Gray Dogwood Control
Gray dogwood is a deciduous, thicket-forming shrub that can grow to a height of 15 feet (5 meters). It has entire, oppositely-arranged leaves born on twigs that are at first green but become gray or gray-brown with age. The lanceolate to elliptical leaves are 2 to 4 inches (5 to 10 cm) in length, a third to half as wide as long, and taper to a broadly pointed tip. The lower leaf surface is whitish. Flowering occurs from May through July, and fruiting dates are July through October. The small, creamy-white flowers occur in branched clusters. White fruits are supported on red stalks, an attractive characteristic in ornamental uses.
Gray dogwood resembles three other Missouri native dogwood species: Rough-leaved dogwood (Cornus drummondii), swamp dogwood (Cornus amomum ssp. obliqua) and stiff dogwood (Cornus foemina ssp. foemina). It can usually be distinguished from these other species by its leaves with whitish lower surface and without a woolly covering of hairs and by its white rather than bluish fruit. Swamp dogwood and stiff dogwood are generally restricted to wet sites with stiff dogwood being confined to Missouri's Bootheel and adjacent counties. Rough-leaved dogwood typically has young twigs and leaves that are rough to the touch, whereas gray dogwood is smooth. However, the two species do hybridize in the Midwest making identification difficult at times.
Gray dogwood is a native species to North America and occurs from Canada and Maine south to southern Illinois and southern Missouri. In Missouri it can be found in most counties.
Habitat for gray dogwood includes moist or rocky ground along streams and ponds, wet meadows and borders of prairies, thickets along fence rows and roadsides, upland rocky thickets bordering glades, and along bluffs. In the tallgrass prairies of western Missouri, gray dogwood tends to be restricted to the dry, rocky exposures within prairies and to edges along fence rows and wooded draws. In the loess hill prairies of northwest Missouri, this shrub can encroach on open prairies and, through competition and shading, reduce the area available for herbaceous prairie vegetation.
Gray dogwood is a woody perennial that forms thickets from rhizomes. Sexual reproduction begins at about three to four years. One viable seed is produced in each fruit. Hybridization occurs between gray dogwood and the similar species listed above.
A variety of bird species eat the fruits and disperse the seeds below perching sites. At least one report suggests that gray dogwood seeds have a low rate of germination. Dormancy may not be broken during the first winter following deposition. Its ability to effectively spread vegetatively may compensate for a lower reproduction by seeds. Ground cover vegetation diminishes beneath thickets of gray dogwood although annual weeds can persist.
Effects Upon Natural Areas
Gray dogwood is a native shrub that is a natural component of many woodland and prairie communities. Eradication of this plant is not practical nor desirable. Managers who are concerned by the abundance of gray dogwood on a particular managed area should determine the desired abundance of the shrub on the site before setting goals for control. A sequence of historical aerial photos can be helpful in confirming or refuting the belief that this shrub is increasing coverage at the expense of prairie ground cover on a given site. A knowledge of appropriate levels of shrub cover will allow informed decisions regarding the need for control.
By crowding out native prairie grasses and forbs, gray dogwood can reduce the habitat available for a prairie ground cover. In Missouri, gray dogwood is considered a problem in remnant loess hill prairies of the northwest because it reduces the size of these already diminished communities. In the western U.S., this shrub has invaded former river channels, thus reducing the channel area following water diversions.
Control measures may enlist one or more of the following techniques: prescribed burning, cutting, or herbicide treatments. No biological controls are known. Although grazing is used in management of some Missouri prairies, it is not felt to significantly affect the growth of gray dogwood.
- Prescribed burning: No consensus of opinion was found for optimum time to burn for gray dogwood control. Re-sprouting is likely following fire; and if sufficient fuel is not available for annual burning, then root reserves may soon be replenished to pre-burning levels. Fire is probably more effective when combined with cutting and/or herbicide treatments.
- Cutting: Cutting twice within a growing season combined with prescribed burning after re-sprouting will significantly weaken this shrub. Summer cutting and herbicide application followed by burning the following spring (after bud break) is reported to give control. After a stand has been reduced to an acceptable level, cutting and burning alone should maintain the desired level of abundance.
- Chemical control: As cut stem treatments, both glyphosate (Roundup) and triclopyr have proven effective. A 10- to 20-percent solution in water of either chemical can be painted on stems immediately following cutting during the summer. The higher concentration may be necessary for the larger stems. Mowing of shrubs with a later foliar application of a 1.5-percent solution of glyphosate resulted in 100-percent control of the related rough-leaved dogwood. Ammonium sulfamate (AMS), trade name Ammate X-NI Weed and Brush Killer, has also produced 100-percent control when painted on cut stems in an Illinois study. As concentrate a solution as possible in water was painted on gray dogwood stems immediately after cutting in February.
At a Missouri loess hill prairie in Atchison County, gray dogwoods were cut and cut stems treated with Tordon RTU in April. The area was burned the following spring. This combination of cutting, chemical stem treatment, and burning was effective in areas where prairie vegetation carried the fire. Dogwoods that were not surrounded by prairie vegetation were not impacted by the fire and were re-sprouting vigorously two years later. A thin-line basal bark application of Garlon 4 in March has been used at this same site, but results are not yet available. The thin-line bark treatment allows treatment of a larger number of stems in a shorter time period than the cut stem treatment.
The recommended method of chemical control is the use of glyphosate or AMS because of their relatively low toxicities, lack of persistence in soils, and effectiveness in gray dogwood control. By law, herbicides may only be applied according to label directions.
Failed or Ineffective Practices
Gray dogwood is topkilled by fire but re-sprouts readily. Prescribed burning will probably be ineffective in well established stands unless repeated frequently or accompanied by cutting and herbicide application.
Cutting and treating stems with Tordon RTU in April was ineffective in northwest Missouri, except when followed by a prescribed burn the following spring. Thickets with too little fire-carrying fuel re-sprouted vigorously.