Is cutting and regrowth spraying more effective than cutting and stump painting to kill Asiatic bush honeysuckle (Lonicera spp.)?

Background/Question/Methods

Asiatic bush honeysuckles (Lonicera maackii, L. tatarica, L. morrowii, and L. x bella) are forest invaders throughout the northeastern United States.  Honeysuckles suppress understory herbs, impair tree reproduction, degrade wildlife habitat, and foster other undesirable species.  Numerous control techniques have been developed, but a common approach is to cut stems at the base, and paint the stubs with 20% glyphosate.  This technique is apparently effective (confirmatory data are limited), but is problematic because it employs concentrated herbicide.  Previously we reported that basal cutting immediately after spring leaf expansion followed by regrowth spraying produced equivalent results using less herbicide.  Here we test cutting/painting against cutting/regrowth spraying implemented in early spring, midsummer, late summer, fall, and winter.

The experiment was conducted using a RCB design with five replicate sites in Madison County, IL containing naturally occurring populations.  On each treatment date (above) randomly selected shrubs (measured for canopy diameter) were either cut at the base and painted with 20% glyphosate or cut at the base, allowed ca. 40 d to regrow and sprayed with 1% glyphosate.  Treatment success was evaluated early the following summer by tabulating living and dead shrubs, and harvesting new biomass from survivors.

Results/Conclusions

Basal cutting followed by painting with 20% glyphosate proved to be most effective, killing > 75% of individuals at any time of the year.  Late summer, fall, and winter proved to be the best treatment times, killing > 95% of individuals.  In contrast, cutting followed by regrowth spraying killed 56% of individuals in spring, its best season, followed by late summer (41%).  Mid-summer and fall treatments killed about 20% of individuals.  In two previous trials, spring cutting and regrowth spraying performed far better, killing > 65% of shrubs.  It is not clear why its success declined in this study.  Increasing shrub size reduced the effectiveness of cutting/regrowth spraying, but had no effect on cutting/stump painting.  Shrub size produced patterns of regrowth that differed by season under the cutting/regrowth spraying treatment.  In addition to making a comparison of the two treatments, this study reveals that the widespread practice of cutting shrubs and spraying regrowth without regard to season is largely a wasted effort.