Control of Globodera pallida Using Brassica juncea Seed Meal Extract and the Trap Crop Solanum sisymbriifolium

Globodera pallida, the pale cyst nematode, is a regulated potato pest which is economically detrimental. Restrictions on use of the soil fumigant methyl bromide and lack of resistant russet type varieties for U.S. markets have led to investigations of alternative strategies to control this pest. The efficacy of Brassica juncea seed meal extract (SME; 0, 0.14, 0.28, 0.56, 1.12, and 2.24 t/ha) was studied, either alone or in combination with the trap crop Solanum sisymbriifolium under greenhouse and field conditions. The impact of the application of SME pre- or postplanting of S. sisymbriifolium was also determined. S. sisymbriifolium only induced hatch of G. pallida and significantly fewer (up to 57 and 55% in pre- and postplant experiments, respectively) encysted eggs remained at termination of the experiment compared with the untreated control. However, when SME was applied preplant, the encysted eggs remained unchanged, which may indicate that SME inhibited egg hatch in the presence of S. sisymbriifolium. When applied individually, S. sisymbriifolium in all experiments, or SME at all rates tested in the greenhouse or 0.56 t/ha or higher rates of SME in the field, significantly reduced the viability, hatch, and reproduction of G. pallida. Combined treatment with S. sisymbriifolium and SME at lower rates (0.14 t/ha for preplant or 0.56 t/ha or less for the greenhouse postplant experiment) reduced G. pallida egg hatch further than each strategy alone. In the field, a combination of S. sisymbriifolium and SME at 1.12 t/ha or less reduced G. pallida more effectively than SME alone. SME alone applied at higher rates (0.56 and 1.12 t/ha) in preplant greenhouse trials, whether or not combined with S. sisymbriifolium, eliminated G. pallida reproduction. Under field conditions, SME applied at a rate of 1.12 t/ha highly reduced G. pallida reproduction compared with the untreated control by 97 and 61% in 2019 and 2020, respectively. Furthermore, reproduction of G. pallida was eliminated when SME was combined with S. sisymbriifolium. Our results indicated that a combination of SME and S. sisymbriifolium reduces the amount of SME needed to control G. pallida and further decreases the potential reserve of the viable population remaining after individual treatment with each strategy.