Introduction
Cranberry is a low-growing, woody, perennial, fruiting vine native to North America. Commercial cultivation occurs primarily in Wisconsin, Quebec, Massachusetts, British Columbia, New Jersey, and Oregon (USDA-NASS 2019). Vines are planted with a life expectancy of at least 20 to 25 yr; fertilizers and herbicides are applied to new plantings to encourage the stolons (runners) and vertical stems (uprights) to form a continuous mat of vegetation across the production surface. Due to this horticultural convention, weed management options (e.g., cultivation, tillage, rotation) on established plantings are not feasible. Most of the problematic weed species tend to be perennial vascular plants (Sandler et al. Reference Sandler, Dalbec and Ghantous2015a), with the notable exceptions of the annual parasitic plant, dodder (Cuscuta spp.), and nonvascular mosses, primarily polytrichum moss (Polytrichum commune Hedw.).
Application of herbicides, both PRE and POST, along with hand weeding and mowing, are the main strategies employed to manage weed populations on commercial cranberry farms. Herbicides used in cranberry production are typically applied via irrigation systems (chemigation), cantilevered boom sprayers, ground rigs (e.g., drop spreaders), and aerially (helicopters). Although water volumes for chemigation can vary due to farm-specific factors (e.g., pump systems, sprinkler head arrangements), the average system delivers pesticides in approximately 3,740 L water ha−1. Chemigation is mostly used in Massachusetts, boom spraying predominates in Wisconsin and Quebec, and both methods are often employed in New Jersey cranberry production.
Dodder has been a major pest in cranberry production for decades (Sandler Reference Sandler2018); moss is an emerging and increasing problem in many cranberry growing regions (Ghantous et al. Reference Ghantous, Sandler and Kerrester2019), along with several perennial grasses including broomsedge bluestem (Andropogon virginicus L.), deertongue [Dichanthelium clandestinum (L.) Gould], and little bluestem [Schizachyrium scoparium (Michx.) Nash] (Sandler et al. Reference Sandler, Ghantous and Hedderig2015b). Identifying novel safe and effective pesticides to control established and emerging weeds are industry priorities (Cape Cod Cranberry Growers Association 2020). Based on work conducted since 2017 at the University of Massachusetts Cranberry Station, and at the Rutgers P.E. Marucci Center for Blueberry and Cranberry Research and Extension in New Jersey, sulfentrazone was identified as a promising herbicide for dodder and moss control (Besançon et al. Reference Besançon, Hemstead, Jensen and Carr2018; Sandler and Ghantous Reference Sandler and Ghantous2018).
Sulfentrazone is a selective, soil-applied, PRE herbicide labeled for control of various broadleaved weeds, sedges and grasses in many row and specialty crops (Anonymous 2012). A Group 14 (Weed Science Society of America categorization) herbicide in the aryl triazinone family, sulfentrazone inhibits the enzyme protoporphyrinogen oxidase (PPO or Protox; Shaner Reference Shaner2014). Use of this herbicide would represent a new mode of action that could be used on cranberry, enabling growers to rotate a new mode of action into their weed management programs. Although sulfentrazone is currently used in other small fruit crops such as lowbush blueberry (Vaccinium angustifolium Aiton) that are closely related to cranberry, the label cautions against application to crop foliage. Cranberry is distinct from other berry crops such as blueberry, raspberry (Rubus idaeus L.), and grapes (Vitis spp.) in that it is nondeciduous. Due to the low-growing growth habit and continuous mat of vegetation, any herbicide application to cranberry will contact the crop foliage regardless of timing. It is unknown whether applications to cranberry while foliage is dormant would mitigate injury. Cranberry gradually comes out of dormancy in the spring (Eck Reference Eck1990). The buds for the current season’s growth pass through several stages while still considered dormant. It is unknown whether cranberry becomes more susceptible to herbicide injury as it approaches budbreak.
Application method and timing (i.e., crop growth stage) are known to affect the performance of herbicides. Chemigation and pivot-attached sprayer systems were effective in peanut and cotton when high water volumes were needed to penetrate the plant canopy or to activate PRE herbicides, but chemigation was much less compatible when used for agrichemicals such as defoliants and POST herbicides (Sumner et al. Reference Sumner, Dowler and Garvey2000). Minimal research has focused on whether application method in cranberry (e.g., broadcast application by boom sprayer in 190 to 280 L ha−1 or application by chemigation in approximately 3,740 L ha−1 through the irrigation system) affects crop safety or efficacy of herbicides.
A preliminary study was conducted in 2018 in Massachusetts simulating sulfentrazone application to cranberry by chemigation at one of two bud stages: spring dormant (SD; characterized by tight red buds) or cabbage head (CH; characterized by bud scales loosening). No yield reduction was observed with the highest rate of sulfentrazone tested at 420 g ha−1 applied at the CH phenology stage, even though the number of flowering uprights were significantly decreased (20%) compared with sulfentrazone applied at 280 g ha−1 or at the SD stage (36%; Sandler and Ghantous Reference Sandler and Ghantous2019). Visual assessments also indicated no treatment effect for rate or timing of application. Therefore, the researchers concluded that low or high sulfentrazone rates chemigated in spring prior to the loosening of the terminal bud scales were safe to use on cranberry. These chemigation results contrasted with a 2018 study in New Jersey using sulfentrazone applied to cranberry by boom sprayer that indicated sulfentrazone application rate and timing could affect cranberry safety depending on the crop phenology stage at which the herbicide was applied (Carr and Besançon Reference Carr and Besançon2019).
These preliminary data suggest that application volume, rate, and timing may impact crop safety, and it warranted further investigation. In addition, it is also unknown whether washing off sulfentrazone from the cranberry canopy through irrigation could mitigate the potential for injury at sensitive growth stages. For example, previous research has shown that terbacil would severely injure strawberry when applied after the three-leaf stage, but that injury can be significantly reduced when irrigation follows herbicide application (Polter et al. Reference Polter, Scheerens and Doohan2004, Reference Polter, Scheerens and Doohan2005
To clarify use patterns that could be recommended to promote crop safety with sulfentrazone on cranberry, we conducted six field trials, including one in Massachusetts and five in New Jersey, at four different sites. Our objective herein was to evaluate cranberry response to sulfentrazone rate, timing of application based on bud development stage, spray application volumes, and postapplication wash-off.
Materials and Methods
Boom Application Study
In 2018, field trials were conducted on 26-yr-old ‘Early Black’ cranberry vines at a producer’s farm in Southampton, NJ (39.54°N, 74.43°W), and on 12-yr-old ‘Demoranville’ cranberry vines at the Rutgers P.E. Marucci Center for Blueberry and Cranberry Research and Extension, in Chatsworth, NJ (39.82°N, 74.53°W). In 2019, a similar trial was set up on 12-yr-old ‘Stevens’ cranberry vines at a grower’s farm in Pemberton, NJ (39.56°N, 74.29°W). The 2018 trials were conducted on Atsion sand with pH 4.3 and 2.2% organic matter, whereas the 2019 trial was conducted on a Berryland Mucky Sand with 1.6% organic matter and pH 4.6 (USDA-NRCS 2020b). Sulfentrazone (Zeus® XC, 0.6 kg a.i. L−1, FMC Corporation, Philadelphia, PA) was applied PRE at one of two different dormant cranberry bud phenology stages: spring dormant (SD), characterized by tight red buds; or cabbage head (CH), characterized by bud scales loosening. Applications at the SD and CH stage were sprayed on April 28 and May 9, 2018, and April 24 and May 6, 2019, respectively. Activation of sulfentrazone was achieved by watering plots with 2.5 cm of overhead irrigation within 6 to 12 h of herbicide applications. To simulate cantilevered boom spray applications, a CO2-pressurized backpack sprayer equipped with XR8004 flat-fan nozzles (TeeJet, Glendale Heights, IL) was calibrated to broadcast 190 L ha−1 at 138 kPa. The study was conducted as a two-factor factorial arrangement in a randomized complete block design with four replications. Main factors were timing of application (SD and CH phenology stage) and herbicide rate with sulfentrazone applied at 280 or 420 g ha−1. A nontreated weed-free control was also included. Individual plots were 3.3 m2 and uniformly covered by fully developed cranberry vines.
Cranberry tolerance to sulfentrazone was assessed 2, 4, and 8 wk after treatment (WAT) by visually scoring crop canopy in each plot for overall leaf injury and vine stunting on a 0% (no injury or stunting) to 100% (complete necrosis of aboveground cranberry vegetation or absence of new growth) scale (Frans et al. Reference Frans, Talbert, Marx and Crowley1986). The development of new shoots was visually evaluated by ranking them on a visual scale of 0 (e.g., no new shoots) to 5 (e.g., maximum shoot elongation in the absence of herbicide treatment). A more exhaustive evaluation of cranberry growth as affected by herbicide applications was conducted by randomly collecting 15 uprights per plot 8 WAT to determine the number of terminal buds that did not produce a shoot and measure the length of primary new shoots, the number of reproductive structures (flowers or fruit), and the number of axillary shoots. Ripened fruit were harvested on October 4, 2018, and October 1, 2019, by collecting berries from two 930-cm2 areas in the central section of each plot. Both samples were subsequently mixed and the number and weight of commercially acceptable berries as well as the proportion of damaged (e.g., rotten, insect injury, other causes) fruit were determined in the laboratory.
Mitigation Study
An experiment was conducted in New Jersey in 2019 and 2020 at the previously mentioned site in Pemberton, NJ, to determine cranberry tolerance in response to sulfentrazone sprayed at two application volumes and two bud phenology stages. Application volumes were selected to represent spray amounts delivered either through regular cantilevered boom applications or through chemigation. The same study was also conducted in 2019 at the University of Massachusetts Cranberry Station in East Wareham, MA (41.76°N, 70.67°N; 10-yr-old ‘Stevens’) on a Freetown coarse sand with less than 1% organic matter and pH 4.9 (USDA-NRCS 2020a). The studies were conducted as a two-factor factorial arrangement in a randomized complete block design with four replications. A nontreated weed-free control was also included. Main factors consisted of timing of application (SD and CH phenology stages) and spray volume at either 190 L ha−1 (comparable to boom application volume) or 3,740 L ha−1 (comparable to chemigation volume). The simulation of boom application included herbicide spray alone or followed by 0.25 cm of water to evaluate mitigation of potential crop injury. Sulfentrazone at 420 g ha−1 was applied at the SD and CH stage on April 24 and May 1, 2019 in Massachusetts; April 25 and May 6, 2019, and April 28 and May 13, 2020 in New Jersey, respectively. Plot size was 1 m2 in Massachusetts and 3.3 m2 in New Jersey, and 50-cm-wide buffers were added between plots to restrain herbicide drift to neighboring plots, facilitate foot traffic, and conduct ratings without stepping in treated plots.
For the New Jersey site, cantilevered boom application was simulated as previously described for the boom application study, whereas chemigation was simulated using a CO2-backpack sprayer fitted with XR8010 flat-fan nozzles (TeeJet, Glendale Heights, IL) and calibrated at an application pressure of 414 kPa. For the Massachusetts study, cantilevered boom application and chemigation were simulated using a CO2-pressurized backpack sprayer fitted with an 8002VS flat-fan nozzle (TeeJet, Glendale Heights, IL) calibrated at an application pressure of 206 kPa. For each study, simulated boom application was delivered in a single pass, whereas simulated chemigation was delivered in multiple passes depending on the type of spray equipment used.
Visual evaluations of leaf injury and stunting associated with sulfentrazone applications were conducted in New Jersey following the protocol described above. In addition, quantitative upright response data were collected. In Massachusetts and New Jersey, a total of 10 and 15 uprights, respectively, were randomly collected from each plot 8 WAT. Uprights were collected again at harvest on September 18, 2019 in Massachusetts, and on September 19, 2019 and September 9, 2020 in New Jersey. Uprights were measured in the laboratory to determine the length of new growth, the number and the length of axillary shoots, and the number of reproductive structures (flowers or fruit). Ripened cranberry fruit were harvested from a 930-cm2 area of each plot in Massachusetts, and from two 930-cm2 areas within each plot in New Jersey. Fruits were placed in a sieve with 5.6-mm openings to remove fruit too small to be sellable. The fruit were then visually sorted to remove rotten or damaged fruit; poor fruit were counted. The remaining sellable fruit were counted and weighed to determine sellable yield.
Statistical Analyses
All statistical analyses were conducted using the generalized linear mixed model (GLIMMIX) procedure in SAS version 9.4 (SAS Institute Inc., Cary, NC). Each combination of site (including variety) and year was considered as a site-year sampled from a population as proposed by Carmer et al. (Reference Carmer, Nyquist and Walker1989). Site-year, replications nested within site-year, and all interactions containing site-year were designated random in the model. Sulfentrazone rate, timing of application, method of sulfentrazone delivery, and interactions between them were considered as fixed effects. The weed-free control was excluded from the two-way ANOVA for visual crop injury and shoot development because these ratings were determined as a percentage of the weed-free control. When main affect interactions were not significant, data were pooled appropriately and noted below. Yield and shoot growth measurement data were subjected to a one-way ANOVA since the nontreated weed-free control was included in the analysis. Because of unequal variance, visual estimates of crop and fruit injury were arcsine square root transformed before analysis prior to ANOVA (Grafen and Hails Reference Grafen and Hails2002) and back transformed for presentation purposes. The significance of the fixed effects was tested using Fisher’s protected LSD test with significance set at P = 0.05. If no interactions were observed, data were combined over fixed effects. Nontreated plots were not included in analysis of visual injury.
Results and Discussion
Boom Application Study
Visual Crop Injury Ratings
The application timing by sulfentrazone rate interaction was significant for crop injury 2 WAT and crop stunting 4 WAT. For all other observations, data are presented by main effect in the absence of significant interaction between timing and rate of sulfentrazone application. Leaf injury 2 WAT was similar for low and high sulfentrazone rates applied at the SD stage or a low sulfentrazone rate applied at the CH stage with 2% to 6% injury (Table 1). By contrast, applying a high sulfentrazone rate at the CH stage increased cranberry leaf necrosis to 23%. Crop necrosis did not persist beyond 2 WAT, with at most 3% at 4 WAT and 1% at 8 WAT, regardless of timing of application or sulfentrazone rate (data not shown). Cranberry vine stunting was quite noticeable 2 WAT with significant effects of both sulfentrazone rate (P = 0.0333) and timing of application (P < 0.0001). Applying the high rate of sulfentrazone or delaying sulfentrazone application to the CH stage increased cranberry stunting by 23% and 15%, respectively, compared with applications at the low rate or at the SD stage (Table 1). Stunting 4 WAT was still 12% higher with the high sulfentrazone rate applied at the CH stage than with the low rate at the SD stage. However, no difference between treatments was observed 8 WAT with stunting ranging from 9% to 12% (data not shown).
Boom application study. Visual evaluation of cranberry injury response to rate and timing of boom-applied sulfentrazone at Southampton, NJ, and Chatsworth, NJ, in 2018; and at Pemberton, NJ, in 2019.
a Data were pooled over site-years and main effects when rate × timing interaction was not significant. Main effect means (n = 24) within a column followed by the same letters are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05.
b Abbreviation: SD, spring dormant = tight red bud; CH, cabbage head =loosening of bud scales; WAT, weeks after treatment.
c Necrosis (leaf injury) and vine stunting were rated relatively to the nontreated weed-free control on a 0% (no necrosis or stunting) to 100% (plant death or absence of new growth) scale.
Visual Shoot Elongation Ratings
Timing of application did not affect elongation of new shoots emanating from the terminal bud, as determined by visual ratings (Table 2). Sulfentrazone, regardless of application timing or rate, consistently reduced shoot elongation at 2, 4, and 8 WAT, compared with the nontreated control (data not shown). Sulfentrazone at the high rate reduced shoot elongation by 37% at 2 WAT compared with the low rate (Table 2). Shoot elongation following sulfentrazone applied at the high rate was still impaired 4 and 8 WAT by 17% and 12%, respectively, compared with the low rate. The terminal shoot growing annually at the end of cranberry uprights bears the flowers. Thus, reduction in the development of the terminal shoot may result in potential yield decline.
Boom application study. Visual evaluation of cranberry terminal upright elongation in response to rate and timing of boom-applied sulfentrazone at Southampton, NJ, and Chatsworth, NJ, in 2018; and at Pemberton, NJ, in 2019.
a Data were pooled over site-years and main effects when rate × timing interaction was not significant. Main effect means (n = 24) within a column followed by the same letters are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05.
b Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales; WAT, weeks after treatment.
c Terminal upright elongation was rated relatively to the nontreated weed-free control on a 0 to 5 scale with 0 = no terminal shoot and 5 = maximum elongation of the terminal shoot.
Stem Measurements
The visual observation of persistent overall vine stunting and reduction of terminal shoot elongation following sulfentrazone boom application prompted a quantitative assessment of cranberry upright development at 8 WAT (Table 3). The percentage of dead buds at the apex of cranberry uprights was higher with the high rate of sulfentrazone at the CH stage (45%) than the low rate at the SD stage (21%) or than nontreated vines (13%). For uprights that produced a shoot, the high rate of sulfentrazone used at the CH stage caused a 24% reduction in shoot length in comparison with nontreated plants. The cumulative number of fruits and flowers per upright decreased by 24% and 32% with the low and high rates of sulfentrazone, respectively, applied at the CH stage compared with the nontreated plants. Concurrently to the increased necrosis of the apical bud, the high rate of sulfentrazone at the CH stage also stimulated the development of secondary shoots from previously dormant buds. For instance, 40% of the uprights bore an average of 0.64 axillary shoots per upright with a high rate of sulfentrazone at the CH stage versus 22% and 0.25 axillary shoots per upright for the nontreated vines (Table 3).
Boom application study. Development of cranberry terminal upright 8 wk after treatment (in response to rate and timing of boom-applied sulfentrazone at Southampton, NJ, and Chatsworth, NJ, in 2018; and at Pemberton, NJ, in 2019.
a Data were pooled over site-years. Means (n=12) within a column followed by the same letters are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05.
b Reproductive structures are the cumulative number of flowers and fruit counted on the terminal shoot.
c Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales.
Cranberry Yield
Commercial yield was significantly reduced by the high rate of sulfentrazone, dropping by 6.3 megagrams (Mg) ha−1 (−36%) with application at the SD stage and 9.7 Mg ha−1 (55%) with later application at the CH stage (Figure 1). A low rate of sulfentrazone at the CH stage also tended to decrease yield by 5.3 Mg ha−1 (−30%) compared with cranberry vines that remained untreated. Fruit density was reduced between 43% and 57% with sulfentrazone applied at the CH stage (data not shown).
Boom application study. Cranberry commercial yield response to boom-applied sulfentrazone at Southampton, NJ, and Chatsworth, NJ, in 2018; and at Pemberton, NJ, in 2019. Fruit were collected approximately 5 mo after treatment. Data were pooled over site-years. Means (± SE, n = 12) sharing a same letter are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05. Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales.
Mitigation Study
Because of the divergent phytotoxicity results observed between simulated chemigation in Massachusetts and boom-sprayed sulfentrazone in New Jersey, a joint study was conducted in both states to compare both methods of sulfentrazone delivery, and to evaluate whether washing-off with water following boom application might mitigate the injury and yield reduction reported in the previously discussed boom application study. Timing by method of application interaction was not significant for visual observations at all rating events; therefore, results have been averaged over main effects.
Visual Crop Injury Ratings
Sulfentrazone applied on SD cranberry caused only minor crop injury 2 and 4 WAT, whereas later application at CH resulted in 6% to 10% leaf necrosis (Table 4). Chemigating sulfentrazone or boom application followed by (fb) wash off did not significantly reduce the level of necrosis injury at any rating time compared to boom application alone. Crop stunting 2 WAT was affected by both timing and method of application (Table 4). Late application at CH caused 53% crop stunting versus only 1% at SD. The SD and CH applications were separated by 11 d in 2019 and 15 d in 2020, and minimal shoot extension occurred during this time. Thus, the lack of shoot growth explains the absence of stunting injury 2 wk after herbicide was applied at the SD stage. More stunting was noted 2 WAT with chemigation (31%), or with boom application fb wash off (33%) than with boom application alone (17%). Sulfentrazone is readily root-absorbed by various crops and weed species (Bailey et al. Reference Bailey, Hatzios, Bradley and Wilson2003; Dayan et al. Reference Dayan, Weete and Hancock1996; Thomas et al. Reference Thomas, Troxler, Smith, Fisher and Wilcut2005), and root uptake of this weak acid herbicide (pKa = 6.56) has been shown to increase as soil pH decreases because of higher water solubility and greater proportion of sulfentrazone in a lipophilic form (Ferell et al. Reference Ferrell, Witt and Vencill2003). Thus, we hypothesize that the higher volume of spray solution required by chemigation or generated by washing off the boom application may have caused sulfentrazone to penetrate deeper into the soil and reach the cranberry rhizosphere where sulfentrazone can be readily absorbed since the pH of cranberry bogs rarely exceeds 5. Following the onset of cranberry annual growth, evaluations 4 WAT showed more crop stunting with SD (17%) versus CH (10%) applications. However, by 8 WAT, crop stunting was reduced to 5% on average with no difference between the two timings of application. The difference noted at 2 WAT between the three methods of application was not observed 4 and 8 WAT with an average of 13% and 5% cranberry stunting, respectively.
Mitigation Study. Visual evaluation of cranberry injury response to timing and method of sulfentrazone application at East Wareham, MA, in 2019; and Pemberton, NJ, in 2019 and 2020.
a Sulfentrazone was applied at 420 g ai ha−1 in a single pass. Data were pooled over site-years and main effects when timing x method interaction was not significant. Main effect means (n = 36 for timing; n = 24 for method) within a column followed by the same letters are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05.
b Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales; CHEM, chemigated at 3,740 L ha−1; BOOM, boom sprayed at 190 L ha−1; BOWA, boom sprayed at 190 L ha−1 followed by 0.25 cm water wash-off; WAT, weeks after treatment.
c Necrosis (leaf injury) and vine stunting were rated relatively to the nontreated weed-free control on a 0% (no necrosis or stunting) to 100% (plant death or absence of new growth) scale.
Visual Shoot Elongation Ratings
Visual ratings of shoot growth development indicated that applications at SD reduced the development of the terminal new shoot 2 and 4 WAT compared with applications at CH (data not shown). This may merely reflect the phenology lag between the two timings of application with longer extension of new shoots occurring after CH than SD. No effect of the method of application was noted on visual rating of shoot growth (data not shown).
Stem Measurements
Measurements of uprights 8 WAT showed that the proportion of dead apical buds increased to 40% on average with boom application and boom application fb wash off at CH compared to 15% dead buds for the nontreated plants (Table 5). The length and the number of flowers borne by the newly developed terminal shoot was reduced by 11% and 30%, respectively, with boom application fb wash off at CH compared with nontreated plants. Axillary shoots sprouted on 37% of uprights sprayed with boom-applied sulfentrazone fb wash off versus 19% for the nontreated plants. We hypothesize that this may be the result of greater necrosis of the terminal bud with CH application as observed in the boom application studies. Necrosis of the terminal bud releases the dormancy of lateral buds that will develop into nonreproductive shoots (Shear Reference Shear1916). It is also important to note that chemigation or boom application of sulfentrazone at SD did not affect the development of the terminal shoot nor stimulate the emergence of nonproductive axillary shoots. Measurements taken at harvest did not show any significant difference between treatments regarding the length of new uprights or the number and length of axillary shoots, indicating that some compensation of early injury may have occurred during the growing season (data not shown). However, the proportion of collected uprights that had a dead terminal bud tended (P = 0.0527) to remain higher on average (15%), with boom application at the CH stage alone or fb wash off compared with the nontreated control (8%).
Mitigation Study. Development of cranberry terminal upright 8 wk after treatment in response to rate and timing of boom-applied sulfentrazone at East Wareham, MA, in 2019; and Pemberton, NJ, in 2019 and 2020.
a Sulfentrazone was applied at 420 g ai ha−1 in a single pass. Data were pooled over site-years. Means (n = 12) within a column followed by the same letters are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05.
b Reproductive structures is the cumulated number of flowers and fruit counted on the terminal shoot.
c Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales; CHEM, chemigated at 3,740 L ha−1; BOOM, boom sprayed at 190 L ha−1; BOWA, boom sprayed at 190 L ha−1 followed by 0.25 cm water wash-off.
Cranberry Yield
No significant yield reduction was noted with SD applications, regardless of method of sulfentrazone delivery (Figure 2). Chemigation of sulfentrazone at CH did not significantly reduce commercial fruit yield; however, boom application at this stage caused yield to drop by 30% compared with the nontreated control, even after this application was washed off with 0.25 cm of water. However, no significant reduction in individual fruit weight was noted, with 1.3 g on average for fruits from plots where sulfentrazone was boom applied at the CH stage versus 1.5 g for fruits from the nontreated control (data not shown).
Mitigation study. Cranberry commercial yield response to sulfentrazone method of application in 2019 at East Wareham, MA, and Chatsworth, NJ; and in 2020 at Pemberton, NJ. Fruit were collected approximately 5 mo after treatment. Data were pooled over site-years. Means (± SE, n = 12) sharing a same letter are not significantly different from each other according to Fisher’s protected LSD test at P ≤ 0.05. Abbreviations: SD, spring dormant = tight red bud; CH, cabbage head = loosening of bud scales; CHEM, chemigated at 3,740 L ha−1; BOOM, boom sprayed at 190 L ha−1; BOWA, boom sprayed at 190 L ha−1 followed by 0.25 cm water wash-off.
Implications for Control
Boom-applied sulfentrazone resulted in early season cranberry injury and caused significant yield reduction when applied at 420 g ha−1 regardless of timing for the boom application study, but only at the CH stage for the mitigation study. Further statistical analysis across both studies of sulfentrazone boom-applied at 420 g ha−1 revealed a treatment by variety interaction with significant yield reduction occurring only at the CH stage for the ‘Stevens’ variety, and at both SD and CH stage for the ‘Early Black’ and ‘Demoranville’ varieties (data not shown). This result warrants further investigation of cranberry varietal sensitivity to sulfentrazone applied at 420 g ha−1. Similar injury (e.g., partial leaf necrosis or stunting) have been reported for a wide variety of annual crops such as soybean (Swantek et al. Reference Swantek, Sneller and Oliver1998; Taylor-Lovell et al. Reference Taylor-Lovell, Wax and Nelson2001), peanut (Grey et al. Reference Grey, Bridges and Brecke2000), and potato (Bailey et al. Reference Bailey, Wilson and Hines2002; Hutchinson et al. Reference Hutchinson, Boydston, Ransom, Tonks and Beutler2005). Reduction in plant height ranging from 0% to 60% has been identified as an indicator of soybean sensitivity to sulfentrazone applied PRE at 500 g ha−1; the cultivar-specific response being attributed to differential rates of metabolism and intrinsic tolerances to herbicide-induced peroxidative stress (Dayan et al. Reference Dayan, Weete, Duke and Hancock1997). Leaf necrosis resulting from over-the-top sulfentrazone applications at 410 g ha−1 has been reported on various field-grown ornamental species with phytotoxicity mostly apparent on new shoots and mainly due to contact rather than translocation (Collins et al. Reference Collins, McNeil and Weston2001). A similar response was noted in this study, especially when sulfentrazone at 420 g ha−1 was applied, when cranberry had already started annual growth.
Previous studies have demonstrated that sulfentrazone soil adsorption decreased as soil pH increased, especially at pH values higher than the sulfentrazone pKa of 6.56 (Grey et al. Reference Grey, Walker, Wehtje and Hancock1997). However, the potential for sulfentrazone injury also increased with low organic matter or clay content and in coarse-textured soils (Grey et al. Reference Grey, Walker, Wehtje and Hancock1997; Ohmes and Mueller Reference Ohmes and Mueller2007; Szmigielski et al. Reference Szmigielski, Schoenau, Johnson, Holm, Sapsford and Liu2009; Taylor-Lovell et al. Reference Taylor-Lovell, Wax and Nelson2001). In New Jersey and Massachusetts, cranberries are typically grown on sandy soils with less than 2% organic matter, which can increase sulfentrazone bioavailability and phytotoxicity potential. The uptake of sulfentrazone by plant roots has been shown to increase as soil pH decreases because a low-pH soil environment will increase the proportion of the more lipophilic neutral form (Ferrell et al. Reference Ferrell, Witt and Vencill2003). Soil pH of cranberry bogs usually ranges between 4 and 5, which could increase sulfentrazone uptake by cranberry roots and explain transitory injury noted with sulfentrazone applied at the SD stage. Results of this study show that boom-applied sulfentrazone at 420 g ai ha−1 and at CH (the end of cranberry dormancy) reduced fruit yield 33% to 72% depending on the cranberry cultivar when compared with the untreated control. Crop damage from boom-applied sulfentrazone at CH was not mitigated by washing the herbicide from the vines with water with commercial yield comparable to boom application alone. In an experiment conducted in in New Jersey in 2020, boom-applied sulfentrazone over the top of cranberry vines after CH but before bloom caused severe necrosis of newly formed uprights, illustrating cranberry sensitivity to sulfentrazone used as a foliar contact herbicide (TEB, unpublished data). Similar sensitivity at the CH stage may explain the severity of the injury and corresponding yield reduction associated with boom applications. Conversely, simulating chemigation of sulfentrazone at 3,740 L ha−1 of water did not cause significant crop injury or yield reduction at the SD or CH stage. It is possible that the large volume of water used for chemigation and the repeated wetting of the crop foliage reduced the deposition of sulfentrazone on cranberry canopy and prevented damage to developing cranberry tissues. However, it remains to be determined whether the application method affects the efficacy of weed control.
A few commercial formulations of sulfentrazone recently added cranberry to their label without restricting applications to a specific crop stage. Recent experiments conducted in Massachusetts and New Jersey indicate that PRE-applied sulfentrazone will provide greater than 60% control of polytrichum moss 5 mo after treatment, regardless of rate (280 or 420 g ha−1) or timing of application (SD or CH phenology stage; Ghantous Reference Ghantous2020; TEB, unpublished data). This suggests that growers in New Jersey and Massachusetts may rapidly adopt sulfentrazone for controlling increasingly troublesome moss in cranberry beds. Considering that the results of this study highlight the importance of application to dormant vines to minimize potential crop damage and yield decrease, recommendations for application of sulfentrazone over the top of cranberry vines before scales of the terminal bud start loosening to protect developing tissues from herbicide contact would be prudent practice at this time.
Acknowledgements
Funding to support this research was provided by the IR-4 Project, The Cranberry Institute, the Cape Cod Cranberry Growers’ Association, Ocean Spray Cranberries, the Cranberry Research Foundation, the New Jersey Blueberry and Cranberry Research Council, and the American Cranberry Growers’ Association. We thank Baylee Carr, Maggie Wasacz, and Krystal DeMoranville for their technical support. No conflicts of interests have been declared.
