Control of Black Vine Weevil 

 in Potted Nursery Plants 



DR.. STANLEY R. SWIER, ALAN ROLLINS, RACHAEL LAMARCHE, AND MEGGAN HODGSON 



C'ontrol of the black vine weevil is very difficult. 

 The weevil emerges from overwintering sites in 

 spring and seeks out host plants. The adult chews on 

 leaves, causing characteristic notches. These notches 

 are particularly common on taxus and rhododendron. 

 The larvae feed on the roots, reducing growth and 

 predisposing the plant to 

 winter kill. If the plants 

 are kept warm, larvae 

 will feed during the win- 

 ter. Since the adult is 

 active all summer, con- 

 trolling the adult re- 

 quires frequent sprays 

 to the foliage through- 

 out the growing season. 

 A better strategy is to 

 target the larvae which 

 do the most severe dam- 

 age. We investigated some 

 promising chemical and 

 biological controls for 

 larval control in 1997. 

 Van Berkum's Nursery 

 generously provided us 

 with 160 potted plants 

 (Bridget bloom, Heucherella 

 alba) at no cost. FMC 

 Corp. provided financial 

 support for labor. Nema- 

 todes were obtained from 

 The Green Spot. The 



black vine weevil eggs were obtained from the Con- 

 necticut Agricultural Experiment Station in Windsor. 

 The trial was conducted at the UNH Kingman Farm. 



Ten replications of six treatments were applied to 

 seven-inch pots. Talstar granules were incorporated 

 into the media based on the bulk density (0.24 g/cc). 

 Merit was applied according to pot size. Both these 

 granules were incorporated into the pots on June 10 

 and the plants repotted. Surface applications of Tal- 

 star Flowable and Lorsban granules were done on 

 June 30. The first application of nematodes was ap- 

 plied July 13 and repeated every two weeks for a to- 

 tal of four applications. We chose the nematode 

 Heterorhabditis bacteriophora because of its ability to ac- 

 tively seek out prey in soil. The liquid formulations 

 and nematodes were poured over the surface of the 



Means followed by the same number are not significantly 

 different (p=0.05, Scheffe) 



1. 132 ml of solid ion /pot 2. Four applications 



pot. All granular formulations and nematodes were 

 watered in after treatment. Since the weevil larvae 

 are sensitive to heat, the pots were buried in soil to 

 the rim. Pots were shaded with 60% black green- 

 house shading material suspended eight feet above 

 the pots. Plants were watered as necessary. Over 

 50,000 black vine 

 weevil eggs were 

 placed in the pots on 

 June 30 and August 

 20. On October 17, 

 the pots were re- 

 moved from the soil 

 and checked for live 

 larvae. 



As you can see 

 from the table, Talstar 



F, Lorsban (Dursban) 



G, and the nematodes 

 performed well. Merit 

 (Marathon) gave fair 

 control. We have 

 shown that nema- 

 todes worked well 

 under these condi- 

 tions. Potted media 

 lacks nematode pred- 

 ators and has suffi- 

 cient pore space for 

 nematode movement. 

 Nematodes applied to 

 dense soils may not 



work as well. Excellent control may have been pos- 

 sible with fewer applications of nematodes, but sev- 

 eral applications are usually necessary to account for 

 nematode mortality. The granular formulation of 

 Talstar has been reported to give black vine weevil 

 control for two years once incorporated in the media. 

 Its failure in this test may be to some unusual prop- 

 erties of the media or other unknown factors. These 

 data are the results of limited research trials for your 

 information. When using these pesticides, you must 

 follow all label directions. UNH Cooperative Exten- 

 sion does not endorse these or discriminate against 

 other such products. 



Stan Swier, entomology specialist, UNH Cooperative Ex- 

 tension, is at 603-862-1733. 



)UNE. JULY. 1998 



