An area of a shrink-swell clay soil (Tunica clay, Vertic Haplaquept) with an established population of redvine, trumpetcreeper, honeyvine milkweed, redberry moonseed, and maypop passionflower was treated with dicamba once in the fall of 1983. The effect on perennial vines was determined for the following 4 yr in three rotational cropping systems involving winter wheat, soybean, corn, and sorghum, all with and without irrigation. Dicamba reduced the population of perennial vines 80% over 4 yr. Redvine and trumpetcreeper, the first and second most abundant species, were reduced by over 83 and 76%, respectively. Yield of soybean increased 17% in 1985 and 1987 while corn yield increased 9% in 1986 with dicamba use. In 1984 no effects on crop yield were measured. This inconsistent crop yield reponse after dicamba treatment, even though perennial vines were suppressed, must be considered in evaluating the economics of using dicamba for perennial vine control.

Studies were conducted to evaluate seed and root reproduction and herbicide sensitivity of maypop passionflower (Passiflora incarnata L. ♯ PAQIN). Water-leached seeds that were not exposed to light had the greatest germination (53%). Depending on soil type, seedlings emerged from depths of 10 to 12 cm. Most rapid germination and seedling development occurred between 30 and 35 C. Plants rapidly produced an extensive system of lateral roots and rhizomes that had regenerative capability at maturity. Root or rhizome sections of only 0.5 cm in length had a 20% regeneration rate. Desiccation effectively reduced viability of root and rhizome pieces. Effective herbicide control was limited to the triethylamine salt of triclopyr {[(3,5,6-trichloro-2-pyridinyl)oxy] acetic acid} at 2.2 ai kg/ha, alkanolamine salt of 2,4-D [(2,4-dichlorophenoxy)acetic acid] at 1.7 kg/ha, and dicamba (3,6-dichloro-o-anisic acid) at 0.3 to 0.6 kg/ha.