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Top 10 Ways to Improve Weed
Control in Greenhouses
Chris Marble
University of Florida/IFAS
Mid-Florida Research and Education Center
Poor weed control results in:
• Unmarketable plants
• Smaller plants (60% + reduction
in growth)
• Increased risks for
diseases/insects
• Can be a safety hazard
• Higher production costs
• Water
• Fertilizer
• Labor
Weeds love greenhouses!
• Optimum light, water, fertilizer, humidity
• Many annual weeds can thrive year-round
• Few herbicide options
• They will take over quickly
Exponential Weed Spread
• Bittercress and oxalis – up to 5,000 seeds per plant/year
• Seeds expelled over 5 to 10 ft.
• 90% germination rate:
• 1 plant = 4,500 seedlings = 20.2 million seedlings in 10-12 weeks
If you build it, they will come.
• From where?
• Contaminated seed
• Infested plugs/liners
• Through vents, doors,
windows
• On people, animals,
equipment
• Irrigation water
• Dirty pots
Top 10 Ways to Improve Weed
Control Inside Your Greenhouse
1. Use high quality media
• Most greenhouse mixes are relatively weed free
• Some peat sources are diminishing
• Using more of the harvested material (top portions)
• Note any new weed problems when changing
suppliers/mixes
Photo credits: Cheryl Boyer
2. Maintain clean floors
• Bare soil floors increase weed occurrence
• Gravel, nursery cloth (fabric mulch), concrete are
good choices
• Clean up spills and organic debris
• Repair torn fabric
Brooms and fabric are more effective than herbicides!
3. Prevention Practices
• Inspect all liners and new plant materials
• Screen greenhouse vents
• Keep media storage areas weed-free
• Control weeds outside of the greenhouse
Controlling weeds outside the
Greenhouse
• Goal: reduce airborne seed,
prevent perennials from
growing under foundation
• Keep surrounding areas
frequently mowed
• Vegetation free strips (~3 ft.)
recommended near
foundation
• Geotextile fabric, gravel
Controlling weeds outside the
Greenhouse
• Tank mix PRE and POST herbicides
• Use non-volatile herbicides around greenhouses
• Do not use soil sterilant herbicides
• Do not use volatile herbicides (2,4-D, others)
• Close windows and vents before spraying outside
(Neal, 1997 “Greenhouse Weed Control”)
4. Sanitation practices
• Clean tools and equipment
before bringing them inside
• Clean used pots and trays
• Do not store filled pots outside
prior to seeding/potting
5. Hand-weed regularly
• Regularly scout for escaped weeds
• Ensure weeds do not go to seed
• Pull weeds when small:
• Large weeds can dislodge small liners/cuttings
• Never leave pulled weeds near crop or on floor
6. Know your weeds
Woodsorrel/Oxalis
• Cool-season perennial (can be year-round)
• Spreads by rhizomes/stolons
• Seeds expelled 16’
• ID: “okra” fruit, heart-shaped leaves
Know your weeds
Bittercress
• Cool-season annual (year-round)
• Spreads by seed, expelled up to 6 ft.
• Produced seed in 5 weeks or less
• ID: cigar-shaped fruit, basal leaves
Know your weeds
Artillery Weed/Pilea
• Creeping herb, sometimes
used as ornamental
• Remove all portions of the
plant (stems easily root)
• ID: Numerous small succulent
light green leaves; fern-like
appearance; flowers in leaf
axils
Fatoua villosa (Mulberry weed)
•
•
•
•
Annual
Heavy seed production
Effective control with mulching
EZ ID: looks like mulberry seedling growing in pots with flowers in leaf
axils; pubescent all over
Know your weeds
Liverwort
• Spreads by spores – very quickly
• Can survive anytime temperatures
are mild and moist – prefers shade
• Moss-like mats on soil surface and
ground cloth, media surface
• Can prevent water/fertilizer from
reaching crop
• EZ ID: Umbrella or cup-like heads,
dense green mats
Know your weeds
Nostoc “algae”
• Not a true algae but a
“cyanobacteria”
• Favored by wet environments
• Will dry up, but can survive harsh
conditions
• Herbarium sample began metabolizing
after being dried for 80+ years (Lipman,
1941)
• Very slippery when wet
• ID: dark green/black gelatinous
masses
http://en.wikipedia.org/wiki/Nostoc_commune
7. Cultural control practices
•
•
•
•
Improve drainage/grade
Gravel floors
Check irrigation uniformity
Don’t overwater
• Micro-irrigation systems
• Cyclic irrigation practices
• Water earlier in the day
Emma Lookabaugh, bugwood.org
Rachel McCarthy, bugwood.org
8. Use Postemergence Herbicides
Contacts
Systemics
• Reward (diquat)
• Scythe (pelargonic acid)
• Axxe/Racer (ammonium
nonanoate)
• TerraCyte (sodium
carbonate peroxyhydrate)
• GreenMatch EX (lemon
grass oil)
• Avenger AG (d-limonene,
citrus oil)
• WeedPharm (acetic acid)
• Finale (glufosinate)*
• RoundUp Pro (glyphosate)
• Grass Herbicides:
• Envoy (clethodim)
• Fusilade (fluazifop-butyl)
9. Preemergence Herbicides
• Marengo® (indaziflam) – new chemistry in ’13
• Only PRE for use in greenhouses
• Long-lasting control of annual broadleaf and
grasses
• Use when no plants are present/fans turned off
• NEVER apply over the top!
• Water in ¼ to ½ in. after application
• Ventilate houses for 24 hrs. after application
• Very low volatility
Marengo Preemergence Control
5 Months After Treatment
Untreated Control
Marengo®
Image courtesy of Dave Barcel, OHP Inc.
Marengo Volatility Trials: Auburn, AL
• Plants were potted three weeks before initiation of
study (1 flat per rep).
• Two rates of indaziflam (7.4 and 14.8 oz/A).
• Treated over-the-top (contacting foliage) or treated
gravel only (to test volatility)
Marengo Volatility Trials: Auburn, AL
• Immediately after application, each bed was
covered with an 8’x8’ mini-greenhouse structure
(46” high). [PVC pipe covered with white co-poly
plastic].
• Due to heat, plants got about .6” of water daily.
• Shade cloth installed over the top of all minigreenhouses.
Trial: Charles Gilliam, Auburn University
Trial: Charles Gilliam, Auburn University
1. Gravel only – in
ground beds (x)
2. Gravel only – in
ground beds (2x)
3. OTT – in ground
beds (x)
4. OTT – in ground
beds (2x)
5. OTT – outside
ground beds (x)
6. OTT – outside
ground beds (2x)
7. Non-treated – in
ground bed
8. Non-treated –
outside ground bed
Petunia – 30 DAT
1. Gravel only – in
ground beds (x)
2. Gravel only – in
ground beds (2x)
3. OTT – in ground
beds (x)
4. OTT – in ground
beds (2x)
5. OTT – outside
ground beds (x)
6. OTT – outside
ground beds (2x)
7. Non-treated – in
ground bed
8. Non-treated –
outside ground bed
Impatiens – 30 DAT
Edwards, Gilliam, Marble. 2013. Can Indaziflam be used in greenhouse production of annuals? SNA Proceedings 58:309-313.
Marengo® herbicide
• Good tank mix partner (RoundUp and others)
• Mix Marengo first, then the tank mix partner
• Up to 8 months of control in some cases
• Granular formulation available for use in container
production
• Can control oxalis, annual bluegrass, crabgrass early
postemergence
Herbicide Use inside Greenhouses
• Turn off circulation and ventilation fans
• Note rain-fastness of herbicide (cut off irrigation)
• Avoid drift
• Use larger droplet sizes on nozzles
• Use lower pressure in sprayers
• Do not spray sidewalls, ceilings, etc.
• Condensation may drip onto plants
Herbicide Use inside Greenhouses
• Read the label!
• Some herbicides have many aliases
• Only legal to use ones labeled for greenhouses
• Fluazifop butyl – Fusilade II labeled for use in
Greenhouses; Ornamec® 170 (same active) is does
not list greenhouse on label
• Most greenhouse herbicides are off-patent
• Make sure greenhouse use is permitted on product you
are using
10. Non-chemical controls
• Mulching can be an effective weed control
practice
• When to use:
• Chemically sensitive plants
• Areas where herbicides can’t be applied
• Longer-term crops
• Keys to effective mulching:
• Use coarse, organic medias (pinebark nuggets, etc.)
• 0.5 to 1 inch. deep
Photo credit: AM Murphy
Photo credit: C. Gilliam
Photo credit: C. Gilliam
Non-chemical controls
• Solarization
• Can be effective for existing weeds
• Requires several weeks, warm weather
• Seeds can remain dormant until
conditions become ideal
• Steaming
• 180° for at least 30 min.
• Equipment, cost concerns
• Flaming
• Most enjoyable method!
• Generally not recommended inside GH
Image courtesy of thermalweedcontrol.com
1-10-100 Rule
1
10
100
Prevention Cost
Sanitation, prevention, proper
cultural practices
Correction
Cost
Herbicides, minimal hand
weeding, etc.
Failure Cost
Excessive hand weeding,
reduced growth, crop loss
Questions?
Chris Marble
[email protected]
Office: 407-410-6960
Cell: 256-390-5456