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 ft 2 ) 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
Greenhouse Trial Wheat Gluten Rates ranging from 900 to 8000 lbs/a (21 to 184 lbs/1000 ft 2 ) 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 ft 2 ) 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) Mustard Seed Meal 575 lbs/a (=1980 lbs/a in the band) Corn Gluten Meal 870 lbs/a (=3000 lbs/a in the band
Effect of organic amendments and herbicides on weeding time of strawberries. hrs/a 600 500 400 300 200 100 0 2000-01 2001-02 Corn gluten (low) Corn gluten (high) Wheat gluten Mustard seed (low) Mustard seed (high) Untreated Goal Prowl Goal + 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 Uncut canes Cut canes
Blackberry & Brush Blocker Diluted, foliar 6.4 fl.oz./400 ft 2 Full strength, cut stem 1/3 qt/400 ft 2
Blackberry & Brush Blocker Summer Treatment Diluted, foliar 11.3 fl.oz./400 ft 2 Full strength 1/3 qt/400 ft 2
Blackberry control after cut-stem treatment with several products % 100 80 60 40 B&BB cut Check cut 20 0 April May June Aug
Blackberry control after foliar treatment with several products % 25 20 15 10 B&BB Untreated 5 0 April May June Aug
Blackberry & Brush Blocker Summer Treatment, Bittersweet Nightshade Full strength, 1.3 qt/400ft 2
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
% 60 50 Effect of organic herbicides for annual weed control 40 30 20 10 2 DAT 4 DAT 8 DAT 15 DAT 0 B&BB early B&BB late Pine oil early Pine oil late
Effect of vinegar for annual weed % 60 50 40 30 20 10 0 White early White late control Cider early Cider late 2 DAT 4 DAT 8 DAT 15 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
% 100 Effect of organic herbicides for weed control 80 60 40 4 DAT1 8 DAT2 20 0 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
% 80 70 60 50 40 30 20 10 0 Effect of organic herbicides on Canada thistle Initial burn Mid-season Season long Clove oil Pine oil Vinegar Paraquat
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