Effect of dormant-season applications of 2,4-D on pruned and nonpruned Tokay grapes

In one experiment, Tokay grapevines pruned in December were sprayed 16 days later with either a water- or oil-soluble amine of 2,4-D at various concentrations. Spray was applied to vine plus soil, base of trunk plus soil, and soil only. An ester form at 10,000 ppm was applied to soil only. Spray treatments using the water-soluble amine were repeated on another series of vines in February. All treatments were repeated on unpruned vines.

Both oil- and water-soluble forms at 2,500 or 10,000 ppm, sprayed on pruned vines plus soil in December markedly delayed bud break. Fewer formative effects were found following the February treatments. Cluster appearance, crop weight, berry size, Balling reading, total acid, and pruned brush weight were not significantly affected except that some clusters had a few shot berries.

Sprayed, nonpruned vines were not significantly affected with respect to number of shoots, brush weight, crop weight, or fruit quality; however, a few formative effects were produced by some treatments.

Two tests with drop applications of 2,4-D at concentrations of 10 to 500,000 ppm were made during the dormant season. In one test, treatments were applied to pruning cuts, buds, or internodes of the spurs. Greatest delay in bud break and severest injury to shoots resulted from application to the pruning cut. Internode treatment showed least damage and delay. In a second test, 2,4-D at 1,000 ppm was applied to pruning cuts at various intervals after pruning. A delay of 11 days resulted in much less injury than occurred when treatments were applied immediately after pruning.