Reducing the use of insecticides for grasshopper control in lentils

Project Code PRR07-370

Project Lead

Mark Goodwin  Pulse Canada

Objective

To develop a grasshopper hatching model, train growers and agronomists to identify damaging grasshoppers, and develop a reduced risk method for late season grasshopper control

Summary of Results

Background

Grasshoppers are a serious pest limiting lentil production in Western Canada. However, among over 80 grasshopper species in Canada, only about four are known to cause economic losses to agricultural crops. Pest grasshoppers can cause significant yield loss in lentils because these consume flowers in addition to leaves and developing pods. Therefore, the economic threshold for lentils is lower (2 grasshoppers/m2) compared to other crops. Currently, lentil growers rely on few available options of control products, some of which are relatively old chemistries and under regulatory re-evaluation.

Lower risk alternative solutions are needed to allow sustainable pest management. This 3-year project aimed to improve grasshopper management through the development of three distinct tools: a field guide allowing growers to recognize and identify pest from non-pest grasshopper species; a biological control method; and a decision support system to assist growers in their management decisions. The project involved collaborations between the University of Lethbridge, Pulse Canada and the Saskatchewan Pulse Growers (SPG).

Approaches

The project was conducted from 2007 to 2010 as three separate components taking place at the University of Lethbridge laboratories in Alberta, commercial lentil fields in Saskatchewan, and pasture lands in Alberta.

Component 1: Dr. Dan Johnson of University of Lethbridge compiled over 60 original images of various grasshopper species and growth stages, together with management information into a practical field guide booklet. This booklet aimed to provide growers with a tool helping them differentiate among species, recognize the different life stages of the four main species of pest grasshoppers, and take appropriate, knowledge based management actions. Several training sessions were offered through workshops, web seminars and traditional grower meetings to introduce and promote the booklet to growers and agronomists. Participants at training sessions were surveyed to assess and compare grower knowledge and their grasshopper management practices at the beginning and at the end of project.

Component 2: Efficacy of Metarhizium anisopliae S54 strain, an indigenous fungus discovered in Alberta soil which had previously been identified as a potential microbial control agent for grasshoppers, was evaluated against the standard commercial product (Lorbsan). Trials were conducted in lentil crops in Elrose, Saskatchewan in 2008 as well as in pastures in Pearce and Cold Lake, Alberta in 2009. Metarhizium spores were produced by growing the fungus on barley kernels in the lab at the University of Lethbridge. The spores, suspended in a water or oil carrier, were applied using a conventional sprayer. The sprayer delivered 50L solution carrying either 25 or 50g spores per hectare. Grasshopper populations were monitored for mortality incidence in preselected sampling areas prior to and 0, 6 and 15 days after treatment.

Component 3: Dr. Dan Johnson and associates at University of Lethbridge used information technology and weather modelling software to develop a web-based, in-season grasshopper risk warning tool that would provide more accurate predictions than traditional models based on previous fall pest counts. The model analysed large sets of historical data to identify key relationships between grasshopper development and weather factors. The identified relationships formed the basis of the risk warning tool.

Results

Component 1: The Grasshopper Identification and Control Methods booklet was published in spring 2008. The booklet was printed in a durable format and thousands of copies were distributed on demand from growers through various extension, education and grower organizations, including the SPG, Saskatchewan Department of Agriculture, Canola Council of Canada, Alberta Fieldmen, and University of Lethbridge. Feedback from participants in training session showed that a large majority of growers are committed to farming practices that reduce unnecessary spraying. Surveyed growers indicated that they understood the value of being able to identify which species of grasshoppers need to be controlled and which do not. The level of awareness among growers about making spray decisions based on harmful grasshopper species present in the field increased from 4 to 46% over the course of 3 years of this project. The booklet was shown to help growers make informed pest control decisions leading to reduced pesticide use and reduced pest management costs.

Component 2: In 2008, three grasshopper pest species were identified within the experimental site: the two-striped grasshopper (about 59% of the population), the lesser migratory grasshopper (26%) and Packard’s grasshopper (8%). Grasshopper mortality reached 68-75% 6 days after the spray application with M. anisopliae strain S54 from an initial mean density of 5.8 grasshoppers/ 0.25m2. By day 15, grasshopper density was reduced by up to 83%. The biocontrol provided efficacy levels comparable to those attained by the commonly used Lorsban, with the higher spore concentrations providing better results. Record cold and wet weather in the following year led to poor grasshopper population, thus efficacy results were inconclusive. M. anisopliae strain S54 is currently being pursued for commercial development and registration in Canada.

Component 3: The forecasting model consisted of an equation that predicted grasshopper emergence and growth as a function of weather. The model was translated into an online tool consisting of risk maps indicating the dynamics of timing and geographic extent of early spring hatching and various growth stages of main damaging grasshopper species across the Prairie Provinces (Alberta, Saskatchewan, and Manitoba). A “beta” version of the tool was launched on a pilot basis through the SPG website in summer 2009. The maps were updated twice weekly and associated with comments interpreting risk expectations and recommended actions. Although low pest pressure prevailed, validation of projections against actual data from 83 sites indicated that the tool can potentially provide reliable estimates of grasshopper instar development in the field.

Information about the new tools developed through this project was disseminated to thousands of lentil and other field crop growers and agronomists in the prairie region. Integrated adoption of these tools has the potential to help growers effectively time scouting activities and control measures, thus improve the efficacy of existing control options while minimizing unnecessary sprays. The project also provides potential alternative solution (e.g. biocontrol) to help address the trade barrier issue associated with the relatively low maximum residue limits set for insecticides in some international markets and restrictions on insecticide use close to harvest.

For more details, please contact Dr. Dan Johnson or Mark Goodwin.

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