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Watermelon Cannonballus Disease – What Causes Watermelon Root Rot

Watermelon Cannonballus Disease – What Causes Watermelon Root Rot


By: Darcy Larum, Landscape Designer

Watermelon root rot is a fungal disease caused by the pathogen Monosporascus cannonballus. Also known as watermelon vine decline, it can cause massive crop loss in affected watermelon plants. Learn more about the devastating disease in this article.

Root and Vine Rot of Watermelon Crops

This disease is prevalent in hot climates and has been known to cause massive crop loss in the United States in Texas, Arizona, and California. Watermelon cannonballus disease is also a problem in Mexico, Guatemala, Honduras, Brazil, Spain, Italy, Israel, Iran, Libya, Tunisia, Saudi Arabia, Pakistan, India, Japan, and Taiwan. Watermelon vine decline is generally a problem in sites with clay or silt soil.

The symptoms of monosporascus root and vine rot of watermelon often go unnoticed until a few weeks before harvest. Early symptoms are stunted plants and yellowing of the plant’s old crown leaves. The yellowing and dropping of foliage will quickly move along the vine. Within 5-10 days of the first yellow leaves, an infected plant may be completely defoliated.

Fruits may suffer from sunburn without the protective foliage. Brown soggy streaking or lesions may be visible at the base of infected plants. Fruits on infected plants may also be stunted or drop prematurely. When dug up, infected plants will have small, brown, rotted roots.

Watermelon Cannonballus Disease Control

Watermelon cannonballus disease is soil borne. The fungus can build up in the soil year after year in sites where cucurbits are regularly planted. Three to four year crop rotation on cucurbits can help control the disease.

Soil fumigation is also an effective control method. Fungicides delivered by deep irrigation in early spring may also help. However, fungicides will not help already infected plants. Usually, gardeners are still able to harvest some fruit from infected plants, but then plants should be dug up and destroyed to prevent more spread.

Many new disease resistant varieties of watermelon are now available.

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Program Areas

Cucurbit yellow vine disease first appeared on squash and pumpkins in the Cross Timbers Vegetational Area of Texas and Oklahoma in 1988. By 1991 it was causing large scale losses of watermelons and cantaloupe in this same region. The presence of the disease has since been confirmed in Arkansas, Colorado, Kansas, Nebraska, Massachusetts, Missouri, and Connecticut. In states that have a history of CYVD, disease incidence is often spotty within a field, and adjacent fields may or may not be affected. It may be absent in some years or may cause widespread crop failure in other years.

In 2004, two pumpkin farms in Ellington, Connecticut had outbreaks of CYVD. In the first field, the foliage on a few dozen vines turned bright yellow at fruit set. These plants were misdiagnosed as having bacterial wilt and were rogued from the field to help prevent secondary spread of the disease by the insect vector. No further symptoms were observed in this field until just before harvest, when the vines declined. Fruit became soft and were lost to a combination of diseases, including Fusarium crown and fruit rot, Phytophthora blight, Sclerotinia white mold and possibly CYVD. Samples from this first field were not sent to Oklahoma for CYVD testing until after the disease had been confirmed on a second nearby pumpkin field. Vines in the second field began to show symptoms in late August as the fruit began to reach full color. Foliage on many of the vines began to turn yellow and decline. Fruit from this field was harvested early and sold around Labor Day to avoid crop losses. Both fields had been rotated out of cucurbit crops for the previous 2-3 years, and both were treated with an insecticide for cucumber beetles and the recommended program of systemic and contact fungicides to stop the cucurbit disease complex: powdery and downy mildew, black rot, scab, and Plectosporium blight.

Cucurbit yellow vine disease is caused by the bacteria, Serratia marcescens. The bacteria survives the winter in squash bugs and is spread to the young plants in the spring when the bugs colonize and feed on cucurbit crops. Young seedlings in the first true leaf stage of development are more susceptible to disease transmission than older seedlings.

Spread of CYVD between plants within the field is not thought to contribute much to disease severity because the progression of symptoms is usually very slow. The bacteria reside and multiply in, and eventually clog the phloem tissue of the plant vascular system. Usually symptoms are not detected until just prior to harvest.

However, some symptomatic or asymptomatic immature plants may collapse suddenly in the middle of the season or just after fruit set. Typically, all the leaves turn yellow within a few days, starting about a week or two before harvest. Terminal leaves stand erect, fail to expand, and the margins curl inwards. Older leaves develop scorched margins and may die. The phloem in the crown and lower stem turns honey-colored. Eventually, the root begins to decompose, a process that is hastened by secondary rot organisms, and the whole plant begins to decline and die. Watermelon fruit turn yellow as the leaves begin to discolor. Other fruit usually fail to show symptoms.

In Texas, many growers have successfully used early-planted straightneck summer squash ('Lemon Drop'or 'Hyrific') as a trap crop in the border rows of their watermelon fields to attract and control squash bugs to manage CYVD.

Trap crop plants should be 2-3 weeks older than the main crop to attract the bugs. One researcher said that up to 100% of the bugs will be attracted to the border rows and killed by insecticide applications, and that the technique has almost eliminated CYVD in his region over the past 5 years. This trap crop technique is remarkably similar to the perimeter trap crop system New England growers have been using to control cucumber beetles and bacterial wilt on cucurbit crops. Squash bugs are most attracted to Hubbard squash, summer squash, pumpkins, watermelons, muskmelons, cucumbers, and butternut squash in decreasing order. Using our existing perimeter trap crop system, with early-planted 'Blue Hubbard' around later planted pumpkins (or other cucurbits), may control four pests (squash bugs & CYVD, cucumber beetles & bacterial wilt) with as few as one border spray. Time the trap crop spray just prior to main crop emergence, and if a second application is needed, at the first true leaf stage of the main crop.

  • Bonjour, E. L., W. S. Fargo, and P. E. Rensner. 1990. Oviposition Preference of Squash Bugs (Hemiptera: Coreidae) Among Cucurbits in Oklahoma. J. Econ. Entomol. 83(3): 943-947.
  • Bruton. B. D. 1998. Association of a Ploem-Limited Bacterium with Yellow Vine Disease in Cucurbits. Plant Dis. 82: 512-520.
  • Dogramaci, M., J. Shrefler, B. W. Roberts, S. Pair, and J. V. Edelson. 2004. Comparison of Management Strategies for Squash Bugs (Hemiptera: Coreidae) in Watermelon. J. Econ. Entomol. 97(6): 1999-2005.
  • Kabrick, L. 2002. New Cucurbit Disease Discovered in Missouri. Missouri Environ. & Garden. Vol. 8., no. 8.
  • Mitchell, F., S. Pair, B. Burton, and J. Fletcher. 2004-2005. Personal Communication.
  • Pair, S. D., B. D. Bruton, F. Mitchell, J. Fletcher, A. Wayadande, and U. Melcher. 2004. Overwintering Squash Bugs Harbor and Transmit the Causal Agent of Cucurbit Yellow Vine Disease. J. Econ. Entomol. 97(1): 74-78.

By: T. Jude Boucher, University of Connecticut, May 2005. Reviewed 2012.

The information in this document is for educational purposes only. The recommendations contained are based on the best available knowledge at the time of publication. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension System does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available. The University of Connecticut, Cooperative Extension System, College of Agriculture and Natural Resources is an equal opportunity program provider and employer.


Monosporascus Root Rot and Vine Decline

CAUSAL AGENT

DISTRIBUTION

SYMPTOMS

Initial symptoms include stunting and poor growth of plants. However, this may go undetected if an entire field is uniformly affected. The older crown leaves begin to turn chlorotic, wilt and collapse within weeks of harvest. Within five to ten days of the first foliar symptoms, most of the canopy may be killed. Tan to reddish-brown lesions form on the roots. Root infection leads to a loss of feeder roots. Eventually the root system may become necrotic, resulting in plant death. Large, black perithecia form on dead roots and are often visible. Fruit of diseased plants are smaller or cracked and may abscise from the pedicle before ripening and have reduced sugar content. Fruit may also become sunburned due to lack of foliage. Stem lesions are generally lacking and above ground symptoms may be confused with other vine declines.

Perithecia on melon roots. (Courtesy of Gerald Holmes)

CONDITIONS FOR DISEASE DEVELOPMENT

Infection by Monosporascus cannonballus is believed to occur early in the season however, tissue colonization is encouraged as the soil temperature increases. This rise in the soil temperature encourages perithecia formation in the roots. Ascospores are the long-term survival structures of the fungus. Disease spread is by movement of infested soil or infected plant material.

CONTROL

Management of Monosporascus cannonballus has proven to be difficult due to its heat tolerance and thick-walled resting structures. Avoid planting melons and watermelons in known infested fields. Also, avoid excessive irrigation, which may only delay plants collapse. Allowing infested roots to dry out in the field followed by fumigating soon after harvest has shown to be beneficial. The use of rootstocks has been beneficial in watermelon, although additional work is needed for melon. Chemigation through drip irrigation lines has also been shown to be effective.


Resistance in melon to Monosporascus cannonballus and M. eutypoides: Fungal pathogens associated with Monosporascus root rot and vine decline

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Ana Pérez‐de‐Castro, Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Camino de Vera 46022, Valencia, Spain.

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto Agroforestal Mediterráneo, Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Valencia, Spain

Ana Pérez‐de‐Castro, Instituto de Conservación y Mejora de la Agrodiversidad (COMAV), Universitat Politècnica de València, Camino de Vera 46022, Valencia, Spain.

Gabriel Castro and Gorka Perpiñá contributed equally to this article.

Funding information: Generalitat Valenciana, Grant/Award Number: PROMETEO2017/078 Ministerio de Economía y Competitividad, Grant/Award Number: AGL2014‐53398‐C2‐2‐R Spanish Ministerio de Ciencia, Innovación y Universidades, Grant/Award Number: AGL2017‐85563‐C2‐1‐R

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Abstract

The fungal species Monosporascus cannonballus and M. eutypoides have been described as the causal agents of Monosporascus root rot and vine decline disease (MRRVD), which mainly affects melon and watermelon crops. Resistance to M. cannonballus has been reported in some melon cultivars (ssp. melo). Moreover, melon ssp. agrestis accessions have proven to be better resistance sources. This is the case of the Korean accession ‘Pat 81’, highly resistant under field and artificial inoculation. The objective of the work here presented was the evaluation of the resistance to MRRVD of different accessions representing the variability of Cucumis melo ssp. agrestis, against both, M. cannonballus and M. eutypoides, in a multiyear assay under different infection conditions. In general, M. eutypoides was less aggressive than M. cannonballus in the different environmental conditions. There was a strong influence of temperature on MRRVD, with more severe symptoms with higher temperatures and with variable effect of infection on plant development depending on the fungal species considered. Resistance to MRRVD has been confirmed in ‘Pat 81’ and in its derived F1 with a susceptible Piel de Sapo melon. Among the new germplasm explored, African accessions (both wild agrestis and exotic cultivated acidulus) showed good performance in artificial inoculation assays and in field conditions. These sources do not present compatibility problems with commercial melons, so they can be introduced in backcrossing programs. The accession assayed of the wild relative Cucumis metuliferus, also resistant to Fusarium wilt and to root‐knot nematode, was highly resistant to MRRVD. The interest of this accession mainly relies in its advantages as a rootstock for melon.

Appendix S1: Supporting Information

TABLE S1 Correlations between vigour, root and vine weight and length parameters, disease indices and parameters measured with WinRhizo, for the six artificial inoculation assays.

TABLE S2 Root and vine weight and length parameters, disease indices and parameters measured with WinRhizo, for the six artificial inoculation assays.

Please note: The publisher is not responsible for the content or functionality of any supporting information supplied by the authors. Any queries (other than missing content) should be directed to the corresponding author for the article.


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