Taxonomy: Geminiviridae, Begomovirus, Cucurbit leaf crumple virus
The most up-to-date and complete virus taxonomy is available on the International Committee on Taxonomy of Viruses webpage.
Cucurbit leaf crumple virus (CuLCrV) was discovered in volunteer watermelons collected in fall 1998 growing in a commercial melon field in the Imperial Valley of California; collected leaves exhibited striking leaf crumpling and downward curling (epinasty) and high populations of sweetpotato whitefly (Bemisia tabaci MEAM1) (Guzman et al., 2000, Plant Dis. 84). The same year, CuLCrV was also found causing disease outbreaks in commercial fields of melons, squash, and watermelon in the southwestern United States and northern Mexico (Brown et al., 2000, Plant Dis. 84). Since then, this whitefly-transmitted virus has spread across much of the southern United States along with the invasive sweetpotato whitefly. Cucurbit leaf crumple, as the disease is known, may reduce yields of all cucurbit crops, including squash, pumpkin, and watermelon.
Watermelon plants infected with CuLCrV typically first show symptoms in new leaves, including the striking crumpling and downward curling. Leaves become pale green to yellow and show varying degrees of stunting, distortion, and mottling (Figures 1 and 2). Internode length of vines is not typically affected. Once plants are infected and symptoms begin to develop, fruits are no longer set. Fruit on infected plants may fail to mature and are not marketable due to unsightly bumps or irregularities. In the southeastern United States and the Yucatan Peninsula of Mexico, watermelon yields can be reduced by CuLCrV (Keinath et al., 2018, Plant Health Prog. 19; Rodríguez-Negrete et al., 2021, Plant Dis. 105).
On muskmelon and cantaloupe, infected leaves are light green, stunted, crumpled, and curl downwards. Infected fruit produced on diseased plants may be discolored with mottling on the rind. Casaba and honeydew melons generally do not show typical symptoms of cucurbit leaf crumple when infected by CuLCrV (Hagen et al., 2008b, Plant Dis. 92).
In some cases, symptomatic CuLCrV-infected cantaloupe and watermelon plants can recover from infection such that new leaves exhibit few or no symptoms due to the plant defense response (Hagen et al., 2008a, Phytopathol. 98). Interestingly, this phenomenon tends to be observed in the western United States. The reason for this regional difference is not known but may relate to cultivar variation, environmental factors, and mixed infection with other viruses. For example, co-infection with cucumber mosaic virus prevents recovery of CuLCrV symptoms in melon plants (Hagen et al., 2008a).
CuLCrV causes severe symptoms on most squashes and pumpkins. These infections often affect entire plants, which can lead to substantial economic loss. Leaves are distorted, crumpled, and curled and can display strong mosaic mottling in some varieties (Figure 3). Fruit can exhibit severe symptoms, including bumps, distortion, and mottling (Figure 4).
Symptoms of CuLCrV infection may be confused with symptoms caused by squash leaf curl virus (SLCuV), another whitefly-transmitted begomovirus that infects squashes, pumpkins, watermelon, and melons, and occurs in the same areas of the western United States as CuLCrV. Note that leaves infected by CuLCrV typically curl downward, whereas those infected by SLCuV curl upwards.
CuLCrV is spread by adult sweetpotato whiteflies (Bemisia tabaci MEAM1, Figure 5) in a persistent manner, which means that once the virus is acquired, a whitefly can transmit the virus for life. With climate change, populations of whiteflies have increased dramatically in the southeastern United States in recent years. The outbreaks of CuLCrV in the United States are more common in cucurbit crops transplanted in late summer and fall than in the spring because populations of whiteflies tend to be greater in the fall (Hagen et al., 2008b). In general, severe, widespread outbreaks of cucurbit leaf crumple are usually associated with high populations of the whitefly vector.
Although CuLCrV was initially detected in the western and southwestern United States, where cantaloupe and honeydew melon are the predominant cucurbit crops, CuLCrV has thus far had limited economic impact in that region. However, CuLCrV has been a much more serious threat in the southeastern United States where watermelon and squash production are more prevalent.
In the southeastern United States, snap beans (Phaseolus vulgaris) and the wild cucurbits smell melon (Cucumis melo Dudaim Group) and balsam apple (Momordica charantia) can be infected by CuLCrV (Adkins et al., 2011, Virus Res. 159). Buffalo gourd (Cucurbita foetidissima) is a suspected host in the western United States. These wild cucurbits likely serve as reservoirs for the virus between cucurbit crops. Whiteflies that feed on wild cucurbits or other CuLCrV-infected plants can acquire the virus and transmit it to cucurbit crops.
Since its initial detection in North America, CuLCrV has spread to other regions of these countries:
United States: California (1998), Arizona (1998-1999), Texas (1998-1999), Florida (2006), Georgia (2009), South Carolina (2017)
Mexico: Coahuila (1998-1999), Campeche (2019)
Note: Years in parentheses indicate when CuLCrV was first identified in that location.
Because of climate change and increasing populations of whiteflies, cucurbit crops in other countries and regions should be monitored for symptoms resembling CuLCrV and tested when appropriate. For the most up to date information on geographic incidence, please visit this website (www.eCucurbitviruses.org).
Symptoms alone cannot be used to accurately diagnose CuLCrV infection. Laboratory testing is necessary for confirmation of CuLCrV infection. Various molecular assays involving PCR (polymerase chain reaction; Guzman et al., 2000; Brown et al., 2000; Hagen et al., 2008b; Jailani et al., 2022, Physiol. Mol. Plant Pathol. 116) have been developed for CuLCrV detection; some assays allow for simultaneous detection of several whitefly-transmitted DNA and RNA viruses infecting cucurbit crops. No serological test is available for CuLCrV detection.
Contact your local plant diagnostic laboratory to determine testing capabilities.
Visit the Diagnostics Page for more information on diagnostic laboratories in your state, protocol publications, and/or the References page for references describing appropriate CuLCrV detection methods.
Preventative approaches are necessary to adequately manage CuLCrV in late summer and fall cucurbit crops with the principles of exclusion, eradication, avoidance, and protection by using healthy transplants, removing cucurbit weeds, and reducing whitefly populations. There are no commercial cultivars of watermelon, squash, or pumpkin with resistance to CuLCrV infection; however, a source of resistance has been identified in melon (McCreight et al., 2008, HortScience 43).
(principle: exclusion)
Inspect seedlings to be sure that transplants are free of virus symptoms and whitefly eggs, nymphs, and adults. Do not establish new cucurbit fields near existing fields with CuLCrV-infected plants or high whitefly populations.
(principle: eradication)
Remove cucurbit weeds and volunteer plants near or in the production field before transplanting. Reduce or eliminate virus and whiteflies by destroying foliage and vines after crop harvest with a non-selective herbicide prior to planting new crops to avoid whiteflies moving CuLCrV to new seedlings. Adding insecticide or oil to the herbicide provides no additional benefits. Survey established fields for whiteflies before destruction of the crop to determine if treatment is necessary.
(principle: avoidance)
Row covers and silver reflective polyethylene mulch can help to repel whiteflies early in the season before vine growth covers the mulch. Row covers used for four weeks after transplanting will delay virus infection. After this period of protection, row covers must be removed to allow pollination of flowers.
(principle: protection)
A neonicotinoid insecticide should be applied to seedlings in the greenhouse shortly before transplanting or as a drench in the field shortly after transplanting.
Management during the cropping season includes several applications of insecticides effective against local populations of whiteflies.
Consult local state or regional publications or specialists for recommendations of effective insecticides, as whiteflies can easily become resistant to insecticides used frequently.
Gilbertson, R. L. 2017. Cucurbit leaf crumple virus. In Keinath, A.P., Wintermantel, W.M., and Zitter, T.A. (eds.), Compendium of Cucurbit Diseases and Pests, 2nd edition (pp. 111-113). American Phytopathological Society Press, St. Paul, MN.
Visit the References page for a list of full citations of referenced articles.
This work is a publication of the Emerging Viruses in Cucurbits Working Group (EVCWG). It is supported by funding from the USDA NIFA (Agreement 2018-70006-28884) through the Southern IPM Center’s grant program project S22-026. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and the Emerging Viruses in Cucurbits Working Group and do not necessarily reflect the views of the USDA NIFA or the Southern IPM Center.
This publication may be distributed without alteration for nonprofit educational purposes provided that appropriate credit is given to the authors and the Emerging Viruses in Cucurbits Working Group. Permission for any other uses should be requested from the Emerging Viruses in Cucurbits Working Group.
Authors: Anthony P. Keinath, Clemson University, and Kai-Shu Ling, USDA-ARS
Senior editors: Rebecca A. Melanson, Mississippi State University, and William M. Wintermantel, USDA-ARS
Reviewers: Robert Gilbertson, University of California – Davis, and Scott Adkins, USDA-ARS
The Emerging Viruses in Cucurbits Working Group and its outreach activities are supported by funding from the Southern IPM Center’s Southern IPM Grants 2022. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and the Emerging Viruses in Cucurbits Working Group and do not necessarily reflect the view of the Southern IPM Center.
Last updated August 2022 / Privacy
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