roots during the transplant process. For example, balled and burlapped trees are estimated to contain only 5-20% of their original root mass after digging. For container-grown trees, the medium in which the transplant is growing can be a major factor -- many of the soilless mixes used for container stock are highly porous, dry out very quickly, and are very difficult to re-wet. This situation creates moisture stress in the rootball regardless of the availability of water in the surrounding soil. The problem often continues until the roots grow beyond the rootball. Contrary to popular opinion, it often takes woody transplants two years to become completely established in a new site. The rule of thumb: for each inch of tree caliper, one year of recovery from transplant shock is necessary. As a consequence, these trees should be given extra care and attention during extended periods of drought.
Established trees and shrubs are also affected by drought, especially those planted in marginal sites such as those with pavement over roots, those in pockets of soil on ledges or in sandy soils, or those that have been improperly planted. Drought can exacerbate event the most subtle of improper planting practices! Native plants are usually adapted to regional and seasonal fluctuations in the amounts of available water. Therefore, only unusually severe drought is likely to injure plants that are growing naturally in a given site. However, most of the trees that we deal with are landscape trees which we have selected and planted and therefore frequently subject to drought-stress.
Symptoms:
Symptoms of drought are manifest in many different ways depending on the plant species and the severity of the water deficit. However, it is generally agreed that symptoms are often not evident until some time after the event has occurred even as much as one to two years later! Unfortunately, symptoms of drought stress are usually subtle, not specific, and not diagnostic. This makes accurate diagnosis very difficult. Symptoms are quite variable and include loss of turgor in needles and leaves, drooping, wilting, curling, yellowing, premature leaf or needle drop, bark splitting, and tip and branch dieback. Leaves on deciduous trees often develop a marginal scorch and interveinal necrosis whereas needles on evergreens turn brown at the tips or appear off-colored. Trees can also exhibit general thinning of the canopy, poor growth, and stunting. Many woody species exhibit symptoms of general “decline”. In extreme cases, drought can result in tree death.
Secondary or Opportunistic Problems
In addition to direct root damage, a significant secondary effect of drought is that it weakens trees and predisposes them to secondary invaders and opportunistic pests. Among the key secondary problems are:
1) Winter Injury - Drought-stressed trees are not as winter-hardy as their healthy counterparts.
2) Root Problems - Injured or weakened root systems are more susceptible to root rots. Example:
a. Armillaria Root Rot
Causal agent: Armillaria mellea
Hosts: many species including pine, fir, oak, maple.
3) Cankers - Weakened trees have slowed “defenses” and wound healing is inhibited. Examples:
a. Nectria Canker
Causal agent: Nectria spp.
Hosts: many species, maple, birch.
b. Hypoxylon Canker
Causal agent: Hypoxylon spp.
Hosts: many species, oak.
4) Wood Rots - Slowed defenses limit compartmental-ization and reaction to invasion by wood rotting fungi. Examples:
a. Fomitopsis on red spruce
b. Fomes on maple
c. Polyporus
5) Sensitivity to Pesticides - Weakened trees are more sensitive to pesticides; compounds that do not cause problems for healthy trees can result from phytotoxicity on drought-stressed trees.
Examples: various herbicides, insecticides, fungicides.
6) Sensitivity to De-icing Salts - Weakened trees are more sensitive to de-icing salts, especially sodium chloride.
7) Miscellaneous Diseases - An increase in the frequency and severity of several disease has been associated with drought stress. Examples:
a. Diplodia Tip Blight
Causal agent: Sphaeropsis sapinea
Hosts: pine, esp. 2-3 needled species
b. Rhizosphaera Needlecast
Causal agent: Ryizosphaera kalkhoffii
Hosts: spruce, esp. blue spruce
c. Cytospora Canker
Causal agent: Leucostoma kunzei
Hosts: spruce, esp. blue spruce
d. Verticillium Wilt
Causal agent: Verticillium spp.
Hosts: many trees species, esp. Japanese maple
Management Strategies
While there is no cure for this problem, the effects of drought can be minimized by following some preventative measures:
1) Water in periods of low soil moisture
Trees and shrubs require approximately one inch of water per week. Special attention to young trees is important. Water is best applied at one time as a slow, deep soaking of the entire root zone to a depth of approximately 1218 inches. The length of time required to “deepwater”; will vary depending on soil type and water pressure: clay soils usually require more time than sandy soils. Frequent, light, surface watering will not help the tree and can actually cause harm by promoting growth of surface roots. A deep soaking just before the ground freezes in the fall will also help the winter hardiness of droughtstressed plants.
2) Select the appropriate site and follow good planting practices - Droughtstress can magnify even the most subtle improper planting practices (e.g., planting too deep, too shallow, failure to remove or cut burlap).
3) Select native plants or match plant species to site conditions - Droughtsensitive (dogwood, some oaks, ash, birch) vs. droughttolerant (most pines, many Prunus, larch).
4) Mulch to maintain soil moisture
Properly applied mulches can be very helpful. Mulches are usually applied 1-3 inches thick and spread evenly out to the drip line of the tree. It is also important to keep the mulch 6-12 inches away from the trunk. Mulches that are applied too thick or too close to the base of the tree (“volcano” or “pyramid” mulches) can be harmful! Irrigate prior to mulching.
5) Prune any dead or weakened tissues to avoid secondary problems
6) Maintain plant vigor by following good cultural practices - It is generally accepted that trees under stress should not be fertilized. However, applications of biostimulants, mycorrhizae or similar compounds can be beneficial and can help to stimulate root growth and regeneration.
Dr. Sharon M. Douglas
The Connecticut Agricultural Experiment Station
Due to a prolonged period of lack of rainfall throughout the state, turf has gone off color, and where irrigation has not been available on a regular basis, is the color of straw. What happens to the turfgrass plant when these stresses act upon it? What steps can be taken to encourage recuperation?
Heat Stress: When stressed by high temperatures, turf reduces its growth in several ways. Shoot growth, root growth, tillering, stand density, and leaf size all decrease. Photosynthesis plummets, and carbohydrate production is severely decreased. Because the turf is thus weakened, its recuperative potential is reduced. Those swards which had well developed, deep root systems and dense canopies have fared better than those which did not. Turf growing on poor, shallow, or compacted soils has been especially hard hit.
Heat stress injury is often aggravated by water stress. As transpiration from leaves rises in response to high temperatures, leaf stomata close down. The result is a loss of the cooling effect which transpiration has on a leaf surface. Leaf temperature rises and plant injury at the cellular level increases. When cellular injury is allowed to continue, we begin to actually see the damage. Turf wilts, leaves begin to die and turn brown. Syringing (very light watering) especially sensitive turf can help to cool down the leaf surface and therefore decrease heat damage.
Drought: When a turfgrass plant experiences water stress, it reacts by closing down leaf stomatal openings. This is a positive physiological method which helps to conserve water. As noted above, this stomatal closing increase leaf temperature. Unless water is supplied to the plant in adequate quantity, leaves begin to lose turgidity. Plants wilt. Photosynthesis decreases. The plant is weakened. Carbohydrate (energy) reserves within the plant are reduced; the plant is unable to replenish these reserves, and may enter into a starvation situation.
Secondary Problems: Turf weakened by heat and water stress is susceptible to additional damage from secondary causes. These should be minimized whenever possible to ensure survival of the turf.
Watch closely for insect infestations. Chinch bugs thrive in hot weather. Their damage may be mistaken for drought injury. While reports of infestations have been scattered so far, there are pockets of activity in the state. Monitor carefully. Japanese beetles have been busily laying eggs in turf that is not too severely damaged. If soil moisture levels increase or are kept adequate through some irrigation, look for hatching of grubs and larval activity soon. In areas where soil is very dry and if moisture is not replenished, Japanese beetle egg hatch may be very low.
Ant populations have mushroomed in some locations. The tunneling and mound building activity has aggravated an already excessively dry soil situation and caused severe root injury. Billbugs and sod webworms may be causing damage in some lawn locations. Black turfgrass ataenius has been particularly troublesome on some golf courses. This is a season in which close monitoring for insect activity and population levels is a must to avoid unnecessary pesticide application, to salvage turf, and to manage the budget.
Traffic on heat and drought stressed turf will only increase the damage, not only to leaves and roots but more importantly to the crown. If possible, reduce traffic and use on heavily stressed areas. As weather cools, moisture becomes more available and growth resumes; traffic and use may be gradually increased.
Management Strategies: Turfgrass managers should take steps now to increase the ability of stressed and damaged turf to recover. Any steps which favor turfgrass growth, especially root growth, will tip the scales in favor of the turf.
The recuperative ability of a turfgrass rests in large part in the crown. It is from the crown that tillers, rhizomes, stolons, leaves, and roots emerge. While leaves may die, the crown has the ability to withstand high stress, and unless conditions have been severe for a prolonged period, the crown has the ability to resume growth when water is again available. When lower temperatures, especially at night, resume, the potential for crown growth and recovery increase still further. Management practices which encourage the recovery and activity of the crown, as well as regrowth and development of the root system, will hasten the recovery of the turf on the whole.
If possible, replenish soil moisture. This should be done so that the soil is moist to as deep an extent as is practical and possible. This will encourage root growth downward, so that a greater volume from the available soil moisture reservoir can be pumped by the plant.
Fertilization of heat and water stressed turf should focus on encouragement of root growth, and not excessive shoot growth. Though the tendency may be to get something green growing fast, remember that the long term survival of the plant is most important. High nitrogen fertilization, especially with predominantly water soluble or high salt index fertilizers, should be avoided. High nitrogen fertilization, while encouraging leaf growth, can slow the replenishment of carbohydrate reserves, especially necessary for recovery, production of new plant tissue, and winter survival.
Potassium fertilization can increase heat and drought resistance as well as disease and cold resistance. Root development is encouraged by adequate potassium. Research has shown that potassium has a positive influence on recovery of water stressed turf, especially when applied in a balanced combination with nitrogen and phosphorous. Slow release fertilization of damaged turf is preferred. A 1:1 ratio of nitrogen to potassium will encourage root development and stress resistance. For those areas with very sandy and well drained soils, a ratio of 1:2 (N:K) may be used.
When mowing, allow the turf to grow to the highest cut practical for the specific turfgrass and use intended. Let the clippings lie. Be sure blades are very sharp.
Evaluate: As conditions, both naturally occurring and manipulated by the turf manager, begin to favor the recovery and regrowth of damaged turf, continue to evaluate the level of damage. If necessary, begin overseeding and renovation procedures after mid-August.
Mary Owen
UMass Extension Educator - Turf