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E. Johnson - Scott Research Farm

Problem

Post-emergence harrowing generally results in low selectivity, which is the ratio between weed control and crop injury. Many organic growers have suggested that selectivity of postemergence harrowing could be improved with changes in implement design. This study’s objectives were to determine if selectivity differed between a Lely Flex-tine harrow and a tine harrow; and to determine whether multiple passes will optimize weed control in field pea.

Background

The flex-tine weeder is a common implement used in Europe by organic growers in crops such as sugar beets and potatoes. The flextine harrow is also referred to as a finger weeder. The springy tines of the flex-tine harrow are gentle enough not to harm the crop while uprooting or covering small weeds. The long, thin spring-tines may be pushed aside by a well-established crop, allowing for selective weed control between rows. The amount of soil disturbance caused by the flex-tine harrow can be adjusted by adjusting the angle of the tine relative to the soil surface. Fifty-two percent of organic growers surveyed in Saskatchewan use post-emergence harrowing as a weed control practice. There are very few published papers on postemergence harrowing in western Canada. Results of a 12-year study at Indian Head showed that yield of barley and spring wheat grown under weed-free conditions was not reduced by a single harrow pass conducted at emergence, the 1.5 or 2.5 leaf stage. Kirkland reported that multiple post-emergence harrowing passes reduced wild oat panicles and fresh weight in spring wheat in two years out of a three-year study. However, spring wheat yield was improved in only one year of the study. Three to four passes were required in order to obtain a 40 to 80% reduction in wild oat fresh weight. Studies have shown that field pea can tolerate post-emergence tillage performed with a harrow or rotary hoe. Yield responses from post-emergence tillage in field pea have ranged from 0 to 18%.

Study description

The study was conducted on wheat stubble from 1999-2001 An early spring cultivation was performed on the experimental area. Wild oat and wild mustard were seeded across the plots at a target density of 100 plants/m for each species. A second shallow cultivation was done immediately after weed seeding to uniformly distribute the weed seeds. Field pea ( Grande) was seeded in early May at a rate of 220 kg/ha (80 viable seeds/m ) with a hoe-drill plot seeder (22cm row-space) according to the treatment design. Field pea was inoculated with 5.6 kg/ha of granular inoculant applied in the seed row. The experiment was conducted according to a randomized complete block design. Treatments included a factorial combination of harrow type (tine and flex tine), levels of flex tine soil disturbance (low, moderate, and high), and number of operations (one - four passes). Settings for the flex-tine harrows are illustrated in Figure 1. Our strategy for multiple harrow passes was: one pass = single harrowing at crop’s three to four node stage; two passes = single harrowing at crop’s three to four node stage and a single harrowing one week later; three passes = double harrowing at crop’s three to four node stage and a single harrowing one week later; and four passes = double harrowing at crops’ three to four node stage and a double harrowing one week later. Untreated and herbicide (imazamox + imazethapyr 50:50 applied at a rate of 30 g ai/ha ) checks also were included in addition to the factorial arrangement of harrow type and passes. Treatments were replicated four times. Subsubplots were 2 m x 5 m. Data collected included field pea density, total weed density and fresh weight, and seed yield.

Major findings

The tine harrow and moderate and high disturbance settings of the flex-tine harrow caused a decline in field pea density as the frequency of harrowing increased (Figure 2). The flex-tine harrow’s low disturbance setting resulted in minimal crop injury with plant densities similar to the herbicide treatment and the untreated check. Highest weed densities were recorded with the flex-tine harrow at the low disturbance setting (Table 1). All other harrow types and settings resulted in similar weed densities. Two or more harrow passes resulted in the lowest weed densities for all the harrow types and settings. We found no significant difference in weed fresh weight between harrow types or disturbance settings (Table 2). Although the flex-tine harrow’s low disturbance setting resulted in the highest weed densities, maintaining sufficient plant populations allowed the crop to compete more effectively with weeds. Three or more passes resulted in up to a 40% decline in weed fresh weight (relative to the untreated check), independent of harrow type or setting. All harrow types and settings resulted in similar field pea yields (Table 3). Highest yields were obtained with the three pass system which resulted in approximately 20% higher crop yield than the untreated check. Herbicides improved crop yield by 60%. Results from this study are consistent with other studies comparing harrow types. A tine harrow was more effective in reducing broadleaf weed numbers than a rotary harrow, however it caused more crop injury. Rasmuusen reported that a flexible chain harrow was a more efficient weed killer than a spring-tine harrow but it also caused more crop damage in field pea and spring wheat. He concluded that similar results could be obtained with all harrow types, if their settings are adjusted to give similar plant covering effects.

Table 1. Tine harrow, flex-tine harrow setting, and number of post-emergence passes - effect on weed density (plants/m²). Scott, SK. 1999-2001

Table 2. Tine harrow, flex-tine harrow setting, and number of post-emergence passes - effect on weed fresh weight (g/m²). Scott, SK. 1999-2001

Table 3. Tine harrow, flex-tine harrow setting, and number of post-emergence passes - effect on field pea yield (kg/ha). Scott, SK. 1999-2001.

Conclusions

Crop injury could be reduced by using a low disturbance setting on the flex-tine harrow. The flex-tine harrow can be easily adjusted to vary the amount of soil disturbance and crop covering. The harrow should be set to minimize a reduction in plant density. High levels of soil disturbance did not result in improved weed control. The three-pass system employed in this study resulted in a 50% reduction in weed biomass and a 20% increase in field pea yield.

Acknowledgements

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

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