Michael Smart and Michael Grodowitz
February 13, 2008

No funding was provided in either the Corps' or USDA budgets for aquatic plant related efforts in Lake Gaston during FY 07. A Technical Report describing the results of FY06 efforts was prepared and submitted to APHIS and the Weed Control Council in September, 2007.

Other funds were used to finance a site visit in September, 2007 for the purpose of evaluating test plantings and grass carp exclosures installed in 2006. During this trip we took the opportunity to visit the Caledonia prison farm to evaluate ongoing efforts to rear hydrilla biocontrol insects and produce nursery-grown aquatic plant propagules for use in future restoration efforts. In addition we continued observations on a 2006 study comparing the growth of monoecious and dioecious hydrilla biotypes. Funding provided under the Corps' APCRP was used to continue work with hydrilla flies on monoecious hydrilla.

Grass carp monitoring (funded in 2006) continued during 2007 and will be reported elsewhere.

Test plantings were conducted in 2006 at three sites: Flat Creek, Hubquarter Creek, and Lizard Creek. Test plantings included three floating leaved species (water shield, water lily, and American lotus) and five submersed species (American pondweed, Illinois pondweed, coontail, southern naiad, and wild celery). Both northern and southern ecotypes of wild celery were evaluated. All of the species had exhibited growth within protective exclosures at all sites during 2006. In September 2007, results differed by site and species.

Flat Creek: Hydrilla was prevalent throughout the site. Water shield, southern wild celery and white water lily, and American lotus persisted in some of the exclosures. Only American pondweed and Illinois pondweed survived in all of the 2006-planted exclosures. Both of these species and American lotus exhibited spread beyond the exclosures.

Hubquarter Creek: There was some water shield present at the site, no hydrilla. This site may have been treated in 2007. Water shield, American pondweed, Illinois pondweed, and white water lily, persisted in some of the exclosures. Only American lotus survived in all of the 2006-planted exclosures and this species exhibited considerable spread beyond the exclosures.

Lizard Creek: All of the 2006 plantings survived within the exclosures. In addition we observed considerable spread (beyond the exclosures) of American lotus, Illinois pondweed, and southern wild celery. We also observed one colony of American pondweed growing within a colony of American lotus. Coontail and water shield were prevalent in the area, but there was little/no hydrilla.

These results indicate that several of the tested native species are good candidates for restoration of native aquatic plants in Lake Gaston.

Grass carp exclosures, evaluated in 2006 showed evidence of grazing in only one (Site #1) of the 12 sites. Three of the sites (#s 9, 11, and 12) had been treated in 2006, however. In September, 2007, we observed a reduction in percent cover of unprotected hydrilla in two sites (Sites # 1 and 3). However, we observed a change in species composition (from hydrilla to chara) at sites #9 and 10, and in the unprotected plot at site #12. We also observed reductions in hydrilla canopy height at two additional sites (# 4 and 5). These results suggest that the grass carp were having more of an effect on hydrilla in 2007 than in 2006. Of the 12 sites only three (#6, 7, and 8) showed no difference in hydrilla growth between the protected and unprotected plots.

The Caledonia prison farm aquatic plant nursery is not quite as far along as we had hoped. A lack of funding prevented us from providing the level of technical support and oversight required. Problems with water quality and sediment fertility hampered production of aquatic plants in 2007, but we believe that these problems have been resolved and anticipate production of useable plant propagules during 2008.

Monoecious and dioecious hydrilla biotypes were grown in mesocosms located at the Lewisville Aquatic Ecosystem Research Facility in Lewisville, Texas to compare the phenology of the two types. During the first year of growth both biotypes produced similar amounts of shoot biomass. The monoecious biotype senesced and produced an abundance of turions in late fall. The dioecious biotype did not. Both biotypes produced tubers. During the spring of the second year most of the monoecious tubers sprouted whereas only about half of the dioecious tubers sprouted and that did not occur until midsummer. During the fall of the second year the monoecious biotype produced large numbers of tubers and some turions, while the dioecious biotype did not produce many turions. In a separate experiment, only about 5% of monoecious shoot fragments collected in the fall settled and rooted compared to 80% for dioecious fragments.

Hydrilla fly rearing on monoecious hydrilla was a focus of 2007 biocontrol efforts. A laboratory/greenhouse colony was initiated at ERDC using standard rearing procedures. The colony has gone through several generations though numbers during the winter have been low due to the difficulty of obtaining monoecious plant material. Monoecious hydrilla has proven to be difficult to culture under greenhouse conditions during the winter months in Vicksburg, MS. Also, a monoecious hydrilla pond was started at LAERF. Flies moved over readily during late summer from nearby dioecious hydrilla ponds but numbers remained low.

The Caledonia prison farm fly rearing facility experienced difficulties with water quality, precluding the development of high quality hydrilla in their ponds. As a result fly populations did not develop during 2007. Steps have been taken to rectify the situation and production is expected to commence in 2008.

Establishment and over-wintering of the flies continues to be evaluated. A brief visit to previous release sites was made in September, 2007. Unfortunately, the entire larger site could not be examined for establishment because suitable transportation was unavailable. Additional observations are needed to confirm establishment.

A single release of about 2,000 to 5,000 flies was made in late September, 2007, at the second original release site from insects reared on monoecious hydrilla at ERDC. This was done late in the season so establishment could not be determined.