Rebecca Champagne1, Eric Gallandt2, and Dan Brainard3
1PhD Candidate, Ecology and Environmental Sciences, 2Professor, University of Maine, and 3Associate Professor, Michigan State University
Interim report: February 19, 2021
Take-home points:
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Crop mortality at the first cultivation event was higher for treatments receiving low seedbank management, but not different between treatments at the second cultivation event approximately two weeks later.
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Intrarow weed efficacy was greater in stacked tool treatments regardless of seedbank management. Surrogate mustard and amaranth efficacy were greater in stacked tool treatments as well.
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Low seedbank management systems have resulted in an increasing germinable weed seedbank even with tool stacking, while high seedbank management systems have shown a declining seedbank.
Problem
Physical weed control (PWC) remains necessary in organic vegetable production to prevent significant yield loss, but its effectiveness can be low and variable. Tools targeting the intra-row often have poor selectivity, i.e. the ability to kill weeds, but not the crop (Ascard and Mattsson, 1994; Melander et al., 2005). To avoid crop damage tools may be operated less aggressively and adjusted further from crop rows, but cultivation efficacy can become low, resulting in higher densities of surviving weeds, increased seed rain, and a build-up of the weed seedbank. Tool “stacking” is one way to increase efficacy but may only kill a proportion of the weed seedlings present (Brown and Gallandt, 2018). In addition to improving the efficacy of cultivation tools, comprehensive weed seedbank management also serves as a way to manage weeds over a longer period of time. Practices such as tarping, false and stale seedbeds, and cover cropping may encourage germination loss and preempt seed rain, thereby reducing the germinable seedbank.
Approach
We assessed crop mortality, intrarow weed control efficacy, crop yield, and weed seedbank assays in a full factorial, randomized complete block design with four replications ( Fig. 1a ). Cropping system treatments examined two levels of weed seedbank management, and two levels of cultivation tools. Weed seedbank management consisted of: low management (L), where weeds were targeted during the critical weed-free period with two cultivation events, or high management (H) that included two cultivation events, plus the addition of tarping prior to crop planting, pre-emergence flame weeding (2020), rogue hand-weeding after last cultivation, and the use of cover crops following crop harvest. Cultivation tools included: finger weeders used alone (1), or finger weeders plus ridgers or torsions “stacked” on the toolbar (2) ( Fig. 1b ).
Figure 1. a) table beet ‘Boro’ at Roger’s Farm, and b) ridgers used for soil hilling in stacked cultivation treatments.
Results
In 2020 two cultivation events were performed, approximately four and six weeks after planting (WAP). The first cultivation event used finger weeders versus finger weeders plus ridgers for soil hilling, and the second cultivation event used finger weeders versus finger weeders plus torsions. Crop mortality was greater in low seedbank management systems in the first cultivation, but no differences were detected in the second cultivation (data not shown). Beets in the low seedbank management systems likely had increased competition with weeds at emergence, and therefore had less vigor to withstand cultivation.
Intrarow ambient weed efficacy ( Fig. 2 ) in the first cultivation was significantly higher for stacked tool treatments ( p =0.0002), and similar results were observed for intrarow surrogate weed efficacy ( p =0.0004; data not shown). However, intrarow ambient weed efficacy was not different between cropping systems in the second cultivation. As the beet leaves became larger and created more of a canopy, they may have shaded out weeds, resulting in less vigorous weeds which were more susceptible to cultivation.
Weed seedbank assays from the first two years of the experiment show two trends. The number of germinable weed seeds m-2 has increased from 2019 to 2020 in treatments receiving low seedbank management, regardless of tool stacking. Lack of additional strategies that target the seedbank in these systems could result in more weeds going to seed. In the high seedbank management systems, the number of germinable weed seeds m-2 has decreased from 2019 to 2020. Seedbank assays will be collected again in the spring of 2021 and 2022.
Figure 2. Mean (±SE) intrarow ambient weed efficacy (%) at first cultivation event (n=16). Different letters indicate significant differences between means at α=0.05. Beets were cultivated at 3-4 true leaves, approximately four WAP. H= high seedbank management, L= low seedbank management; 1= single cultivation tool, 2= stacked cultivation tools.
Figure 3. Germinable weed seedbank density per square meter by cropping system for 2019 versus 2020. H= high seedbank management, L= low seedbank management; 1= single cultivation tool, 2= stacked cultivation tools.
Next Steps
Yield data from 2020 will be analyzed, as well as analyses including year as a random factor to determine temporal differences between cropping systems.
A partial budget analysis will be used to determine production costs and net returns for each cropping system, and this information will be used when discussing results with farmers who may be interested in implementing tool stacking or additional seedbank management.
Literature Cited
Ascard, J. and Mattsson, B. 1994. Inter-row cultivation in weed-free carrots: the effect on yield of hoeing and brush weeding. Biological Agriculture & Horticulture. 10:161-173.
Brown B., and Gallandt, E.R. (2018). Evidence of synergy with ‘stacked’ intrarow cultivation tools. Weed Research 58: 1-8.
Melander, B., Rasmussen, I.A. and Bàrberi, P. 2005. Integrating physical and cultural methods of weed control—examples from European research. Weed Science. 53:369-381.