Some Effects of 2,4-Dichlorophenoxy Acetic Acid and Related Compounds on the Grapevine

¹ Department of Viticulture and Enology University of California, Davis

1. Drops containing 2,4-D in range from 0.00001 fo 600 µg were placed on April 13, 1954, at the base of the upper surface of leaf blades of young Tokay shoots 1 to 2 inches long. The fourth or fifth leaf from the base was treated. Two weeks after treatment 2,4-D in range from 1 to 600 µg resulted in abnormal venation of leaves on the apical 6 inches of the shoots.

2. In other experiments drops containing 2,4-D were placed at the base of leaves near the base of shoots 12 to 18 inches long. It usually took 10 µg to injure the shoots. When the apices of young Tokay shoots were treated, 0.1 µg resulted in abnormal venation in many of the shoots.

3. Tokay vines were sprayed on April 25, May 19, and June 7 with 2,4-D at 0, 0.2, 2, 20, 200, or 2000 ppm, except that The 200 and 2000 ppm concentrations were omitted at The last spraying. Concentrations of 200 or 2000 ppm killed the foliage, although water sprouts developed. The second treatment was more toxic than the first. Little injury to foliage resulted from the third treatment. In both treatments clusters were killed by 2,4-D at 200 or 2000 ppm, and at 20 ppm weight of clusters was reduced, partly because the berries were stunted.

4. The effect of 2,4-D drift into vineyards on shoot development, carbohydrate storage, and fruiting was observed. With drifts early in the growing season, which reduce crop but do not destroy the shoots, the vines recover rapidly. In French Colombard, Palomino, and Valdepenas in a coastal vineyard, production approximated 86 per cent of a normal crop the year following severe early-season injury.

5. A 5 per cent suspension of Norit A sprayed on vines gave appreciable protection against 2,4-D subsequently applied. Dowax 222 and VL 600 gave no protection.

6. A University vineyard at Davis was apparently uniformly affected by drifting 2,4-D. The sensitivity of the different varieties was classified into four groups according to the degree of injury. Similar observations were made in the Martini Vineyard at Napa into which 2,4-D had drifted.

7. The apical 6 inches of Tokay shoots about 12 inches long were dipped in solulions containing 2,4-D, 2,4-DP, 2,4,5-T, 2,4,5-TP, 4-CPA, or 4-CPP at concentrations varying from 0.0001 to 100 ppm. The propionic homologues of 2,4-D and 2,4,5-T were more toxic than the acetic, but the reverse was true in the case of 4-CPA. 2,4,5-T was more toxic than 2,4-D, and 4-CPA was the least toxic compound.

8. Muscat of Alexandria vines were sprayed on August 9, 1954, with 2,4-D, 2,4-DP, 2,4,5-T, 2,4,5-TP, 4-CPA, and 4-CPP at 0, 5, 20, or 50 ppm. In this experiment 2,4-DP was less toxic than 2,4-D. A similar experiment using 100 and 300 ppm of the compounds showed that 2,4-D and 2,4,5-T were about equally toxic.