Greenhouse Floors

Ed Peachey and Lloyd Nackley
Revised: 
March 2019

Diligent sanitation is the key to successful weed control inside greenhouses. Weed control also requires special precautions and the use of herbicides that have little or no chance to vaporize. Consequently, only a few herbicides are registered for use inside entirely enclosed greenhouses. Always turn off ventilation fans while applying postemergence herbicides, and avoid contact with desirable vegetation.

clethodim (Envoy Plus)

Rate 0.09 to 0.24 lb ai/a (12 -32 fl oz) with max of 64 fl oz/season)

Time Apply postemergence to actively growing annual or perennial grasses as listed on label.

Remarks Consider environmental and plant growth conditions that affect leaf uptake (see label).

Caution Do not exceed 68 fl oz/a per season.

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

Chemical family Cyclohexanedione

diquat (Reward)

Rate 1 to 2 pts/a (0.25 to 0.5 lb ai/a)

Time Apply with nonionic surfactant any time weeds are small and actively growing.

Remarks Avoid spray contact with desirable ornamental plants. Acts as a contact herbicide; absorbs energy produced by photosynthesis, forming peroxides that disrupt living cells.

Caution A moderately toxic herbicide that requires protective face shields, respirators, and clothing for handling and application. Do not ingest or inhale spray mist.

Site of action Group 22: photosystem I electron diversion

Chemical family Bipyridilium

dithiopyr (Dimension 2EW and other products)

Open shadehouse-type structures

Rate 0.375 to 0.5 lb ai/a (1.5 to 2 pts/a)

Time Apply to bare ground.

Remarks Dimension 2EW may be applied in open shadehouse-type structures where the natural flow of air is unimpeded. For best weed control, apply to soil that is free from clods, weeds, and debris such as leaves. Requires activation with 0.5 inch or more of rain or irrigation.

Caution Do not apply within three weeks prior to enclosing greenhouses or poly-type structures.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Pyridine

glyphosate (numerous products)

Rate Consult labels

Time Apply to actively growing weeds when desired vegetation is out of greenhouse and air circulation fans are turned off.

Remarks Consult label for rates and application times.

Caution Do not exceed 10.6 lb ai/a per year.

Site of action Group 9: inhibits EPSP synthase

Chemical family None generally accepted.

indaziflam (Marengo G)

Rate 0.048 lb ai/a (200 lb/a product).

Time Make applications to these sites during clean up, sanitation, and preparation prior to plant production.

Remarks Marengo G may be used in ornamental production facilities on floors of hoophouses, lathhouses, and shadehouses to provide bare ground and general weed control beneath benches and potted plants. In production nurseries, containers or plants can be moved onto the treated ground bed area after it has been irrigated to activate the herbicide and the treated surface is allowed to dry.

Caution Do not apply Marengo G to areas where water can potentially move Marengo G off the application area.

Site of action Group 29: inhibits cellulose biosynthesis

Chemical family Alkylazine

isoxaben (Gallery 75 DF)

Open shadehouse-type structures

Rate 0.495 to 0.99 lb ai/a (0.66 to 1.33 lb/a)

Time Make applications to these sites during clean up, sanitation, and preparation prior to plant production.

Remarks Gallery may be applied in open shadehouses-type structures where the natural flow of air is unimpeded. Identify weeds and adjust rates according to weeds present or expected.

Caution Do not apply in enclosed greenhouses or in enclosed shadehouse-type structures. Do not apply within three weeks prior to enclosing greenhouses or poly-type structures.

Site of action Group 21: inhibits cell wall synthesis Site B

Chemical family Benzamide

oryzalin (Surflan AS)

Open greenhouse-type structures only

Rate 2 to 4 lb ai/a (2 to 4 quarts/a Surflan AS)

Time Prior to weed emergence.

Remarks Inhibits cell division or mitosis, primarily in roots.

Caution Do not apply in enclosed greenhouses or enclosed shade-house type structures.

Site of action Group 3: microtubule assembly inhibitor

Chemical family Dinitroaniline

pelargonic acid (Scythe)

Rate Broadcast: 3 to 10 gal product/100 gal water. Spot spray: 1 to 10% solution (1 to 13 fl oz/gal) to cover 400 sq ft

Time Apply to thoroughly wet weed foliage in and around greenhouse, under benches, or preemergence in seedling beds.

Remarks Avoid contact with desirable plants. Disrupts cell membranes, causing leakage and symptoms of leaf burn.

Site of action Group 26: unknown

Chemical family Carboxylic acid