1. Herbicide Application over Hardwood Afforestation site release Morning Glory
Robert Hane1, Joshua Adams1, Michael Blazier2
1School of Agricultural Sciences & Forestry, Louisiana Tech University; 2LSU AgCenter Hill Farm Research Station
Methods
Abstract
Site was ripped late summer before planting
RoundUp (glyphosate) was applied one week prior to planting to remove competition
Winter planting (December 2015) of 5 variations of Hybrid Sweetgum (Liquidambar formosana x styraciflua)
Complete random design
Ground line diameter and height were recorded pre- and post-growing season
Various herbicide timings were applied to each rip (with 5 replications per timing)
Each row received 1 of 4 application timings of Oust XP (sulfometuron methyl)
Early- Before bud swell (January 29)
Mid- just prior to bud swell (Febuary 17)
Late- after bud swell (March 4)
None
Oust XP label does not recommend spraying over Sweetgum after bud swell due to risk of damage to the crop trees
A tally was made in October of Morning Glory infested trees
Herbicide application is an important step in successful hardwood afforestation. The purpose of our genetic herbicide trial was to determine which timing of herbicide application (Oust XP) was the most efficient at controlling the weeds and releasing untested hybrid sweetgum trees planted in Height and ground line diameter were measured for each tree prior to the growing season, and again at the end of the growing season. While taking measurements late in the growing season we noticed some of the trees were partially or completely covered by Smallflower Morning Glory (Jacquemontia tamnifolia). Enough trees were affected to warrant a full tally of the site for Morning Glory and determine if any causes were apparent. Rows receiving a treatment of Oust XP for herbaceous weed control were approximately ten times more likely to be bound by Morning Glory than the seedlings that were not treated with herbicide. Seedlings that were bound by Morning Glory had significantly more diameter growth than unbound seedlings, but there was no statistical difference in the height of the seedlings. Due to the fact that Morning Glory germinates in the summer it was able to take full advantage of the competition-free study plot and overtop the seedlings. It is thought that increased diameter growth exhibits a response to the Morning Glory overtopping seedlings.
Figure 2: Robert Hane spraying Oust XP over hybrid sweetgum
Results
Discussion
Exclusion of weeds early in the growing season led to more cases of Morning Glory later in the growing season
Individual herbicide treatments did not show significant differences
Sweetgum seedlings overtopped by Morning Glory dedicated more resources to diameter growth to support the added weight of the climbing vine
In one growing season height was not affected by Morning Glory, consecutive growing season were not tested
Figure 3: Percent of trees in each treatment affected by Morning Glory
Figure 5: Ground line diameter with and without Morning Glory competition
There was a statistical difference among herbicide treatments and no herbicide control [P=0.028](Figure 3)
Less than 1% of trees in control rows were affected by Morning Glory
When all herbicide timings were combined, the difference between herbicide plots and no herbicide controls was also significant [P=0.004] (Figure 4)
6.7% of trees in herbicide rows were affected by Morning Glory
Morning Glory caused an increase in diameter growth compared to trees unaffected by Morning Glory [P=4.32E-5] (Figure 5)
Trees bound by Morning Glory grew 2.66mm more in diameter than trees unaffected by Morning Glory
Morning Glory did not statistically affect height growth [P=0.86] (Figure 6)
Conclusion
Morning Glory steals sunlight and soil nutrients from crop trees
Morning Glory can stress seedlings and leave them vulnerable to other problems
In the first growing season no height reduction was detected but allocation of resources was already shifting towards diameter growth
At least one year is available to complement herbicide control to prevent negative impacts from future infestations
The benefits of Oust XP should be weighed against the possibility of invasion from other weeds like Morning Glory
Figure 1: Example of Morning Glory interacting with young Hybrid Sweetgum
Figure 4: Percent of trees affected by Morning Glory with and without herbicide application
Figure 6: Height of trees with and without Morning Glory competition