Dry-matter Accumulation, Partitioning, and Development of Alfalfa Regrowth After Stubble Defoliation by the Variegated Cutworm (Lepidoptera: Noctuidae)

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Abstract
The impact of stubble feeding by Peridroma saucia (Hübner) on alfalfa growth, development, and dry-matter partitioning during the second growth cycle was investigated in a 3-year study. Densities of more than six larvae per 0.1 m2 completely suppressed regrowth and caused significant delays in the development of subsequent regrowth. Lower densities only partly suppressed regrowth and did not consistently delay plant development. Larval damage produced large reductions in stem density during the first 2 to 3 weeks of regrowth, but these reductions were transitory and did not persist after the third week. Densities of 1.5 and 3 larvae per 0.1 m2 did not consistently affect growth rates or partitioning of subsequent regrowth; densities of ≥6 larvae per 0.1 m2 caused regrowth to produce stem height at a significantly faster rate. The rate of production of main-stem nodes was not affected, and the production of leaves per stem declined significantly. Larval damage also suppressed daily rates of dry-matter production. Most of this reduction, however, was caused by a reduction in the support component of growth. Leaf growth rate was not suppressed, and leaf area production actually increased in severely defoliated treatments. Damaged plants produced more leaf area per unit of total dry weight through relative increases in both leaf weight per unit of total dry weight and leaf area per unit of leaf weight. Damaged plants seemed to minimize the adverse effects of P. saucia stubble feeding by maintaining growth rates of leaves at the expense of support structures.