Field studies were conducted in commercial muscadine vineyards in western North Carolina in 2018 and eastern North Carolina in 2019, 2020, and 2021 to determine tolerance of younger (< 9 yr) and older (≥ 9 yr) bearing muscadine grapevines to 2,4-D directed beneath the crop postemergence (POST). Treatments included 2,4-D choline at 0, 0.53, 1.06, 1.60, and 2.13 kg ae ha−1 applied as a single treatment in May or June (spring) at immediate pre-bloom, and sequential treatments at 0.53 followed by (fb) 0.53, 1.06 fb 1.06, 1.6 fb 1.6, or 2.13 fb 2.13 kg ha−1. The first sequential treatment was applied in spring fb another application of the same amount in July (summer) at pre-veraison. No differences in injury on muscadine grapevines were observed from 2,4-D treatments. Differences among treatments were not observed for yield of younger vines. However, for older vines, a difference due to 2,4-D rate was observed in 2018, when yield was higher when 2,4-D was applied at 1.6 kg ha−1 compared with nontreated grapevines, and when 2,4-D was applied at 0.53 and 2.13 kg ha−1. A rate-by-timing interaction was observed in 2019 when yield was lower from 0.53 kg ha−1 2,4-D summer application compared with all other summer treatments but similar to the nontreated. However, no biological pattern was observed from either of these differences. No differences among treatments were observed for fruit pH, titratable acidity, or soluble solid content of either younger or older vines.

Field studies were conducted on southern highbush blueberry in Elizabethtown and Rocky Point, NC, in 2019, 2020, and 2021 to determine tolerance to 2,4-D choline as a postemergence-directed application. In separate trials for younger and older bearing blueberry bushes, both 2,4-D choline rates and application timing were evaluated. Treatments included 2,4-D choline at 0, 0.53, 1.06, 1.60, and 2.13 kg ae ha–1 applied alone in winter during dormancy, and sequential treatments at 0.53 kg ae ha–1 followed by (fb) 0.53, 1.06 fb 1.06, 1.6 fb 1.6, or 2.13 fb 2.13 kg ae ha–1. The first application of the sequential treatments was applied in winter followed by another application in spring during early green fruit. Injury to blueberry from 2,4-D choline treatments was not observed for either maturity stage, and fruit yield was not affected by any of the treatments. Differences among treatments were not observed for fruit soluble solid content (SSC) in older bushes, or for fruit pH, SSC, and titratable acidity (TA) in younger bushes. In older bushes, fruit pH and TA had rate-by-timing interactions, and TA had a farm-year interaction with differences at Rocky Point in 2019 and Elizabethtown in 2020, but biologically no pattern was observed from the treatments.