Whitefly-transmitted viruses: emerging and chronic threats to vegetable production in Georgia and southeastern USA

Summary

Whitefly-transmitted Tomato yellow leaf curl virus (TYLCV) remains a chronic threat to tomato production in Georgia as well in southeastern United States. TYLCV is listed as one of the top ten destructive plant viruses in the World. In addition, two other viruses devastated cucurbit production – Cucurbit leaf crumple virus (CuLCrV) and Cucurbit yellow stunting disorder virus (CYSDV). CYSDV was identified for the first time in Georgia. At least 40,000 acres of tomato and cucurbits are grown in Georgia annually. Losses due to these viruses has been immense and above normal in 2016. There is no actual estimate of losses in dollars; even at a conservative estimate, that amount is expected to be in the tens of millions of dollars.

Situation

TYLCV was first reported in Grady, Tift, and Colquitt counties of Georgia in 1999, the report was then confirmed in 2001. Losses continued through the years. From 2009-2015, numerous tomato fields were severely affected by TYLCV (up to 100%) in Tift, Colquitt, and Macon counties. CuLCrV was identified for the first time in 2012, but was not a major issue until 2016. In 2016, the virus came back with a vengeance. Several squash fields in Tift and neighboring counties were just plowed under. CYSDV was identified in Georgia for the first time. Resistant cultivars are only available for TYLCV and it is not complete. For cucurbit viruses there is no available commercial resistance. Management has largely focused on using insecticides more frequently. Despite such usage, losses continued to mount and increased the cost of production.

Response

In the last five years, we have addressed the TYLCV issue. Our efforts largely focused on management and basic aspects of transmission by whiteflies. Even though, TYLCV resistant cultivars are available, they are planted in less than one third of the tomato acreage. We are currently conducting research to assess how these cultivars could be best integrated into the management program. We intend to integrate the usage of these resistant cultivars with cultural tactics, such as reflective mulches, and also with an insecticide rotation schedule. Such an approach will not minimize the usefulness of individual techniques; instead will attempt to exploit their synergistic effects. With this goal in mind, we are conducting multistate (GA-FL-SC) research to address this issue. We have come up with a risk management plan for growers throughout the region. Additionally, we are conducting extensive research in the laboratory to understand the effects of the virus on host plants, as well as the effects of the virus on vector fitness and biology. The influence of such effects on virus acquisition and transmission is also being investigated. These details could help formulate better management strategy soon. In 2016, our laboratory was involved in extensive testing of cucurbit samples and insect samples upon requests from growers, extension agents, and extension faculty. The identified viruses are being characterized and established in the greenhouse to conduct extensive research. Basic and applied research projects are being formulated and built on some preliminary data obtained in 2016.

Impact

Growers are already beginning to realize that spraying insecticides alone might not be sufficient to reduce whiteflies and TYLCV incidences, particularly under high-pressure scenarios. Our research has indicated the presence of alternatives that they could use without having to significantly compromise on yields. Resistant cultivars are currently being considered at least in the fall season. Through our research, we were able to demonstrate that TYLCV could be significantly reduced, or yield losses due to TYLCV incidence could be significantly reduced. A web-based risk assessment guide will be made available online to growers next month. This will provide growers options to minimize risks. Our laboratory has spent a substantial time this fall identifying viruses affecting cucurbit crops and examining whitefly biotypes. This has helped growers and extension agents understand more about the problem. Ongoing research will help address the issue of whitefly-transmitted viruses in cucurbits more effectively in the coming years.

State Issue

Agricultural Profitability and Sustainability

Details

• Year: 2016
• Geographic Scope: Multi-State/Regional
• County: Tift
• Program Areas:
  • Agriculture & Natural Resources