Controlling Kudzu in CRP Stands
David J. Moorhead, Forester, Extension Forest Resources, The University of Georgia
Kevin D. Johnson, Forester, Forest Management, Georgia Forestry Commission
Introduced to the United States at the turn of the century from Japan, kudzu, Pueraria lobata, was extensively planted throughout much of the southeast as an ornamental plant, for a forage crop, and most importantly for erosion control. Kudzu's rapid growth of up to several feet a day, made it ideal for stabilizing ditches, gullies and steep slopes. Once widely promoted, kudzu can be a serious pest of CRP pines and control is difficult and expensive.
Kudzu is a perennial, leguminous vine. It is deciduous, losing its leaves in the fall following a killing frost. Fragrant purple flowers form in late June to early July on vines draped three feet or higher into trees, fences and other objects. Flowers are rarely produced in open patches on flat ground. The hard-coated seeds can remain viable for several years before they germinate. Burning scarifies the hard seed coat permitting germination.
Vines grow from buds on a root crown at the soil surface. As the vines spread, rooting occurs from buds at each node on a vine. With vine growth of up to 50 feet in a single growing season, a single plant can spread to cover large areas each year. Roots developing from the vine nodes usually enlarge into root crowns from which additional vines will arise. Mature stands of kudzu may have root crowns every 1 to 2 square feet.
Roots of the established crowns can reach several inches in diameter and may grow to depths of three feet. They have a high starch content that supports early spring growth and regrowth if vines are damaged by mowing or grazing in the summer. The fleshy, starch-rich roots make control difficult because this stored food reserve supports regrowth. To completely eradicate kudzu, it can take three to ten years of repeated treatments to deplete root reserves.
Most kudzu infestations in CRP pines originate from old, well-established root stocks at field edges, and/or in older stands next to fields. Annual cultivation once kept vines from running into the fields. Once trees were established, runner vines can invade the young pine stands. So control is necessary, not only in the young pines, but in the adjacent field borders as well.
With a large root system packed with starch and aggressive growth habit, eradication of kudzu requires persistent treatment. Several strategies can be employed to eradicate kudzu, including herbicides, prescribed burning, mowing, and livestock grazing. When selecting control strategy consider restraints which may prevent broadcast applications of herbicides, use of tractors to spray, or mow, and the presence of desirable vegetation in the patch. Because kudzu can reach depths of four feet or greater, the thick mat of vines and leaves can hide gullies, ditches, logs, wells and other hazards. Carefully check the site after a prescribed burn, or in winter or early spring when the leaves have fallen to determine if obstacles to application exist.
Mowing - Repeated mowing can weaken and ultimately control kudzu. Mowing is generally a good first step towards control, provided it can be done without risk to the tractor operator. Close mowing reduces the tangle of leaves and vines and treatment of regrowth is much easier accomplished. Thick mats of vines are often difficult to mow with light-duty rotary mowers. Flail mowers with horizontal blades cutting in a chopping action may operate more effectively.
Grazing - Using kudzu as a forage for cattle and other livestock was an early promotion with its introduction into the U.S. Kudzu hay has excellent nutritional value and is palatable to livestock. To control kudzu by grazing it is necessary to adequately fence the entire patch and to provide sufficient additional grazing areas on which to rotate livestock as the kudzu is grazed down. Only by repeatedly grazing the regrowth over successive growing seasons will the root reserves of starch be depleted.
Burning - Prescribed fire can be used to consume vines and leaves to permit inspection of the site and to determine the size and density of the kudzu root crowns. Burning should be done in the winter or early spring. Using spring burns limits exposure of bare soil to winter rains minimizing soil erosion on steep slopes. Prescribed burning is useful in promoting seed germination prior to a herbicide treatment.
Herbicides - Application of herbicides is a common and expensive option to control kudzu. Several herbicides are labeled for kudzu control (Table 1). Their use requires careful site evaluation and prescription in accordance to the information contained on the manufacturers pesticide label. Herbicides can be used in combination with other treatments such as prescribed fire, mowing, or following grazing which reduces the lush vegetation and allows easier application to somewhat weakened plants.
PERSISTENCE!! - Each individual crown must be controlled in a patch, otherwise the rapid spread from even a single crown will negate all prior eradication efforts. All of the herbicide treatments listed above require follow up spot treatments for several years after initial application to completely eradicate kudzu.
Table 1. Herbicides for kudzu control.