February 2014 Plant Disease Update

Diplodia tip blight stundeted brown pine shoot tip
Stunted, brown pine shoot tip due to Diplodia tip blight.

Most plant pathogens are not yet active at this time of year; however, damage from earlier infections may be evident on certain tree species, such as pine. A common problem on 2- and 3-needled pines is the fungal disease, Diplodia tip blight. This disease causes especially severe symptoms on Austrian pine, but may also affect Japanese black pine and Mugo pine. The fungal pathogen is active in the spring when it attacks new shoot tips, causing stunting of young shoots and browning of newly emerging needles. Upon close inspection, black, pimplelike fruiting bodies may be seen emerging from the surface of necrotic needles. Stem infections, resulting in resinous cankers, may also occur. Severely infected Austrian pines often die.

austrian pine with diplodia tip blight
Mature Austrian pine with browning caused by Diplodia tip blight

Controlling the disease involves pruning out the “clubbed” shoot tips and cankered stems to remove fungal inoculum, disinfesting pruning tools with 70% isopropyl alcohol or a 10% solution of household bleach between cuts. After pruning, a registered fungicide should be applied in early spring to prevent new infections. Most fungicide labels recommend applications as new growth emerges, again when needles emerge from the sheath, and when needles have attained 2/3 of mature length.