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Survival and Emergence of Volunteer Castor Seed in Soil¹

Volunteer castor (Ricinus communis L.) seedlings are a severe weed problem in crops grown after castor. Emergence and development of castor were investigated in the greenhouse and field to determine if certain cultural practices would reduce the abundance of volunteer castor seedlings. Castor seed remaining on soil after harvest of dwarf-internode hybrids ranged from 52,000 to 2,260,000 seeds/ha. Seedling emergence was lower when exposed castor seed were subjected to high rainfall (20 cm) during the winter. Seedling emergence was higher the following spring when rainfall was low after harvest. There was no difference in emergence from seed planted in January to May. Plant height and foliar development were suppressed, however, when exposed seed were planted later, indicating that seedling vigor would be lower if soil preparation were delayed after castor harvest. Castor readily emerged from seed planted 20 cm deep in a greenhouse or in the field. Maximum emergence was 84% from seed planted 10 to 20 cm deep in warm sandy loam. Consequently, volunteer castor populations in subsequent crops would be lowest following moist winters and delayed, shallow coverage of seed.

Key Words: Weed establishment • Seed depth

² ~Associate Professor, Texas A&M University Agr. Res. & Ext. Center at Lubbock, Lubbock, Texas 79401.

Received for publication March 21, 1972.