Grass Suppression in Row Middles (chemical mowing)

glyphosate (numerous product names)

Rate Read label carefully for crops listed and geographic location.

Time Apply 6 to 8 oz/a to suppress (chemically mow) perennial grass covers between tree rows in orchards.

Remarks Use the 8 oz/a rate to treat tall (coarse) fescue, fine fescue, orchardgrass, or quackgrass covers. For best suppression of these species, add ammonium sulfate at 1.7 lb/10 gal of spray solution. Use the 6 oz/a rate, without ammonium sulfate, when treating Kentucky bluegrass covers. Apply treatments in 20 gal/a spray volumes to actively growing grass covers. For best spray distribution and coverage, use flat fan nozzles. Additional nonionic surfactant may be added at 0.5% concentration when using surfactants with at least 50% ai, or a 1% surfactant concentration for those with less than 50% ai. For best results, mow grass in spring for uniformity, then apply appropriate rate 3 or 4 days after mowing. Low rates will not adequately suppress broadleaf weeds such as dandelion or plantain. If broadleaf weeds infest more than 10% of ground cover, tank mix 2,4-D labeled for orchard use.

Caution Chemical mowing is not recommended if orchard weed management is primarily reliant on glyphosate. Low rates of glyphosate applied multiple times per year may significantly increase the chance of selecting glyphosate resistant populations. Do not treat grass covers under poor conditions such as drought stress (drip irrigation), disease, or insect damage; suppression may be poor.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted

sethoxydim (Poast)

Rate 0.09 lb ai/a (0.5 pint/a Poast)

Time Apply to grasses in orchard floor middles one time only, to suppress growth.

Site of action Group 1: acetyl CoA carboxylase (ACCase) inhibitor

Chemical family Cyclohexanedione

2,4-D amine (Saber, Weed Rhap A-4D, or Dri-Clean Herbicide)

Rate 0.95 to 1.4 lb ae/a (2 to 3 pints/a Saber for stone fruits and nuts only); 3 pints/a for Weed Rhap A-4D)

Time Do not apply during bloom. Preferred timing is late autumn, after harvest but before first frost. Apply after irrigation rather than before, to avoid moving the herbicide into the root zone. Apply as a directed spray as needed to young, actively growing weeds in the prebud to early bud stage of growth.

Remarks Apples and pears: Minimize use in pears after fruit set due to possibility of early ripening. Apparently, Gala, Fuji, and Golden Delicious apples are more sensitive to 2,4-D than are other cultivars. Do not allow spray to contact pear leaves, fruit, tree trunks, or root suckers. Preharvest interval is 14 days. Stone fruits and nuts: 2,4-D can be applied up to twice per season. Preharvest interval is 40 days for stone fruits, 60 days for nuts. Application timing on other fruits and nuts excludes preharvest interval requirements. Mimics natural plant hormones.

Caution Avoid high pressures or other factors that can increase drift. Reduce possible root uptake by avoiding irrigation or rain within 10 days after application. Do not use on light, sandy, or bare soils. Do not use when temperatures exceed 90°F. Do not graze or feed cover crops from treated areas to livestock.

Site of action Group 4: synthetic auxin

Chemical family Phenoxy acetic acid