Weed of the Month: Maypop Passionflower

Published: August 4, 2010

Figure 1. Maypop passionflower seedling.

Maypop Passionflower (Passiflora incarnata) is a fast-growing perennial vine that is often planted as an ornamental due to its attractive, showy flowers. In recent years, maypop passionflower has escaped cultivation to become a problematic weed in many areas such as no-till agronomic crops, pastures, hay fields, and roadsides. Maypop passionflower is also known as wild passionflower, purple passionflower, or white sarsaparilla, and is a native of the southeastern United States.

Maypop passionflower seedlings have cotyledons that are very thick and have a waxy appearance along with the first true leaf, which is often heart-shaped (Figure 1). Seedlings are rarely encountered, however, as new maypop passionflower sprouts more commonly arise from the underground perennial rootstocks. After the first true leaves have emerged, the remaining leaves are arranged alternately along the stem, are about 2 ½ to 6 inches in length and 5 to 6 inches in width, and are typically divided into three to five lobes that each originate from a common point (Figure 2).

Figure 2. Mature maypop passionflower growing in a pasture.Image from Iowa State University.

The stems of passionflower are green and can be either smooth or covered in short hairs. Stems also have tendrils that help the plant to climb onto and over nearby objects. The heights of the stems vary greatly depending on what structure is supporting the plant.

Maypop passionflower has showy flowers that are white to bright pink or purple in color and usually 2 to 3 inches in diameter (Figure 3). Numerous flowers emerge from the leaf axils and in Missouri, flowers can occur from July to September.

Figure 3. Flowers of maypop passionflower

The fruit of maypop passionflower are also very distinctive. The fruit are generally egg-shaped to round in outline, ranging in size from slightly larger to a hen's egg to the size of a baseball. Initially the fruit are green in color but become yellowish-red with maturity. Some claim the name "maypop" comes from the popping sound the immature fruit make when you step on them.

Due to their thick, deep rhizomes, mechanical or cultural control of maypop passionflower can be very difficult. With perennial species that have deep underground rootstocks and/ or rhizomes, tillage often serves to break up the perennial rootstocks which can then regenerate and ultimately produce larger infestation. This is certainly the case with maypop passionflower; Wehtje et al. (1985) found that approximately 80% of rhizomes that were cut into 1-inch segments were able to regenerate and form brand new plants.

Figure 4. Maypop passionflower fruit.

Very little information has been published on the control of maypop passionflower with herbicides. In a pasture or hay field setting, some research has shown that higher rates of 2,4-D (sold as a variety of trade names), triclopyr (in Remedy, Garlon, PastureGard, and Crossbow), picloram (in Tordon, Grazon P+D, and Surmount) and dicamba (in Banvel, Clarity, Weedmaster, etc.) should provide good control of maypop passionflower. In fencerows, landscapes, or other areas where spot spraying is acceptable, a 1 to 5% solution of glyphosate should also provide good control of maypop passionflower.