PHENOLOGICAL STUDIES OF CARBOHYDRATE ALLOCATION IN HYDRILLA

Hydrilla (Hydrilla verticillata (L.f.) Royle), a nonindigenous submers ed aquatic plant, was first introduced into the United States in the 1 960's. Hydrilla exhibits aggressive growth, forming dense canopies of biomass at the sur-face of the invaded aquatic systems, affecting fish eries, water quality, transportation and recreational usage. Studies o f the phenological seasonal cycles of invasive plants indicate optimal riming to appl!? management techniques. Biomass and total nonstructur al carbohydrate (TNC) allocation of dioecious hydrilla were studied in outdoor ponds in Texas between January 1994 through July 1995. Biomas s increased from Ma! through September growing from overwintering shoo ts and root crowns, lot tubers. Tuber germination occurred in August. Tuber and turion production occurred from October through April. A car bohydrate storage minimum was observed in late July for 1994 and June for 1995, with storage generally split between stolon (7% TNC), root c rown (10% TNC) and lower stem (16% TNC). Tubers and turions ranged fro m 58 to 68% TNC. These studies provide more insight into the timing of major allocation sl.lifts in the hydrilla seasonal growth cycle.