- Author: Lynn M. Sosnoskie
I've spent a portion of the last four four years (at UC - Davis) engaged in research to evaluate the management of weed in specialty crop systems. In 2017, I will officially accept a position with Washington State University. However, before I depart, I wanted to summarize a number of my research results in a series of easily accessible blog posts. Attached is a PDF version of my report (originally submitted to the California Tomato Research Institute, who funded a significant amount of studies) on the efficacy of PRE and POST herbicides on field bindweed (Convolvulus arvensis) suppression. The summary is as follows:
California leads the nation in the production of processing tomatoes with respect to acres planted and harvested, yield per acre, total production, and total value of production. In 2012, California growers harvested approximately 300,000 acres of processing tomatoes, worth an estimated $1.4 billion, with Fresno, Kings, Merced, San Joaquin, Stanislaus and Yolo Counties each producing crops valued at more than $100 million.
Historically, processing tomato production has been heavily dependent on pre-plant, inter-crop tillage operations and in-crop cultivation for weed control (Mitchell et al. 2012; Shrestha et al. 2007; Sutton et al. 2006). While effective at managing many weed species, especially during the seedling stage, frequent mechanical disturbances can negatively impact human and environmental health by increasing dust production and greenhouse gas emissions, and by reducing soil quality (Reicosky et al. 1997; Mitchell et al. 2012). Physical weed suppression programs are also accompanied by significant financial costs with respect to labor, fuel, and equipment purchase and maintenance (Mitchell et al. 2012). As a result, California tomato growers have been steadily transitioning towards minimum-tillage production systems.
The adoption of reduced-tillage programs in processing tomatoes has been facilitated by growers' decisions to switch from furrow- to sub-surface drip-irrigation (Mitchell et al. 2012). Because drip-irrigation limits soil surface wetting, the density and biomass of many small-seeded, annual, broadleaf weed species, such as common lambsquarters (Chenopodium album L.), pigweeds (Amaranthus spp.), and black nightshade (Solanum nigrum L.), can be significantly reduced relative to furrow irrigation systems (Shrestha et al. 2007; Sutton et al. 2006). Consequently, weed management practices for drip-systems may be less dependent on physical control measures, such as cultivation and hand-weeding (Mitchell et al. 2012; Shrestha et al. 2007; Sutton et al. 2006).
The use of drip-irrigation and minimum-tillage can, however, create an environment where field bindweed (Convolvulus arvensis L.), a deep-rooted and drought tolerant perennial, can survive, grow, and compete with crops (Sharma and Singh 2007; Shrestha et al. 2007; Wiese and Lavake 1986). With respect to processing tomatoes, interspecific interference for up to eight weeks after transplanting (WAT) can significantly reduce fruit number and quality. Furthermore, field bindweed vines can become physically entwined in the crop canopies, which, in turn, can reduce crop harvest efficiency (Mitich 1991). The purpose of our research over the last four years has been to evaluate currently recommended and novel weed control practices for the suppression of field bindweed. Our results have shown:
Trifluralin, rimsulfuron (PRE), and sulfentrazone have some activity (for up to 4 to seeks weeks) against perennial bindweed vines, while S-metolachlor does not. Trifluralin, rimsulfuron, and S-metolachlor are labeled for use in tomatoes for the residual control of emerging weeds (http://ipm.ucanr.edu/PMG/r783700311.html). In addition to perennial bindweed suppression, rimsulfuron is effective against most nightshade species, pigweeds, and lambsquarters; trifluralin will control many annual grasses as well as some broadleaf weed species. S-metolachlor, while not effective against bindweed, can suppress nutsedge and nightshades. Sulfentrazone has/has had a supplemental label (as Zeus) allowing for its use in transplanted tomatoes for the suppression of yellow nutsedge.
Most soil-applied herbicides require 0.5 to 1 inch of precipitation or irrigation for activation. Furthermore, water needs to be distributed evenly to ensure adequate coverage and maximum control. Although drip-irrigation can reduce labor costs, prevent some disease development, improve water use efficiency, and reduce surface wetting, which reduces weed seed germination, it may not be effective at activating many residual herbicides. Growers with significant field bindweed problems should be mindful of how their irrigation protocols may affect herbicide performance. Results from trials not discussed in this report have shown that the activities of rimsulfuron and sulfentrazone against field bindweed were significantly improved when sprinkler irrigation was used for herbicide activation.
The application of trifluralin, sub-surface (SSL), using a spray blade is currently labeled for bindweed control in grapes in California. Although SSL applications of trifluralin appear to be effective at suppression bindweed in processing tomatoes, this strategy is not labeled for use in this crop. Crop injury is a significant concern when transplant root-balls are not positioned below the treated zones. Carryover effects on rotation crops were not investigated in these trials and is a significant concern.
Rimsulfuron is labeled for POST use in processing tomatoes (http://ipm.ucanr.edu/PMG/r783700311.html) although its efficacy as a POST herbicide, with respect to field bindweed control, is poor. As was discussed, previously, rimsulfuron applied PRE may suppress the emergence of field bindweed vines. Paraquat and carfentrazone are both labeled for the control of emerged weeds prior to transplanting, although perennial weed control will not be long lasting as both products are contact herbicides and will do little more than burn off any above ground foliage. Glyphosate, was the most effective POST product for suppressing field bindweed growth across all trials; it is labeled for use as a pre-plant burn down. One of the tenets of integrated pest management is to start off clean and remain clean to prevent weed interference in the current and future crops. Growers with significant bindweed problems should strive to ensure effective burn down of existing vines prior to crop planting and following harvest; the management of bindweed in rotation crops and following rotation crop harvest is also encouraged.