9. malezas
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MALEZAS
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Quelite
Soya
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Métodos de control de malezas
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• Cuando empieza a diferenciar entre el cultivo y las especies competidoras
• Causa/Efecto– Menos malezas, mas rinde
• Perfeccionamiento de los métodos de control– Herramientas
– Métodos
– Sistemas
Cuando empieza el hombre a controlar las malezas?
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Físicos Fuego, inundación, pastoreo, cobertura (mulch)
Mecánicos Manuales (azada), corte, labranza
Culturales Cultivos de cobertura, rotaciones, fecha de
siembra, distancia entre surcos
Biológicos Insectos entomófagos, enfermedades
Químicos
Hay muchos métodos de control
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Métodos físicos
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• Pros
– “Gratis”
– Rápido
– Libera nutrientes
– Malezas difíciles
• Contras
– Costo energético alto
– Difícil de controlar
– Destruye estructura
– Especies adaptadas
– Efectos indeseados
Fuego
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viento
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Flaming can be an effective nonselective, nonchemical method of weed control. It has been more effective against broadleaf weeds than grasses. Experiments were conducted with a conveyor bench burner apparatus to evaluate flaming to kill broadleaf and grass seedlings at the 0- to 2- and 2- to 4-leaf stages. Most 0- to 2-leaf green foxtail seedlings were killed when flamed at 2, 4, and 6 km/h conveyor speed. A few plants survived when flamed at 8 km/h. Green foxtail seedlings at the 2- to 4-leaf stage were more tolerant to flaming than 0- to 2-leaf green foxtail, and substantial numbers of plants survived at all flaming speeds except 2 km/h. Barnyardgrass was more tolerant to flaming than green foxtail, and many 0- to 2- and 2- to 4-leaf seedlings survived after flaming. However, fresh weight of the live plants at 14 d after treatment was reduced. Some large crabgrass plants survived flaming at both growth stages. Flaming at 2 km/h reduced seedling number and fresh weight, but there was significant regrowth. Common ragweed was more susceptible to flaming at the 2- to 4-leaf stage than at the 0- to 2-leaf stage. Redroot pigweed and common lambsquarters were susceptible to flaming at both 0- to 2- and 2- to 4-leaf stages.
Cisneros and Zandstra. Weed Technology22(2) 290-295. 2008
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• Márgenes del Nilo
– Fertilización y control de plagas
• Arrozales
– Reduce el número de especies pero beneficia a las adaptadas (puede aumentar su número)
– No afecta las no germinadas
• Requerimientos especiales
– Agua, perfil de suelo, estructuras
Inundación
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• Sistemas mixtos
• Pastoreo rotativo intensivo (Voisin)
• No solo es de muy bajo costo sino que transforma la maleza en alimento
– Estiercol bueno para la materia orgánica
• Requiere planificación y entrenamiento
Pastoreo
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• Consiste en cubrir la superficie no ocupada por el cultivo
• Pedregullo, chips de madera, plástico
• Mas común en algunos cultivos intensivos (frutilla, arándanos) y en paisajismo
• Tipo y cantidad de cobertura depende de la disponibilidad local de materiales
Cobertura (mulching)
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Métodos mecánicos
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• Posiblemente el primer método de control
• Todavía en uso en muchas partes del mundo
• Limita seriamente la superficie que puede cuidar cada operario
– Superficies pequeñas (horticultura)
– Agricultura orgánica
Control manual/Azada
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• Parques, jardines, praderas
– Frutales
• Impedir que la maleza fructifique
– Hay malezas que se adaptan al corte
• Requiere pasadas periódicas
– Anuales, evitar la producción de semillas
– Perennes, agotar las reservas
Corte
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• Ventajas
– No afecta la estructura del suelo, no remueve semilla enterrada, no favorece la erosión
• Desventajas
– Insumos, malezas adaptadas, uso limitado
Corte
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• Primer método de control efectivo en cultivos extensivos (labranza mecanizada)
• La mecanización de la labranza permitió un aumento dramático de la superficie de una explotación particular
• Se basa en la destrucción física de la plántula o planta, no afecta a las semillas
Labranza
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• Ventajas
– Elimina sin posibilidad de resistencia
– Expone partes que de otra manera permanecerían protegidas
• Desventajas
– “Recicla” semillas
– Rompe la dominancia apical
– Erosión
¿Buena o mala?
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• Arado de reja, 12%
• Cincel, 34%
• SD, 67%
Semillas en superficie
1997 1998 1999
SD -- 5 561 99
SD POST 10 30 26
Conv. -- 164 241 174
Conv. POST 156 37 19
Cincel -- 255 503 334
Cincel POST 147 34 79
Plantas de Chenopodium album por m2 al momento de la aplicación
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El uso provechoso de estas tecnologías está fuertemente
condicionado por las características del suelo y clima
del lugar donde se las use
El laboreo o la siembra directa no son, de por sí, una panacea o una verdad axiomática, son herramientas cuyas utilidades y limitaciones dependen del ambiente donde se las aplique
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Artico Zona templada Trópico
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• La elección de cual sistema usar debe estar en función de:
– Suelo y clima
– Necesidades y posibilidades del productor
– Disponibilidad de maquinaria
Elección racional
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• Los cultivos RR (Roundup Ready)permitieron control efectivo de malezas sincontrol mecánico
– Pero la ausencia de control mecánico se hace notar en malezas resistentes
• Nuevos cultivos incorporan nuevas resistencias
– Pero todavía son pocos los herbicidas disponibles
La nueva tecnología facilita la SD
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Métodos culturales
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• Objetivo: ocupar el lugar de las malezas
– Trigo, Vicia villosa
• Limitante: humedad disponible
Cultivos de cobertura
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• Distintos cultivos = Distintos herbicidas
– Evita el “acostumbramiento”
• Gran herramienta contra el desarrollo de resistencia
Rotación de cultivos
Maíz Soya Trigo/soya de segunda
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• No son métodos de control por sí solos
• Permite usar mejor el cultivo como método de supresión de las malezas
• Limitantes: disponibilidad de híbridos/variedades, maquinaria
Fecha de siembra/Distancia entre surcos
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Renner and Mickelson (1997) found that a closedsoybean canopy suppressed late-emerging weedsand any weeds that survived a POST herbicide.Kells et al. (2004) and Young et al. (2001) found thatsoybean planted in either 19-cm or 38-cm rowssuppressed weed growth after glyphosateapplication more than soybean planted in 76-cmrows. More rapid canopy closure in narrow rowsreduces weed germination and growth followingherbicide application (Renner and Nelson 1999).Howe and Oliver (1987) found that soybean plantedin 20-cm rows reduced pitted morningglory(Ipomoea lacunosa L.) leaf area index and seedproduction, compared with those growing insoybean planted in 1-m rows
Arce, Pedersen and hartzler. Weed Technology 23(1): 17-22. 2009
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Control biológico
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• Especies exóticas invasivas
– Plantas fuera de su hábitat natural que al encontrar condiciones favorables y no tener su control natural se vuelven invasivas
• Pocos casos exitosos en el mundo
• No es un emprendimiento comercial
– Universidades, gobierno
• Equilibrio delicado
Insectos entomófagos
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• Opuntia stricta, introducida en Australia como cerco vivo en el siglo XIX
• Se expandió hasta ocupar 24 millones de hectáreas en 1926
• 3000 T de pentóxido de arsénico
• Se introdujeron 52 especies de insectos que se alimentaban de Opuntia
• Cactoblastis cactorum (1925)
Algunos éxitos
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• 1968: se introduce el insecto Rhinocyllus conicus para controlar Carduus nutans en praderas del oeste de EEUU
• El control fue efectivo pero pronto el escarabajo empezó a alimentarse de otras plantas nativas
• Hoy se considera un error grave la introducción de este insecto
Y algunas metidas de pata
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• Control de malezas acuáticas con carpas
• Esporas de hongos (bioherbicidas)
– Colletotrichum gloeosporoides f. sp. aeschynomene para el control de Aeschynomenes virginica
– Phytophtora palmivora en frutales en Florida
– Colletotrichum gloeosporoides f. sp. malvaepara control de malva
Otros programas
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Abstract: An isolate of the fungus Dactylaria higginsii obtained from purple nutsedge in
Florida was highly pathogenic to Cyperus spp. The potential of this isolate as a bioherbicide was field tested in natural populations of purple nutsedge in Gainesville and Jay, FL. The fungus was applied in 0.5% Metamucil® as a carrier, and the treatments were: carrier only, 105 conidia/ml +
carrier, and 106 conidia/ml + carrier. Treatments were applied as single, double, or triple postemergence (POST) sprays at biweekly intervals. The disease and secondary infections
developed in about 5 and 15 d after inoculation, respectively, killing most of the infected leaves. All weed growth parameters and disease progress rates were affected by inoculum dosage and
inoculation frequencies. Three inoculations, each at 106 conidia/ml, provided effective control of purple nutsedge compared to a single inoculation, as measured by shoot dry weight, tuber
numbers, and tuber dry weight. Higher rates of disease progress and disease levels, defined by the area under the disease progress curve (AUDPC), occurred with three inoculations at 106
conidia/ml. Disease progress was slower and the level of weed control was lower at 105
conidia/ml compared to the higher inoculum level. Three applications of 106 conidia/ml provided >90% nutsedge control. Dactylaria higginsii appears to be an effective bioherbicide candidate
deserving further development for commercial use.
Kadir et al. Weed Technology 14(1), 1-6.2000
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USDA establece el ARS (Agriculture ResearchService)
1919, laboratorio en París, Francia Se expande a Roma y Tesalonica
200 agentes de control
Japón (Corea del Sur) China (Sino-American collaborative biological
control lab) Argentina, South American Biological Control
Lab (Hurlingham)
Investigación en biocontrol
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Control químico
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• Pre-siembra incorporados
• Pre-emergencia
• Post-emergencia
Herbicidas