Illinois Natural History Survey - University of Illinois

VEGETATION MANAGEMENT GUIDELINE
White Poplar(Populus alba L.)


SPECIES CHARACTER

Description
White poplar can grow to 50 feet (15.3 meters) tall and has white-grayish bark. Young twigs and terminal buds are woolly. The leaves are white and woolly on the underside. Leaves on larger shoots tend to be palmately 3-7 lobed and, on shorter shoots, tend to be ovoid or irregularly dentate. White poplar is dioecious, that is, staminate and pistillate flowers occur on different trees. The seeds produced are minute and have silky hairs. No female trees are known to occur in Illinois. All reproduction occurs by root sprouts.

Distribution
White poplar is native to Europe and Asia. It was introduced in the United States as a shade and ornamental tree, but is rarely used today for these purposes. It frequently escapes cultivation. It is found throughout Illinois and threatens some natural areas. White poplar should be accurately identified before attempting any control measures. If identification of the species is in doubt, the plant's identity should be confirmed by a knowledgeable individual and/or by consulting appropriate books.

Habitat
White poplar grows in open sunny habitats. It will grow in most soil types and under varied conditions.

Life History
In Illinois, white poplar appears to reproduce primarily by vegetative means. Suckers arise from adventitious buds produced on the extensive lateral root system. Profuse suckers from the "mother" plant will form large vegetative colonies. The vegetative colonies (clones) form dense groves that are the primary threat this species poses to natural areas. The dense groves shade out native vegetation. Suckering will occur naturally but also can be enhanced by disturbance to the plant and/or its suckers. Top removal and fires can stimulate suckering.
A single white poplar tree can produce thousands of seeds. The seeds are wind- dispersed and can travel over long distances. However, spread and establishment of this species by seed does not seem to be a problem in Illinois, as most colonies can be traced back to a planted tree.

Effects Upon Natural Areas
White poplar is an aggressive exotic tree species that can take over portions of natural areas, especially prairie communities, shading out native vegetation. It easily escapes cultivation and, if left unchecked, it can form dense groves that are hard to eradicate. White poplar is an aggressive exotic tree species that can take over portions of natural areas, especially prairie communities, shading out native vegetation. It easily escapes cultivation and, if left unchecked, it can form dense groves that are hard to eradicate.

 


 

CONTROL RECOMMENDATIONS

Very little research has been done on control of white poplar,and control methods listed are ones successful with aspen species. Aspens are similar in their growth and life history. Use of cutting, girdling, burning, and herbicides offer the best control. In many cases, the best solution is a combination of these control measures.

Cutting and Girdling
Girdling can be an effective control method, when feasible. Girdling lessens the amount of resprouting, although dense resprouting can still occur. White poplar produces more suckers than quaking aspen or cottonwood, when each species is girdled. The large parent tree and any suckers over 2 inches dbh (diameter breast height) should be girdled. Phloem should be removed without damaging the xylem. Girdles should be checked after a few weeks to make sure that bark does not develop over the cut area. In conjunction with girdling, all small suckers should be cut.
For girdling to be effective, use an ax or saw to make 2 parallel cuts 4-5 inches apart, cutting through the bark slightly deeper than the cambium. The bark is then either knocked off, using a blunt object like an ax head, or peeled away, using a blunt ax blade. Girdled trees take time to die and the results may not be seen until a year later. Basically, the tree is slowly starving to death. Suckers should be cut if any develop.
As with most woody plants, cutting the stem or trunk close to ground level is a method of control. Cutting during summer months (June through August) appears to decrease suckering. Summer cutting affects the plant when its root resources are low and the possibility of adverse weather during the fall and winter may further harm the plant. Cutting twice (June and August) also can be effective. Yearly recutting of any new suckers is necessary for good control. All plants and suckers should be cut each time to stress the plant as much as possible. If this is not possible a combination of prescribed burning and cutting may be an effective control. It may take years to use up most of the root resources of the plant totally and thus kill it. Once the number of large suckers has decreased, prescribed burning, as discussed below, will aid with control. At first, cutting may increase the number of suckers, so it is important to continue cutting once started.

Prescribed burning
Prescribed burning can be effective in controlling poplar species, but repeated burns are needed. Several years of burning are usually necessary to control poplar species. Cutting and prescribed burning are best used together. The fire should carry into and through the poplar clone. For thick clones, cut poplar for 1 or 2 years before the burn to allow herbaceous fuel to build up in the clone. If this is impractical, work around the edges, cutting into the clone and allowing fire to burn into edges of the clone. Year after year, work farther into the clone, allowing fire to penetrate farther.
Repeated burns are necessary! A single burn may increase the number of suckers. Good results are possible with intervals of 3 consecutive burns with 2-year intervals between the 3 years of burning. All above-ground suckers and trunks must be killed the first year for maximum effectiveness. Even biennial burns will help control white poplar, especially if used in conjunction with cutting.

Herbicides
Triclopyr herbicide (Trade name Garlon 4 or 3A) is effective as a bark or cut-surface treatment. A 20-30% solution of Garlon 4 in diesel fuel can be applied in a thin stream to all sides of the stem, 6 inches above the base of the plant. Although this thinline treatment usually will only work on stems less than 6 inches in diameter, it will also work on some trunks larger than 6 inches because poplar species have thin bark. A narrow band of Garlon 4 encircling each stem is needed to be effective. This method should not be used in high quality natural areas because the diesel fuel may kill vegetation around the tree.
Basal bark treatment with Garlon 4 also is effective. Two to 2 1/2 oz. of Garlon 4 is added to one gallon of diesel fuel. Spray this mixture, using a hand sprayer, to the basal portion of the white poplar trunk. Spray to a height of 12-15 inches (30.5-38.1 cm.). A thorough spraying is necessary. Spray until run-off at the ground line is noticed. As with the above herbicide treatment, this treatment should not be used in high quality natural areas because the diesel fuel may kill vegetation around the tree.
Cut-surface treatment with Garlon 3A also is effective in controlling white poplar. Undiluted or diluted Garlon 3A at a rate of 50% water can be applied to the cut surface. It can either be sprayed, using a low pressure hand sprayer, or wiped, using a sponge applicator (similar to paint applicators), on the cut surface. Either a stump or girdle can be used for the cut surface. Girdles around the stem can be made quickly, using a chainsaw. Application should be within a few hours of cutting.
Use of Triclopyr is best done in the dormant season to lessen damage to nontarget species. Great care should be exercised to avoid getting any of the mixtures on the ground near the target plant since some nontarget species may be harmed. Avoid using Triclopyr if rain is forecast for the following 1-4 days; otherwise runoff will harm nontarget species. By law, herbicides only may be applied as per label directions and by licensed herbicide applicators or operators when working on public properties.
Glyphosate (trade name Roundup) can be foliar-sprayed on white poplar leaves as a control. Glyphosate is a nonselective herbicide, so care should be taken to not let it come in contact with nontarget species. Foliar spray of glyphosate should not be used in high quality areas because of potential damage to nontarget species. For good control, all leaves on all shoots should be treated. Glyphosate should be applied by hand sprayer at a 1 1/2% solution (2 oz. of Roundup/gallon of clean water). Spray coverage should be uniform and complete. Do not spray so heavily that herbicide drips off the target species. The herbicide should be applied while backing away from the treated area to avoid contacting the wet herbicide.

 


 

FAILED OR INEFFECTIVE PRACTICES

No effective biological controls are known that are feasible in natural areas.

 


 

ACKNOWLEDGEMENTS

Dr. Robert M. Mohlenbrock and the Southern Illinois University Press generously permitted use of illustrations from their Illustrated Flora of Illinois.

 


 

REFERENCES

Gleason, H. A., and A. Cronquist. 1963. Manual of vascular plants of northeastern United Sates and adjacent Canada. Van Nostrand-Reinhold Company, New York. 810 pp.

Mohlenbrock R. H. 1973. Forest trees of Illinois. Illinois Department of Conservation, Springfield. 332 pp.

The Nature Conservancy. Element Stewardship Abstract for Populus balsamifera, P. grandidentata, P. tremuloides. The Nature Conservancy. Minneapolis, Minnesota.

 


 

PERSONAL COMMUNICATIONS

Packard, Steve. 1989. The Nature Conservancy, Chicago, Illinois.

 


 

Written for the Illinois Nature Preserves Commission by:
William Glass
Illinois Department of Conservation
Division of Natural Heritage
100 First National Bank Plaza, Suite 205
Chicago Heights, Illinois 60411



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