2017 ASHS Annual Conference

Aronia (Photinia melanocarpa) is a deciduous, cold-hardy shrub that has gained popularity due to high concentrations of polyphenols in the fruit and its adaptability in the landscape withstanding harsh Midwestern climates (zones 3 – 8). Since aronia is fairly new to the market, there is limited research evaluating herbicide use on plant establishment. Therefore, the objective of this experiment was to evaluate the effect of preemergent herbicides applied to newly potted container grown aronia plants. Bareroot liners were transplanted on May 25, 2016 into 1 gallon containers (3.785 L) filled with Fafard Mix 52 amended with 19N-1.7P-6.7K, 5 to 6-month control release fertilizer (Harell’s). Three herbicides were applied one day after potting (May 26, 2016) and six weeks after initial application (July 13, 2016): 0.5 lb ai (1×), 1.0 lb ai (2×), and 2.0 lb ai dithiopyr; 0.98 lb ai (1×), 1.97 lb ai (2x), and 3.94 lb ai (4×) dimethenamid-p; 1.0 lb ai (1×), 2.0 lb ai (2×), and 4.0 lb ai (4×) isoxaben. Plants were evaluated at 1, 2, and 4 weeks after treatment (WAT) for phytotoxicity symptoms on a 0 to 10 scale (0 representing no injury and 10 representing complete kill) and at the end of the experiment final growth indices [FGI = ((height + width + perpendicular width) ÷ 3)] was recorded. Application of dithiopyr (all rates) caused slight leaf curling initially, but dissipated overtime with no visible symptoms at the end of the experiment. Plants treated with dimethenamid-p exhibited leaf curling and tip burn with symptoms more pronounced following the second application of dimethenamid-p at the 4× rate. At the end of the experiment, plants treated with dimethenamid-p at 2× and 4× were smaller than 1× and nontreated plants. Phytotoxicity ratings were greater following all isoxaben applications 1 week after initial and second application. Plants receiving isoxaben at the 4× rate had the greatest injury at the termination of the experiment compared with all other treatments. However, isoxaben application did not affect overall growth (FGI) of aronia. In general, phytotoxicity ratings were apparent after initial herbicide applications, but symptoms diminished over time and only dimethenamid-p negatively affected aronia growth compared with nontreated plants. These results will help determine impacts of herbicides for producers of container-grown aronia and allow for more informed management decisions related to herbicide treatments.