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. photo by Jude Boucher click for a larger image

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.

It is critical to control early-season adult squash bugs as they colonize the field to successfully manage this disease. Insecticide applications should target young seedlings (< 3-5 true leaves) as soon as squash bugs are present on the plants. New generation synthetic pyrethroids (i.e. Capture) tend to work better than most other materials to control the squash bug. Spraying seedlings with synthetic pyrethroids should also control cucumber beetles and bacterial wilt. Thionex may also be effective on the squash bug and cucumber beetle. Sevin is no longer effective for squash bug control in CT. Since most fruit is not affected, fruit from infected pumpkins, winter squash, cantaloupe, or muskmelon vines should be harvested and marketed early to avoid crop loss.

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.

References:

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 Bug

s (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, an

d U. Melcher. 2004. Overwintering Squash Bugs Harbor and Transmit the Causal Agent of Cucurbit Yellow Vine Disease. J. Econ. Entomol. 97(1): 74-78.

T. Jude Boucher, University of Connecticut
May 2005