Evaluation of Met52 for the control of Thrips in onion

Project Code BPR11-030

Project Lead

Mary Ruth McDonald - University of Guelph
Luc Brodeur - Research Inc., Sherrington, Québec
Mary Weber Henricks - Agriculture and Agri-Food Canada, Harrow, Ontario

Objectives

To develop efficacy and crop tolerance data in support of a regulatory submission of Met52 (Metarhizium anisopliae strain F52) for the control of thrips (Thrips tabaci) in onions

Summary of Results

Background

Onion is a major vegetable crop in Canada, with an average annual production of approximately 155,000 metric tons. Eighty percent of this production is concentrated in Quebec and Ontario. Onion thrips (Thrips tabaci Lindeman) is one of the most frequent and potentially serious pests of dry bulb onions in Canada. This is an extremely polyphagous pest, but onion and other onion relatives are their favourite hosts, and difficult to treat, given the pest behavior of hiding deep within the whorl of the leaves. During hot and dry summers, increases in the thrips populations can occur very rapidly, causing substantial damage that reduce yield, bulb diameter and storage potential. Thrips can also act as vector for the transmission of virus and fungus, especially Alternaria porri, causing purple blotch of onions. Canadian growers have to make between 2 to 10 insecticide applications each year to control onion thrips. The large numbers of insecticide sprays have contributed to the development of resistance to some insecticides over years. Therefore, new insecticides and alternative control measures are needed in order to keep onion thrips under control. At the annual Biopesticide Priority Setting Workshop in March 2010, onion thrips was selected as a priority pest and Met 52 (Metarhizium anisopliae strain F52) was identified as a potential solution for the control of this pest.

Met52 is an entomopathogenic fungus and its spores germinate, and mycelia penetrate and grow within the insect, causing death of insect within a few days. In the absence of suitable insect hosts spores can remain in the soil for years without germinating, providing longevity from a single treatment. In this project, the biopesticide Met52 will be tested for its efficacy and crop tolerance in field for the control of onion thrips.

Approaches

Field trials were conducted at three locations in 2011, one in Quebec and two in Ontario. The experimental design consisted of 7 treatments with 4 replicates. Onions were sowed or transplanted in field during May to June depending on the trial location. Six foliar applications were carried out with the first application in mid-July. The assessments were carried out at a 4-7 day interval after the first application. Nymphs and adults of thrips were counted from a random sample of 10 plants per plot and at the same time the severity of damage was assessed for those sampled plants using a 0-3 scale for brownish leaf surface and stunting or distortion of leaves. Crop tolerance to Met52 was assessed at the same time efficacy assessments were made using a 0-100 scale which described crop injury related to test item application. Onions were harvested in a 4-meter row per plot and yield was tested for total and marketable onions and percentage of unmarketable onions.

Results

The results obtained in three trials from different locations indicated that Met52 did not provided significant efficacy for the control of thrips in dry onions based on measures of number of thrips per plant and damage severity. Besides its inefficacy in reducing pest populations, three trials showed that the tested product did not succeed in reducing onion damage caused by thrips feeding. Although the data from the University of Guelph indicated that Met52 treatments numerically provided higher onion yield and more larger-size onion bulbs compared to the untreated, statistical significances between the treatment and non-treatment were not detected in yield and bulb size. Moreover, the addition of sugar to Met52 solutions (to act as a lure for the thrips) did not show the improvement of efficacy for the control of onion thrips in three trials.

Discussion

Met52 efficacy for the control of onion thrips was not demonstrated through this project. Some challenging environmental conditions during the 2011 growing season at these sites may have affected Met52 performance in field. Frequent significant rainfalls occurred regularly at the Harrow site after the first application. This may have washed most of the thrips population away so that populations had been remained too low to show any meaningful results. In Sherrington site, Quebec, at the beginning of the season thrips populations remained very low and treatments began late in the season; however, due to the high temperature and infrequent rains encountered until mid-August, thrips populations exploded and proved difficult to control, even for those regional producers using registered conventional pesticides. Therefore, it is possible that additional trials conducted under more normal weather patterns would demonstrate Met52 efficacy for the control of onion thrips.

For more information, please contact Mary Ruth McDonald, Luc Brodeur, and Mary Weber Henricks.

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