Use of Boron for the Control of Eutypa Dieback of Grapevines

Eutypa dieback is a perennial canker disease of grapevine (Vitis vinifera) caused by Eutypa lata. The fungus produces ascospores, which infect grapevines through pruning wounds during the dormant season. Management of the disease has been achieved with fungicide applications during the dormant period. However, no effective fungicide was available for this purpose after Benlate was withdrawn from the market. Boric acid (17.5% a.i. boron), a potential alternative to Benlate, was tested in the present study against E. lata. The EC₅₀ values for inhibition of mycelial growth and ascospore germination were 125 and 475 μg of boric acid per ml (22 and 83 μg a.i./ml), respectively. Two boron-based treatments were developed and tested in vitro and in four field trials during 2001 to 2003. One product, biopaste, contained 5% boric acid (8.75 mg a.i./ml) in a commercial paste. The second product, bioshield, contained 5% boric acid in a spore suspension of Cladosporium herbarum. Both products significantly reduced disease in vitro and in field trials in comparison with a water control treatment. Boron was not found to accumulate in leaves and shoots, but bud failure at the first node below the treated wound occurred at a higher rate than in untreated vines.