Conifères : Identifier, Résoudre Les Problèmes
Conifers are for the most part solid plants with relatively few phytosanitary problems. However, they are threatened by a few specific enemies and diseases against which it is important to fight.
Identify, solve problems
- Pine processionary: Caterpillars that live in large colonies, form in the ridge of large conifers (especially pines), nests that give the impression of giant spider webs. These larvae, very stinging, feed on needles and can defoliate an adult tree in a few days. In the course of spring, they leave the nest in single file (hence their name processionary) to reach the ground where they pupate.
- Red spiders: Severe in hot, dry weather, these mites show a predilection for blue-foliage conifers and some dwarf forms. Munching the epidermis of the foliage, the red spiders cause a sudden browning, as if the plant had been burned. A strong attack kills a conifer in a week.
- Buprest: This bluish green beetle, less than 1 cm long, attacks juniper, cypress and cedar. The white larvae, 1.5 to 2 cm long, carve sinuous galleries under the bark, at the base of the branches and in the trunk. The plant reacts by a quick drying of the attacked parts. The weakening is fast because larval damage interrupts the flow of sap.
- Decay: This serious disease caused by the fungus Phytophthora cinnamomi, attacks the roots and collar (junction of the stem and roots) conifers, mainly: false cypress and thujas (especially Thuja occidentalis), but also: cryptomeria, juniper ( especially Juniperus conferta), cypresses, pines, cedars. This disease is especially observed in plants grown in pots or pans. It is also prevalent on rhododendrons, azaleas, heather and arbutus.
Soft spots of brown rot are followed by purplish necrosis on the underground part. Particularly in hot weather, wilting and then browning and general drying of the foliage are observed.
- Leaf spots: Due to several species of fungi, they develop mainly during wet springs, mainly conifers planted in heavy and moist soil or in a shady situation. Light brown or blackish brown spots of about 1 mm in diameter appear on the foliage. In the case of a strong attack, the foliage turns brown and the branches can dry out. Young subjects are more sensitive than adult plants.