Organic Weed Control Tips

The major challenge in Florida during the transition stage is control of weeds, especially perennial weeds such as Bermudagrass, teaweed, tropical spiderwort, and others that reseed readily. A common organic farming practice is to till the land, leave it barren and allow several generations of weeds to germinate, then till the land again. Growers often till the land as many as six times during a growing season to eradicate weeds and prevent reseeding before they start farming organically. This practice results in high levels of soil erosion and subsequent loss of organic matter from the fragile Florida soils.

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Start With Soil

One of the underlying principles of organic farming is the building of healthy soils with good structure, high organic matter, diverse soil micro and macro fauna, and high water-holding capacity. Such soils can in turn support healthy plants which can better resist disease, insect, and weed pressure. Loss of nutrients and organic matter through erosion depletes soil fertility, and is further aggravated by the fact that synthetic fertilizer cannot be used in organic farming.

Management required for successful transitioning from conventional to organic farming varies with soil type, slope, drainage, fertility levels, weed species, disease concerns, and the subsequent crop. Planting a mixture of grasses or grasses and leguminous crops immediately after tillage is suggested as a way to reduce potential erosion losses. An example of a good combination of grasses includes a mixture of millet and bahiagrass. Millet establishes very quickly and can prevent erosion during the early stages of succession. Bahiagrass is among the best adapted grasses for Florida. It is deep-rooted and can take up nutrients and recycle them from greater depths in the soil horizons. These nutrients would otherwise be lost. Bahiagrass has to be killed through tillage or smother crops. When bahiagrass dies, the roots decay and create channels in the soil profile that increase aeration and water infiltration.

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Small-grain cover crops can be planted into bahiagrass late in the fall with some aggressive tillage. These small-grain crops can be rolled in the spring to smother the bahiagrass, and legumes (peas or beans) may be planted to recharge the soil nitrogen before another nitrogen-requiring vegetable is planted. Forage legumes can also be seeded with bahiagrass. This practice will add nitrogen to the soil. Both summer and winter legumes can be used. The legumes can be drilled into bahiagrass with a sod seeder or over-seeded into bahiagrass after it has been chopped. Burning bahiagrass as a way to establish a good legume crop is not generally recommended because it results in loss of organic matter. It is a good idea for growers to consult their local county Extension agents or Extension forage specialist to select the adapted legumes, seeding rates, and planting method. The seed mixtures should be chosen carefully depending on the time of year and plans for cropping. Research has shown that tilling the field more than once during the growing season does not necessarily result in better weed control. Mixtures of grasses and leguminous plants discussed so far act as mulches in suppressing weeds. Other mulches, including plastic and organic mulches, can be used to suppress weeds.

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