In 1992, we received a USDA grant to study pesticide effectiveness and other squash vine borer (SVB) control options on pumpkins and summer squash in Connecticut. Four experiments were conducted during the 1992 and 1993 seasons. The 1992 results of the spray trial and a variety trial for resistance/tolerance to SVB are presented in this article. 1993 results will be included in the presentation, as will information on monitoring for SVB with pheromone traps.

Description and Damage

The SVB is an important pest of vine crops such as winter squash (except butternut), summer squash, pumpkins and gourds. Eggs of this moth hatch sometime during the summer months, depending upon temperatures, and young larvae tunnel into stems and vines, injuring or killing runners or entire plants. Soft rot organisms, which gain access through these entry wounds, often increase the degree of damage to the plant. When abundant, 20 or more large (1 1/4 inches in length), fat (1/3 inch in width), white larvae may be found tunneling in a single plant. When populations are extreme, larvae may even attack the fruit directly, rendering them valueless. In some years, SVB has produced a total crop loss at various Connecticut locations. In other years or at other farms, SVB populations and damage occur at such low levels that growers are completely unaware of their presence.

1992 Spray Trial

All chemicals registered for SVB control (except malathion) were field tested for efficacy on pumpkins and summer squash. These insecticides included Thiodan 3E, Methoxychlor 2E, Asana XL, Ambush 2E and Rotenone 1D. Each product was applied four times on a weekly basis, beginning in July when the first adult SVB moth was detected.

All the insecticides tested, with the exception of Rotenone, reduced SVB larval infestations on both commodities compared with unsprayed control plots. Rotenone’s failure to control SVB may have been due to the excessive precipitation which occurred during the treatment period (142% compared with the 30-year average). These rains may have washed the dust formulation from the plants. Rotenone’s ineffectiveness may also have been related to its naturally shorter period of residual activity compared with the other insecticides tested.

Despite differences among treatments in SVB larval infestation rates, yields were not significantly increased by any of the insecticide treatments on either crop in 1992. In fact, the use of Methoxychlor significantly reduced pumpkin yields (56%) compared with untreated control plots. Lower yields for this treatment appeared to be unrelated to SVB infestation levels, as no larvae were found in any of the pumpkin plants treated with Methoxychlor. Although not always statistically significant, it was interesting that plants in the Methoxychlor treatments produced fewer and smaller fruit, resulting in lower overall yields for both commodities. Smaller fruit size and fewer fruit indicate that this chemical may have hormonal or phytotoxic activity, or an adverse effect on pollination. Analysis of the 1993 results may contradict or verify these results and possibly shed some light on the cause of Methoxychlor’s lower yields.

Variety Trial 1992

Treatments included the four popular commercial pumpkin varieties, Connecticut Field, Ghost Rider, Pankow’s Field, and Wizard, compared to the industry standard (Howden) as the control. Summer squash varieties Golden Girl, Goldbar, Precious, and Smoothie were compared with Early Prolific Straightneck as the control.

Larval infestations were not significantly different between the controls and the other varieties of pumpkins and summer squash tested. The low SVB larval infestations experienced in 1992 did not reduce overall yields per acre, fruit number per plant or fruit size. Goldbar summer squash produced significantly more fruit per plant and had higher overall yields than the control, but did not experience enough SVB pressure to be considered resistant or less susceptible to attack.

Low SVB Population in 1992

SVB populations were extremely low and late to develop throughout Connecticut in 1992. At the University’s research farm in Storrs, the infestation rate for untreated summer squash averaged less than one larva per plant in 1992 compared with eight larvae per plant in 1991. The unusual weather conditions probably played a major part in reducing SVB damage. Unusually abundant and continual rainfall during the 1992 growing season may have helped the plants compensate for mild injury by providing a constant moisture supply. In addition, heavy rainfall during egg hatch may have increased SVB mortality by washing young larvae from the plants and drowning them before they entered the stems.

Record-low summer temperatures (3 degrees below normal) delayed the peak moth flight until 22 July and slowed egg and larval development by more than three weeks. As a result, much of the summer squash harvest occurred before the majority of SVB eggs had even hatched, and many larvae were still quite small during pumpkin harvest in mid-September. Thus, both crops were exposed to unusually small larvae (for late summer) with minimal injury resulting per insect. The previous season (1991), larvae at the same site were full grown by 8 August, killed 17% of the untreated squash plants, and reduced yield by 36% compared with a sprayed treatment.

Conclusions

Do not assume that you have to spray for SVB on your farm. As these results demonstrated, insecticide sprays provided no economic benefit in 1992. In addition, it seems that most growers with severe SVB problems are farming rocky upland soils and have usually discontinued plowing in favor of harrowing. The practice of moldboard plowing buries overwintering SVB larvae deep in the soil and reduces the number of moths that emerge. Over time, plowing can reduce the SVB population. If your farm has a history of severe SVB damage, and you feel you need to spray, time applications with egg hatch. We are currently working on a pheromone-trapping system for this pest, which should help time applications in future years if they are necessary.

By: Jude Boucher, Vegetable Crops IPM Program Coordinator, University of Connecticut,
And: Roger Adams, University of Connecticut, Dept. of Plant Science, U-67, Storrs, CT 06269-4067. Reviewed 2012.

Originally published in: Proceedings, 1993 New England Small Fruit and Vegetable Growers Conference and Trade Show, December 14 – 16, 1993, Sturbridge Host Hotel, Sturbridge, Massachusetts

This information was developed for conditions in the Northeast. Use in other geographical areas may be inappropriate.

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