Organic Weed Control Cultural & Mechanical Methods Corn (next to a field of oats/peas/barley) that has recently been cultivated for the second and last time with a high-clear- ance cultivator. Peter Martens, cultivating soybeans on a John Deere 3020 with JD725 front-mount cul- tivator and a IH133 rear-mount cultivator, both with C-shank teeth. The front has half by Mary-Howell & Klaas Martens sweeps, the back has sweeps. The front cultivator is modified to have two gangs per row eeds happen. That is a fact of instead of the standard single gang in the middle of the row. The rear cultivator is modi- fied with a side shifter to keep it aligned with the front cultivator on side hills. life for organic farmers, and Wtherefore many of our field soil conditions, weather, crop rotations weed control is a multi-year, whole-farm, operations are designed to make sure that and field histories, machinery, markets multi-faceted approach — and you are the health and quality of our crops are not and specific market quality demands, and probably doing much of it already without jeopardized by the inevitable weed pres- available time and labor. You must have realizing the effect your actions have on sure. Planning an effective the ability to adjust your weed pressure. Reprinted from weed-control program weed-control strategies to the Writing in 1939, German agricultural involves many different unique and ever-changing researcher Bernard Rademacher stated, aspects of organic crop challenges of each year. “Cultural weed control should form the production. As farmers August 2002 • Vol. 32, No. 8 Above all, you must be basis for all weed control,” and that “the begin to explore organic observant, and, in the words other various means should be regarded as possibilities, the first two questions of William Albrecht, you must learn “to auxiliary only. The necessary condition for invariably seem to be: “What materials do see what you are looking at.” any successful weed control is the promo- I buy for soil fertility?” and “What tion of growth of the crop species. machinery do I buy to control weeds?” CULTURAL WEED CONTROL Vigorous plant stands are the best means We asked these questions when we start- Do you think that weeds just happen, for eradicating weeds.” The same wisdom ed organic farming, but we rapidly real- that there is little you can do to limit your must be applied to organic agriculture ized that this is not the best way to under- weed population other than cultivate? today, actively incorporating the philoso- stand successful organic farm manage- Then think again! Before you even think phy that good agronomic practices that ment. about cultivating, there are many things result in vigorous, competitive crop plants To plan an effective weed-control pro- that you can actively do to change field are the real key to successful weed control. gram, you must integrate a broad spec- conditions so that they favor crop growth Many agronomic procedures that trum of important factors, including your and discourage weed pressure. Cultural encourage healthy soil conditions with a diverse microbial population can also reduce weed pressure. Optimizing the biological terrain of the soil for the crop will create an unfavorable environment for many weeds, effectively reducing weed numbers and vigor. This concept forms the core of effective weed control in an organic production system. Contrast this to the weed-control strategies of conventional farming, with heavy use of salt fertilizers, herbicides, monoculture and imbalanced cation satu- rations. Indeed, that environment could accurately be described as one of cultural weed enhancement. The conventional field environment presents heavy pressure to select for herbicide-resistant weeds that thrive under these conditions. Each year, these highly adapted weeds find the same favorable conditions and reproduce abun- dantly. It is really no wonder that most Lely weeder. herbicides are only effective for a few years before a newer, stronger (and more crop can establish dominance quickly. tions, but it also seems to reduce the pres- expensive) chemical is needed to control Using high-quality, vigorous seed, sure from certain weed species that are weeds sufficiently. well-adjusted planting equipment, adapt- favored by hard, tight soils. It is important to know your enemy. All ed varieties, optimal soil fertility, good 3. Crop Rotation. Diverse crop rota- weed species have their weaknesses and soil drainage and tilth, and proper soil tions are essential to build a healthy, sus- their strengths, usually occurring at dis- preparation will usually result in rapid, tainable organic system and break pest tinct stages of their life cycles or resulting vigorous crop growth. and weed cycles. In general, it is best to from specific growth patterns. Different 2. Soil Fertility & Condition. In an alternate legumes with grasses, weeds present problems at different times organic system, it is important to rely on spring-planted crops with fall-planted of year, or with different crops. Some the biological activity of the soil as the crops, row crops with close-planted crops, weed-control strategies, such as disking a main source of fertility and favorable soil heavy feeders with light feeders. Careful field infested with quackgrass, may even physical structure. An active and diverse use of cover crops during times when the increase the prevalence of certain species soil microbial population is the key to ground would be bare adds valuable nutri- of weeds under specific conditions. growing healthy, high-yielding organic ents (especially nitrogen), adds organic Grassy weeds often require different con- crops. Successful organic fertility man- matter, improves soil microbial diversity, trol measures than do broad-leafed weeds. agement should primarily feed the soil and prevents erosion. Maintain a Correctly identifying the species of weeds microbial life in a long-term manner, long-term balance of diverse crops on a that are causing major prob- rather than simply feeding farm, taking into account any necessary lems in your fields is critical Reprinted from the plants. Soil organic mat- soil conservation practices, livestock to choosing and timing ter is a tremendous source requirements, time constraints and market effective control measures. of plant nutrients and water- profitability. It is valuable to have a good August 2002 • Vol. 32, No. 8 holding capacity. Soil tests 4. Allelopathy. Some plant species weed-identification book can be useful, but only if the compete with each other by releasing and use it regularly during the season until results are interpreted appropriately for an chemical substances from their roots that you are confident recognizing your most organic system. Careful attention to the inhibit the growth of other plants. This common and troublesome weeds. balance of key nutrients can often reduce “allelopathy” is one of nature’s most While no factor can truly be viewed as weed problems and enhance crop plant effective techniques of establishing plant separate, it is important to examine some growth. One common mistake made by dominance. Allelopathic crops include of the primary management concepts that many organic farmers is the improper barley, rye, annual ryegrass, buckwheat, contribute to effective cultural weed con- application of manure or improperly fin- oats, sorghum, sudan-sorghum hybrids, trol. ished compost. This can throw off the bal- alfalfa, wheat, red clover and sunflower. 1. Crop Competition. The most effec- ance of certain soil nutrients and micro- Selecting allelopathic crops can be useful tive way to control weed growth is to have bial life and can often increase weed in particularly weedy fields with reducing highly competitive crops. A vigorously growth. Some soil fertility amendments, overall weed pressure. growing crop is less likely to be adversely such as gypsum, can increase the loose- 5. Variety Selection. Careful selection affected by weed pressure. It is imperative ness and tilth of the soil. This improves of crop varieties is essential to limit weeds to create conditions where the intended success for mechanical-cultivation opera- and pathogen problems and satisfy market allow the resulting flush of germinating weeds to be killed during final field prepa- ration. Organic gardeners call this tech- nique “stale seed bed.” Weed seeds are stimulated to germinate by the first tillage, then they are killed by the second, final field preparation. Many organic farmers find that in heavily infested fields, late spring plowing will reduce weed pressure by killing weeds that have started to grow and burying many germinating weed seeds. Plowing can have a different positive effect by inverting weed seeds that have started to germinate down deeply where they won’t grow, and bringing other weed seeds that have not yet been stimulated to germinate to the surface. By the time these new weed seeds “get the message” to germinate, you can already have your crop growing. It is important to note that weather con- Cultivating corn, with view of IH133 rear-mount cultivator with C-shank teeth. ditions dictate how effective tillage is in controlling weeds. Naturally, the best needs. It is important to consider planting cal control, they can adjust weed species weed control will be achieved with tillage disease-resistant varieties if certain to ones that are easier to control, and, on a hot, sunny day. Tilling soil that is too pathogens are prevalent in the area. Any most importantly, cultural weed-control wet will result in compaction and loss of crop variety that is able to quickly shade practices can produce high-quality, vigor- soil structure, which will then favor cer- the soil between the rows and is able to ous, high-yielding organic crops. tain types of weeds that prefer hard grow more rapidly than the weeds will ground and will also make later cultiva- have an advantage.