Landscape and Nursery - Needlecast Diseases

The following is information on two common needlecast diseases of evergreens in Delaware that are now showing up.

Two major needlecast diseases have been observed this past week. Rhabdocline needlecast infects Douglas fir especially in Christmas tree plantations and nurseries where trees are planted close together. In spring needle spots are yellowish to reddish brown. Sometimes spots coalesce to discolor the entire needle. Discolored needles are cast in spring after spore discharge. Infections of newly emerging needles persist until the following spring when infected needles drop. It is usually not a serious disease in the landscape but Christmas tree growers and nurserymen should be checking trees for symptoms. If found, prepare to spray with chlorothalonil (Bravo, Daconil) when the first buds break and again 2-3 more times at 2-3 week intervals depending on the weather.

Rhizosphaeria needlecast, like Rhadbocline, infects spruce needles in spring and infected needles turn brown in fall to early spring. The first sign of infection occurs in late fall or in spring one year after infection. At that time, the fruiting bodies (pycnidia) of the fungus emerge from the stomata or "breathing" pores of infected needles--visible with a hand lens. Fruiting bodies resemble tiny black dots in neat, even rows. The second summer after infection, symptoms appear as yellow needles, which later turn purplishbrown and drop from the tree. A few of these infected needles may persist on the tree over the winter and drop off the following spring. Because of the long delay between infection in spring and needle drop the following summer, the ends of infected branches appear green and healthy. Branches appear to lose their needles from the trunk outward. Branches that repeatedly lose needles for three or four years may die. Norway spruce is more resistant than Colorado spruce, but both are affected. If control is needed, spray with chlorothalonil when the needles are half grown and repeat 2-3 times.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Landscape and Nursery - Needlecast Disease Pictures

The following are pictures of two needlecast diseases of evergreens being found in Delaware at this time.

Close-up view of Douglas-fir needles showing symptoms of infection with Douglas-fir needlecast fungus (Rhabdocline pseudotsugae). Photo by Mike Schomaker, Colorado State Forest Service, Bugwood.org.

Rhabdocline needlecast. Photo by John W. Schwandt, USDA Forest Service, Bugwood.org. Rhabdocline apothecia are released when flaps of leaf epidermis fold back on either side of the midrib.

Symptoms of Rhizosphaera needle cast, which can be a component of the spruce decline syndrome. Photo by Joseph O'Brien, USDA Forest Service, Bugwood.org.

Rhizosphaera needle cast close up of infected needles with pycnidia (top) and healthy needle (bottom). Photo by Michael Kangas, NDSU - North Dakota Forest Service, Bugwood.org.

Nursery and Landscape - Watch for Rhabdocline Needlecast in Douglas Fir

Rhabdocline needlecast is often seen in plantings of Douglas firs. The following is an article on the subject.


Rhabdocline needlecast is an important disease to know and control if you grow Douglas fir or have properties with Douglas fir. Only Douglas fir is susceptible to this needlecast. Badly infected trees will lose a considerable number of one and two year old needles, which renders the plants unsaleable come Nov. and Dec. in nurseries and Christmas tree plantings. The plant tissue covering the spore bearing structures is just splitting and the buds are emerging in this area, so the timing is right for a treatment in the next few days. Now would be a good time to scout plantings for symptoms and treat if the disease is seen. Bravo Weather Stik or other labeled formulation of Bravo or Daconil (chlorothalonil) is the least expensive and effective if applied at the proper time.

Cultural Control
>Control vegetation around base of trees to increase air circulation and reduce moisture conditions necessary for infection.
>Plant healthy stock.
>Identify disease early to minimize losses.
>Shear trees in healthy plantations first to avoid contamination of these plantations by workers' clothing and equipment.
>Sterilize tools by dipping in denatured alcohol for 3 minutes after shearing infected plantations.

Chemical Control

Trees should be sprayed with chlorothalonil (Bravo or Daconil 2787). Foliage should be completely covered. Three fungicide applications are generally recommended. The first should be made when at least 50% of the buds have broken and the new growth is 1/2 inch long. Make two more applications at two to three week intervals after the first.

Information from Bob Mulrooney, Extension Plant Pathologist, UD.

Nursery and Landscape - Needlecasts on Douglas Fir

Christmas tree growers and nurserymen will need to watch out for needlecasts on Douglas Fir. The following is an article on the subject.

Rhabdocline and Swiss Needlecasts of Douglas Fir - What’s the Difference?

In general, there are at least 40 needle casts in the United States; most affect pine, spruce, fir, larch, cedar, hemlock, and Douglas-fir. These diseases are caused by fungi that have only one infection period per year; in most cases (but not all), the new growth is infected with the disease agent and is eventually cast from the tree (hence the name) once the infection cycle is complete.

Two of these needle casts affect only Douglas-fir: Rhabdocline needlecast (caused by the fungus Rhabdocline pseudotsugae) and Swiss needlecast (caused by the fungus Phaeocryptopus gäumannii).

Rhabdocline needlecast is well established in Christmas tree plantations; incidence of Swiss needlecast, on the other hand, is very low. Still, growers want to know, “what’s the difference?” Disease development is similar, but symptoms and signs are different Symptoms of Rhabdocline needlecast include the development of redbrown spots that become evident during the winter on one-year needles. A week or two before budbreak, orange fruiting bodies develop on the lower needle surface. When the fruiting structures are mature, they rupture and release abundant spores during wet weather. These spores infect expanding buds. Once these new needles fully elongate and the weather is warm and dry, spores are no longer released, and the older, infected needles are cast from the tree. Symptoms on the newly infected needles do not appear until the following fall or winter, and spores are not produced again until the following spring.

Unlike Rhabdocline needlecast, the fruiting structures produced by the Swiss needle cast fungus consist of rows of very tiny, black fruiting structures emerging through the stomates of the lower needle surface. Needles affected by the disease may turn off color or brown, or may even remain green. Spore release from these fruiting bodies begins at budbreak but can continue until August, and it may be several years before fruiting structures are produced in these infected needles to complete the disease cycle. Once needles are shed, affected branches are thin and trees may be unfit for sale.

Cultural management for these two diseases is similar
• Use healthy stock and provide an optimal growing environment.
• Inspect trees during late winter/early spring and look for symptoms and signs. The pattern of infection will likely follow portions of the canopy or field where moisture in the canopy is most abundant.
• Remove sources of inoculum. For best results, remove old and severely infected trees now. Prune severely affected branches during dry weather.
• Manage the moisture. Choose sites with good air drainage. In existing plantations, reduce humidity and promote rapid drying of needles through spacing and row orientation, and remove weeds.
• Use resistant seed sources when available.

Chemical controls used for Rhabdocline needlecast are also sufficient for Swiss needlecast. For Rhabdocline needlecast, begin sprays of chlorothalonil when the first 10% of the trees in the planting first break bud (or the candles are about 1/2 inch long). Repeat the sprays at 7- to 14-day intervals until needles are fully elongated or conditions are no longer favorable for disease development. Add a spreader sticker to enhance coverage. Other compounds labeled for control include copper (hydroxide, salts, sulfate), mancozeb, Spectro (chlorothalonil + thiophanate-methyl), Stature (mancozeb + dimethomorp; nursery and greenhouse only), and thiophanate-methyl.

For Swiss needlecast management alone, spray chlorothalonil (one application) when candles are 1/2 to 2 inches long. Other labeled compounds include azoxystrobin, mancozeb (2-wk intervals through infection period), Manhandle, Spectro, or thiophanate-methyl. Refer to label for timing and rates. For all fungicides, thorough coverage is essential.

Reprinted from "Rhabdocline and Swiss Needlecasts of Douglas Fir - What’s the Difference?" by Ann B. Gould, Ph.D., Specialist in Plant Pathology, Rutgers University. From the March 13 edition of the Plant and Pest Advisory, Landscape, Nursery, and Turf edition.