Although conifers are evergreen trees, they are susceptible to a lot of diseases, pests, and fungi which can affect them in different ways. Conifers turning brown is one of the most common symptoms related to the species. Let’s take a look at some of the most common reasons behind this and how you can fix them.
Some of the most common reasons behind conifers turning brown include pests such as cypress aphid and scale insects, diseases such as needle cast, blight, pestalotiopsis dieback, and corneum canker. Other reasons include improper growing conditions, improper pruning, road salt, and winter browning.
Can Conifers Turn Brown?
Although conifers are evergreen in nature, they can still turn brown or yellow due to improper growing conditions or diseases and pests.
Brown patches can start to form anywhere in the hedge. They develop mostly in the summer season when the tree is going through its active growth. The brown patches can range in size anywhere from 1 inch to 3-4m.
Although the brown patches can develop on any conifer species, the most susceptible species include Cuprocyparis, Leylandii (Leyland cypress), Chamaeyparis lawsoniana (lawson cypress), and Thuja Plicata (western red cedar).
What are Some of the Common Causes Behind Conifers Turning Brown?
The causes for conifers tuning brown can range from pests, diseases, improper trimming, and bad growing conditions. Let’s take a look.
Pests
Cypress Aphid
Cypress Aphid or Cinara Cupressivora is the most common reason behind brown patches on conifers. Joint research between RHS and East Malling Research found that Cypress Aphid is responsible for about 50% of browning cases.
Damage due to cypress aphid is usually seen between late spring and summer. Although it can be found at almost any height of the foliage, it is most commonly seen at the base of the hedge.
You can look for large greyish greenflies but often the browning developed long after the pests have left the tree. You can still look for clues such as cast aphid skins and black fungal growth. The fungal growth is often seen around the sugary honeydew excreted by the pests.
Scale Insects
Scale insects, majorly Juniper scale are another common reason behind turning conifers brown. They also work similarly to the cypress aphid by sucking the sap out of the foliage.
Juniper scale are often thought to be the cause behind some dieback but these insects are quite common and can be incidental to the problem. One way to check if they are the cause of the dieback is to look for them around healthy parts of the foliage. If there are a similar number of insects on the healthy side, then they won’t likely be the problem.
Diseases
Pestalotiopsis Dieback
Pestalotiopsis are usually the cause of browning if you live in an area that receives wet summers. It can be identified as tiny, black fruiting bodies scattered over the affected foliage.
Although this disease attack plants and trees which are already damaged or weak, it can cause some severe dieback once present.
Coryneum Canker
Coryneum canker is caused by the fungus Seiridium Cardinale. Some of the most common symptoms are yellowing or browning of the foliage and eventually branch dying off. Leyland cypress and western red cedar are the most affected species.
Coryneum canker is most commonly found in larger trees and it rarely occurs in smaller hedges.
Honey Fungus or Phyophthora Root Rot
If you notice the browning affects the entire foliage or almost the entire tree, then it can be due to a root disease known as honey fungus or phytophthora root rot.
Needle Cast
Needle cast often results in shedding of the foliage but one of the earlier onset symptoms includes yellowing or browning of the needles. You might also see some small fruiting bodies on the needles.
Remove any affected branches or needles as soon as you spot them and treat the tree with a fungicide.
Needle Blight
Needle blight affects not only the needle but also the twigs of the tree. It usually starts from the base of the foliage and if left untreated can spread to the entire tree as well. In some cases it can also kill branches and even the entire tree. You can use copper fungicide spray to prevent this.
Improper Hedge Trimming
Improper hedge trimming or overenthusiastic hedge trimming at the wrong time of the year is one of the most common reasons behind the browning of conifers. Trimming during the autumn season, on hot days, or during a drought brings a lot more stress on the tree than usual.
It is recommended to trim the trees between April to early August and not more than 2-3 times a year. After trimming, make sure to give the tree a good feed in the late winter which should be followed by the addition of mulch to help the tree retain moisture.
Road Salt
If the affected conifers have been planted alongside roads, then the salt which is used during the winter season on roads can affect the trees. On the good side, this is easily preventable by keeping the tree well hydrated, pruned, and properly spaced.
Winter Browning
If the region you live in faces rapid temperature fluctuations, extremely cold winters, hot and dry summers, and habitual freeze and thaw cycles, then the browning can be a result of winter browning.
If the tree does not have enough water storage to last through the winter, the needles will start yellowing and browning. This drying rate can be affected by the factors listed above.
Winter browning can be seen in the winter and spring season. It is recommended to water the tree during the dry autumn spells to keep them hydrated throughout winter.
Growing Conditions
Other growing conditions such as winter frost, the climate being too dry, strong dry, and cold winds can prevent the foliage from regenerating and can even damage healthy trees. (According to Daniel Akins)
Too Little Rain
People often don’t pay enough attention to providing enough water to conifers due to their evergreen nature. But during especially hot and dry summers, lack of rain and water can start drying out the foliage which results in yellowing or browning of the foliage.
Magnesium Deficiency
Magnesium deficiency in the soil can also turn the conifer foliage yellow or brown. The brown spots in this case look extremely dry and often start off on the underside and the middle of the foliage.
How Can You Prevent and Control the Browning of Conifers?
Let’s take a look at some of the steps which you can take to prevent and revive browning conifers:
- Providing enough water
It is important to water your conifers especially during the hot summer months and in autumn to protect them from winter browning. People often don’t pay attention to providing water to conifers but it is as important as any other species.
- Make changes to the compost
Conifers need compost which is good at retaining moisture. Normal garden compost may not suffice in some cases. It is important to boost your soil with leaf mold or leaf bark-based compost because of their water retention ability.
- Conifers need space
Conifers can get quite big and they need quite a lot of space to grow. Make sure there are no competing plants or trees right next to them.
- Choosing the right spot
Browning is quite common in conifers which are exposed to strong winds. Place them in a sheltered spot where they don’t get pummelled by the wind.
- Provide Drainage
Make sure that the conifer is placed in well-drained soil and water doesn’t get puddled up around the tree.
- Provide enough nutrients
Conifers need a good winter feed to make them ready for their active growing season in the summer. Get the soil tested to find out if it is devoid of any essential nutrients and mulch the top layer of the soil around the tree. You don’t need to feed them more than once a year as overfeeding can also lead to issues.
- Do not over-prune and time the pruning correctly
Green needles of a conifer are the young new healthy growth of the tree. The needles in the inner section of the foliage which don’t receive a lot of sunlight start turning brown and begin to die off. If you start cutting your foliage back to these needles, you will be left with brown needles which will never recover.
You should always prune the conifers only till the healthy green needles. Pruning them at the right time is also important. It is not recommended to prune conifers during the winter months. The preferred timing should be April, June, and early August.
While pruning conifers, remove any competing plants and trees within a 1ft radius of the foliage. During late winters, you should add some organic mulch to the base of the tree.
Conclusion
Reasons for conifers to turn brown range from diseases such as pestalotiopsis dieback and caryneum canker, pests such as cypress aphid and scale insects, improper growing conditions, improper pruning, winter browning, or road salt. Make sure the conifer is provided with the right growing conditions and don’t prune them during the winter months.
- Related reading: How to Kill Conifers
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