DAMAGE TO GROWTH OF ALFALFA, MEDICAGO SATIVA L., AND ASSOCIATED CARRYOVER EFFECTS CAUSED BY THE POTATO LEAFHOPPER, EMPOASCA FABAE (HARRIS) (TOTAL NONSTRUCTURAL CARBOHYDRATE)

MICHAEL CHARLES SHAW, Purdue University

Abstract

Cage and field studies were conducted to determine the effects of injury from the potato leafhopper (PLH), Empoasca fabae (Harris), on growth of alfalfa, Medicago sativa L., and the time at which these effects occur. Individually caged alfalfa plants were infested with adult PLH populations ranging from 0 to 1.0 per stem when plants were 8 cm tall. Stunting of plants was found to occur early in the growth period of the plants. No significant stem elongation occurred after 11 days of infestation on plants infested with more than 0.75 adults per stem. Stunting was associated with a reduction in mean internode length. PLH damage increased the relative proportion of leaf to stem mass, but reduced total dry matter per stem by as much as 60%. Total nonstructural carbohydrate (TNC) root reserves were reduced by PLH feeding in treatments infested with 0.50 or more adults per stem. Most dry matter and root TNC was accumulated during the later stages of plant development and it was during this period that these parameters were most affected. Effects of PLH damage were not restricted to growth of the infested cutting, but also affected the following cutting by reducing plant vigor associated with TNC reserves in roots. PLH induced carryover effects reduced plant height ca. two weeks following harvest but height was not affected by harvest. TNC concentrations in roots were reduced only during the period of PLH infestation and by harvest of the next cutting were fully recharged. Carryover effects reduced the number of stems per plant on regrowth following harvest by ca. 50%, which in turn reduced plant yield. Field studies were conducted where PLH infestations were controlled at stubble, 5-10 cm and 15-20 cm stages of growth. Although PLH populations were above economic thresholds for each application, root carbohydrate reserves, percent crude protein and total protein yield were protected from loss due to damage from this insect by all treatments.

Degree

Ph.D.

Subject Area

Entomology

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