Stunted Pines and Brown Needles: Diplodia Tip Blight

Diplodia tip blight is a serious disease of mature Austrian, Scots (Scotch), and Mugo pines in Kentucky. The disease is caused by the fungus Sphaeropsis sapinea.  In the landscape, tip blight is normally not observed until pines reach about 12 years old and begin to bear cones. Continuous infections (3 to 5 consecutive years) can greatly weaken and eventually kill affected pines.

Infection occurs in spring; however, disease symptoms become more obvious in mid- to late-summer and fall. Needles in early stages of development stop growing as a result of shoot infections. These stunted needles eventually die and turn straw-colored (Figure 1). Infection progresses to healthy needles and cones.

Disease Management:

·         Apply fungicides (chlorothalonil, propiconazole, or thiophanate methyl) to trees just as buds swell in spring. Apply a second spray when the candles are about half elongated and a third spray as needles begin to emerge from the needle sheaths.

·         Remove and destroy dead twigs, branches, and cones as they occur. Do not prune when trees are wet.

·         Destroy all blighted needles, twigs, and cones debris as they fall to the ground.  The fungus overwinters in debris, especially infected cones and diseased needles.

·         Trees under stress tend to be more susceptible to tip blight. Fertilize and water trees as needed to promote vigor.

 For more information on tip blight or pine diseases:

Needle Cast Diseases of Conifers  http://www2.ca.uky.edu/agc/pubs/id/id85/id85.pdf

Twig, Branch, and Stem Diseases of Pine  http://www2.ca.uky.edu/agc/pubs/ppa/ppa16/ppa16.pdf

Department of Plant Pathology, Extension Publication page  http://www2.ca.uky.edu/agcollege/plantpathology/extension/pubs.html

Skimpy Spruce – Defoliation from the Bottom Up

Rhizosphaera needle cast, the most common disease of spruce in Kentucky, causes needle drop in lower branches, resulting in a distinct thinned appearance.  The fungal pathogen Rhizosphaera kalkhoffii primarily infects spruce but can also affect some pine species. 

Figure 1 – Needles infected with Rhizosphaera turn purplish brown during summer.

Symptoms are often noticed during summer when needles on lower branches turn purplish or brown (Figure 1).  Within a few weeks, needles fall and lower limbs are left bare (Figure 2).  Small, dark fruiting bodies called pycnidia form in stomata (pores in needles) and can be used to confirm diagnoses (Figures 3 & 4).  Pycnidia can easily be recognized with a hand lens or with the naked eye. 

Figure 2 – Needle drop and thinning of lower canopy are classic symptoms of Rhizosphaera needle cast in spruce.

The life cycle of the fungus extends over a 15-month period.   Infection takes place as spores (conidia) within these pycnidia are rain splashed from needle debris onto foliage.  This infection process occurs primarily during spring, but it can continue as long as conditions are rainy, such as this past summer.  During the winter or following spring, pycnidia develop in infected needles, plugging stomata.  Needle discoloration and needle drop occur during summer of the second season, resulting in thinning of lower canopies.  If defoliation occurs 3 to 4 consecutive years, branch death is likely.  Stressed trees are more susceptible to infection by R. kalkhoffii than healthy plants. 



Figure 3 – Fungal pycnidia are often visible without a hand lens.

Disease management should consist of good cultural practices such as improved vigor and reduced plant stress, proper spacing to improve air circulation, and most importantly, good sanitation habits.  During rainy seasons or in plantings with a history of disease, fungicides may be applied two consecutive years during spring when fungi are most active.  Fungicides that include chlorothalonil, copper, or mancozeb are effective when applied during needle emergence (mid-April) and again four weeks later.  For more information, see Homeowner’s Guide to Fungicides. 

Figure 4 – Fungal pycnidia protrude from stomata.

White Pine Decline versus White Pine Root Decline: What's the Difference?

Decline of White Pine

Decline is common among white pine in Kentucky.  Two distinct diseases with similar names are often confused, but they are distinctly different.  Note that white pine decline is an abiotic malady that leads to slow decline, while white pine root decline is a fungal disease that causes sudden plant death.  More details follow:

White Pine Decline

Symptoms

White pine decline causes needle s to yellow and drop prematurely, causing a noticeable thinning of the canopy (Fig 1).  Other symptoms include unusually shorter needles; needle tips may become brown.  Bark of individual branches may become shriveled and needles on those branches become wilted or limp (Fig 2).

Figure 1.  White pine decline, an abiotic malady, is caused by environmental conditions.  Symptoms include thinning needles and reduced plant vigor.

Cause

White pine decline is not caused by a pathogen.  Symptoms are induced by environmental conditions such as

·         high soil pH

·         high soil clay content

·         restricted root-growth

·         compacted soil

·         mechanical disturbances that cause root injury  

Figure 2.  Wrinkled bark is common on trees suffering from white pine decline.  Needles above damaged bark become wilted and drop.

Disease Management

The best way to manage white pine decline is through prevention. Select sites with the following characteristics:

• acidic soil (pH of 5.5 and not above 6.5)
• sandy or loamy rather than clay soils
• large area for root development

·         loose soil free from soil compaction

·         sufficient soil moisture (regular irrigation and mulch)

·         vigorous plants (control insect pests and fertilize trees regularly)

Once decline begins, it may be difficult to reverse.  However, the following practices may be implemented.

·         lower soil pH by applying granular sulfur according to soil test results

·         aerate soil by vertical mulching or other means

·         fertilize and water to eliminate stress

White Pine Root Decline

Symptoms

Trees may be infected for several years without showing symptoms.  However, once symptom development begins, homeowners often notice delayed bud break and reduced candle elongation in spring.  Mature foliage then fades, droops, and turns brown rapidly (Fig 3-4).  Conversely, nearby trees may appear healthy; mortality appears quite random with a few trees dying each year. Resin flow (pitch) is visible at the tree base and is associated with a dark brown girdling canker under the bark (Fig 5).  The trunk may be flattened on the affected side.

Figure 3.  White pine root decline, a fungal disease, causes rapid wilting of white pine. 

Cause

White pine root decline, is caused by the fungus, Leptographium procerum that infects inner bark and sapwood of roots and lower trunks of white pine.  Although the disease is most serious on white pine, the fungus also can infect Scots and Austrian pines.  Losses within an infected planting range from 20 to 50%.

Figure 4.  Rapid wilting is often followed by rapid browning (needles intact) when trees are suffering from white pine root decline.

Trees planted on wet sites are more susceptible to infection, although other stresses may also cause trees to become susceptible to the disease.  Once infection occurs, the fungus may be spread from tree to tree by contaminated insects as they move from diseased trees to healthy trees nearby.  Galleries of insects such as the pine root collar weevil may be found in cankers and provide a place for the fungus to sporulate.  Weevils and other bark-infesting insects may serve as vectors for this disease.

Figure 5.  Pitch is often associated with trunk cankers caused by white pine root decline.

Disease Management

Cultural practices help reduce disease spread by insect vectors. No fungicide is available for disease management.

·         avoid  wet sites

·         do not replant eastern white pine among stumps of recently killed trees

·         remove and destroy infected trees including stumps,

·         collect samples for diagnosis by removing tissue from the canker face (bark removed) and shipping in a plastic bag.

 

Revision of original by John Hartman.