Conifers are lovely 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 you will find statewide). Many of the conifers that are planted in our landscapes are not well-adapted to the heavy, organic, and sometimes quite wet soils we have 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
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 because trees went into winter already stressed.
Management
Newly planted trees with smaller, less-established root systems should be watered until the ground freezes. 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 in early fall as well. Avoid planting conifers after 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, burned areas from evergreen trees and shrubs in the early spring since 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 be evidence that there was some root damage.
Proper placement of winter injury sensitive plants, such as yew or arborvitae, can reduce the chance of winter damage. Avoid planting them on the south or southwest side of buildings or in exposed areas. 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 not sufficient 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 over winter.
Water loss is also high in summer months. Newly planted conifers not regularly watered will start to see brown branch tips and brown needles that eventually fall off.
Management
Make sure all newly planted trees are watered when the original rootball or the surrounding soil is dry. Continue watering from planting through summer until the ground freezes in the fall. Always check soil moisture before watering. Conifers generally grow poorly in overly wet soils and excessive watering will cause root rot and death. The systems look remarkably similar to 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 and sprout. What few they have are most likely to be in the younger outer growth and if the branch tips are pruned off prematurely, then it is much less likely for the tree to flush out 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 usually found on the south or southwest side of conifers since those areas generally receive most of the sunlight during the winter months. Damage may also appear on the windward side, which may be to the north. Much like issues related to desiccation and dry soil conditions, this issue is often more prevalent on newly planted trees.
Management
Ensure plants are receiving enough moisture through 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.
Excess Soil Moisture
In many landscapes across Iowa, it is common to see stressed conifers due to excessive soil moisture. Large amounts of rain that saturate the soil for long periods are problematic for some trees. Conifers especially need well-drained soils. When young trees are watered too frequently, they can also seed issues. If they are planted in a clay soil or any areas where soil can remain saturated for even short time periods, conifers 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.
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
There are several disease issues that can impact certain species of conifers in Iowa. These issues often look similar to 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 look at diseased pine needles will show 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 rob trees of energy, causing them to be 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 it own management procedure. Preventive measures are typically the most effective, which include avoiding planting susceptible trees and removing infected trees. 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 below.
- 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 it is a problem. Issues like spider mites can cause needle discoloration with eventual browning. Other pests, like the larvae of Zimmerman pine moth and pine wood nematodes will disrupt water movement in the plant leading to entire branches turning brown.
Management
Accurate identification of the pest is important to providing the right treatment. Timing of pesticide sprays is important to catch pests at their most vulnerable state.
More information on specific pests can be found below.
Seasonal Needle Loss
The term "evergreen" used to describe conifer trees isn't exactly accurate. 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. The oldest (innermost) needles are eventually shed from trees such as pine, spruce, and fir. The discoloration and loss of needles can be alarming to tree owners that are not aware of this normal process. Some fear that a disease is rapidly occurring.
Despite being called "evergreens", conifers do not keep all their needles indefinitely. Older needled turn yellow or brown, die, and are shed regularly. 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.
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. However, browning of the needles at other times of the year may be a sign of disease. Environmental stresses, such as drought and hot temperatures, may cause greater-than-normal loss of needles. The normal pattern of seasonal needle loss is a gradual discoloration and eventual loss of inner needles from the top to the bottom of the trees. In contrast, fungal diseases often cause browning of the newest (outermost) needles, death of entire branches, or thinning of needles on just the lower branches.
Herbicides
Damage from off-target or accidental herbicide applications can vary from browning to leaf cupping, petiole twisting, epinasty, blotches, and distortion/deformation (especially on new growth), among other things. Herbicide damage can result from many things, including drift from a nearby application, a 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 to ornamental plants and hope they will recover. Learn more in this article: Herbicide Injury to Garden Plants.