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diplodia tip blight

Browning and death of branch tips are quite common in older, well-established pine plantings. Such damage often is due to Diplodia tip blight (Sphaeropsis tip blight).

Infection kills current-year shoots and eventually may kill whole branches. This disease, caused by a fungus, becomes increasingly more common and destructive as trees age, although young trees can be affected. Austrian pine is the most severely affected of the pines, but Ponderosa, Scotch and Mugo pine also are susceptible.

* Symptoms

The most conspicuous symptoms of Diplodia tip blight are stunted new shoots with short, brown needles still partially encased in their sheathes. Infected shoots are killed quickly and may be located throughout the tree, although damage generally is first evident in the lower branches.

The severity of damage may vary considerably throughout the tree, with some branches that have been infected several years in a row dying back completely. After two or three successive years of infection, treetops also may be extensively damaged. Repeated infections reduce growth, deform trees and ultimately kill them.

Small, black, pimple-like structures develop at the bases of infected needles and on the backsides of pine cone scales. These structures produce additional fungal spores that can re-infect the tree.

* Pests causing similar symptoms

Diplodia tip blight can be confused with damage from pine tip moths; however, pine tip moth damage can be distinguished by the presence of larvae or tunnels found when an affected shoot is slit open.

It also should not be confused with pine wilt, a diseased caused by trunk-dwelling nematodes, which is killing many pines across Nebraska. Pine wilt primarily affects Scotch pine trees and kills the entire tree very quickly -- usually within a matter of two or three months.

* Control

New shoots are most susceptible during two weeks starting when the buds begin to open and continue to be susceptible through mid-June. Infections are worse during years with very wet springs, which promote disease infection. High humidity also promotes the germination of spores. Fungus spores are dispersed primarily on rain splash from March to October.

Infection also may be higher this year because trees are drought-stressed after last summer. Trees often experience a biological lag time of two to three years in recovery after stress. That means trees are in a vulnerable state going into the 2013 growing season, and we could see higher levels of infection this year.

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Two applications of fungicide are recommended. The proper growth stage for applications usually falls during the third week in April and a second application in the first week of May for eastern Nebraska.

Applications should be made as buds at the tips of the branches begin to open, with a second application seven to 10 days later. A third application may be beneficial in trees that are heavily infected, or if wet spring conditions persist into early June.

For homeowners, Bordeaux mixture, liquid copper, Cleary's 3336 (thiophanate-methyl), or propiconazole (Banner MAXX) are effective. Read and follow all label directions carefully before application.

Prune out dead branches to reduce disease pressure.

More information:

Diseases of Evergreen Trees, Nebraska Forest Service (nfs.unl.edu/documents/foresthealth/diseasesevergreen.pdf)

Sphaeropsis Tip Blight of Pine, University of Nebraska- Lincoln Extension (www.ianrpubs.unl.edu/epublic/pages/publicationD.jsp?publicationId=996)

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Sarah Browning is an Extension educator with University of Nebraska-Lincoln Extension in Lancaster County. Reach her at 402-441-7180; 444 Cherrycreek Road, Suite A, Lincoln, NE 68528; or sbrowning2@unl.edu.

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