{"id":13022,"date":"2018-07-06T10:59:05","date_gmt":"2018-07-06T14:59:05","guid":{"rendered":"https:\/\/mundoagro.cl\/?post_type=columnas&p=13022"},"modified":"2020-07-06T17:34:30","modified_gmt":"2020-07-06T21:34:30","slug":"sin-miedo-al-frio","status":"publish","type":"post","link":"https:\/\/mundoagro.cl\/sin-miedo-al-frio\/","title":{"rendered":"Sin miedo al fr\u00edo"},"content":{"rendered":"
Se llama heladas a\u00a0 la\u00a0 exposici\u00f3n\u00a0 a\u00a0 temperatura\u00a0 del\u00a0 aire\u00a0 igual\u00a0 o\u00a0 menor\u00a0 a\u00a0 cero\u00a0 cent\u00edgrados,\u00a0 frente\u00a0 a\u00a0 la\u00a0 que\u00a0 el\u00a0 agua\u00a0 se\u00a0 congela.\u00a0 Heladas\u00a0 intensas\u00a0 por\u00a0 extenso\u00a0 per\u00edodo\u00a0 de\u00a0 tiempo\u00a0 pueden\u00a0 causar\u00a0 da\u00f1o\u00a0 en\u00a0 tejidos\u00a0 vegetales\u00a0 sensibles.\u00a0 Para\u00a0 frutales,\u00a0 esta\u00a0 combinaci\u00f3n\u00a0 ocurre\u00a0 en\u00a0 primavera,\u00a0 con\u00a0 condiciones\u00a0 meteorol\u00f3gicas\u00a0 inestables\u00a0 en\u00a0 el\u00a0 momento\u00a0 en\u00a0 que\u00a0 los\u00a0 tejidos\u00a0 vegetales\u00a0 est\u00e1n\u00a0 m\u00e1s\u00a0 tiernos\u00a0 y\u00a0 expuestos\u00a0 (floraci\u00f3n\u00a0 y\u00a0 cuaja).\u00a0 En\u00a0 las\u00a0 \u00faltimas\u00a0 temporadas,\u00a0 ha\u00a0 prevalecido\u00a0 la\u00a0 incertidumbre\u00a0 acerca\u00a0 de\u00a0 la\u00a0 ocurrencia\u00a0 de\u00a0 heladas\u00a0 que\u00a0 puedan\u00a0 causar\u00a0 da\u00f1o\u00a0 a\u00a0 huertos\u00a0 frutales.\u00a0 Heladas\u00a0 importantes,\u00a0 por\u00a0 magnitud\u00a0 y\u00a0 duraci\u00f3n,\u00a0 ocurrieron\u00a0 en\u00a0 septiembre\u00a0 de\u00a0 2013,\u00a0 cuando\u00a0 afectaron\u00a0 carozos,\u00a0 perales\u00a0 y\u00a0 vides\u00a0 en\u00a0 O\u2019Higgins,\u00a0 y\u00a0 kiwis\u00a0 en\u00a0 El\u00a0 Maule.\u00a0 En\u00a0 octubre\u00a0 de\u00a0 2014\u00a0 se\u00a0 registr\u00f3\u00a0 una\u00a0 helada\u00a0 de\u00a0 menor\u00a0 magnitud,\u00a0 pero\u00a0 con\u00a0 manzanos\u00a0 reci\u00e9n\u00a0 cuajados\u00a0 en\u00a0 El\u00a0 Maule,\u00a0 y\u00a0 una\u00a0 serie\u00a0 de\u00a0 heladas\u00a0 en\u00a0 los\u00a0 primeros\u00a0 d\u00edas\u00a0 de\u00a0 septiembre\u00a0 de\u00a0 2016\u00a0 afect\u00f3\u00a0 a\u00a0 cerezos\u00a0 con\u00a0 avanzada\u00a0 fenolog\u00eda,\u00a0 tambi\u00e9n\u00a0 en\u00a0 El\u00a0 Maule.\u00a0 Esto\u00a0 evidencia\u00a0 la\u00a0 necesidad\u00a0 de\u00a0 conocer\u00a0 el\u00a0 fen\u00f3meno\u00a0 de\u00a0 la\u00a0 helada\u00a0 y\u00a0 su\u00a0 efecto\u00a0 sobre\u00a0 los\u00a0 frutales,\u00a0 como\u00a0 las\u00a0 diferentes\u00a0 alternativas\u00a0 de\u00a0 control,\u00a0 para\u00a0 enfrentar\u00a0 estas\u00a0 situaciones\u00a0 con\u00a0 el\u00a0 mayor\u00a0 acierto.<\/p>\n
TIPOS\u00a0 DE\u00a0 HELADA<\/p>\n
<\/a>Son\u00a0 dos\u00a0 los\u00a0 tipos\u00a0 de\u00a0 heladas\u00a0 que\u00a0 afectan\u00a0 a\u00a0 la\u00a0 agricultura\u00a0 chilena:\u00a0 helada\u00a0 por\u00a0 radiaci\u00f3n\u00a0 y\u00a0 helada\u00a0 de\u00a0 advecci\u00f3n\u00a0 o\u00a0 polar.\u00a0 La\u00a0 helada\u00a0 radiativa\u00a0 se\u00a0 produce\u00a0 por\u00a0 p\u00e9rdida\u00a0 de\u00a0 energ\u00eda\u00a0 desde\u00a0 el\u00a0 suelo\u00a0 a\u00a0 la\u00a0 atm\u00f3sfera\u00a0 durante\u00a0 la\u00a0 noche.\u00a0 \u00c9stas\u00a0 son\u00a0 t\u00edpicas\u00a0 de\u00a0 condiciones\u00a0 postfrontales\u00a0 en\u00a0 invierno,\u00a0 dadas\u00a0 por\u00a0 d\u00edas\u00a0 despejados,\u00a0 sin\u00a0 viento\u00a0 y\u00a0 baja\u00a0 humedad\u00a0 relativa.\u00a0 La\u00a0 temperatura\u00a0 de\u00a0 dichas\u00a0 heladas\u00a0 no\u00a0 suelen\u00a0 ser\u00a0 menor\u00a0 a\u00a0 -3\u00b0C\u00a0 y\u00a0 no\u00a0 influye\u00a0 m\u00e1s\u00a0 all\u00e1\u00a0 de\u00a0 los\u00a0 primeros\u00a0 tres\u00a0 metros\u00a0 de\u00a0 altura.\u00a0 Por\u00a0 otro\u00a0 lado,\u00a0 las\u00a0 heladas\u00a0 advectivas\u00a0 son\u00a0 masas\u00a0 de\u00a0 aire\u00a0 fr\u00edo\u00a0 que\u00a0 se\u00a0 desplazan\u00a0 desde\u00a0 el\u00a0 Polo\u00a0 Sur.\u00a0 Al\u00a0 contrario\u00a0 de\u00a0 las\u00a0 heladas\u00a0 radiativas,\u00a0 al\u00a0 contener\u00a0 una\u00a0 gran\u00a0 masa\u00a0 de\u00a0 aire,\u00a0 pueden\u00a0 alcanzar\u00a0 30\u00a0 metros\u00a0 de\u00a0 altura\u00a0 y\u00a0 con\u00a0 temperatura\u00a0 similar\u00a0 en\u00a0 todo\u00a0 su\u00a0 perfil,\u00a0 de\u00a0 al\u00a0 menos\u00a0 -3\u00a0 \u00f3\u00a0 -4\u00a0 \u00b0C.\u00a0 \u00c9stas\u00a0 son\u00a0 t\u00edpicas\u00a0 de\u00a0 primavera\u00a0 y\u00a0 demarcan\u00a0 perfectamente\u00a0 su\u00a0 paso\u00a0 de\u00a0 acuerdo\u00a0 a\u00a0 la\u00a0 topograf\u00eda.\u00a0 Un\u00a0 evento\u00a0 de\u00a0 este\u00a0 tipo\u00a0 puede\u00a0 permanecer\u00a0 por\u00a0 muchas\u00a0 horas\u00a0 afectando\u00a0 al\u00a0 frutal\u00a0 (5\u00a0 a\u00a0 7\u00a0 horas).\u00a0 Son,\u00a0 sin\u00a0 duda,\u00a0 las\u00a0 heladas\u00a0 m\u00e1s\u00a0 destructivas\u00a0 para\u00a0 la\u00a0 fruticultura,\u00a0 por\u00a0 sus\u00a0 caracter\u00edsticas\u00a0 y\u00a0 por\u00a0 el\u00a0 momento\u00a0 en\u00a0 que\u00a0 ocurren,\u00a0 cuando\u00a0 los\u00a0 tejidos\u00a0 frutales\u00a0 son\u00a0 m\u00e1s\u00a0 sensibles\u00a0 a\u00a0 la\u00a0 baja\u00a0 temperatura.<\/p>\n DA\u00d1O\u00a0 POR\u00a0 HELADA<\/p>\n Se\u00a0 han\u00a0 descrito\u00a0 dos\u00a0 formas\u00a0 por\u00a0 las\u00a0 cuales\u00a0 los\u00a0 tejidos\u00a0 vegetales\u00a0 son\u00a0 da\u00f1ados\u00a0 en\u00a0 presencia\u00a0 de\u00a0 helada.\u00a0 El\u00a0 descenso\u00a0 de\u00a0 temperatura\u00a0 produce\u00a0 un\u00a0 gradiente\u00a0 de\u00a0 potencial\u00a0 h\u00eddrico\u00a0 en\u00a0 el\u00a0 tejido,\u00a0 a\u00a0 medida\u00a0 que\u00a0 el\u00a0 agua\u00a0 de\u00a0 los\u00a0 espacios\u00a0 intercelulares\u00a0 va\u00a0 congel\u00e1ndose.\u00a0 Con\u00a0 ello,\u00a0 el\u00a0 agua\u00a0 contenida\u00a0 en\u00a0 el\u00a0 protoplasma\u00a0 celular\u00a0 (parte\u00a0 de\u00a0 la\u00a0 c\u00e9lula\u00a0 que\u00a0 incluye\u00a0 la\u00a0 membrana,\u00a0 citoplasma\u00a0 y\u00a0 n\u00facleo) comienza\u00a0 a\u00a0 salir,\u00a0 hasta\u00a0 producirse,\u00a0 eventualmente,\u00a0 plasm\u00f3lisis\u00a0 celular.\u00a0 As\u00ed,\u00a0 el\u00a0 da\u00f1o\u00a0 ocurre\u00a0 una\u00a0 vez\u00a0 que\u00a0 la\u00a0 c\u00e9lula\u00a0 no\u00a0 puede\u00a0 retornar\u00a0 a\u00a0 su\u00a0 estado\u00a0 original.\u00a0 La\u00a0 otra\u00a0 forma\u00a0 de\u00a0 da\u00f1o\u00a0 se\u00a0 debe\u00a0 a\u00a0 la\u00a0 acci\u00f3n\u00a0 destructiva\u00a0 de\u00a0 los\u00a0 cristales\u00a0 de\u00a0 hielo,\u00a0 formados\u00a0 durante\u00a0 la\u00a0 helada.\u00a0 Si\u00a0 el\u00a0 descenso\u00a0 de\u00a0 temperatura\u00a0 es\u00a0 muy\u00a0 r\u00e1pido,\u00a0 no\u00a0 da\u00a0 tiempo\u00a0 a\u00a0 la\u00a0 salida\u00a0 de\u00a0 agua\u00a0 de\u00a0 la\u00a0 c\u00e9lula\u00a0 y\u00a0 se\u00a0 producen\u00a0 cristales\u00a0 de\u00a0 hielo\u00a0 intracelulares\u00a0 que\u00a0 provocan\u00a0 la\u00a0 destrucci\u00f3n\u00a0 de\u00a0 sus\u00a0 componentes.\u00a0 Otra\u00a0 v\u00eda\u00a0 similar\u00a0 se\u00a0 atribuye\u00a0 a\u00a0 los\u00a0 cristales\u00a0 de\u00a0 hielo\u00a0 formados\u00a0 en\u00a0 los\u00a0 espacios\u00a0 intercelulares,\u00a0 que\u00a0 da\u00f1ar\u00edan\u00a0 la\u00a0 membrana\u00a0 citoplasm\u00e1tica,\u00a0 al\u00a0 tiempo\u00a0 que\u00a0 \u00e9sta\u00a0 aumenta\u00a0 de\u00a0 volumen\u00a0 por\u00a0 ingreso\u00a0 violento\u00a0 de\u00a0 agua,\u00a0 ocasionado\u00a0 por\u00a0 el\u00a0 incremento\u00a0 de\u00a0 la\u00a0 temperatura\u00a0 ambiental\u00a0 al\u00a0 retirarse\u00a0 la\u00a0 helada\u00a0 (Yuri,\u00a0 1992).\u00a0 Por\u00a0 lo\u00a0 anterior,\u00a0 se\u00a0 se\u00f1ala\u00a0 que\u00a0 una\u00a0 alta\u00a0 velocidad\u00a0 en\u00a0 el\u00a0 cambio\u00a0 de\u00a0 temperatura\u00a0 del\u00a0 aire\u00a0 incrementa\u00a0 el\u00a0 da\u00f1o\u00a0 de\u00a0 la\u00a0 helada.<\/p>\n En\u00a0 frutales,\u00a0 floraci\u00f3n\u00a0 y\u00a0 postcuaja,\u00a0 corresponden\u00a0 a\u00a0 los\u00a0 estados\u00a0 fenol\u00f3gicos\u00a0 en\u00a0 que\u00a0 los\u00a0 tejidos\u00a0 son\u00a0 m\u00e1s\u00a0 sensibles\u00a0 a\u00a0 temperatura\u00a0 de\u00a0 congelaci\u00f3n,\u00a0 dado\u00a0 su\u00a0 car\u00e1cter\u00a0 terso\u00a0 por\u00a0 su\u00a0 temprana\u00a0 edad.\u00a0 Heladas\u00a0 advectivas,\u00a0 de\u00a0 gran\u00a0 magnitud\u00a0 t\u00e9rmica\u00a0 (temperatura\u00a0 igual\u00a0 o\u00a0 menor\u00a0 a\u00a0 -3\u00a0 \u00b0C)\u00a0 y\u00a0 duraci\u00f3n\u00a0 (cuatro\u00a0 horas\u00a0 o\u00a0 m\u00e1s),\u00a0 pueden\u00a0 ocasionar\u00a0 importantes\u00a0 da\u00f1os\u00a0 a\u00a0 las\u00a0 flores\u00a0 o\u00a0 frutos\u00a0 reci\u00e9n\u00a0 formados.\u00a0 Heladas\u00a0 de\u00a0 este\u00a0 tipo\u00a0 pueden\u00a0 causar\u00a0 desde\u00a0 ca\u00edda\u00a0 de\u00a0 frutos\u00a0 reci\u00e9n\u00a0 cuajados\u00a0 hasta\u00a0 deformidad\u00a0 o\u00a0 formaci\u00f3n\u00a0 de\u00a0 russet\u00a0 en\u00a0 forma\u00a0 de\u00a0 anillo,\u00a0 t\u00edpico\u00a0 da\u00f1o\u00a0 de\u00a0 helada.<\/p>\n MONITOREO\u00a0 Y\u00a0 PREDICCI\u00d3N<\/p>\n Es\u00a0 importante\u00a0 establecer\u00a0 la\u00a0 din\u00e1mica\u00a0 de\u00a0 la\u00a0 temperatura\u00a0 del\u00a0 aire,\u00a0 tanto\u00a0 para\u00a0 anticipar\u00a0 la\u00a0 ocurrencia\u00a0 de\u00a0 una\u00a0 helada\u00a0 como\u00a0 para\u00a0 estimar\u00a0 el\u00a0 momento\u00a0 de\u00a0 puesta en\u00a0 marcha\u00a0 del\u00a0 sistema\u00a0 de\u00a0 control.\u00a0 En\u00a0 la\u00a0 actualidad,\u00a0 si\u00a0 bien\u00a0 se\u00a0 pueden\u00a0 predecir\u00a0 los\u00a0 eventos\u00a0 de\u00a0 helada,\u00a0 y\u00a0 son\u00a0 difundidos\u00a0 a\u00a0 trav\u00e9s\u00a0 de\u00a0 alertas\u00a0 y\u00a0 boletines,\u00a0 a\u00a0 nivel\u00a0 predial\u00a0 es\u00a0 necesario\u00a0 monitorear\u00a0 la\u00a0 temperatura,\u00a0 para\u00a0 decidir\u00a0 el\u00a0 sistema\u00a0 de\u00a0 control\u00a0 y\u00a0 su\u00a0 inicio.<\/p>\n