organic weed control products for use in lawns and gardens– weed control ranged from 97% for...

Organic Weed Control Products for Use in Lawns and Gardens

Tim Miller WSU NWREC

Natural Herbicides for Weed Control

• In today’s class, we’ll talk about: – Preplant incorporated and

preemergence products (applied to soil as an amendment or as a surface treatment)

– Postemergence products (applied to weeds that are up and growing either as a foliar or a drench)

Organic Amendments for Weed Control

• PRE/PPI products –Corn gluten meal –Wheat gluten –Mustard seed meal –Distillers grain

Corn Gluten Meal • Protein fraction of corn grain extracted by the

wet-milling process (high fructose corn syrup) • Root formation during germination is inhibited

in susceptible species – Some level of weed control achieved by water

stressing seedlings • Contains 10% nitrogen • Sold as organic amendment for use in turf

and small fruits/vegetable gardening

Corn Gluten Meal • Greenhouse Trial

– Rates equivalent to 2900, 5800, and 8700 lbs/a (67, 133, and 200 lbs/1000 ft2)

– Weed control ranged from 97% for purslane to 0% for quackgrass (seedling) at the low rate and from 100% for purslane, green foxtail, dandelion (seedling), and black nightshade to 45% for velvetleaf at the high rate

– Roots were more inhibited than shoots, control improved by incorporating the product

Wheat Gluten

• Two wheat proteins (gliadin and gluteanin) become elastic when mixed with a liquid and kneaded – Gluten traps carbon dioxide formed from

fermentation by yeast in dough, causing bread to rise

• Like corn gluten, wheat gluten is a source of nitrogen (12%)

• Sold as a food product to bakeries

Wheat Gluten • Greenhouse Trial

– Rates ranging from 900 to 8000 lbs/a (21 to 184 lbs/1000 ft2)

– Weed seed germination was reduced by 50% or more for 8 species at 900 lbs/a and for 12 species at 2700 lbs/a

– Shepherd’s-purse, henbit, annual bluegrass, and Canada thistle (seedling) were most sensitive

– Root inhibition was greater than shoot inhibition

Mustard Seed Meal • Dry portion of mustard seed after the

crushing process removes the oil • Contains high quantities of glucosinolates

(sulfur-bearing molecules) – When moistened, enzymatic degradation of

glucosinolates (myrosinase) releases isothiocyanate, a volatile biocide

– Some level of weed control achieved by killing germinating seedlings

• Contains ~7% nitrogen

Mustard Seed Meal • Field and Greenhouse Trials

– Rates up to 2000 lbs/a (46 lbs/1000 ft2) – Weed control ranged from 25% to over

90%, depending on species – Crop injury

• Killed certain vegetable seedlings • Slowing of growth of perennials

– Also provided some control of fungal pathogens and destructive insects in soil

So…Do They Work?

So…Do They Work? • Corn Gluten Meal

– Not very well – In my trials, I’ve never seen greater

than about 20% weed control from applications of corn gluten meal

– Applications may encourage slugs, crows, and dogs

– Research continues with Hydrolyzed CGM • Amino acids that are not active are

removed, leaving those dipeptides that are active

So…Do They Work?

• Wheat Gluten – Not very well – I saw no weed control in my trials – As with corn gluten meal,

applications may attract slugs

So…Do They Work?

• Mustard Seed Meal – Yes, perhaps too well – Very “hot” on seedling weeds…

…but also on seeded crops (veggies) and on perennials like strawberries

– A similar effect has also been observed from cover cropping mustard family species

Organic Amendments and Herbicides in Strawberry

• Corn gluten meal, mustard seed meal (high and low glucosinolate), and wheat gluten applied post-transplant in 2000 and 2001 – Goal, Prowl, and Goal + Prowl also applied

post-transplant – All treatments applied again in spring of 2001

and 2002

• Hand weeding times noted throughout the growing season

• Berries harvested, 2001 and 2002

Corn Gluten Meal 435 lbs/a (=1500 lbs/a in the band)

Corn Gluten Meal 870 lbs/a (=3000 lbs/a in the band

Mustard Seed Meal 575 lbs/a (=1980 lbs/a in the band)

Effect of organic amendments and herbicides on weeding time of strawberries.

0

100

200

300

400

500

600

2000-01 2001-02

hrs/

a

Corn gluten (low)Corn gluten (high)Wheat glutenMustard seed (low)Mustard seed (high)UntreatedGoalProwlGoal + Prowl

Natural Herbicides for Weed Control

• POST products –Vinegar (acetic acid) –Pelargonic acid –Clove/Cinnamon oil –Pine oil –Limonene –Lemongrass oil

Use of Acetic/Citric Acid for Blackberry Control

• Various products tested for blackberry control (conducted in 2002) – Blackberry & Brush Blocker, Crossbow,

Roundup, and Finale tested

• Products were applied as cut-stem (crowns mowed to 6”) and foliar treatments in mid-February (late dormant)

• Foliar B&BB, Roundup, and Finale applied again in late May (non-dormant)

Untreated Blackberries

Cut canes

Uncut canes

Blackberry & Brush Blocker

Full strength, cut stem 1/3 qt/400 ft2

Diluted, foliar 6.4 fl.oz./400 ft2

Blackberry & Brush Blocker Summer Treatment

Full strength 1/3 qt/400 ft2

Diluted, foliar 11.3 fl.oz./400 ft2

Blackberry control after cut-stem treatment with several products

0

20

40

60

80

100

April May June Aug

B&BB cutCheck cut

%

Blackberry control after foliar treatment with several products

0

5

10

15

20

25

April May June Aug

B&BBUntreated

%

Full strength, 1.3 qt/400ft2

Blackberry & Brush Blocker Summer Treatment, Bittersweet Nightshade

Scythe Foliar, 10%

Interceptor Foliar, 20%

Using Vinegar Drenches • Blackberry work (mine)

– One pint of B&BB reduced re-sprouting of clipped blackberry crowns by 67%

– At the price of $20/gal = $2.50 per crown

• Cranberry work (Kim Patten, WSU Long Beach) – One gallon vinegar (5% acetic acid) per

weed in cranberry bogs gave excellent control of some perennial weeds

– At Safeway price $3.50/gal (per weed)

Control of Annual Weeds With Vinegar Products

• Two household vinegars (5% acetic acid) – White distilled – Cider

• Blackberry & Brush Blocker • Study conducted in 2003

Effect of organic herbicides for annual weed control

0

10

20

30

40

50

60

B&BBearly

B&BB late Pine oilearly

Pine oillate

2 DAT4 DAT8 DAT15 DAT

%

Effect of vinegar for annual weed control

0

10

20

30

40

50

60

Whiteearly

White late Ciderearly

Cider late

2 DAT4 DAT8 DAT15 DAT

%

Control of Annual Weeds from Two Applications of Organic Herbicide

• Vinegar (Weed Pharm, 20% acetic acid) • Clove oil (Matran 2, 10 and 20%) • Pine oil (Interceptor, 10 and 20%) • Study conducted in 2004 • Products applied twice, one week apart

– First application to cotyledon-stage annual weeds

• Tested with and without two surfactants

Effect of organic herbicides for weed control

0

20

40

60

80

100

4 DAT18 DAT2

%

Weed Pharm Matran Interceptor Alone, with Humisol, with Yucca Extract

Multiple Applications of Organic Herbicides for Control of Canada

Thistle in Raspberry

• Various products tested for Canada thistle control (conducted in 2006) – Organic herbicides

• Clove oil (20%), pine oil (20%), and vinegar (20% acetic acid)

– Conventional herbicides • Gramoxone, Goal, and Finale

Organic Herbicides for Control of Canada Thistle in Raspberry

• Applied as foliar treatments – Organics applied five times

• Four pre-harvest, at weekly intervals from early May through early June

• Once post-harvest, in August

– Conventional products • Once pre-harvest in early May • Once post-harvest in August

– All Canada thistle plants removed by hand just prior to harvest (early July)

Untreated

Untreated

Paraquat

Clove oil

Pine oil

Vinegar

Effect of organic herbicides on Canada thistle

01020304050607080

Initial burn Mid-season Season long

Clove oilPine oilVinegarParaquat

%

Organic Herbicides • Of the several non-selective herbicides

evaluated for organic weed control: – Acetic acid: General consensus is that products

should contain a minimum of 20% acetic acid; acetic acid and limonene should be used full strength (no dilution)

– Clove oil and pine oil: General consensus on rate is for 15 to 20% of the product in water

– Pelargonic acid: New formulation may become organically certified. General consensus on rate is for 5 to 10% of the product in water

Bottom Line: Organic Herbicides • PPI products can be active on seedling

weeds – Mustard Seed Meals can be hot enough to

injure certain vegetable crops and perennials

• POST products can be active on seedling weeds – Acetic acid and oil extracts are best applied on

warm, dry days and generally require repeat applications to effectively control weeds over time

– Injury to adjacent plants may occur