Seed Yield and Oil Content of Cuphea as Affected by Harvest Date

Received for publication September 1, 2004. Cuphea (Cuphea viscosissima Jacq. x C. lanceolata W.T. Aiton) can serve as an oilseed crop substitute for small- and medium-chain triglycerides, which are in high demand for chemical manufacturing. Domesticated genotypes of cuphea show good potential for agricultural production, but their indeterminate growth may result in seed shatter if left in the field too long. Little information exists on when to harvest cuphea to obtain greatest seed yield and oil content. A study was conducted on a Barnes soil in west-central Minnesota to determine the best time to harvest cuphea when sown at an optimum time in the spring. Harvests were taken at 1- to 2-wk intervals from mid-August through mid-October during 2001 and 2002. Seed yields were greatest within a time period of about 20 d in late September to early October. Soon after a killing frost ((less than)–2°C), 5 October in 2001 and 9 October in 2002, yield declined sharply at a rate of about 10.6 kg ha^–1 d^–1, probably due to increased shattering. However, shattering due to mechanical harvesting was greater than that from natural causes. Total seed oil content also was influenced by harvest date. Across years, oil content averaged 247 g kg^–1 in August, increasing to 304 g kg^–1 by late September and thereafter. For greatest seed yield and oil content, the optimum time to harvest cuphea is in late September to early October in west-central Minnesota. However, until more shatter-resistant, determinate genotypes are developed, improved harvest management is needed to reduce shatter-induced yield los