Biological control of root weevils in strawberries

Background

There are limited options for management of root weevils in berry crops. No successful monitoring program has been developed and there are few chemical options. Root weevils are causing damage at an increasing number of locations in Ontario and losses can be devastating in infested fields. A team of researchers across Canada is currently studying the situation in several provinces, in an attempt to develop IPM strategies for monitoring and control of this pest. Meanwhile, growers need immediate options. Beneficial nematodes are commercially available, although very expensive (ie $400-$600 per acre). Application conditions are very specific and control has been very sporadic in the past. A new strain of nematode has recently become available in Ontario, which is more cold tolerant and perhaps better suited for our conditions.

Objective

To compare two types of beneficial nematodes for control of black vine and other root weevils in strawberries.

Methods

Two strains of beneficial nematode, Nemasys L (Stienernema krausii), Nemasys H (Heterorhabditis megidis), were applied to 10 m plots in a three year old strawberry field known to be infested with root weevils, predominantly black vine weevil. Plots were replicated 10 times and the untreated check plot was treated with water. Applications were made Sept 21, 2006 by hand at labeled rates, using a 5 L water per plot, followed by 15 L water per plot. Plots were assessed May 16 by sampling three cores per plot and examining soil for larvae and pupae. Differences in plant health were observed between plots, but all plots showed noticeable levels of root weevil injury. Plant biomass was estimated by taking fresh weight of above ground plant material, biomass, clipped from 2 m area of the plot.

A second trial was set out in October 2007, using Nemasys L, at an infested site near Cambridge. Treatment was applied using a field sprayer followed by sprinkler irrigation. Plots will be assessed in 2008.

Results

Both strains of nematode provided some degree of control, although only the Nemasys L was statistically different from the control.

Root weevil control in strawberries: treatments applied October 2006, assessments May 2007

Other comments

Beneficial nematodes work best when applied to moist soil. Application in evening or in dull overcast conditions is preferred. High water volumes are required to move the product into the soil, and irrigation immediately following the application is recommended. Avoid application in the heat of the day or in bright sunlight. Application costs per acre can be reduced by banding the product over the rows. There are several suppliers of beneficial nematodes, see ontario.ca/crops for a list of suppliers (under resources and services click on sources of crop inputs, and then beneficial insect and mite suppliers). Order product at least a week in advance of application. The product has a limited shelf life and should be stored in a cool dry place.

Acknowledements

CORD IV funding from the OBGA was used for student assistance and in the purchase of beneficial nematodes.

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