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FORAGE & GRAZING LANDS

Growth and Complexity of White Clover Stolons in Response to Biotic and Abiotic Stress

USDA-ARS Pasture Systems and Watershed Management Research Unit, Curtin Road, University Park, PA 16802-3702

^* Corresponding author (mas44{at}psu.edu).

White clover (Trifolium repens L.) persists in pastures mainly by stolon growth. Morphologically complex (i.e., highly branched stolons) plants of white clover generally persist longer. We hypothesized that biotic and abiotic stresses limit white clover production on grazing lands by fragmenting plants into smaller, less competitive individuals. We measured changes in the size and structure of plants in a white clover–orchardgrass (Dactylis glomerata L.) sward during a drought (1999) and a favorable growing season (2000) in grazed pastures on a southeastern Pennsylvania farm. A natural infestation of clover root curculio [Sitona hispidulus (Fabricus)] and blue clover weevil [Ischnopterapion virens (Herbst)] provided an opportunity to examine the interaction of abiotic and biotic stress on stolon structure. White clover plants were dug from two orchardgrass (‘Pennlate’)–white clover (‘Will’) pastures during April to November 1999 and 2000. Stolon structure and damage from blue weevil and curculio larvae were determined monthly. Drought in 1999 reduced stolon production, branching, and rooting in white clover. Stolon length (cm m^-2) in 1999 was 50% of that in 2000. Clover root curculio damaged up to 25% of clover roots and 20 to 40% of stolons were damaged by weevils. Insect damage was greatest on primary stolons. With favorable rainfall during late 1999 and in 2000, white clover recovered from fragmentation and produced nearly twice the stolon length, mass, and density in the next grazing season despite insect damage levels of 10 to 30%. Climate and biotic stresses are the major factors controlling oscillations of white clover stolon density in pastures of the northeastern USA.