Submitted to: Plant Disease
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/31/2014
Publication Date: 7/1/2014
Citation: Maul, J.E., Himmelstein, J., Everts, K.L. 2014. Impact of five cover crop green manures and Actinovate on Fusarium Wilt of watermelon. Plant Disease. 98(7):965-972. Interpretive Summary: Current triploid watermelon cultivars have little resistance to Fusarium wilt, caused by Fusarium oxysporum f. sp. niveum (FON) and yield losses are increasing in the eastern U.S. A Vicia villosa (hairy vetch) green manure, suppressed watermelon Fusarium wilt in previous trials, but the mechanism of this suppression was unknown. The objective of this experiment was to determine if the V. villosa cover crop suppression of Fusarium wilt was via a general suppression mechanism or by a mechanism specific to hairy vetch. To test this a watermelon production system that employed four cover crops (Vicia villosa, Trifolium incarnatum, Secale cereale, Brassica juncea) and bare fallow treatment were maintainted in 2009-2011 at three locations in the mid-Atlantic region. An additional treatment was the inclusion of a biocontrol product, Actinovate, which is a suspension of the actinomycete Streptomyces lydicus. The cover crops were grown and incorporated as green manures into the soil prior to planting the watermelon. FON was applied three days after transplanting watermelon at the Salisbury location and five days after transplanting in Beltsville. Symptoms of Fusarium wilt, plant vigor, and fruit yield were monitored. Both Vicia villosa and T. incarnatum significantly suppressed Fusarium wilt of watermelon as much as 21%, compared to watermelon in non-amended plots. Trifolium incarnatum was the only cover crop that yielded significantly more fruit than non-amended treatments (129% more fruit/ha), but only in some of the locations. The Actinovate product either did not reduce Fusarium wilt or the magnitude of the reduction was small. These results suggest that the observed suppression of Fusarium wilt, caused by FON, can be mitigated significantly by inclusion of legumionous cover crops in rotation in watermelon production systems. Although general suppression of FON can be observed when cover crops are integrated into watermellon production systems, there is still a need to determine the mechanism of suppression of FON by cover crops. These results can be used by farmers to plan crop rotations in watermelon production systems that suppress diease and add fertility to the soil.
Technical Abstract: Triploid watermelon cultivars are grown on more than 2,023 ha in Maryland and in Delaware. Triploid watermelons have little host resistance to Fusarium wilt of watermelon (Fusarium oxysporum f. sp. niveum). The effects of four different fall-planted cover crops that were tilled in the spring as green manures (Vicia villosa, Trifolium incarnatum, Secale cereale, Brassica juncea) and bare-ground, were evaluated alone and in combination with the biocontrol product Actinovate (Streptomyces lydicus) on Fusarium wilt severity, and watermelon fruit yield and quality. Six field experiments were conducted over three years in Beltsville and Salisbury, MD and Georgetown, DE. Both Vicia villosa and T. incarnatum significantly suppressed Fusarium wilt of watermelon as much as 21%, compared to watermelon in non-amended plots. Trifolium incarnatum was the only cover crop that yielded significantly more fruit than non-amended treatments (129% more fruit/ha), but only for one field trial. The Actinovate product either did not reduce Fusarium wilt or the magnitude of the reduction was small. Actinovate significantly reduced Fusarium wilt by 2% in 2009, as much as 7% in 2010 and increased Fusarium wilt severity by 2.5% in 2011. Actinovate significantly increased yield for one field trial, but only when applied to non-amended or S. cereale amended plots. This is the first report of a reduction in Fusarium wilt following a T. incarnatum cover crop incorporated as a green manure.