Evaluating Interceptor – an organic herbicide

E. Johnson, K. Sapsford, R. Holm, R. Kutcher, W. May, G. Lafond, T. Hogg, B. Nybo, S. Anderson and J. McConnell

Problem

Organic producers are not allowed to use synthetic pesticides in their production system. However, herbicides derived from natural sources may be allowable. Interceptor is a herbicide registered and certified for organic production in New Zealand. A non-selective organic herbicide could be very useful in replacing pre-seeding or pre-emergence tillage. This study’s objectives were: 1) to evaluate Interceptor’s efficacy in controlling annual indicator weeds, and 2) to define application parameters that may improve Interceptor’s efficacy.

Background

Interceptor is a non-selective, contact herbicide derived from an extract of pine oil. Since the herbicide kills by contact, uniform spray deposition on the target plant is required for maximum efficacy. We did preliminary greenhouse and field studies to evaluate Interceptor’s efficacy in organic field crop production, using canola and tame oat as indicator ‘weeds’ in both studies. Preliminary greenhouse studies were done at the Scott Research Farm. Interceptor application resulted in quick desiccation of canola plants but had little activity on oat plants in the greenhouse studies. This is likely due to the contrasting leaf orientations of canola and oat. Canola's broader leaves are horizontally oriented, while oat has thin, vertically oriented leaves. Broad, horizontal leaves receive more spray droplets and the spray is more likely to be retained on the leaf. Greenhouse studies also suggested that weed control with Interceptor could be improved by increasing carrier volume from 10 gpa to 20 gpa.

Study description

Field studies were conducted at all SPOKE sites plus the Kernen Crop Research Farm at Saskatoon. Canola and oat were seeded at target densities of 150 and 200 plants m respectively. Plot size varied by location. Interceptor was applied at three rates: 10%, 20% and 30% v/v concentration. Included in the study were an untreated check and an industry standard (glyphosate). Glyphosate rates were 0.25, 0.50 and 0.75 liters/acre. Interceptor was applied with standard spraying equipment using a carrier volume of 20 gpa. Glyphosate was applied at 5 to 10 gpa. Herbicides were applied when the plants were in the three-to-five leaf stage. Experimental design was a randomized complete block. Visual control ratings (0 to 100% control) were taken three, seven, and 14 days after application. Plant biomass data were collected 14 to 21 days after seeding.

Major findings

Trends were similar for all locations -- we combined data. Interceptor caused some leaf burn on oats, but control ratings averaged less than 10% (Table 1). There was no significant reduction in wild oat biomass from Interceptor treatments at all rates. Since Interceptor is strictly a contact herbicide, spray coverage is critical. Oat has a narrow leaf with a vertical orientation, therefore spray retention is generally low. Interceptor gave slightly better results on canola, but overall control was still not satisfactory (Table 2). Interceptor was very fast acting on canola -- symptoms appeared within a few hours. Initial control ratings for Interceptor were higher than for glyphosate. However, significant regrowth occurred one to two weeks after Interceptor application. Final control ratings for Interceptor ranged from 10 to 26% depending on rate. The 30% Interceptor rate resulted in about a 22% reduction in canola fresh weight, relative to the untreated check. Glyphosate application at rates above 0.50 liter/acre resulted in a 99% reduction in both oat and canola fresh weight.

Table 1. Efficacy of Interceptor and Glyphosate in the control of tame oat. Mean of eight Saskatchewan locations. 2001

Table 2. Efficacy of Interceptor and Glyphosate in the control of canola. Mean of eight Saskatchewan locations. 2001.

Conclusions

Interceptor herbicide is not effective as a non-selective herbicide using conventional field application technology. Control may be slightly improved with flooding type nozzles that improves spray coverage; however, it is doubtful that small changes in application technology would result in an acceptable level of weed control. High rates of active ingredient are required with Interceptor, which would further reduce its applicability in extensive field crop production. In spite of its limitations for field crop production, Interceptor herbicide may have potential as a herbicide for the domestic market. Many urban municipalities are restricting the use of pesticides. In an urban situation, the high concentration required is not an issue due to the small areas usually treated. Since domestic application is usually done with a hand sprayer, spray coverage may be improved. Homeowners who wish to use a herbicide derived from a natural source may find the fast acting nature of the herbicide appealing -- symptoms appear in hours.

Acknowledgements

Funding provided by the Canada-Saskatchewan Agri-Food Innovation Fund

Originally published in Research Report 2002, Canada-Saskatchewan Agri-Food Innovation Fund