Diplodia Blight (Tip Blight) of Pines

The Role of Stress

Stressful conditions such as drought and root damage play a big role in the development of Diplodia blight. Drought can trigger the development of severe symptoms, which may continue for many years after the drought ends.

Activities that contribute to root damage include trenching, compacting the soil and planting trees too deep. Overwatering trees also damages roots.

Factors favoring Diplodia blight are:

Pines that appear healthy may have latent (dormant) infections that may be triggered under certain conditions, resulting in rapid symptom development.

In particular, Diplodia blight often develops following hailstorms because the latent infections take advantage of hail-damaged branches. In such cases, some trees may recover with the loss of only a few branches, while trees more severely damaged may die.

Disease Development

Infection of shoots occurs during mild, rainy weather in spring. Shoot death occurs quickly, and the stunted dead needles often remain attached to the twig.

Over the years, multiple infections cause entire branches to die, often beginning low in the tree. Frequently these lower limbs are pruned off, but the disease continues to kill branches higher up until only the top portion of the tree remains green. Scattered branch death and top kill are also frequently observed in diseased trees.

Severe damage is generally seen in mature trees, although young trees planted below older pines may be affected. Trees with extensive damage may ultimately die.

Susceptible Trees

Most pines are susceptible to Diplodia blight. Among common landscape pines, Austrian pine is the most severely affected. Extensive damage usually develops by 30-40 years of age.

Ponderosa pine commonly shows symptoms when under stress. Scotch pine is less often affected and eastern white pine is rarely damaged. Spruce, fir and other conifers are rarely affected.

Symptoms

The most distinguishing characteristic of Diplodia blight is the presence of dead, stunted needles at the tips of branches (hence the common name, “tip blight”). The needles die in spring when the developing shoots are attacked and killed by the fungal pathogen.

Another identifying characteristic is the presence of tiny black structures resembling pepper grains on the base of stunted needles and on the ends of cone scales. This is the reproductive stage of the Diplodia fungus. These structures release billions of spores that can initiate new infections.

Fungicide Treatments

Fungicide sprays applied in spring can help prevent infection of the new shoots. Generally, three sprays are required:

• At budbreak (around the third week of April)
• Just before needles emerge

• 7-14 days later

Use a fungicide with an effective active ingredient (see below). Because many other diseases are commonly called "tip blight," check that the label lists Diplodia or Sphaeropsis tip blight.

Fungicides Labeled for Diplodia Blight*
Active Ingredient:
Thiophanate-methyl

• Cleary's 3336 (F, WP)
• Ferti-lome Halt Systemic Fungicide
• Topsin M
• AllBan
• Nufarm T-methyl

Propiconazole

• Banner MAXX
• Lesco Spectator

Copper Salts of Fatty & Rosin Acids

• Camelot

Bordeaux mixture

*Trade names are examples of available products. No endorsement is implied. Always follow pesticide label instructions

Managing Diplodia Blight

Follow these practices to limit stress and improve your tree's ability to fight disease:

Water when the soil is dry, but don't overwater. If it does not rain, apply 1 inch of water per week in clay soils, or 2 inches in sandy soils. Water only once or twice a week, soaking the soil well. Allow the soil to drain between waterings to allow oxygen back into the soil. Do not overwater. Automatic sprinklers that run daily or every other day can severely stress trees.

Mulch with woodchips to improve soil conditions for the roots. Maintain 2-4 inches of mulch around the tree in an area 6 feet or more in diameter. Do not pile mulch against the trunk. Fallen needles can be left as part of the mulch; they do not need to be removed.

Keep competitive weeds away, especially bromegrass.

Protect the roots from damage caused by digging, trenching, compaction and changes in soil grade. Keep in mind that some roots extend well beyond the crown of the tree.

Avoid planting new pines beneath old infected pines. The cones on mature pines produce enormous numbers of fungal spores, resulting in continual attacks on nearby young trees.

Use proper planting techniques. Dig a wide, shallow hole. The main roots should be level with the soil surface, not deep in the hole. Remove all twine, wire and burlap, and spread the roots out as much as possible.

In pine stands, maintain proper stocking levels to limit competition among trees.