Pine needle cast

Symptoms

On the needles, especially the older and previous-year ones, yellow and then brown discolourations appear in autumn or late summer, often with dark transverse lines separating the healthy and infected sections. In spring the infected needles turn brown en masse and fall, stripping the lower parts of the shoots. On the dead, fallen needles black, lens-shaped fruiting bodies form, which release spores that infect the new growth; most dangerous to young pines and nursery seedlings. The discolouration usually begins as small yellow spots that spread along the whole length of the needle until it turns reddish-brown. The dark transverse lines (the so-called boundary lines) are the most recognisable feature - they outline the dead sections on a still-green needle. The heaviest needle drop occurs in spring, in April and May, just before the new growth develops; under heavy pressure only the youngest needles at the tip remain on the shoot, giving the characteristic 'paintbrush' habit and weakening growth, while the youngest seedlings may die. The black fruiting bodies on the fallen needles are elongated and boat-shaped, and open with a longitudinal slit in wet weather, ejecting ascospores that infect the freshly grown needles in summer and autumn. Scots pine is the most susceptible, but the disease also affects Austrian pine and dwarf mountain pine. It is worth distinguishing the two causal species: Lophodermium seditiosum is an aggressive parasite of living, young needles and is responsible for damaging needle casts in nurseries, whereas L. pinastri colonises mainly ageing or weakened needles and tends to be a saprotroph - its mere presence on fallen needles need not indicate serious disease.

Treatment

Raking up and removing the fallen, infected needles reduces the source of spores for spring. In nurseries and young plantings with heavy disease pressure, fungicide sprays are applied from July into autumn, during the period of spore release and infection. It is essential to protect the new, current-year needles - they are the target of the summer and autumn infections - so the treatments are repeated every 2-3 weeks throughout the whole spore-release period rather than just once. Effective options are contact fungicides based on copper (protective, coating action) and systemic triazole fungicides (DMI) that penetrate the needle tissue; alternating them reduces the risk of the fungus developing resistance. Heavily infected seedlings should be culled before planting out, so as not to carry the disease into the crop. In mature stands chemical control is usually uneconomical and technically difficult - there the mainstay remains silvicultural and sanitary measures rather than spraying.

Prevention

Thinner sowing and planting for better ventilation, avoiding excessive moisture and overcrowding of seedlings. It helps to choose resistant pine provenances and to isolate young plantings from older stands that serve as a source of infection. Establish nurseries and crops away from older pines, which are a reservoir of spores, preferably on the windward side. Limit prolonged wetting of the needles: water in the morning, avoid evening overhead watering, and ensure weed control and efficient water drainage so that humidity among the seedlings drops quickly. Balance the fertilisation - an excess of nitrogen produces soft, lush needles that are more easily infected, while an adequate supply of potassium improves their resistance. Carry out regular autumn inspections to detect the first discoloured, transversely lined needles early, and never plant out material showing symptoms of the disease.

How to tell it apart from look-alikes

Control — organic and chemical methods

We give active-ingredient groups and modes of action, not brand names — specific products and their approval vary by country and are sometimes withdrawn. Always check and follow the current label.