G.L. Graham and G. Chiasson
Partner: Bleuets NB Blueberries
Abstract: Lambkill (Kalmia angustifolia) and rhodora (Rhododendron canadense) are potentially difficult weeds to control in wild
blueberry fields. Weed control and crop injury can be variable at registered rates of dicamba and 2,4-D ester, so a full evaluation of registered and
reduced herbicide rates is needed. A trial was established in the fall of 2008 in the sprout year of a newly developed blueberry field that had been pruned
in two consecutive years. The trial design was a randomized complete block design with two treatment factors. The first treatment factor was dicamba rate
(0, 1100 g ai/ha, 2200 g ai/ha and 3400 g ai/ha) and the second was 2,4-D ester rate (0, 1980 g ai/ha, 3400 g ai/ha), for a total of twelve distinct treatments.
Increased crop injury was demonstrated as the rate of either herbicide was increased. Crop injury improved to commercially acceptable levels as the trial
progressed. At least 2.2 kg/ai/ha dicamba was required for lambkill control, while 2,4-D alone had limited lambkill control after the initial rating date. A low
rate of dicamba suppressed rhodora, where adding 2,4-D ester improved control. Higher rates of dicamba did not show an improvement in rhodora control when 2,4-D
ester was added. The labelled rate ranges for dicamba were the most effective tested.