Development of a synergistic control technology for root weevils in strawberries

Project Code PRR07-530

Project Lead

James Coupland - FarmForest Research

Objective

This project aims to develop a root weevil management system for strawberries which will significantly enhance the effectiveness of nematode biological control through the synergistic effects of a low dose of imidacloprid. This method can significantly lower the amount of pesticide being used and may be relevant to other systems where there are similar soil pest problems.

Summary of Results

Background

There are a number of species of root weevil that can damage strawberry plants, with species such as the black vine weevil (Otiorhyncus sulcatus) and the strawberry root weevil (O. ovatus) considered the most common and destructive pests in several areas of Canada. Adult root weevils do little damage to strawberries except for slight feeding on the leaves, though occasional feeding occurs on the fruit. Most of the economic damage is caused by larvae feeding on the roots of strawberries. Strawberry plants may be seriously damaged when larval populations are high.

Management options for root weevils on strawberries are limited. Previously registered materials included organophosphate insecticides that have been withdrawn from the market due to worker safety concerns. Terranem (Heterohabditis bacteriophora) (Koppert Biological Systems) is a biological control product registered for black vine weevil.

Entomopathogenic nematodes can provide successful biological control of soil borne pests. The degree of control however, can be impacted by timing, dose and environmental and physical factors. There is evidence that imidacloprid, an insecticide registered for aphids on strawberry and for aphids, white grubs and defoliating insects on other crops, can act synergistically to augment the effectiveness of nematodes against soil pests. This synergism has been observed in laboratory studies. Work is required to validate this effect in the field. If successful, this technology could be an important solution in the management of weevils and could result in reducing the amount of pesticide required and contriibute to reducing pesticide risk to the environment and human health.

The management of root weevils and the need for reduced risk or biopesticide products has been identified as a priority issue by the strawberry industry through stakeholder consultations.

Approach

Trials were conducted with potted strawberry plants and field plantings, from 2007 to 2010. The trials were designed to test the effect of imidacloprid and nematodes, alone and in combination, on black vine weevil larvae. Treatments included a control, imidacloprid at the rate of 850 ml per hectare, (the lowest label rate for a drench), nematodes (Heterohabditus bacteriophora) at the rate of 500,000/ m2 and imidacloprid and nematodes in combination.

In pot trials, strawberry plants of the variety “Annapolis” were inoculated with 20 black vine weevil sterilized eggs on four different dates to establish pots with 11 week, 8 week, 6 week and 4 week old larvae. When the youngest larvae were 4 weeks old, all treatments were applied to the pots. Treatments included a control, imidacloprid at the rate of 850 ml per hectare, (the lowest label rate for a drench), nematodes (Heterohabditus bacteriophora) at the rate of 500,000/ m2 and imidacloprid and nematodes in combination. The plants were placed in a greenhouse. Once larvae reached 10 weeks of age, the plants were dissected to establish the survival rate of weevil.

In field trials, the same four treatments were applied to 2 m x 10 m plots, replicated 4 times in a randomized complete block. Ten plants, elected randomly from each plot, were checked for the presence of black vine weevil larvae and pupae.

Results

The results of pot trials suggested that there is a synergistic effect of using imidacloprid and nematodes together, with the effect dependent on the age of the black vine weevil larvae. Eight week old larvae appeared to be the most impacted by the combined application. In the field trials, populations of root weevils were very low and as a result, no significant differences were detected among the treatments. Again, further studies are required to elucidate the age effect and potential synergistic impact of imidacloprid and entomopathogenic nematodes.

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