PINE NEEDLE RUST
Pine needle rust caused by the fungus, Coleosporium asterum.
Needle rust is most prevalent on young trees up to sapling size throughout the Lake States (fig. 5). The disease does not usually seriously damage trees. But in high hazard sites, where abundant goldenrod and big leaf aster can serve as the alternate host for the rust, the foliage is often killed. This causes reduced tree growth and unsightly foliage. Needle rust, when combined with insects or other agents that attack current-year shoots, can kill small trees.
This fungus needs both pine and goldenrod or aster to complete its 1-year life cycle. Windborne spores (aeciospores) erupt from orange blisters on the pine needles (fig. 7). These infect alternate hosts during early summer. Windborne spores (sporidia) produced on the alternate hosts infect pines in late summer (fig. 6). Needle rust overwinters in pine needles and produces spores the next spring, completing the life cycle.
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|Figure 6 ||Figure 7 |
Control of this disease may be desirable in young or newly established Christmas tree plantations, in nurseries, or in other high-value stands that are severely infected. Here are some controls that will help reduce the impact of the disease under such conditions:
- Avoid planting sites or nursery locations where goldenrods and asters grow abundantly.
- Before August, kill goldenrods or asters concentrated within 1,000 feet (305 m) of nurseries and young newly established plantations by applying an herbi-cide registered for such use.
- Mow goldenrods and asters before August to avoid using an herbicide. This method does not kill the plants and would have to be done each year until the tree crowns shade out the herbaceous cover.
- Establish barriers 16 to 26 feet (5 to 8 m) tall of non-susceptible plants to intercept spores and to change air currents between pine and the adjacent alternate host. This helps reduce the number of spores reaching pine needles.
- Plant conifers that are resistant to Coleosporium needle rust, such as white, Norway, blue, and black spruce, white pine, and balsam fir, where it is impossible to control alternate hosts. However, be sure other diseases that attack these species are not prevalent in the area.
- Mow or poison brushy, tall grassy, or weedy fields before August to reduce moisture on local sites and discourage infection. This will also reduce spore pro-duction on alternate hosts and accelerate pine growth by eliminating plant competition.
- Avoid humid planting sites for pine such as: small forest openings with diameter less than height of sur-rounding trees, sites north or west of a stand of tall trees, steep north or west slopes.
- Plant healthy nursery stock.
Nicholls, T.H.; Patton, R.F.; Van Arsdel, E.P. 1968. Life cycle and seasonal development of Coleosporium pine needle rust in Wisconsin. Phytopathology. 58(6): 822-829.
Nicholls, T.H.; Anderson, R.L. 1978. How to identify and control pine needle rust disease. St. Paul, MN: U.S. Department of Agriculture, Forest Service, North Central Forest Experiment Station. 8 p.
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