Response of the Weed Maryland Meadowbeauty (Rhexia mariana L.) and Blueberry to Flumioxazin PRE

ABSTRACT

Field studies were conducted in 2007 and 2008 in North Carolina to determine the response of the weed Maryland meadowbeauty and blueberry to flumioxazin PRE (pre-emergence). No injury to non-bearing (blueberry plants not mature enough to produce fruit) or bearing (blueberry plants mature enough to produce fruit) blueberry from flumioxazin PRE was observed. In non-bearing blueberry, control of meadowbeauty was greater than 97% 90 DAT (days after treatment) with the registered rate of 0.42 kg ai ha^–1 flumioxazin. Across two studies in bearing blueberry, a single application of flumioxazin at 0.42 kg ai ha^–1 controlled meadowbeauty 79% to 92% 90 DAT. Flumioxazin at 0.21 kg ai ha^–1 applied twice 60 d apart resulted in greater than 96% meadowbeauty control 90 d after the first application. Treatments of flumioxazin applied as a single application or two applications applied sequentially 60 d apart in bearing blueberry had yields ranging from 3150 to 6065 kg ha^–1and 3551 to 5735 kg ha^–1, respectively, and did not have a negative effect on blueberry yield regardless of application rate compared to the nontreated check.

KEYWORDS:

• Herbicide tolerance
• herbicide efficacy
• yield

Nomenclature

flumioxazin;	=	Maryland Meadowbeauty, Rhexia mariana L.; blueberry, Vaccinium spp.
PRE	=	Preemergence
DAT	=	Days after treatment

Introduction

North Carolina is the sixth largest producer of blueberries (Vaccinium spp.) in the United States with approximately 2500 ha harvested in 2013 (USDA, 2014). Within North Carolina, blueberries are the most lucrative fruit commodity with a value of $71 million (USDA, 2014). The shallow root systems of blueberry cause the crop to be particularly vulnerable to competition from weeds (Demchek et al., 2014) and likely injury from exposure to herbicides (W. Mitchem, personal communication). Due to the high value of the crop, weed control and crop tolerance to herbicides are of great concern to blueberry producers. The roots of many weeds occupy the same soil zone as the shallow root systems of blueberry, and young bushes less than 3 years old are especially vulnerable to injury from weeds (Pritts and Hancock, 1992). Weeds compete with the crop for nutrients and can serve as alternate hosts for pathogens and insects (Pritts and Hancock, 1992). Additionally, the weed communities observed in blueberry fields are dominated by difficult to control perennial species, such as pine (Pinus spp.), holly (Ilex spp.), greenbriar (Smilax spp.), small deciduous trees, and various species of herbaceous perennials. These species can interfere with blueberry production and harvest.

One of the most aggressive perennial weeds in North Carolina blueberry fields is Maryland meadowbeauty [Rhexia mariana L. (Melastomataceae)]. Maryland meadowbeauty (hereafter known as meadowbeauty) is an herbaceous perennial that reproduces both sexually and vegetatively (Craine, 2002). After a meadowbeauty plant flowers in late summer, shoots with overlapping leaves and short internodes are produced from shallow rhizomes and remain small until growth resumes in the spring (James, 1956). The ability to reproduce in this way enables the species to grow in high densities and spread aggressively in some environments (Craine, 2002).

The natural habitat of meadowbeauty is very similar to that of blueberries and this weed can be found in wet, open areas from Massachusetts to Florida, and as far west as southern Indiana, Missouri, and Texas (Gleason and Cronquist, 1991). In Massachusetts, meadowbeauty and highbush blueberry (Vaccinium corymbosum L.) are commonly associated in natural communities that occur in acidic, nutrient-poor, wet soils. Meadowbeauty also depends on full sunlight for survival. In North Carolina, meadowbeauty is common in highly disturbed areas like roadside ditches, agricultural fields, and forest edges. Meadowbeauty has invaded disturbed and undisturbed areas in Florida (Craine, 2002).

Flumioxazin was recently registered for use in blueberry (Anonymous, 2011). Flumioxazin is a N-phenylphthalimide herbicide that inhibits protoporphyrinogen oxidase in the chlorophyll biosynthetic pathway (Bigot et al., 2007; Scott et al., 2001) and results in light-induced lipid peroxidation and destruction of cellular membranes (Moreland, 1999). When applying PRE, flumioxazin controls many annual broadleaf weed species, including pigweeds (Amaranthus spp.), nightshades (Solanum spp.), common lambsquarters (Chenopodium album L.), and Florida pusley (Richardia scabra L.) (Anonymous, 2011). In addition to blueberry, flumioxazin is registered for use in grape, fruit and nut trees, and strawberry (Anonymous, 2011). Because flumioxazin controls many broadleaf weed species and certain fruit crops have shown tolerance to flumioxazin, the objective of these studies was to determine the efficacy of flumioxazin on meadowbeauty and the tolerance of non-bearing and bearing blueberry to flumioxazin PRE.

Materials and methods

Field experiments were conducted in non-bearing (less than 3 years old and too immature to produce fruit) and bearing (older than 3 years and mature enough to produce fruit) blueberry bushes in grower fields near the communities of Harrells (34° 36ʹ 58ʺ N, 78° 20ʹ 15ʺ W) and Burgaw (34° 36ʹ 12ʺ N, 77° 51ʹ 13ʺ W), NC in the southeastern coastal plain. The soil at Harrells was a Lynn Haven (sandy, siliceous, thermic Typic Alaquods)—Torhunta (coarse-loamy, siliceous, active, acid, thermic Typic Humaquepts) complex with CEC 10.7, pH 3.8, and 3.9% organic matter. The soil at Burgaw was Murville Muck (sandy, siliceous, thermic Umbric Endoaquods) with CEC 7.9, pH 4.7, and 4.1% organic matter. Treatments were applied with a CO₂ pressurized backpack sprayer equipped with two DG8002 TeeJet Drift Guard flat-fan nozzles (TeeJet Technologies, Wheaton, IL, USA) spaced 51 cm apart with each nozzle delivering 187 L ha^–1 at 289 kPa at a walking speed of 4.8 km h^–1. A pass was made on each side of a blueberry row. Each plot was 1.2 m wide by 5 m long and included four blueberry bushes. The experimental design was a randomized complete block with four replications.

Crop injury was determined visually 14 d after treatment (DAT) and weed control ratings were determined 30, 60, and 90 DAT (this timing was at harvest) after treatments were initiated using a scale of 0 (no crop injury or no control) to 100% (crop death or complete control) (Frans et al., 1986).

Non-bearing blueberry studies

In 2008, two experiments were conducted on ‘O’Neal’ and ‘Legacy’ blueberry at Harrells and Burgaw, respectively. Treatments included flumioxazin PRE at 0, 0.21, 0.28, 0.35, 0.42, and 0.49 kg ai ha^–1. Glufosinate herbicide at 1.12 kg ai ha^–1 was applied to all plots to control emerged weeds. Treatments were applied when blueberry were flowering to leaf out at Harrells on 21 March 2008 and at Burgaw on 17 March 2008.

Bearing blueberry

Single application flumioxazin studies

Experiments were conducted in ‘Croatan’ and ‘O’Neal’ blueberry at Harrells and Burgaw in 2007 and 2008. Treatments included flumioxazin PRE at 0, 0.21, 0.28, 0.35, 0.42, 0.49, 0.56, 0.63, 0.7, and 0.76 kg ai ha^–1. In 2007, in order to remove emerged weeds, all plots were mowed and plant debris was raked from plots prior to application of flumioxazin. In 2008, glufosinate at 1.12 kg ai ha^–1 was applied to the entire test area when flumioxazin treatments were applied. In 2007, treatments were applied at Harrells and Burgaw on 13 July (postharvest, blueberry with leaves). In 2008, treatments were applied at Harrells on 31 March (blueberry with leaves) and at Burgaw on 12 March (blueberry in flower to leaf out).

Sequential application flumioxazin studies

Experiments were conducted in 2008 at both grower locations in bearing blueberry bushes. Treatments were a factorial arrangement of flumioxazin rate by application timing. Treatments included flumioxazin applied at 0, 0.21, 0.28, 0.35, and 0.42 kg ai ha^–1 applied as single treatments and as sequential treatments. Application timings included the initial application (Early PRE) and the sequential application applied approximately 60 d after the initial application (Late PRE). Hexazinone, the grower standard treatment in North Carolina, was applied Early PRE at 0.75 and 1.5 kg ai ha^–1 for comparison. To control all emerged weeds, glufosinate at 1.12 kg ai ha^–1 was included with Early PRE treatments and paraquat at 0.84 kg ai ha^–1 was included with all Late PRE treatments. Early PRE treatments and Late PRE treatments were applied at Harrells on 31 March (blueberry with leaves) and 26 May 2008 (blueberry with leaves and immature fruit), respectively. Early PRE and Late PRE treatments were applied at Burgaw on 12 March and 15 May 2008, respectively.

In experiments conducted in bearing blueberry bushes, ripe and nonripe fruit were harvested from two bushes in each plot. All fruit including nonripe fruit were harvested at one time to insure that the farmer did not harvest fruit prior to data being collected. Fruit was sorted into ripe and nonripe fruit and weighed. The weight of nonripe fruit was converted into ripe weight [Eq. (1)]:

(1)

Average individual ripe and nonripe berry weights were determined by weighing 10 sets each of 250 ripe and nonripe berries and then dividing by the total number to obtain the average. Total yield per plot was calculated by taking the sum of the ripe fruit weight and the converted nonripe fruit weight. Analysis of variance (ANOVA) was conducted and means were separated using Fisher’s protected LSD (p = 0.05).

Results and discussion

Blueberry injury

No crop injury from flumioxazin was observed visually in non-bearing or bearing blueberry (data not shown). These results are similar to conclusions reported in other experiments in peach (MacRae et al., 2002) and grape (W. Mitchem, personal communication).

Meadowbeauty control

Non-bearing blueberry studies

Meadowbeauty was present at both Harrells and Burgaw locations. No differences among herbicide treatments was observed at 30, 60, and 90 DAT between locations; therefore, treatments were averaged across locations (Table 1). Control of meadowbeauty in nonbearing blueberry with single applications of flumioxazin PRE was 94% or greater 30 DAT, 96% or greater 60 DAT, and 92% or greater 90 DAT. However, meadowbeauty control did not differ among flumioxazin rates (Table 1). Thus, 0.21 kg ha^–1 or greater flumioxazin PRE gave excellent (92% to 97%) control at 30, 60, or 90 DAT and control by 0.21 kg ha^–1 was similar to all rates of flumioxazin above 0.21 kg ha^–1.

Table 1. Effect of flumioxazin on Maryland meadowbeauty control in non-bearing blueberry 30, 60, and 90 DAT averaged across locations at Harrells and Burgaw, NC in 2008.

	Maryland meadowbeauty
Flumioxazin, kg ai ha^–1	30 DAT^z	60 DAT	90 DAT
	% control
0.21	97	96	92
0.28	94	96	92
0.35	96	97	93
0.42	94	98	97
0.49	97	100	97
LSD (0.05)	NS	NS	NS

^zAbbreviations: DAT, days after treatment; NS, not significant.

Bearing blueberry

Single application flumioxazin studies in bearing blueberries

Meadowbeauty was present at both locations in 2007 and 2008 in the flumioxazin studies that involved single application. No difference in meadowbeauty control occurred between years; therefore, treatments were separated by location but averaged across years (Table 2). At 30 DAT, no difference was observed in meadowbeauty control among herbicide treatments at both locations, and control was 97% or greater. At 60 DAT, a treatment by location interaction was observed with herbicide treatments at the Harrells location control ranging from 77% to 94%, with the greatest control from 0.49 to 0.76 kg ha^–1 flumioxazin. However, control was 94% or greater for all treatments at Burgaw 60 DAT and control across treatments did not differ at this location and rating date. Differences in control among herbicide treatments at both locations 90 DAT (at harvest) were observed, and control ranged from 46% to 93%. The greatest meadowbeauty control at 90 DAT was observed from flumioxazin at 0.42 (Harrells) or 0.49 (Burgaw) kg ha^–1 or above.

Table 2. Effect of flumioxazin PRE on Maryland meadowbeauty control in bearing blueberry 30, 60, and 90 DAT^z (at harvest) at Harrells and Burgaw, NC.

	Maryland meadowbeauty
	Harrells			Burgaw
Rate, kg ai ha^–1	30 DAT	60 DAT	90 DAT	30 DAT	60 DAT	90 DAT
	% control
0.21	97	77	46	100	94	53
0.28	98	77	53	100	94	68
0.35	98	82	60	100	95	76
0.42	98	87	88	100	91	79
0.49	99	90	84	100	94	84
0.56	98	93	88	100	94	86
0.63	99	94	88	100	93	83
0.70	99	95	91	100	92	86
0.76	98	94	93	100	98	90
LSD (0.05)	NS	6	20	NS	NS	8

^zAbbreviations: DAT, days after treatment; NS, not significant.

In blueberry, a single application of flumioxazin can be applied at the maximum registered rate of 0.42 kg ha^–1 in a 12-month period (Anonymous, 2011). Flumioxazin at 0.42 kg ha^–1 controlled meadowbeauty 98 to 100% 30 DAT at both locations. Flumioxazin at that rate controlled meadowbeauty 87% to 91% at 60 DAT and 90 DAT across locations.

Sequential application flumioxazin studies in bearing blueberries

A treatment by location interaction was present 30 and 60 DAT with the single (Early PRE) application treatments of flumioxazin and with the at harvest rating with the sequential (two applications spaced 60 d apart) application treatments. Thus, data for each location are presented separately (Table 3). At 30 DAT with the Early PRE application, control of meadowbeauty was 97% or greater for all treatments at both Harrells and Burgaw. By 60 DAT with the Early PRE application, control from flumioxazin was 76% to 88% at the Harrells location but remained 98% or greater at Burgaw. Meadowbeauty control at harvest for Harrells and Burgaw was greater than 96% for all rates of flumioxazin applied sequentially. However, at harvest those treatments of flumioxazin applied in a single application at the Early PRE timing gave 34% to 81% meadowbeauty control at Harrells and 83% to 97% at Burgaw. The analysis indicates that sequential applications of flumioxazin may be necessary to obtain extended residual control of meadowbeauty. The grower standard herbicide hexazinone did not give acceptable control at Harrells but did at Burgaw.

Table 3. Meadowbeauty control by flumioxazin applied Early PRE or Early PRE followed by Late PRE (60 DAT) at Harrells and Burgaw, NC in 2008.

	Meadowbeauty
			Harrells			Burgaw
Herbicide	Rate, kg ai ha^–1	Timing^z	30 DAT^y	60 DAT	At harvest	30 DAT	60 DAT	At harvest
			% control
Nontreated	0		0	0	0	0	0	0
Flumioxazin	0.21	a	98	77	34	100	99	97
Flumioxazin	0.28	a	100	79	49	100	99	92
Flumioxazin	0.35	a	99	86	63	100	99	83
Flumioxazin	0.42	a	99	88	81	100	99	92
Flumioxazin	0.21	a + b	98	76	98	100	99	99
Flumioxazin	0.28	a + b	97	76	96	100	99	99
Flumioxazin	0.35	a + b	100	86	100	100	99	99
Flumioxazin	0.42	a + b	100	88	99	100	99	99
Hexazinone	4.73	a	21	11	22	100	98	76
Hexazinone	9.46	a	25	19	13	100	99	90
LSD (0.05)			7	15	22	1	1	9

^zTiming: a, single application applied Early PRE; a + b, sequential application of Early PRE followed by Late PRE (60 DAT).

^yAbbreviations: DAT, days after Early PRE application. At harvest evaluation is approximately 90 d after Early PRE application and 30 d after Late PRE application.

Sequential applications of flumioxazin can be applied at the maximum rate of 0.21 kg ha^–1 per application not to exceed 0.42 kg ha^–1 during a 12-month period. Control of meadowbeauty at the registered rate of 0.21 kg ha^–1 applied sequentially (Early PRE plus Late PRE) gave greater than 98% control at blueberry harvest at Harrells and Burgaw (Table 3).

Overall, control of meadowbeauty with flumioxazin at Burgaw was generally greater than the control at Harrells. This result is true of the single application trials in non-bearing and bearing blueberry bushes as well as the sequential application trials. Differences in control between locations are possibly due to a greater density of meadowbeauty at Harrells. Additionally, PRE applications of flumioxazin require moisture to activate the herbicide on soil for residual weed control. The soil at Burgaw was generally wetter than that at Harrells, possibly resulting in more effective herbicide activation and greater residual control. An additional observation was that a higher rate of flumioxazin was needed in bearing blueberries to give excellent control of meadowbeauty than in nonbearing blueberry. A possible explanation for this observation is that nonbearing blueberry fields have been recently tilled prior to establishment. Whereas with bearing blueberry fields, it is likely that meadowbeauty increases in density as a blueberry planting matures.

Blueberry yield

The single and the sequential treatments of flumioxazin did not have an effect on blueberry yield relative to the nontreated check. However, the mean yields were different between locations for the single and the sequential studies. For the single application study of flumioxazin in bearing blueberry, yields were 3150 kg ha^–1 at Harrells and 6065 kg ha^–1 at Burgaw (Table 4). For the sequential study application of flumioxazin in bearing blueberry, Harrells had a mean yield of 3551 kg ha^–1, whereas Burgaw had a mean yield of 5735 kg ha^–1 (Table 4). The lower yields at Harrells may be attributed to variety-related yield reductions experienced by the grower or less than optimum pH of soil at this location (Demchek et al., 2014).

Table 4. Comparison of blueberry yield of the flumioxazin applied Early PRE or Early PRE followed by Late PRE (60 DAT) treatments at Burgaw and Harrells, NC with mean yield reported by the state of North Carolina.

	Blueberry yield
Location	Single,^z kg ha^–1	Sequential, kg ha^–1
Harrells	3150	3551
Burgaw	6065	5735
LSD (0.05)	788	828

^zAbbreviations: Early PRE, single PRE application of flumioxazin; Early PRE fb Late, sequential applications of flumioxazin Early and Late PRE.

Conclusions

Based on injury ratings determined visually and crop yield, blueberry is tolerant to flumioxazin PRE. Flumioxazin applied PRE in a single or a sequential application does not have a negative effect on blueberry yield, even at rates that exceed the maximum registered rate. In non-bearing blueberry, control of meadowbeauty was 97% at 90 DAT with the registered rate of 0.42 kg ha^–1 flumioxazin. Control of meadowbeauty in bearing blueberry with a single application of flumioxazin at the registered rate of 0.42 kg ha^–1 ranged from 79% to 88% at 90 DAT (at harvest). Sequential applications of flumioxazin at 0.21 kg ha^–1 per application resulted in control greater than 96% at harvest. The level of meadowbeauty control with a single application of flumioxazin 90 DAT was considerably lower than the level of control achieved with a split application of flumioxazin 60 DAT with the final application in the sequential treatment. Therefore, flumioxazin applied PRE at the registered rate of 0.21 kg ha^–1 per two sequential applications in a 12-month period is an effective herbicide to provide PRE control of meadowbeauty from seed.

Acknowledgments

We wish to thank the North Carolina blueberry growers for their assistance and Dr. Cavell Brownie, Statistician and Emeritus Professor (1982–2007), North Carolina State University Statistics Department, Raleigh, NC, for her assistance.

Funding

This research was supported in part by grants from the North Carolina Blueberry Council, Inc. and Valent USA Corporation.

Additional information

Funding

This research was supported in part by grants from the North Carolina Blueberry Council, Inc. and Valent USA Corporation.