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Spring Webinar Series
20182 p.m. CST
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Upcoming Webinars
• April 4 – North Dakota Cottage Food Law Update– Julie Wagendorf, Director, Food and Lodging Division, North Dakota
Department of Health
• April 11 – Pesticide Safety: Minimizing Exposure– Andrew Thostenson, Pesticide Program Specialist, NDSU Extension
Service
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FSMA Produce Safety Grower Training Workshop
– April 5, 8 am to 5 pm
– Held at ND Farmers Union in Jamestown, ND
– Trainers: Connie Landis-Fisk; Holly Mawby; Julie Garden-Robinson
– Register online on the NDSU “field to fork” website • www.ag.ndsu.edu/fieldtofork• $25, including meals and snacks)
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Zoom Controls
Chat box
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Mute/unmute Open chat box
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Please Complete the Survey• Please complete the short online survey that will be
emailed to you after today’s webinar. It will take just a couple minutes!
• Be sure to sign up for an opportunity to win a prize in the drawing. After submitting the survey, a form to fill out with your name/address will appear.
• Acknowledgement: This project was supported by the U.S. Department of Agriculture’s (USDA) Agricultural Marketing Service through grant 14-SCBGP-ND-0038.
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Weed Management and Soil Fertility for Organic Vegetable ProductionDr. Greta GramigAssociate Professor, NDSU Department of Plant Science
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Weed Scientist, Gardener
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What Causes Weeds?• Human perspectives• Disturbed soils lacking vegetative cover• Immigration / Enemy release• Low diversity ecosystems• Lack of resource niches• Co-evolution
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• Holistic Paradigm:
– Weeds are plants that evolved to occupy particular niches (generally disturbed areas)
– Weeds are SYMPTOMS of a SYSTEM imbalance
– Correct the SYSTEM, correct the SYMPTOM
– Weeds may sometimes have positive functions
• Results of Holistic Approaches
– Weeds always present, but yields largely protected
– Reduction of inputs, more reliance on ecosystem services to achieve fertility and pest management
– Focus on remedying underlying CAUSES of weeds
– Recognize that weeds may have a place in agroecosystems
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Weeds - Always a Challenge!
• Organic gardeners contend with many weed problems, because they cannot use herbicides.
• However, most home vegetable gardeners, whether organic or not, will probably rely mostly on non-chemical weed management techniques.
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Newly Tilled and Planted Garden
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But...... Then Come the Weeds!
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Perennial vs. Annual Weeds• Annual weeds generally have long simple
taproots and can often be easily killed by hoeing or hand pulling.
• Perennial weeds often have complex horizontal root networks and can’t be easily removed via tillage, hoeing, hand pulling.
• Annual weeds can also be suppressed fairly readily with mulch, but even the best mulch usually won’t completely stop perennial weeds.
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Managing Perennial Weeds
• Prevention is key. Start CLEAN. Don’t plant crops into established perennial weeds.
• Dig to remove the plants, roots and all. A garden fork works well to loosen roots.
• Smother with heavy mulch or weed barrier, then remove emerging shoots immediately and often-starve the roots.
• For bad weed patches, cover soil with clear plastic and allow to solarize over a summer.
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Physically Remove Weeds!
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Solarizing
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Set Aside Fallow Each YearGrow a Competitive Cover Crop
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Managing Annual Weeds
• Unlike perennial weeds, annual weeds cannot be eliminated-the soil is loaded with seeds.
• Suppress emergence with mulches, cover crops, or competitive crops
• Without suppression, annual weeds need to be removed via tillage, hoeing, mowing, or hand pulling.
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To Suppress Weeds: Try a Cover Crop!
• Fall planted rye is great for holding N, breaking up heavy clay soils. Suppresses weeds.
• Legumes like sweetcloverare great for adding N.
• Mustard family cover crops can help mitigate soil pests.
• Buckwheat grows quickly, makes P more available.
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Weeds as Cover Crop? As Mulch?
• A dense stand of annual weeds can be cut or pulled and used as a mulch.
• A weed mulch will suppress weeds and break down, adding nutrients to the soil.
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Field Pennycress
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Field Pennycress Mulch
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Mulches: A Physical Barrier Against Weed Emergence
• Plastic mulch (clear, black, colored)– Relatively inexpensive
– Suppresses most annual weeds well
– Does not improve soil
– Contributes to plastic waste
• Organic mulches (hay, straw, leaves, etc.)– Usually some cost involved, except for leaves
– Weed suppression varies with type and depth
– Depending on C/N ratio, can rob N from soil
– Can harbor pests like slugs and mice
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Straw/Hay• Needs to be several inches
thick to suppress weeds.• Decomposes relatively
quickly-adds nutrients.• Hay adds more nutrients
than straw.• Both (but especially hay)
can contain weed seeds.• Both may harbor pests. • Can be expensive.
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Wood Chips• Wood chips can sometimes be free.
• Wood chips suppress weeds at 2-3” deep.
• Over time, wood chips may increase fungal dominance among soil microorganisms.
• Wood chips are coarse, hard to move aside, and interfere with vegetable seedling emerge.
• Wood chips may acidify the soil.
• The C:N ratio is relatively high, so adding extra N might be necessary.
• Some tree species (e.g., black walnut) contain compounds that are toxic to vegetables.
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Deciduous Tree Leaves• Leaves are free and suppress
most annual weeds very effectively.
• Leaves can be easily moved and managed in the garden.
• Leaves form thick mats that can hold in too much moisture-shredded leaves alleviate this problem.
• Slugs love leaf mulch.• Relatively high C:N ratio.
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Newspaper and Cardboard
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Unusual MaterialsCocoa Bean Hulls, Hemp Hurd
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Plant From Starts, Not Seeds
• Planting starts gives crops a head-start.
• Many crops can be started ahead of time.
• A small cold frame can help with producing economical starts.
• Plant later-allow weeds to emerge then remove them.
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‘Lasagna’ No-Till GardeningStraw Bale Gardening (Joel Karsten)
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Soil Fertility 101• Plants need N, P, K (macro); Ca, S, Mg (secondary); Fe, Cu,
Mn, B, Cl, Zn, Mo, Ni (micro).
• Get a soil test. https://www.ndsu.edu/soils/services/soil_testing_lab/how_to_soil_sample/
• Compost, manure, fish emulsion, kelp meal, rock dusts (Azomite), epsom salt (MgSO4), commercial organic fertilizers, KMS, gypsum (Ca and S), dolomite (Ca and Mg), many others!
• https://groworganic.com/media/pdfs/fertilizer-solution-chart-2015.pdf
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Home Composting for OM, N-P-K, and Many Micros Too!
• Start with layer of straw or twigs (for air flow).
• Layer or mix ‘green’ (1/3) and ‘brown’ (2/3) materials.
• Don’t use meat, bones, pet waste, perennial weeds, diseased plants, weed seeds.
• Keep moist, cover if very rainy.
• Turn occasionally (can skip if lazy like me but slower.
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Arbuscular Mycorrhizal Fungi(AMF) and Weeds
• Most crop plants benefit from symbiotic associations with AMF.
• Many weeds do not form these associations.
• Previous studies have indicated that AMF presence can decrease weed growth.
• To encourage AMF: reduce tillage and synthetic fertilizers, grow cover crops.
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Be Nice to Your Soil: Stop Tilling!!!
• Nothing is more detrimental to soil health than tillage!
• Causes loss of organic matter, kills beneficial soil fungi, destroys soil structure.
• Keep the soil covered at all times, dig only as needed to plant crops and pull weeds
• Need to retrain our eye-bare black soil is not good for a healthy garden.
Prairie Road Organic SeedsDeep mulch gardening
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• Weeds are indicators of soil conditions.
• Weeds that root deeply mine soil for nutrients (terminate before seed production occurs).
• Weeds can break up heavy soils and add organic matter, acting like cover crops
Links Between Weeds and Soil Fertility
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Weeds as Indicators• Each weed species differs physiological
in terms of requirements for growth.
• Therefore, weeds can be indicators of soil conditions such as fertility, moisture status, structure, and salinity (EX: kochialoves salt).
• For example, field bindweed indicates compacted or crusted soil structure.
• Legumes such as black medic or clover indicate low soil N content.
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Weeds and Nitrogen Use• Many weedy species are adapted to
high soil N
• One study found that 15 weed species had greater response to N than wheat
• Common lambsquarters, redroot pigweed, kochia, and wild mustard had the greatest response to increased N, both root and shoot
• Bob Quinn, MT organic farmer observation about kochia
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Resource Pool Diversity Hypothesis
• Plant species coexistence may be in part due to diversity of resource niches.
• Previous studies show that plants coexisting in N-limited environment use different forms of N (NO3, NH4, and amino acids).
• What types of N are present in most agroecosystems?
http://www.mnartists.org/artwork/plant-competition
Drawing by Kristi Silber
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Recap• Perennial weeds: remove or starve
roots.• Annual weeds: suppress or remove,
do not allow seed production.• Mulches or cover crops suppress
weeds well AND can also add valuable soil nutrients.
• Test soil to know what nutrients you should add.
• Try out home composting for free nutrients.
• Stop tilling your garden soil – try no-till methods.
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Questions / Comments?
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Questions?www.ag.ndsu.edu/fieldtofork