Diplodia tip blight

What is Diplodia tip blight?

Diplodia tip blight is caused by the fungus Diplodia sapinea, which was called Sphaeropsis sapinea for many years. UMass says it most commonly affects Austrian, Scots, red and mugo pines, and Purdue adds ponderosa pine.

The fungus attacks new shoots while their needles are still growing in spring. Infected shoots stop growing, and their short needles turn brown. Resin often oozes and dries in white patches. Over time it forms cankers on branches, which can kill whole limbs. Damage usually starts in the lower crown and spreads through the tree in later years.

Purdue says trees about 20 to 30 years old are hit especially hard, and Oklahoma State says it is most common on trees 15 years or older. Drought stress makes it worse, and so do rainy springs. The fungus overwinters on cones, dead shoots and cankers, so trees keep reinfecting themselves.

Symptoms and signs

• New spring shoots that are stunted, with short brown or straw-colored needles
• Dead shoot tips, often starting on the lower branches
• White patches and droplets of dried resin on dead shoots and cankers
• Tiny black dots at the base of dead needles (under the needle sheath) and on cone scales
• Resin-crusted cankers on branches, and whole branches dying over years

Diplodia tip blight identification: what to look for

• Symptoms: Current-year shoots are stunted with undersized brown or straw-colored needles, starting on the lower branches.
• Signs: Tiny black fruiting bodies (pycnidia) at the base of dead needles (pull the needle from its sheath), on second-year cone scales and on older infected needles.
• Damage: Resin-crusted, hard cankers on twigs and branches. Over time the disease kills scattered branches throughout the tree (Purdue).
• Timing: New needles are infected from bud opening until they are fully elongated, roughly late April to mid-June in wet weather.

Disease cycle

The fungus overwinters in black fruiting bodies on infected shoots, bark and cones. In wet weather, spores ooze out and spread by splashing rain and wind to newly opening shoots. Needles can be infected only while they are still growing. Wounds from wind, insects, pruning and hail are also common infection sites (UMass). Michigan State notes it can live inside healthy tissue without symptoms, taking advantage of stressed trees. New black fruiting bodies form as the growing season goes on.

When to look: Look in late spring and summer for stunted, browning new shoots. Check cones and needle bases for black dots any time of year.

Diplodia tip blight look-alikes

A few things get mixed up with it:

• Pine tip moth: Larvae hollow out the shoot tip. Break a dead tip open; a hollow center, sometimes with a larva, points to tip moth.
• Drought or winter injury: Oklahoma State notes shoots killed by environmental stress die before new needles emerge, not while they are emerging.

How to manage Diplodia tip blight

Cultural control

• Prune out infected shoots and branches in dry weather, and avoid pruning in spring and early summer, when wounds can be infected (Purdue). Oklahoma State says cut at least 8 inches into healthy wood, but do not remove all the green needles from a branch.
• Clean pruning tools between cuts with a household disinfectant (Oklahoma State).
• Pick up fallen needles, dead shoots and other dead tissue under the tree (UMass).
• Water the root zone during drought, and avoid overhead sprinklers (Purdue).
• Avoid heavy nitrogen fertilizer. UMass says disease gets worse after nitrogen feeding.
• Replace badly infected trees with resistant species (Michigan State).

Chemical control

Fungicides only protect new shoots and are mainly practical for small, high-value trees; Purdue calls spraying impractical for most larger trees. UMass says to start just before bud break and repeat every 7 to 10 days while needles elongate. Active ingredients named include thiophanate-methyl, copper hydroxide, azoxystrobin and mancozeb. Purdue notes trunk injections have not been shown to work. Use only products labeled for this use; the label is the law. Large trees need a licensed applicator for proper coverage (see pesticide applicator license guide).

Use only products labeled for this disease and this site; the label is the law. For trees, work with an ISA Certified Arborist. If you hire someone to apply pesticides, make sure they hold your state’s pesticide applicator license; the rules for each state are in our pesticide applicator license guide.

Prevention

• Think twice about planting more two-needle pines. Purdue notes many people now pick other trees instead.
• Keep pines watered in dry summers.
• Avoid spring and early summer pruning of pines.

When to call a pro

Call an ISA Certified Arborist if a large pine has dead branches throughout the crown or resin-crusted cankers on main limbs. Large trees also need a licensed applicator if spraying is planned.

Related guides: Tree database: mature size and planting distance · Pennsylvania tree identification · Firewood rules by state · All pests and diseases

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