Mycosphaerella gibsonii (needle blight of pine)

Lesions can occur at any point along infected primary and secondary needles (Ivory and Wingfield, 1986). However, they often appear towards the distal part of the needles, especially on 1- to 2-year-old seedlings (Suto, 1979; Ivory, 1987). Ivory and Wingfield (1986) suggest that foliage of the lower crown is usually the most affected due to the occurrence of more favourable conditions for the infection. Observations in the Philippines by Koboyashi et al. (1978) indicated that the disease tends to start in the lower needles and spread to the upper crown later on.

Lesions are usually 5-10 mm long (Diekmann et al., 2002); they tend to progress initially from pale-green spots or bands, to a yellowish to yellowish-brown colour, followed by greyish to blackish-brown colour; eventually they coalesce, resulting in complete needle necrosis and eventual needle cast (Ivory and Wingfield, 1986; Ivory, 1987; Braun et al., 2013). Lesions on needles often lead to defoliation and can be especially damaging on young saplings; defoliation often leads to stunted growth and host plant death (Smith et al., 1997). Resulting necrotic needles are always without the reddish tint that is often characteristic of other infections of needles in Pinus species (CABI/EPPO, undated).

Dark-brown stromata fill the stomatal cavities, and numerous fruiting bodies appear as sooty spots on the lesions and, depending on their abundance, give a grey or black discolouration to the bands on the needles (Ivory and Wingfield, 1986). In warm, damp weather, small, grey brush-like tufts of elongate conidia may be just visible on the erumpent stromata (Ivory and Wingfield, 1986). Spermatia may also be extruded in tiny, clear droplets from spermagonia (Ivory, 1987). The distal portions of affected needles die rapidly and become colonized by various saprophytic fungi, whereas the proximal portions remain alive for some time (Ivory, 1987). Ivory and Wingfield (1986) also note that dead foliage may remain on the tree for many months but can be shed during high wind or heavy rain.

Cultural Control and Sanitary Methods

Gibson (1987) suggests that losses from the disease may be kept to a minimum by providing unfavourable conditions for spread and infection of conidiae of the pathogen. Some measures for control of M. gibsonii were listed by Ivory (1987). General nursery hygiene measures to minimize the risk of infection are listed below:

Additional measures provided by Gibson (1987) for nurseries include:

Singh et al. (1988) observed that in their experimental set-up, in nurseries where infected needles are present in the needle mulch or in mycorrhizal soil, infection appeared on needles within one month of pricking (transplanting). They recommended that: