Weed Management in New Orchard Plantings

Kristen Obeid, Weed Management Specialist – Horticulture Crops

Weed Reduction/Avoidance in the Preplant Year – Select fields with low weed pressure or use a crop rotation that reduces weeds (e.g. field corn, winter cereals). Control perennial weeds with a 2-year strategy, targeting the most susceptible growth stage with herbicides, early bud in thistles, glowering in vetch species.  Plant a cover crop to smother weeds, especially in the fall before planting.  This will prevent winter annuals from establishing.  Use herbicides to control weeds in the cover crop, e.g. 2,4-D in wheat or glyphosate in the spring to kill the cover crop. Mow weeds before they go to seed, especially around the field edges and neighbouring ditches.  If desired sod can be established in the previous year and rows burnt out with glyphosate.  Ensure a weed-free strip of at least 1.5 m wide to avoid competition from the sod.  CAUTION: Avoid herbicide residues by choosing low rates of non-residual herbicides.

It is critical to control weeds in new plantings early, especially in the first three months after planting and continue at least until the end of July (known as the Critical Weed-free Period in orchards).  Research has shown that any weed growth in the first three months after planting will reduce tree growth.  Weeds allowed to grow near new trees will reduce yields even two years later.

Usually, the final tillage after the trees are planted will level the ground around the tree and remove early weeds.  If you are planning to use a mulch (which will suppress weeds as well as preserve soil moisture, but may cause rodent and root health issues), apply it before the next weeds emerge.  There are several herbicides registered for newly planted trees (see Table 1 below or visit https://cropprotectionhub.omafra.gov.on.ca).  NOTE: rates are often lower for new trees to avoid tree damage.  Make sure you match your soil organic matter percentage with your herbicide choices to avoid damaging the trees.  Combining a preemergence herbicide with both grass and broadleaf control and a contact herbicide for emerged weeds will provide the best results.  Preemergence herbicides are not effective when applied to mulch.  Avoid using glyphosate products in the first few years, because there is the possibility of it being absorbed by the trees if there is any off-target movement of the herbicide at the time of application.  This could result in weaker, stressed trees which are more susceptible to disease.

Table 1. Herbicides Registered for New Plantings

Weeds	Trade Name Active Ingredient	Rate	Crop (s)	Notes
Pre-plant Incorporated (PPI)
Broadleaf and grassy weeds	Trifluralin (Treflan, Thrill, Bonanza) trifluralin	1.2-2.4 L/ha	Apple Apricot Cherry Peach Pear Plum	Before planting trees as an orchard floor or pre-plant treatment.Use higher rates on clay soils.
	Trifluralin (Treflan, Thrill, Bonanza) plus Sencor DF trifluralin plus metribuzin	1.2-2.4 L/ha + 550-750 g/ha	Apple Apricot Cherry Peach Pear Plum	Before planting trees as an orchard floor or pre-plant treatment.Use higher rates on clay soils.
Preemergence (PRE)
Broadleaf and grassy weeds	Chateau EZ flumioxazin	298-448 mL/ha	Apple Pear	DO NOT apply to trees established less than one year, unless protected by non-porous wraps, grow tubes or waxed containers.
	s-metolachlor (Dual II Magnum, Komodo, Metallica) s-metolachlor	1.75 L/ha	Apple Apricot Cherry Peach Pear Plum	Apply once per year as a band under the trees before weeds emerge.
	s-metolachlor (Dual II Magnum, Komodo, Metallica) + Princep Nine-T (s-metolachlor + simazine)	1.25-1.75 kg/ha + 1.1-2.2 kg/ha	Apple Apricot Cherry Peach Pear Plum	Apply once per year as a band under the trees before weeds emerge, preferably after rain has settled the soil around the trees.
	Kerb SC  propyzamide	5.6 L/ha	Apple Pear	Established plantings of at least one year only.Apple from September to mid-November when soil is cool and moist but not frozen.
	Princep Nine-T simazine	1.1-2.2 kg/ha	Apple Apricot Peach	Apply post planting, preemergence to weeds.  Preferably after the soil has settled around the trees.DO NOT apply to soils with < 2% organic matter.
	Prowl H20 pendimethalin	3.7 L/ha	Apple Apricot Cherry Nectarine Peach Pear Plum	Apply as a broadcast or banded treatment using ground equipment before weed germination.Apply the spray directly to the ground beneath the trees and/or in areas between the rows.
	Sinbar terbacil	1.25 kg/ha	Apple Apricot Cherry Nectarine Peach Plum	Apply after planting trees, before weeds emerge.DO NOT use on soils with less than 3% organic matter.Avoid contact with tree trunks and leaves.
Broadleaf weeds and yellow nutsedge	Sandea halosulfuron	35-70 g/ha	Apple	Maximum 2 applications, minimum 21 days between applications.DO NOT apply more than 140 g/ha in one season.DO NOT contact green tissue, such as foliage, fruit or green bark.
Postemergence (POST)
Broadleaf weeds	Aim EC + Agral 90 or Merge carfentrazone + surfactant/solvent	37-117 mL/ha	Apple Apricot Cherry Nectarine Peach Pear Plum	Apply with a hooded sprayer between the rows to control weeds < 10 cm tall.
	Bentazon (Basagran, Benta super, Broadloom) + Merge bentazon + surfactant/solvent	1.75-2.25 L/ha + 1-2 L/ha	Apple Apricot Cherry Nectarine Peach Pear	Direct under the trees to small actively growing trees. Use the lower rate of Merge under hot humid conditions. Make only 2 applications, 10 days apart at the low rate during the planting year. Avoid contact with tree foliage.
	Lontrel XC, Pyralid clopyralid	340 mL/ha	Apple Pear	Trees should be established for 1 year. For control of vetch at early flowering stage.  Apply as a spot treatment. Avoid contact with tree limbs.
Broadleaf weeds and yellow nutsedge	Sandea halosulfuron	35-70 g/ha	Apple	Maximum 2 applications, minimum 21 days between applications.DO NOT apply more than 140 g/ha in one season. DO NOT contact green tissue, such as foliage, fruit or green bark.
Grassy weeds	Assure II + surfactant quizalofop-p-ethyl + surfactant	380-750 mL/ha + 5 L/1000 L	Apple Apricot Cherry Nectarine Peach Pear Plum	Use a directed spray application to minimize the amount of spray coming into contact with the fruit trees. Apply to emerged annual grasses and volunteer cereals in the 2 leaf to tillering stage and to quackgrass in the 2–6 leaf stage of growth. Use the 0.38 L/ha (0.15 L/acre) rate for annual grasses and volunteer cereals. Use 0.5 L/ha (0.2 L/acre) to suppress quackgrass and also control barnyard grass. Use the 0.75 L/ha (0.30 L/acre) rate for quackgrass.
	Poast Ultra plus Merge sethoxydim + surfactant/solvent	0.32 to 1.1 L/ha + 1 to 2 L/ha	Apple Peach Plum	Apply to emerged annual grasses at the two to six leaf stage during active growth. Use these rates for specific weeds: annual grasses 0.32 L/ha; volunteer grains 0.47 L/ha; quackgrass (up to 3rd leaf)1.1 L/ha. Complete grass control will take 7 to 21 days
	Venture L fluazifop-p-butly	0.6-2 L/ha	Apple Pear	One application per year in a band under the trees.Apply at the 2-5 leaf stage of development at the following rates: 0.6 L/ha for volunteer corn; 0.8 L/ha for wheat & barley; 1 L/ha for annual grasses and 2 L/ha for quackgrass. DO NOT apply more than once per season. Grasses emerging after the treatment will not be controlled.
Contact Herbicides
Broadleaf and grassy weeds	Axxe Broad Spectrum Herbicide ammonium salt of fatty acid.	45-106 L/ha	Orchards	Non-selective herbicide designed for control or suppression of grass and broadleaf weeds, such as (but not limited to): crabgrass, pigweed, amaranth, carpetweed and liverworts.Best results are obtained with young actively growing weeds < then 10 cm tall.  The product works best during warm and dray conditions.Use as a shielded spray application to control weeds around the base of trees.
	Biolink Herbicide	3-9% spray solutions	Apple Apricot Cherry Nectarine Peach Pear Plum	A contact, postemergence, non-selective herbicide that works best on newly emerged actively growing weeds that < 15 cm tall.For grass and perennial weeds and more mature broadleaf weeds, use the higher application rates.
	Serene acetic acid	179-717.5 L/ha	Apple Apricot Cherry Nectarine Peach Pear Plum	Established plantings of at least 1 year ONLY.DO NOT allow spray to contact any green plant parts of desirable plants.Do NOT apply directly over the top or crop injury can occur.Apply as a uniform band or spot application directed at weeds on the ground between the trunks.  Use higher volumes for larger weeds.DO NOT apply after budbreak unless using hooded or shielded application equipment.Retreatment is required for regrowth of weeds.