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Effect of Leaf Removal at Four Stages of Growth on Yield of Castorbeans¹

Removal of castorbean (Ricinus communis L.) leaves at four growth stages at the rates of 1/4, 1/2, 3/4, and total defoliation resulted in lower yields than the check. Differences between most partial defoliation treatments were not large enough to be significant. Stage of growth when partial defoliation treatments were applied had no significant effect on yield. Total plant defoliation at each of the four dates resulted in yields that were significantly lower than the check. Differences between dates were also significant. Regrowth following the first two total defoliations produced yields that were adequate to justify continuation of fields under farm conditions. Best yield recovery occurred following defoliation at the bloom stage of the primary raceme.

Alternaria leaf spot [Alternarla ricini (Yoshii) Hansford] infection occurred after tertiary racemes started blooming but before quaternary racemes started blooming

Key Words: Ricinus communis L. • hail • defoliation • Alternaria leaf spot [Alternaria ricini (Yoshii) Hansford]

² Research Agronomist, University of Arizona Cotton Research Center, Crops Research Division, ARS, USDA, formerly Assistant Professor, University of Nebraska; and Associate Professor, University of Nebraska, Lincoln.

Received for publication March 7, 1967.