THE FLORIDA CATTLEMAN AND LIVESTOCK JOURNAL
Thinning the Pawpaw Patch
by Brent Sellers and Jay Ferrell
For questions or comments regarding this publication contact: Dr. Brent Sellers, University of Florida, IFAS
Pawpaws (Asimina spp.) are members of the custard family, and 10 species are known to occur in the state. Of these 10, fourpetal pawpaw (Asimina tetramera) is on the endangered species list, but this species is found primarily in coastal pine scrub habitats in Martin and Palm Beach counties. While pawpaw species are native, serve as a host for the zebra swallowtail butterfly, and edible, they can become problematic in grazing areas (Figure 1). In fact, the problem seems to be increasing since we have had more calls on these species this year than in the past.
Most pawpaw species in south Florida are considered to be small shrubs and are 2-4 feet tall (Figure 2). These woody species are usually multi-stemmed and stems arise from a very deep taproot that can be as big as 3 inches in diameter (Figure 3). Leaves are present from early April through October, but may exist through December in some areas of the state. Flowering occurs in April to May and seed production is reportedly low. Flowering often occurs prior to leaf-out in the spring (Figure 4) out.
|Figure 1. Illustration of pawpaw plants invading a pasture. Photograph by B. Sellers.||Figure 2. Pawpaws are typically small shrubs that range from 2 to 4 feet tall in pastures. Photograph by B. Sellers.|
|Figure 3. Pawpaw roots have a very large taproot, and once established are extremely difficult to control.||Figure 4. Flower formation in pawpaw typically occurs before leaves begin to grow in the spring. Photograph by B. Sellers.|
As with lantana, pawpaw control appears to be somewhat difficult. Mowing typically results in an increase in the number of stems, and hand digging is likely the only “mechanical” method of removing pawpaw plants from improved pastures as they do not tolerate root cutting. Considering the long and deep taproot of pawpaw, control with a single herbicide application should not be expected.
Experiments were conducted in a pasture that was heavily infested with pawpaw in central Florida. Herbicide treatments included triclopyr (Remedy Ultra) at 1 qt/A, triclopyr at 1 qt/A followed by triclopyr at 1 qt/A 6 months later, Pasturegard HL at 1 qt/A, and Pasturegard HL at 1 qt/A followed by an additional 1 qt/A 6 months later; methylated seed oil (MSO) was added to each spray mixture at 1% v/v. The initial treatment was applied in May and the sequential treatments were applied in late November. To evaluate the level of pawpaw control, the number of pawpaw stems was counted in each plot on the day of application, 6 months after treatment (MAT), and 12 MAT.
Living stems in plots at 6 MAT were very low at 6 MAT (at the time of the sequential application), with all treatments providing >90% reduction in stems compared to pre-treatment numbers. However, stems densities increased by 12 MAT (6 months after sequential treatment). A single application of Remedy or Pasturegard HL resulted in 49 and 40% less stems compared to pretreatment stem counts, respectively. A sequential application of either herbicide resulted in >70% reduction in pawpaw stems counts compared to pre-treatment levels. Although stem densities did not differ between Remedy and Pasturegard HL plots, pawpaw plants were typically shorter in plots treated with Pasturegard HL, indicating that regrowth of pawpaw plants was slower when treated with this herbicide compared to triclopyr.
In a separate study, these same treatments were applied in late November, but virtually no reduction in living stems was observed 6 MAT. This indicates that early spring (April to May) application may be the best application timing for this species.