Organic Farming (1+1)

Organic Methods of Weed Management

Thermal Weed Control

• Thermal weed control involves the use of flaming equipment to create direct contact between the flame and the plant. This technique works by rupturing plant cells when the sap rapidly expands in the cells.
• Sometimes thermal control involves the outright burning down of the weeds. Flaming can be used either before crop emergence to give the crop a competitive advantage or after the crop has emerged.
• However, flaming at this point in the crop production cycle may damage the crop. Although the initial equipment cost may be high, flaming for weed control may prove cheaper than hand weeding.

Soil Solarization

• During summer and fall, organic farmers sometimes sterilize their soil through solarization.
• During this process, a clear plastic film is placed over an area after it has been tilled.
• Solarization works when the heat created under the plastic film, which is tightly sealed at the edges, becomes intense enough to kill weed seeds.

Mulch

• Mulching or covering the soil surface can prevent weed seed germination by blocking light transmission preventing seed germination.
• Allelopathic chemicals in the mulch also can physically suppress seedling emergence.
• There are many forms of mulches available. Listed are three common ones:
  1. Living Mulch
     • Living mulch is usually a plant species that grows densely and low to the ground, such as clover.
     • Living mulches can be planted before or after a crop is established.
     • It is important to kill, till in, or otherwise manage the living mulch so that it does not compete with the actual crop.
  2. Organic Mulches
     • Such materials as straw, bark, and composted material can provide effective weed control.
     • Producing the material on the farm is recommended since the cost of purchased mulches can be prohibitive, depending on the amount needed to suppress weed emergence.
     • An effective but labor-intensive system uses newspaper and straw.
     • Two layers of newspaper are placed on the ground, followed by a layer of hay.
     • It is important to make sure the hay does not contain any weed seeds.
  3. Inorganic Mulches
     • Materials such as black polyethylene have been used for weed control in a range of crops in organic production systems.

Mechanical Weed Management

• Managing weeds mechanically is both time consuming and labor-intensive but it is also one of the most effective methods for managing weeds.
• The choice of implementation, timing, and frequency will depend on the structure and form of the crop and the type and number of weeds.
• Cultivation involves killing emerging weeds or burying freshly shed weed seeds below the depth from which they will germinate. It is important to remember that any ecological approach to weed management begins and ends in the soil seed bank.
• The soil seed bank is the reserve of weed seeds present in the soil. Observing the composition of the seed bank can help a farmer make practical weed management decisions.

Stale Seedbed

• The stale or false seedbed technique of flushing out weed seeds from the soil works by depleting the seed bank. After the soil is cultivated two to three weeks before sowing, emerging weeds are killed by flaming or light cultivation.
• By helping to reduce the seed bank. This technique reduces subsequent emergences of weeds.

Crop Rotation

• Crop rotation has been at the heart of the organic weed management system since medieval times and has persisted well into the 20th century due to its proven effects on weed populations.
• The goal of a crop rotation is to create an unstable environment that discourages weeds from becoming established in the field. Deciding on the sequence of crops, a farmer must take into account the type of soil he or she is working with, the climate, and the crop. Diverse crop rotations are essential to build a healthy, sustainable organic system and break pest and weed cycles.
• In general, it is best to alternate legumes with grasses, spring-planted crops with fall-planted crops, row crops with close-planted crops, heavy feeders with light feeders. Careful use of cover crops during times when the ground would be bare adds valuable nutrients (especially nitrogen), adds organic matter, improves soil microbial diversity, and prevents erosion.
• Maintain a long-term balance of diverse crops on a farm, taking into account any necessary soil conservation practices, livestock requirements, time constraints and market profitability.

Crop Establishment and Competition

• Make sure crops emerge first to give them a head start in their competition with weeds. Transplanting helps increase a crop’s competitive ability since the plants are larger and easier to establish.
• Sow crops close together by reducing the row spacing. Since the crop will take up more space, it shades the weeds, reducing the weeds’ ability to compete. Another technique involves increasing the seeding rate of a crop. This increases the competitive ability of the crop by increasing the odds that the crop will survive in greater numbers than the weeds.
• The most effective way to control weed growth is to have highly competitive crops. A vigorously growing crop is less likely to be adversely affected by weed pressure. It is imperative to create conditions where the intended crop can establish dominance quickly. Using high-quality, vigorous seed, well adjusted planting equipment, adapted varieties, optimal soil fertility, good soil drainage and tilth, and proper soil preparation will usually result in rapid, vigorous crop growth.

Sanitation

• Using clean seed will prevent the introduction of new weed problems and will avoid planting a generous crop of weeds with your desired crop. Mowing weeds around the edges of fields or after harvest prevents weeds from going to seed.
• Hand-roguing weeds in problem areas, and thoroughly composting manure can reduce the spread of weed seeds and difficult weed species. Thorough cleaning of any machinery that has been used in weedy fields is a good idea, as is establishing hedgerows to limit wind-blown seeds.
• Common sense, yes — and it works! Cultural practices won’t prevent all weed growth, and some mechanical follow- up will usually be necessary, but cultural practices can improve soil conditions, permitting more effective mechanical control, they can adjust weed species to ones that are easier to control, and, most importantly, cultural weed-control practices can produce high-quality, vigorous, high-yielding organic crops.
• It is important to maintain proper sanitation on the farm to reduce the introduction and spread of weed seeds.
• There are several ways to keep weeds and weed seeds from entering the farm. First, any animal manure that will be used on the farm should be composted because weed seeds can pass through an animal’s digestive system unharmed, it is important to compost the manure.
• Composting results in temperatures that become high enough to kill many weed seeds. Second, purchase certified seed that is guaranteed to be free of weed seeds. If you are a farmer interested in saving your own seed, be diligent about collecting clean seed so you do not contaminate your collections. Also make sure to remove weeds before they set seed. Once a weed is allowed to set seed, the number of weed seeds in the seed bank is increased. Last, keep tillage and other equipment clean when moving between fields to reduce the spread of weed seeds.

Allelopathy

• Allelopathy is an alternative and organic approach to weed control that uses chemicals that are excreted from a plant to cause either direct or indirect harm to weeds by negatively affecting their germination, growth, or development.
• Nearby weeds can be affected by allelopathic chemicals entering the rhizophere from the roots or the aerial parts of the crop plant. Crop residues from cover crops, such as fall rye, or other organic mulches can also be used to suppress weeds through such allelopathic interactions.
• This “allelopathy” is one of nature’s most effective techniques of establishing plant dominance. Allelopathic crops include barley, rye, annual ryegrass, buckwheat, oats, sorghum, sudan-sorghum hybrids, alfalfa, wheat, red clover and sunflower. Selecting allelopathic crops can be useful in particularly weedy fields with reducing overall weed pressure.

Soil Fertility & Condition

• In an organic system, it is important to rely on the biological activity of the soil as the main source of fertility and favorable soil physical structure. An active and diverse soil microbial population is the key to growing healthy, high-yielding organic crops. Successful organic fertility management should primarily feed the soil microbial life in a long-term manner, rather than simply feeding the plants.
• Soil organic matter is a tremendous source of plant nutrients and water holding capacity. Soil tests can be useful, but only if the results are interpreted appropriately for an organic system. Careful attention to the balance of key nutrients can often reduce weed problems and enhance crop plant growth. One common mistake made by many organic farmers is the improper application of manure or improperly finished compost.
• This can throw off the balance of certain soil nutrients and microbial life and can often increase weed growth. Some soil fertility amendments, such as gypsum, can increase the looseness and tilth of the soil. This improves success for mechanical-cultivation operations, but it also seems to reduce the pressure from certain weed species that are favored by hard, tight soils.

Variety Selection

• Careful selection of crop varieties is essential to limit weeds and pathogen problems and satisfy market Lely weeder. needs. It is important to consider planting disease-resistant varieties if certain pathogens are prevalent in the area. Any crop variety that is able to quickly shade the soil between the rows and is able to grow more rapidly than the weeds will have an advantage.
• Deep shading crops, which intercept most of the sunlight that strikes the field and keeps the ground dark, will prevent the growth of many weed species. Alfalfa, clover and grasses are particularly good shading crops because any weeds that grow in them will usually be cut when hay is harvested, thereby preventing weed seed production.

Mycoherbicides

• Herbicides especially soil applied, have harmful effects on both human and animal health. In this context, fungal pathogens control specific weeds and continue to survive on the weeds year after year unlike herbicides that are to be applied every year.
• Fungal pathogens as a bioagent in controlling weeds are more popular than bacterial, viral or nematodes because, most of the plant pathogens are fungi, which are destructive and widely prevalent, and they can be safely used in organic farming.
• Phytopathogens normally initiate diseases in specific weeds and produce phytotoxins killing the weeds within 3-5 weeks.

Characteristics of Mycoherbicides

1. They should be culturable in artificial media.
2. They should produce abundant spores.
3. They should be stable in storage.
4. Should be genetically stable.
5. Effective under field condition.
6. Tolerant to variation in temperature.
7. These herbicides should be compatible with other chemicals/culturable practices.
8. For controlling water hyacinth: Alternaria eichhornea, Cercospora piaropi, C. rodmanii, Uredo eichhornea and Rhizoctonia solani.
9. For controlling weeds in rice and soybean field: Colletotrichum gloeosporoids.
10. For controlling Eupatorium reparium : Rust fungus.

List of Fungicides Used to Control Specific Weeds

Mycoherbicides	Weeds to Control	Trade Name
Colletotrichum gleosporoids	Aeschynomene	Collego
Colletotrichum furarioides	Aslepias seriacea	-
Cercospora rodmanii	Eichornea crassipes	ABG 5003
Puccinia chandrillus	Chandrillana juncea	-
Puccinia abrupta	Parthenium hysterophorus	-
Phytophthora palmivora	Morrenia odorata	Devine
Alternaria spp.	Crisium avense	-
Alternaria cassia	Cassia abistifolia	Caset
Alternaria crassa	Datura stromonium	-
Alternaria helianthi	Xanthium stromarium	-
Phomopsis convolvuluus	Convolvulus arvensis	-
Bipolaris halepense	Sorghum halepense	-

• Mycoherbicides under the trade name Collego are popular in USA. Devine is a liquid formulation of pathotype Phytophthora palmivora .
• Colego is wettable formulations of Colletotrichum gloeosporoids.
• The skeleton weed (Chandrillana juncea) was a problematic weed in wheat belt of Australia and has been successfully controlled by rust fungi.