Why Do Conifers Turn Brown?

Right off the bat, your cypress starts to dry out, or an arizonica in your hedge turns brown … Increasing watering is not the solution! It is likely that the origin of the problem is precisely the excess of water, the favorable condition for, in addition, a pathogen to find its opportunity to attack the root or trunk and branches. Here’s how to tackle the problem.

Brownness of conifers is the name given to the symptoms of partial or total desiccation of these plants. It occurs especially in cypress trees, especially Cupressus macrocarpa and  Cupressus  sempervirens (common cypress),  Cupressus x leylandii (Leyland cypress), arizónica hedges ( Cupressus arizonica), but also in Lawson’s false cypress (Chamaecyparis lawsoniana), Cryptomeria japonica, thuyas (Thuja), junipers (Juniperus), firs (Abies and Picea) and pines (Pinus). Conifers in general.

To the pernicious lack of oxygen at the root level, the opportunistic attack of biological agents is usually added to those that precisely favor flooded lands.

The pernicious ponding

This drying out usually occurs in a very high percentage due to the waterlogging of the substrate, either due to excess irrigation, poor drainage, a poorly porous, too heavy or clayey soil, or simply a poorly made planting hole. The consequence: the water fills the pores with the substrate that should occupy the air and the roots soon run out of oxygen. By increasing carbon dioxide in the root environment, a series of chemical reactions is triggered that cause a loss of permeability in the root membranes. When this happens, the plant begins to have difficulty absorbing water and nutrients and the foliage begins to yellow.

The action of biological agents

To the pernicious lack of oxygen at the root level, the opportunistic attack of biological agents is usually added to those that precisely favor the flooded land. This is the case of the Phytophthora cinnamomi, a microorganism (Oomycete) that begins by attacking the secondary roots, responsible for absorbing water and nutrients, causing their rotting; then it invades the primary or structural roots, and finally affects the base of the trunk. The infection soon spreads to neighboring plants. The first manifestations of the attack are the wilting of the foliage, which turns yellow and then dries up. The roots rot and darken.

A fungus that attacks the aerial part

Another pathogen that takes advantage of the plant’s weakness to attack it is the fungus Seiridium cardinale, which affects the trunk and branches. The spores take advantage of any wound in the bark to infect the specimen; a reddish wound is produced in the attacked area, a canker above which the branch takes on a brownish color and dries up. These wounds can be scraped with a very sharp blade, then cover the area with a disinfectant and healing paste; dry branches should be pruned as they are unrecoverable. The application of the appropriate fungicide will prevent and control the disease in the affected specimen and its neighbors. Both Phytophthora cinnamomi and Seiridium Cardinale can also attack without the need for excess water in the substrate.

THE SOLUTIONS

  • Eliminate the problem of waterlogging. Controlling irrigation, both its endowment (amount of water) and frequency, is essential to prevent the accumulation of water in the soil; Likewise, in the case of drip-watered hedges, it is advisable to avoid that the line of drippers wet the trunk (they should be placed at about 20 centimeters). Conifers most sensitive to excess water do not need much watering, and should only be watered when truly necessary. Conifers and hedges are adversely affected by proximity to grassy areas, which are in high need of irrigation.
  • Ensure aeration of the substrate. When planting conifers, it is essential to ensure good drainage of the planting hole, or of the entire area if it is a hedge, and to improve the texture of the soil by intercutting it to increase porosity, which will allow correct gas exchange. If the soil is excessively heavy or water usually accumulates in it naturally, it is preferable not to plant conifers there, which require deep soils with a loamy texture.
  • Respecting the planting framework, especially in hedges (when planting it is mandatory to take into account the size that the plants reach in their adult phase), is another imperative to avoid root clogging and suffocation.
  • Dig. If it is an established plantation, it is important to make holes to aerate the land. Conifers in general benefit from having wide tree pits or nearby beds that allow proper aeration of the root system.
  • Provide balanced fertilization. Resorting to the application of foliar fertilizers, high in nitrogen and amino acids assimilated by the plant through the foliage, produces a very fast greening effect. However, it does not solve the underlying problem, which is the presence of a pathogen or excess water in the substrate.
  • Apply a fungicide. The effectiveness of the phytosanitary will depend on the correct diagnosis. Sending samples to a specialized laboratory will allow you to act accordingly. Garden centers recommend applying a preventive and curative treatment with a fungicide against Phytophthora in April-May, July, and September.
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