Matt Bertucci, University of Arkansas
Like many specialty crops, blackberries have relatively few registered herbicide products for weed control. Many of the herbicide options are registered for burndown applications (before the crop breaks dormancy), preemergence applications targeting weed seeds, or row middle applications. A smaller number of herbicides are registered for banded or directed postemergence (POST) applications at the base of blackberry plants. Thus, any new herbicide registrations would be immediately useful in a chemical rotation and would afford growers new options for weed management. However, for these herbicides to be registered, crop safety must first be demonstrated in field settings. Field trials were conducted in 2022 and 2023 in Arkansas to assess blackberry tolerance to 2,4-D choline (Embed® Extra, Corteva Agriscience) and glufosinate (Rely® 280, BASF Corporation). Trials were conducted separately with different conditions, and results are described briefly below.
2,4-D is one of the oldest synthetic herbicides with characterizations of its herbicidal activity as early as 19441, so it is hardly a new herbicide. However, the choline salt formulation of 2,4-D is a newer, less volatile formulation than the ester or amine formulations. If this less-volatile form (2,4-D choline) is safe for use in blackberries, growers would have a new POST herbicide to target annual and perennial broadleaf weed species. A trial was conducted in 2022 and 2023 in Clarksville, AR at the Fruit Research Station to test the effect of sequential applications of 2,4-D choline on established ‘Natchez’ blackberries. Two rates of 2,4-D choline (Embed® Extra, 3.8 ae/gal) were tested: 3 pt/A (1×) and 6 pt/A (2×) (Table 1). As is common practice, a weed-free treatment was used as a reference, using only registered chemicals or hand-weeding. 2,4-D choline applications occurred in 2022 and 2023 before bud break as a directed application (spray overlapping at crowns of plants), 30 days later as a banded application (spray not contacting the crowns or canes), and again as a postharvest application (Table 2). While symptoms were visible, no substantial crop injury was observed at any rating timing. Plant injury was assessed visually and assigned a 0 to 100% rating, with 0 representing a symptom-free, healthy plant and 100 representing total plant death. Low levels of injury (≤9%) were observed in response to the 2× rate of 2,4-D choline; however, symptoms were restricted to new growth of the lower canes. Generally, the rest of the upper canopy remained free of 2,4-D symptoms, with symptoms primarily visible in lower canopies where newly emerging primocanes intercepted the spray (Figure 1). There were no reductions in marketable blackberry yields or in average berry size in response to 2,4-D choline treatments.
Table 1. Experimental materials applied in accordance with protocol.
| Trade Name | Herbicide | Formulated product rate Per acre | Active ingredient rate lb ae/acre | Application placement and timing | Spray volume gal/acre |
|---|---|---|---|---|---|
| Untreated – Weed Free | – | – | – | No experimental herbicides | – |
| Embed Extra (3.8 lb ae/gal) | 2,4-D Choline | 3 pt | 1.43 | Directed spray followed by (fb) banded spray fb post-harvest spray | 20 |
| Embed Extra (3.8 lb ae/gal) | 2,4-D Choline | 6 pt | 2.85 | Directed spray followed by (fb) banded spray fb post-harvest spray | 20 |
Table 2. Dates of 2,4-D choline applications in each year for blackberry plots in Clarksville, AR.
| Spray event | Year 1 | Year 2 |
|---|---|---|
| Application A (directed) | March 9, 2022 | March 10, 2023 |
| Application B (banded) | April 7, 2022 | April 10, 2023 |
| Application C (post-harvest) | August 11, 2022 | July 25, 2023 |
Glufosinate is a locally systemic POST herbicide that causes symptoms primarily in the contacted foliage. In cropping systems where glufosinate is labeled for use, it may be a preferred option due to the low risk with exposure to sensitive foliage/crops. Because glufosinate does not translocate as thoroughly as other systemic herbicides, like glyphosate or 2,4-D, small amounts of herbicide interception may only cause local symptoms and not harm an otherwise sensitive species. A field trial was conducted in 2022 and 2023 in Fayetteville, AR to test the effect of glufosinate on newly planted ‘Ponca’ blackberries. Saflufencacil and an untreated weed-free check were included as comparisons to the glufosinate treatments. Glufosinate (Rely® 280; 2.34 lb ai/gal) was tested at two rates: 96 fl oz/A (1×) and 192 fl oz/A (2×); and saflufenacil (Treevix®, 0.7 lb ai/lb) was tested at 4 oz/A. Table 3. Herbicide applications occurred two times each season. Initial applications in 2022 occurred on June 21, and plants were shielded from spray interception with wax-lined cartons (Figure 2). No injury was visible in response to any herbicide treatment following applications to shielded plants (Figure 3). A second application of herbicides occurred on August 30, 2022 as a late-summer application. Rating for injury on the 0 to 100 scale (0 = no plant injury; 100 = total plant death), herbicide injury symptoms were very minimal (≤4%; Figure 4) and were restricted to the lower canopy of blackberry plants (Figure 5). In 2023, applications occurred prior to primocane emergence (March 10) and post-harvest (August 7), and symptoms, where present, were similarly restricted to the lower canopy. Blackberry marketable yields and berry size were similar between the glufosinate (1×), saflufenacil, and untreated checks; however, there was a reduction in marketable yield and average berry size for glufosinate at the 2× rate (Table 4). Thus, glufosinate did not cause any problematic visual injury symptoms, but a rate-dependent yield reduction was observed, highlighting the need for proper calibration and careful spraying if glufosinate is registered for use in blackberries.
Table 3. Experimental materials applied in accordance with protocol.
| Trade Name | Herbicide | Formulated product rate | Active ingredient rate lb ai/acre | Application placement and timing | Spray volume gal/acre |
|---|---|---|---|---|---|
| Untreated | – | – | – | No experimental herbicides | – |
| Rely 280 | Glufosinate AMS | 96 fl oz – | 1.76 3.4 | Directed spray to either side and across rows | 20 |
| Rely 280 | Glufosinate AMS | 192 fl oz – | 3.51 3.4 | Directed spray to either side and across rows | 20 |
| Treevix | Saflufenacil MSO | 4 oz – | 0.175 1% (v/v) | Directed spray to either side and across rows | 20 |
Table 4. Summary of blackberry yields and berry weights in response to herbicide treatments in Fayetteville, AR. Yields are summed across all 8 harvests and berry weights were averaged from a 25 berry sample from each harvest.1
| Herbicide | Rate lb ai/acre | Marketable lb/plant | Cull lb/plant | Avg. weight g |
|---|---|---|---|---|
| Glufosinate | 1.76 | 5.65 a | 0.78 | 7.86 a |
| Glufosinate | 3.51 | 3.94 b | 0.69 | 7.33 b |
| Saflufenacil | 0.18 | 5.65 a | 0.78 | 7.81 a |
| Nontreated | – | 5.49 a | 0.78 | 7.95 a |
The findings from these two trials indicate that 2,4-D choline and glufosinate are safe for use in blackberries at the tested rates and application timings. Though, some caution must be exercised for high rates of glufosinate to avoid yield reductions. The work has been summarized and shared with staff at the IR-4 Project and with the respective chemical companies. However, as of this writing, these herbicide registrations have not been approved by the EPA and are not legal for use in blackberries. We are hopeful that changes in the near future. If that is the case, look for new POST herbicide recommendations in the newer versions of the SRSFC Caneberry Integrated Management Guide!
Researchers would like to thank the IR-4 Project for supporting this work and prioritizing these two projects among their many requests.
Figure 1. Blackberry plots 30 days after treatment with banded sprays of 2,4-D choline (1× = 1.43 lb ae/A; 2× = 2.85 lb ae/A). Each treatment is indicated with its own panel. No substantial injury was observed between treatments. Mottling in new leaves and some minor leaf distortion was visible in new growth. Most dramatic symptoms were present in lower leaves near where suckers had intercepted banded herbicides. Photos taken May 5, 2022. Clarksville, AR.
Figure 2. Wax cartons shielding blackberry plants at the time of the initial glufosinate and saflufenacil applications. Photos taken June 21, 2022. Fayetteville, AR.
Figure 3. Blackberry plots 14 days after with shielded sprays of herbicide treatments (Glufosinate 1× = 1.76 lb ai/A, 2× = 3.51 lb ai/A; Saflufenacil 1× = 0.18 lb ai/A). Each treatment is indicated with its own panel. No substantial injury was observed between treatments. Photos taken July 6, 2022. Fayetteville, AR.
Figure 4. Blackberry plots 7 DAT with directed applications of herbicide treatments (Glufosinate 1× = 1.76 lb ai/A, 2× = 3.51 lb ai/A; Saflufenacil 1× = 0.18 lb ai/A). Each treatment is indicated with its own panel. Injury symptoms were very minor and restricted to the lower canopy. So symptoms are difficult to observe from whole plot images. Photos taken Sept 8, 2022. Fayetteville, AR.
Figure 5. Close-up images of blackberry plots 7 DAT with directed applications of herbicide treatments (Glufosinate 1× = 1.76 lb ai/A, 2× = 3.51 lb ai/A; Saflufenacil 1× = 0.18 lb ai/A). Injury did not exceed 4% for any herbicide treatment. Visual injury manifest as necrosis of lower canes where directed sprays were intercepted by green foliage. Photos taken Sept 8, 2022. Fayetteville, AR.
