Boxwood diseases

Boxwood: characteristics

Buxus Sempervirens is a small, slow-growing evergreen shrub, the canopy is very leafy with small, fragrant leaves when rubbed. It is a native plant in different regions and there are more than 80 species spread in various areas of the planet: south-western Europe, south-eastern Asia, Africa, Central America and tropical areas. Only European and Asian varieties tolerate lower temperatures. It is a shrub that requires little care and can be found both as a single plant and as a hedge shrub. In this context it is widespread as the “queen of topiary forms”: the dense evergreen foliage that covers it lends itself well to long-lasting artistic pruning. Topiary art, a gardening technique that consists in modeling the foliage of certain plants by pruning

Recognize and fight the borer

In recent years, a very harmful insect for boxwood has spread in Europe: the borer. Of Asian origin, it is a phytophagous insect, that is, it feeds on plants. It is a moth that in the larval stage feeds on leaves, buds and also on bark. How to notice the presence of the borer? The attacked plant is covered with white cobwebs while the leaves show brown-orange spots. Furthermore, if we observe the lower part, we can see small yellow eggs with a black dot in the center. In the cold season, chrysalises wrapped in cobwebs are also visible. What remedies to take? Leaving the intervention with chemicals for last, we can use pheromone traps that attract adult insects into small trap-bags to be replaced every month or so. Another biological remedy are the products based on Bacilus thuringiensis: it is a bacterium that ingested by the larvae causes their death. If the health of the plant is compromised by a massive borer attack, the only solution is to resort to chemical treatment, which works against both adults and larvae.

Cylindrocladium buxicola: the fungus that causes desiccation

With the arrival of the borer, the buxicola also spreads, a mushroom that has recently arrived in our country from Northern Europe. It attacks both the leaves and the trunk of the boxwood and with a very fast action: within two weeks it can completely defoliate a plant! How to recognize a sick boxwood? At the beginning of the infestation the leaves have light spots surrounded by a reddish halo. As the disease spreads, the spots unite until they completely cover the leaves which, after a while, dry up and fall off. At the same time, the upper twigs of the plant begin to show dark streaks, within which the fungus nestles. How to fight the buxicola infestation? First you need to cut the infected twigs, remove and burn the fallen leaves that contain the spores of the fungus for about 5 years. Then, be careful not to favor the stagnation of humidity under the canopy, preferring irrigation on the ground. The latter must not be treated with nitrogen fertilizers in order not to make the leaves even more palatable for borers and buxicola.

Boxwood Diseases: Diseases caused by other pests

Alongside the relatively recent infestations due to borer and buxicola, there are those caused by cecidomia and psilla. The attack of the caecidomia, a small insect whose larvae feed on the leaves of the boxwood, is easily recognizable: the affected leaves show a swelling inside which the larvae, inactive during the winter, begin to feed in spring causing drying and defoliation of the plant. The best fight against caecidomy is the pruning of the leaves where the insect is present. It should be done in April to precede the fluttering and the laying of new eggs. A very effective biological remedy is pyrethrum extract, which hinders egg laying, with the same function you can also use nettle macerate or garlic extract. Interventions with chemical agents are indicated only if the plant is subjected to a massive infestation. Finally we mention the psylla: its attack is recognizable by a deformation present on the leaves of the shoots that take on a concave shape. If young plants are attacked, the damage is more serious because they slow down their development.

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