Conifers are wonderful evergreen additions to the landscape, but they can have issues in Iowa. Only a handful of conifers are native to the state, with eastern red cedar (Juniperus virginiana) being the only one found statewide. Many of the conifers planted in our landscapes are not well-adapted to the heavy, organic, and sometimes quite wet soils prevalent across much of Iowa. For this reason, we occasionally see problems with conifers.
There are many potential reasons for browning or dieback on plants such as pine, spruce, fir, arborvitae, yew, hemlock, and juniper, among others.
Winter Desiccation | Dry Soil Conditions | Temperature Fluctuations | Frost and Cold Damage | Wet Soil Conditions | Diseases | Insect Pests | Seasonal Needle Loss | Herbicide Damage | More Information
Winter Desiccation
Often, when brown needles and branch tips are observed in spring, winter desiccation is the issue. There are several reasons conifers may dry out over the winter months. This type of injury is almost exclusive to younger, newly planted trees (five years or less in the landscape).
On sunny, windy days during the winter when temperatures are above freezing, needles lose (transpire) water. If the soil is frozen, the transpired water cannot be replaced, and the tree suffers desiccation stress (needle browning and tissue death). Dry conditions during the previous summer months may also be a contributing factor to damage, as trees entered winter already stressed.
Management
Newly planted trees with smaller, less-established root systems should be watered regularly until the ground freezes in the fall. Check the rootball and surrounding soil frequently and provide water when either (or both) are dry. Conifers are best planted in the spring, but they can be planted up until the end of September. Those planted in October or November may not have adequate time to become established before the onset of winter and could be subject to desiccation injury and death.
Avoid pruning browned or burned areas from evergreen trees and shrubs in the early spring, as these branches may still have viable buds that will produce new foliage when growth resumes. If the buds did not survive, prune dead branches back to living tissue. Some plants may appear to be fine for a while, and then begin to decline when conditions become stressful in the summer. This may indicate that some root damage occurred.
Proper placement of winter-injury-sensitive plants, such as yew or arborvitae, can reduce the likelihood of winter damage. Avoid planting them on the south or southwest side of buildings or in areas with direct exposure. Constructing a physical barrier can also protect the plant from the elements.
Dry Soil Conditions
Newly planted trees and shrubs have small, limited root systems that restrict the amount of water they can bring up. When there is insufficient rain or supplemental irrigation throughout the entire growing season, these underdeveloped root systems cannot take up enough water, and needle browning and tip dieback will occur, especially during winter.
Water loss is also high in the summer months. Newly planted conifers that are not regularly watered will start to show brown branch tips and brown needles, which will eventually fall off.
Management
Ensure that all newly planted trees are watered when the original root ball or the surrounding soil is dry. Continue watering until the ground freezes in the fall. Always check soil moisture before watering. Conifers typically grow poorly in overly wet soils, and excessive watering can lead to root rot and death. The systems appear remarkably similar to those found in dry soil conditions.
Do not prune out brown branch tips in winter or spring. Conifers don't have abundant secondary buds from which new growth can sprout. What few they have are most likely to be in the younger outer growth, and if the branch tips are pruned off prematurely, the plant is much less likely to produce new growth.
Temperature Fluctuations
Winter browning may result from the interaction of extreme low temperatures and frequent fluctuations between freezing and thawing. These conditions are typically found on the south or southwest side of conifers, as those areas generally receive the most sunlight during the winter months. Damage may also appear on the windward side, which may be to the north or west. Much like issues related to desiccation and dry soil conditions, this issue is often more prevalent on newly planted trees.
Management
Ensure plants receive sufficient moisture throughout the entire growing season. Avoid planting conifers in overly exposed sites, especially those species that are prone to this damage. When young, it may be beneficial to provide a physical barrier to protect the plant from the elements. Once fully established, these trees are less likely to see damage from temperature fluctuations.
Frost and Cold Damage
Cold damage on conifers and evergreens is rare. Typically, conifers are only damaged by frost or freeze when cold temperatures arrive in late April or early May, as new growth is forming. If damage occurs on conifers from cold temperatures, it happens on new growth
Frost injury symptoms include dying and curling of the newly emerging shoot tips, sometimes appearing only on the windward side of the tree. The damage typically appears right away. However, after experiencing significant cold temperatures, damage may appear later as wilting and browning of the new growth, becoming evident 2 to 3 weeks later. Cold damage to evergreens and conifers can be easily mistaken for herbicide drift. Herbicide injury will also damage other parts of the plant in addition to the new growth.
Often, wilted and brown shoot tips will die. Susceptible plants can become stunted or bushy if injured by frost several years in a row. The plants will not be killed by losing some of their shoot tips, but may look misshapen as laterals take the role of shoot tips. Live, crooked shoots may also be seen late in June or July. Some dead shoots may remain on trees until late fall or the following spring. This can be corrected by pruning the curled tips back to a live bud or side branch.
Management
Once damage has been done, there are no sprays or fertilizer applications that can help the plant recover sooner. Dead shoots can be pruned out, but don't remove excessive green material. Conifers have limited secondary buds, and it is possible to accidentally prune out secondary buds that would've grown to replace the damaged branch tips. Waiting until new growth forms before removing dead branch tips ensures this does not happen. If the brown tips cannot be left on the tree due to aesthetic concerns, prune back to a viable side bud or branch.
Learn more in this article: Cold and Freeze Damage to Garden Plants.
Excess Soil Moisture
In many landscapes across Iowa, it is common to see stressed conifers due to excessive soil moisture. Soils that remain saturated for extended periods are problematic for conifers, as they require well-drained soils; otherwise, they will experience root damage. Root damage prevents the tree from taking up water when it needs it. As a result, we often see browning of needles and needle drop. These same conditions may develop when young trees are watered too frequently.
Managment
Avoid planting conifers in wet, heavy soils. A few species, namely bald cypress (Taxodium), dawn redwood (Metasequoia), and larch (Larix), are better choices for wet or poorly drained soils as they tolerate these conditions. All three of these species, however, are not evergreen and will drop their needles each fall.
After planting, always check soil moisture before watering and skip irrigation should the soil still be wet.
Disease Issues
Several disease issues can impact specific species of conifers in Iowa. These issues often resemble environmental stressors, such as improper soil moisture, desiccation, and temperature fluctuations. With close observation, fungal diseases can be distinguished from environmental stress problems.
- Needle diseases often work from the lower branches upward over a period of time (usually years). Issues like Rhizosphaera and Stigmina needle cast on spruce are common in Iowa. When stresses such as drought are to blame, the symptoms often appear on the entire tree.
- A close examination of diseased pine needles will reveal spots or banded areas on the needles. Death of the needles beyond the banded areas eventually occurs. Brown spot on Scots pine and Dothistroma needle blight on Austrian pine are common in Iowa.
- Diplodia tip blight on Austrian pine is recognized by the development of stunted, brown shoots with short needles.
- Drought stress can deplete trees of energy, making them more susceptible to canker fungi such as Cytospora and Diplodia. Canker fungi encircle twigs and branches, causing individual branches to die, usually in a scattered pattern on the tree. White patches of sticky resin are usually associated with cankered areas.
Management
Management of these diseases starts with an accurate diagnosis. Each fungal disease has its own management procedure. Preventive measures are typically the most effective, which include avoiding the planting of susceptible trees and removing infected ones. Fungicides are labeled for use on many diseases, but should be applied at the first sign of the disease for the best control.
More information on specific diseases can be found in these articles:
- Rhizosphaera needle cast
- Stigmina Needle Cast
- Diplodia Tip Blight and Canker
- Dothistroma needle blight
- Phyllosticta needle blight
- Cytospora Canker
- Kabatina and Phomopsis Tip Blight
- Common Diseases of Conifers in Iowa (Publication)
Insect Pests
Occasionally, insect pests, mites, and nematodes can cause browning and other decline symptoms. The presence of the insect at some point during the growing season is often needed to confirm that insects are causing the problem. Issues like spider mites can cause needle discoloration, which eventually leads to browning. Other pests, such as the larvae of the Zimmerman pine moth and pine wood nematodes, can disrupt water movement in the plant, leading to entire branches turning brown.
Management
Accurate identification of the pest is important for providing the right treatment. The timing of pesticide sprays is important to catch pests at their most vulnerable state.
More information on specific pests can be found in these articles:
Seasonal Needle Loss
The term "evergreen" used to describe conifer trees isn't exactly accurate as conifers do not keep all their needles indefinitely. It's normal for some of the needles on evergreens to turn yellow or brown and fall from the tree in autumn. This seasonal needle loss, also called fall needle drop, is a natural occurrence and is characterized by the oldest (innermost) needles discoloring and falling from the tree.
This can be alarming to tree owners who are not aware of this normal process. For white pines and arborvitae, all of last year's needles are lost simultaneously in the autumn, causing the trees to appear more brown than usual at this time of year. Scots and Austrian pines retain their needles for three years, so their seasonal needle loss is less noticeable. Other conifers, such as firs and spruces, retain their needles even longer, so even though they lose their oldest needles, the effect is virtually unnoticeable.
The degree of needle loss seen can vary from tree to tree and year to year. Needle drop is often especially noticeable after stressful summers or falls.
Deciduous Conifers
Some needled conifers, such as larch (Larix), bald cypress (Taxodium), and dawn redwood (Metasequoia), are deciduous and lose all their needles each fall. All of the needles turn yellow, russet, or orangish to reddish brown and fall from these trees. This is part of its natural annual life cycle. Unfortunate events have occurred in the past, where owners or caretakers of such trees removed them after incorrectly concluding that the barren trees were dead!
Managment
No management is necessary for this issue. Although it may appear alarming at first, seasonal needle loss is a natural part of the life cycle of the tree. Learn more in this article: Seasonal Needle Loss.
Herbicides
Damage from herbicides can vary from browning to needle distortion/deformation (especially on new growth), among other things. Herbicide damage can result from various factors, including drift from a nearby application, misapplication or accidental spraying, and herbicide carryover in contaminated soil, manure, mulch, and compost. Symptoms may develop within a few days to more than a week after the application, depending on the herbicide used, the sensitivity of the plant, and environmental conditions. Damage from herbicides can be easily confused with diseases caused by pathogens (viruses, bacteria, and fungi).
Management
There is little that can be done to "cure" a plant with unintentional herbicide exposure, other than to provide good care and hope it will recover. Learn more in this article: Herbicide Injury to Garden Plants.