Evaluating weed control and response of newly planted peach trees to herbicides

ABSTRACT

Field experiments were conducted in North Carolina to determine peach response to herbicides. Mesotrione, rimsulfuron, and sulfentrazone did not injure newly planted peach trees. However, halosulfuron at the higher rate caused injury to peach trees, but did not reduce tree cross-sectional area or winter pruning weight. Another field experiment was conducted to determine the effect of herbicide-based programs on weed control. Sulfentrazone alone controlled common lamb’s-quarters and henbit but provided poor control of large crabgrass and yellow foxtail. However, a tank mix of norflurazon or oryzalin with sulfentrazone improved control of these weeds over sulfentrazone alone. Terbacil alone or in tank mix rimsulfuron, and flumioxazin alone gave excellent control of large crabgrass and yellow foxtail.

KEYWORDS:

• Crop injury
• orchard
• weed management
• tree fruit
• herbicide efficacy

Peach (Prunus persica L.) production in the USA totaled 850,000 tons and 600 million dollars in crop value in 2015 on 40,400 ha (USDA-NASS, 2016). Weed interference in fruit trees can affect tree growth, fruit bud set, flower initiation, yield, fruit quality, and winter hardiness (Basinger et al., 2018a, 2018b; Buckelew et al., 2018; Majek et al., 1993). Young orchards may take 2–3 years longer to come into fruit production if infested with weeds (Weller et al., 1985). Majek et al. (1993) reported reduction in tree growth, initial fruit production, flower bud initiation, and winter hardiness in newly planted peach trees with two smooth pigweed (Amaranthus hybridus L.) plants per 0.9 m². Previous studies showed that peach trees grown in weedy or sod floor have fewer total and deep roots, with limited lateral root spread as compared to trees grown in weed-free orchards (Parker et al., 1993; Parker and Meyer, 1996). Weeds present in orchard, if not controlled, can also harbor insects such as tarnished plant bug and stink bugs and spider mites (Killian and Meyer, 1984; Meagher and Meyer, 1990). Weed removal over the total orchard floor or only in tree rows significantly reduces vole and northern pocket gopher populations and their damage (Sullivan and Hogue, 1987). Tamaki (1975) found that broadleaf weeds provide an excellent host for green peach aphid (Myzus persicae L. Sulzer). Thus, weed management is very important in peach orchards to avoid all the negative impact of weed on peach tree growth and yield.

Concerning timing of weed control, a critical weed-free period from bloom to 12 wk after bloom provides the largest fruit size, total yield, and fruit number in peach (MacRae et al., 2007). Huffman (2006) found that the critical weed-free period for young fruit trees in Ontario is May to July to maintain trunk diameter growth, while for bearing fruit trees is from bud break to 30 d after bloom to maintain greatest yields. The use of herbicides for vegetation control results in greater tree growth than when vegetation is controlled by cultivation or hand-hoeing (Bussi et al., 1994; Daniell and Hardcastle, 1972).

Managing weeds in the first 3 years after planting a peach orchard is important to maximize tree growth and subsequent returns on investment once trees start producing (Mitchem and Lockwood, 2017). Traditionally in peach orchards, a preemergence (PRE) herbicide is applied in the spring before emergence of weeds, with a postemergence (POST) herbicide applied as needed through summer. Without the use of PRE herbicides, four applications of POST herbicides would be needed for weed control throughout the season (W.E. Mitchem, personal communication). The current PRE herbicides options to use in peach orchards are diuron, flumioxazin, indaziflam, oryzalin, oxyfluorfen, pendimethalin, rimsulfuron, simazine, and terbacil. Traditionally used herbicides diuron, simazine, and terbacil can persist more than 1 year in quantities sufficient to cause damage to plants (Marriage et al., 1975).

The investigation of other potential herbicides for weed control in peach is important due to the limited number of registered herbicides in newly planted peach trees (Mitchem and Lockwood, 2017). Halosulfuron is a sulfonylurea herbicide that is registered to control broadleaf weeds and nutsedge in pome fruits (Maleae) (Anonymous, 2015). Rimsulfuron is another sulfonylurea herbicide used PRE and POST in citrus, grapes, pome fruit, stone fruits, and tree nuts and is also registered to use in peach (Anonymous, 2010; Jhala et al., 2012). Both halosulfuron and rimsulfuron inhibit branched-chain amino acid production in susceptible weeds by inhibition of the enzyme acetolactate synthase (Senseman, 2007). Sulfentrazone is a phenyl triazonlinone herbicide that disrupts cell membrane by inhibition of PROTOX in the chlorophyll pathway, which leads to buildup of toxic intermediates and causes rapid desiccation of foliar plant tissue (Hatzios, 1998; Senseman, 2007). Sulfentrazone is a PRE herbicide registered for use in berries, citrus (Citrus sp.), grapes (Vitis vinifera), and tree nuts (Anonymous, 2016). Sulfentrazone provides control of small seeded broadleaf weeds, some annual grasses, and nutsedge (Collins et al., 2001; Krausz et al., 1998; Wehtje et al., 1997). The addition of herbicides options will allow peach growers the flexibility to rotate herbicide to effectively manage herbicide-resistant weeds. Therefore, the first objective of this research was to determine the effect of halsofuluron, mesiotrione, rimsulfuron, and sulfentrazone at various rates on newly planted peach tree tolerance. The second objective was to determine effect of herbicide-based programs on weed control and peach tree tolerance.

Materials and methods

Field studies were conducted at the Sandhills Research Station, Jackson Springs, NC (35.21° N, 79.63° W), Central Crops Research Station, Clayton, NC (35.65° N, 78.46° W) and an orchard, Vale, NC (35.49° N, 81.52° W), during 2006 and 2007. Soil was a Candor sand (sandy, Kaolinitic, thermic Grossarenic Kandiudults) with 0.60% humic matter at Jackson Springs, Norfolk loamy sand (fine-loamy, Kaolinitic, thermic Typic Kandiudults) with 0.86% humic matter at Clayton, and Pacolet-Bethlehem sandy clay loam complex (fine, Kaolinitic, thermic Typic Kanhapludults) with 1% humic matter at Vale. Prior to planting peach, soils at all study sites were limed to buffer soil pH to 6.2. At Jackson Springs, peach trees 61–76 cm tall ‘Contender’ (freestone fresh-market type) scion on ‘Guardian’ rootstock were planted at 2.74 and 4.88 m in row and 6.10 m between row spacing in January of 2006 and 2007, respectively. At Clayton, peach trees 61–76 cm tall ‘Contender’ scion on ‘Guardian’ rootstock were hand planted at 2.74 m in row and 6.10 m between row spacing on January 2006. At Vale, peach trees 80 cm tall ‘Flavor Rich’ or ‘July Prince’ scion on ‘Lovell’ rootstock were planted at 4.88 m in row and 6.10 m between row spacing on January 2007. The bottom 30 cm of each tree was painted at planting with white latex paint for protection from contact herbicide at all locations.

All studies were conducted in a randomized complete block design with four replications. Each study included a non-treated check. Herbicides were applied with a CO₂-pressurized backpack sprayer equipped with flat fan 8002XR nozzles (TeeJet Technologies, Wheaton, IL) and calibrated to deliver 187 L ha⁻¹ at 220–234 kPa. Treatments were applied POST-directed to the soil at the base of peach trees using a single nozzle boom resulting in a treated area of 0.5 m on each side of row and total strip width of 1 m. Spray of herbicide treatments contacted the bottom 10 cm of peach stem. Herbicide strips in the tolerance studies were maintained weed-free with flumioxazin at 213.3 g ai ha⁻¹ for PRE weed control and paraquat at 0.67–1.0 kg ai ha⁻¹ with nonionic surfactant at 0.25% volume per volume for POST weed control. A graminicide (fluazifop, sethoxydim, or clethodim) was used as needed for perennial grass control.

Peach response to herbicides

A total of four herbicide tolerance studies were conducted (Table 1).

Halosulfuron

These studies were conducted in 2006 and 2007 at Jackson Springs. Halosulfuron was applied at 26.3, 52.5, 79, 105 g ai ha⁻¹. Each plot consisted of four and three peach trees during 2006 and 2007, respectively. Herbicides were applied on 7 June 2006 and 23 June 2007.

Mesotrione

These studies were conducted in 2006 and 2007 at Jackson Springs. Mesotrione was applied at 105.7, 140.3, 211.4, and 280.1 g ai ha⁻¹. Each plot consisted of four and three peach trees during 2006 and 2007, respectively. Herbicides were applied on 21 June 2006 and 23 June 2007.

Rimsulfuron

These studies were conducted in 2006 and 2007 at Jackson Springs. Rimsulfuron was applied at 70, 140, 210, and 280 g ai ha⁻¹. Each plot consisted of four and three peach trees during 2006 and 2007, respectively. Herbicides were applied on 7 June 2006 and 23 June 2007.

Sulfentrazone

These studies were conducted in 2006 at Clayton and in 2007 at Vale. Sulfentrazone was applied two times sequentially at 210, 280, 350, and 420 g ai ha⁻¹. Each plot consisted of four and three peach trees during 2006 and 2007, respectively. Herbicides were applied 22 May and 7 Aug. 2006 at Clayton, and 23 Mar. and 24 June 2007 at Vale. Each plot consisted of four trees. This study consisted of three replications of peach trees ‘Flavor Rich’ scion on ‘Lovell’ rootstock and one replication of ‘July Prince’ scion on ‘Lovell’ rootstock.

Weed control

This study was conducted in 2007 at Vale, NC. Treatments included sequential application of sulfentrazone (210 or 280 g ha⁻¹), terbacil (890 g ai ha⁻¹), flumioxazin (280 g ai ha⁻¹), sulfentrazone (210 or 280 g ha⁻¹) plus norflurazon (1340 g ai ha⁻¹), sulfentrazone (210 or 280 g ha⁻¹) plus oryzalin (1120 g ai ha⁻¹), and terbacil plus rimsulfuron (1120 g ai ha⁻¹) (Table 1). Herbicides were applied 31 Mar. and 27 June 2007. Each plot consisted of two peach trees of ‘July Prince’ scion on ‘Lovell’ rootstock.

Data collection and analysis

Visual estimates of peach tree injury (0 % = no injury, 75% = leaf drop, 100% = plant death) were determined 1, 3, and 5 wk after treatment (WAT) in the halsofuluron, mesiotrione, and rimsulfuron studies, and 4 and 8 wk after first and second application in the sulfentrazone tolerance and weed control studies (Frans et al., 1986). Winter prunings were weighed after open-center pruning from two trees per plot in the halsofuluron, mesiotrione, and rimsulfuron studies. Tree cross-sectional area (TCSA) was measured at the end of the season after leaf fall from all the studies. Visual estimates of percent weed control on a scale of 0 (no weed control) to 100% (complete weed control) and percent bare ground (area weed-free) were recorded 8 wk after first and second application in the weed control study.

All the data were subjected to ANOVA and analyzed by SAS PROC GLM (SAS 9.2, SAS Institute, Cary, NC, USA) with the fixed effect of treatment and random effects of replication, location, and replication within location. Means were separated using Fisher’s protected least significant difference test at the 0.05 significance level. The non-treated check was not included in peach injury and weed control data analysis.

Results and discussions

Peach response to herbicides

Halosulfuron

Peach injury caused by halosulfuron was chlorotic shoot tips, intraveinal chlorosis and shortened internodes of new growth, and narrow and small new leaves. In 2006, no injury was observed at 1 WAT. At 3 WAT, 39 and 50% injury was observed from halosulfuron at 79 and 105 g ha⁻¹, respectively. Other rates of halosulfuron caused ≤10% injury to peach. At 5 WAT, the trees were growing out of the damage with the new growth appearing more normal; however, new leaves were still small and narrow and the previously damaged growth retained intraveinal chlorosis. Injury was observed 12 and 24% from halosulfuron at 79 and 105 g ha⁻¹, respectively. Other rates caused ≤ 1 % injury. No peach injury from halosulfuron was observed during 2007. However, the possible reason behind the injury difference during both years was not clear.

The interactions for year by application rate were not significant for TCSA and winter pruning weight; therefore data was combined for both years. The effect of application rate was not significant for TCSA and winter pruning weight, and values range from 6.8–7.2 cm² and 0.5–0.7 kg per tree, respectively (Table 2).

Table 1. Common and trade name and manufacturer information for herbicides used in all studies.

Common name	Trade name	Manufacture	Address
Flumioxazin	Chateau^® 51DWG	Valent U.S.A. Corp.	Walnut Creek, CA
Halosulfuron	Sandea^®	Gowan Company LLC.	Yuma, AZ
Mesotrione	Callisto^®	Syngenta Crop Protection, Inc.	Greensboro, NC
Norflurazon	Solicam^® 80WDG	Syngenta Crop Protection, Inc.	Greensboro, NC
Oryzalin	Surflan^® 4AS	United Phosphorus Inc.	King of Prussia, PA
Rimsulfuron	Matrix^® 25DF	DuPont Crop Protection	Newark, DL
Sulfentrazone	Spartan^® 4F	FMC Corporation	Philadelphia, PA
Terbacil	Sinbar^® 80WP	Tessenderlo Kerley, Inc.	Phoenix, AZ

Table 2. The effect of halosulfuron on peach tree cross-sectional area (TCSA) and winter pruning weight in 2006 and 2007 at Jackson Springs, NC.^a

Herbicide	Application rate	TCSA	Pruning weight
	g ai ha^−1	cm^2	kg tree^−1
Non-treated	0	6.8	0.6
Halosulfuron	26.3	7.8	0.7
Halosulfuron	52.5	6.8	0.5
Halosulfuron	79	7.0	0.6
Halosulfuron	105	7.2	0.6
LSD (p = 0.05)		NS	NS

^a Data combined for both years.

Mesotrione

Peach injury from mesotrione was not observed at all rating times. The interactions for year by application rate were not significant for TCSA and winter pruning weight; therefore, data was combined for both years. The effect of application rate was not significant for TCSA and winter pruning weight, and values range from 9.5 to 8.6 cm² and 0.8 kg per tree, respectively (Table 3).

Table 3. The effect of mesotrione on peach tree cross-sectional area (TCSA) and winter pruning weight in 2006 and 2007 at Jackson Springs, NC.^a

Herbicide	Application rate	TCSA	Pruning weight
	g ai ha^−1	cm^2	kg tree^−1
Non-treated	0	8.8	0.8
Mesotrione	105.7	9.5	0.8
Mesotrione	140.3	9.4	0.8
Mesotrione	211.4	8.9	0.8
Mesotrione	280.1	8.6	0.8
LSD (p = 0.05)		NS	NS

^a Data combined for both years.

Rimsulfuron

Peach injury was not observed from any rimsulfuron application rate across all rating dates. The interactions for year by application rate were significant for TCSA and winter pruning weight; therefore, data was presented by years. In 2006, peach in the non-treated check was not different from peach in the 280 g ha⁻¹ (highest rate) of rimsulfuron for TCSA and winter pruning weight. However, in 2007, peach in the non-treated check was less in cross-sectional area than peach in the 280 g ha⁻¹ (highest rate) (Table 4). The lack of meaningful differences among rates of rimsulfuron suggests that it did not reduce TCSA or winter pruning weight.

Table 4. The effect of rimsulfuron on peach tree cross-sectional area (TCSA) and winter pruning weight in 2006 and 2007 at Jackson Springs, NC.

		2006		2007
Herbicide	Application rate	TCSA	Pruning weight	TCSA	Pruning weight
	g ai ha^−1	cm^2	kg tree^−1	cm^2	kg tree^−1
Non-treated	0	10.9	0.9	5.1	0.4
Rimsulfuron	70	12.4	1.1	6.4	0.6
Rimsulfuron	140	10.3	0.8	7.2	0.6
Rimsulfuron	210	11.2	0.9	6.2	0.5
Rimsulfuron	280	9.9	0.7	8.5	0.7
LSD (p = 0.05)		1.3	0.3	1.9	NS

Sulfentrazone

Sulfentrazone did not injure peach trees or reduce TCSA relative to the non-treated check (data not shown). Sulfentrazone needs 1.25–5 cm of moisture within 7–10 d after application (Anonymous, 2016). Precipitation was 0.3 cm at Clayton and 0.36 cm at Vale for the first 2 wk after first application, and 1.31 at Clayton and 0.68 cm at Vale for the first 2 wk after second application. Rainfall at both sites subsequent to the first 2 wk after application was lacking and may have mitigated crop injury due to sulfentrazone.

Weed control

Crop response

No peach injury was observed from herbicide treatments at all rating dates. Differences were not found for TCSA among treatments and the commercially registered grower standards flumioxazin and terbacil (Table 5).

Table 5. The effect of various herbicide-based programs on peach tree cross section area (TCSA), weed control, and percent bare ground at Vale, NC, 2007.

			8 WAT^a
Herbicide	Application rate	TCSA	Large crabgrass		Yellow foxtail		Bare ground
	g ai ha^−1	cm^2	^______________________ % ^____________________________________
Non-treated	-	6.0	-^b	-^c	-^b	-^c	55^b	22^c
Sulfentrazone	210	7.3	38	-	16	-	80	81
Sulfentrazone	280	4.9	5	-	5	-	81	50
Sulfentrazone +	210	4.7	82	98	87	99	98	94
norflurazon	1340
Sulfentrazone +	280	5.5	95	96	100	100	99	96
norflurazon	1340
Sulfentrazone +	210	6.2	66	94	87	100	94	94
oryzalin	1120
Sulfentrazone +	280	4.8	93	75	93	75	92	87
Oryzalin	1120
Terbacil	890	6.0	100	100	100	100	100	100
Terbacil +	890	5.2	95	100	100	100	99	100
Rimsulfuron	1120
Flumioxazin	280	5.5	95	100	100	100	98	93
LSD (p = 0.05)		NS	28	NS	22	NS	11	23

^aWAT, wk after treatment.

^bVisual ratings at 8 wk after first application.

^cVisual ratings at 8 wk after second application.

Weed control. At 4 wk after first application, all treatments provided excellent control (≥ 97%) of henbit (Lamiam amplexicaule L.) and common lamb’s-quarters (Chenopodium album L.) (data not shown). At 8 wk after first application, sulfentrazone alone exhibited no control of large crabgrass (Digitaria sanguinalis L. Scop) and yellow foxtail (Setaria glauca L. Beauv.) while the other treatments (with the exception of sulfentrazone at the lower rate combined with norflurazon or oryzalin) exhibited ≥93% control of large crabgrass and yellow foxtail (Table 5). With respect to common lamb’s-quarters, henbit, large crabgrass, and yellow foxtail, rimsulfuron did not increase control of these weeds over terbacil alone. As the season progressed, few seeds of large crabgrass and yellow foxtail germinated due to drought. Therefore, control at 8 wk after second application was not significantly different between treatments (Table 5).

The treatments were significantly different for percent bare ground at all rating dates (Table 5). At 8 wk after first and second herbicide applications, all treated plots except sulfentrazone alone exhibited 87% or greater bare ground, while the weedy check and sulfentrazone alone were 55 to 22 and 50 to 81% bare ground, respectively (Table 5).

In summary, mesotrione and sulfentrazone did not cause any injury to peach trees or reduce TCSA relative to the non-treated check. Henry et al. (2015) observed no phytotoxicity to olive trees and ≥93% control of several broadleaf weeds with PRE applications of mesotrione at 0.14 kg ha⁻¹. In this study, rimsulfuron was also reported to be safe in newly planted peach which is currently registered to use in peach orchards (Mitchem and Lockwood, 2017). Similarly, Jhala et al. (2012) reported no injury on citrus trees when rimsulfuron was applied alone or in tank mixes with flumioxazin, pendimethalin, or oryzalin. POST-directed applications of flumioxazin and rimsulfuron were reported safe to the peach and almond rootstocks grown in stone-fruit tree nurseries at California (Hanson and Schneider, 2008). However, halosulfuron at the higher rates needs further testing to further define conditions associated with injury reported to peach trees during this study. Lanini (2009) reported significant injury (leaf discoloration, loss of leaves, and dead branch tips) on young prune trees from halosulfuron at 52.5 g ha⁻¹.

Sulfentrazone alone provided adequate control of common lamb’s-quarters and henbit. Sulfentrazone did not adequately control large crabgrass and yellow foxtail, but control of these weeds was improved with the addition of norflurazon or oryzalin. Therefore, selection of a tank mix partner should be made based on several factors including mode of action and weed control spectrum of herbicide, weed species, and weed density. Richardson and Zandstra (2009) reported ≥86% control of annual grasses and Virginia pepperweed (Lepidium virginicum L.) with spring application of a tank mix of sulfentrazone plus pendimethalin.

Herbicide-resistant weeds have been reported in pecan orchards in New Mexico (Mohseni-Moghadam et al., 2013). It is very likely that herbicide-resistant weeds also infest NC peach orchards because they are widespread in other cropping systems throughout the state (Heap, 2018). Therefore, the addition of these herbicides will provide diversity with respect to the modes of action of herbicides that can be used to manage weeds in peach orchards. Use of multiple herbicides (PRE and/or POST) with various modes of action would be beneficial for peach producers to achieve year-round weed control as well as to prevent weed shifts and the establishment of herbicide-resistant weed populations.

Overall these results showed that mesotrione, sulfentrazone, and rimsulfuron have the potential to be a useful part of integrated pest management programs for weed management in newly planted peach. Additionally, these herbicides have both PRE and POST activity which would be effective to control existing weeds as well as provide limited residual activity for late season emerging weeds. However, further research is required to register these herbicides (mesotrione and sulfentrazone) in newly planted peach trees. Herbicide residue limits, also called tolerances, would need to be established in peach because it is a crop harvested for human consumption (D. Kunkel, personal communication). Tolerance of peach to sulfentrazone under increased rainfall (timings and amounts) occurrence requires further research as well.

Nomenclature

Flumioxazin, halosulfuron, mesotrione, norflurazon, oryzalin, rimsulfuron, sulfentrazone, terbacil; Peach, Prunus persica; Common lamb’s-quarters, Chenopodium album (L.); henbit, Lamiam amplexicaule (L.); large crabgrass, Digitaria sanguinalis (L.) Scop.; yellow foxtail, Setaria glauca (L.) Beauv.

Acknowledgments

The authors express appreciation to Jeff Crotts, peach grower in Vale, NC, and to the staffs at the Central Crops Research Station in Clayton, NC and the Sandhills Research Station in Jackson Springs, NC.