Organic Farm Calls: Squash Vine Borer and IPM Thresholds

From Sustaining Farming on the Urban Fringe
Recently, an organic grower with a variety of squash crops under low tunnels called Ag Agent Meredith Melendez about wilting plant symptoms.

Squash Vine Borer Injury

The various vine and bush varieties were decimated by squash vine borer (SVB) larvae root damage. Ornamental gourds were especially hard hit.

"Standard" IPM Thresholds Fail
Under Early Organic Squash Cultivation

The USDA NOP Standard does not permit organic farmers to make prophylactic (preventative) insecticide treatments, even of OMRI approved insecticides.

Squash Vine Borer Adult Moth (R. Bessin)

The “standard” squash vine borer (SVB) IPM threshold (about 5 adult moths per pheromone lure trap weekly) on early organic cucurbit crops in NJ leads to intolerable crop losses.

That this threshold seems way too high is an agreed upon observation by local grower experiences and the Rutgers IPM team. Organic cucurbit growers who wait to see SVB wilting injury and root feeding evidence before treating risk losing their crops – especially under low tunnels.

While it is too late for saving squash crops this year, Kris Holmstrom of the Rutgers IPM program recommends that an appropriate organic IPM action threshold is catching a single (1) adult moth in a SVB pheromone lure trap placed near the squash field. One or more adults in the trap represent a valid organic threshold-based application, not a prophylactic treatment.

Treatments directed to the base of plants should commence within one week of this first appearance, and probably continue on a weekly basis as long as adults continue to be caught during the early crop. SVB may not be as big a threat later in the season with more host crops available. Kris says, “I would play it on the conservative side with this SVB pest since it hits small plantings so hard, and organic growers have little in the arsenal.”

Calculating a Backpack Sprayer Entrust Rate 

Applied early, Entrust (OMRI approved Spinosad) has some reported SVB effectiveness with directed sprays to the base of the plant, which may be accomplished by backpack sprayer on small plantings. Label recommendations are available as weight of product per acre. By measuring repeated samples, Ruth Hazzard at UMass determined that a 1-teaspoon volume (shaved level and tamped slightly) of Entrust dry powder formulation is about 1.7 gm. The Entrust rate in a backpack sprayer is about 0.43 gm per gallon of water. In a 3-gallon sprayer, this is equal to about 3/4 teaspoon, or 1.3 gm.

Squash Vine Borer Pheromone Lure Kits

SVB pheromone trap kits are available via mail order from companies like Great Lakes IPM. Starter kits include a universal bucket trap, lure and vaportape for about $13.50 (item number PB-SVB-K). Lures last for up to 4 weeks and replacement lures are about $2.50 each.