miércoles, marzo 21, 2007

Hay que aplicar Dormex o no?

Un debate que comienza a generarse en productores arandaneros al acercarse el invierno es si realmente es necesaria la aplicación de Cianamida hidrogenada (Dormex en su nombre comercial) para alcanzar altas producciones. Debido al alto costo de este producto y a que algunos productores han tenido malas experiencias, publicamos aquí en LATINBERRIES un extracto de un paper de J.G. Williamson, y P.M. Lyrene ambos reconocidos profesores de la University of Florida y responsables del Cooperative Extension Service del Horticultural Sciences Department.
Estos profesores aconsejan el uso del producto siempre y cuando se haga de la forma correcta y en el momento adecuado ya que de lo contrario los efectos pueden ser muy perjudiciales. El año pasado en Argentina, LATINBERRIES pudo saber que muchos comercializadores se atrasaron en la entrega del producto y los productores no pudieron aplicarlo a tiempo. Este año parece que la mayoría ha tomado sus recaudos y ya comienzan a definir las cantidades a aplicar.
Aquí un extracto del paper
Dormex (a commercial formulation of hydrogen cyanamide) is a plant growth regulator that became available for commercial use in Florida blueberries during 2000. Experiments and grower observations have shown Dormex to be a useful tool for stimulating earlier and stronger spring leafing of several southern highbush (and Climax rabbiteye) cultivars in Florida. Where spring leafing has been significantly advanced by Dormex, berries were often harvested earlier than would otherwise be possible. Increased berry weight (size) and a slight increase in total yield have also been noted in some cases, but the main advantage seems to be earlier berry harvests.

Dormex has the potential to damage flower buds. Therefore, it is very important that growers follow the label directions exactly. The label calls for up to 1.5% (v/v) Dormex in 50 to 100 gallons of spray per acre using up to 0.5% (v/v) of one of the nonionic surfactants, Latron B1956 or Agri-Dex. Higher Dormex spray concentrations have resulted in significant flower bud thinning and have reduced total yields. Dormex applied at 1.5 % (v/v) has consistently shown increased leafing and earlier fruit ripening of Misty without significant flower bud thinning. Dormex applied at 1.5 % (v/v) has actually increased total yields in some cases. This is probably a result of increased fruit size combined with minimal, if any, fruit thinning. The effect of Dormex is very localized on plants. Therefore thorough coverage is essential.

Dormex label calls for applications to be made 30 or more days prior to natural budbreak. Additionally, Dormex is most effective when applied to dormant plants after significant winter chilling has occurred. Although the calendar should not be used as the sole determinant to time Dormex spray applications, in Alachua County, late December is usually about 30 to 40 days before flowering for most cultivars grown there. During the last 2 to 3 years, applications of Dormex made in Alachua County between about December 20 and January 3 have usually increased vegetative budbreak and advanced fruit harvest of responsive cultivars. During "normal" winters thus far, differences within this time frame in Alachua County have not been significant. Of course the onset of dormancy, chill accumulation, and the timing of natural budbreak will vary from year to year and from one location to another in Florida. Hence, the timing of Dormex applications should be based on the weather and anticipated date of natural budbreak, not the calendar date.

Application of Dormex to plants that have received little or no chilling resulted in less efficacy and more injury to stems and flower buds. This emphasizes the importance of restricting application of Dormex to the dormant period when some chilling is likely to have occurred, but before flower bud swell has progressed past stage 2 (before flower bud scales begin to separate). Delaying application until, or just prior to, the beginning of flowering has resulted in serious flower bud thinning and yield reduction. The application time for maximum benefit will depend on the winter weather and location of the site.

Most research in Florida has been conducted with the cultivar Misty and to a lesser extent on Gulfcoast, Star, Southmoon, and the rabbiteye variety Climax. Increased vegetative bud break and earlier ripening from Dormex have been demonstrated under a range of environmental and climatic conditions during several seasons in Florida for the variety Misty.
On other cultivars, similar though perhaps less dramatic results have been obtained. Generally, those cultivars that are naturally slow or weak at leafing in the spring should benefit most from Dormex. Some examples of weak or slow leafing cultivars that should benefit from Dormex applications during most years are Misty, Millennia, and Santa Fe. Dormex should not be applied to Sharpblue because Sharpblue flower buds are more susceptible to injury (spray burn) from Dormex than are flower buds of most other cultivars. Dormex can be safely applied to numerous blueberry cultivars currently grown in Florida, however, if a cultivars tolerance to Dormex is unknown, it should be tested and evaluated before Dormex is used on that cultivar.

When used correctly, the potential benefits from Dormex include strong spring bud break and vegetative growth, shorter fruit development periods with earlier harvest periods, increased berry weight (size), and increased yield. These benefits will generally be more prevalent on varieties that are naturally slow or weak to leaf out in the spring. The concentrated bloom and harvest periods and shortened fruit development periods obtained with Dormex could help with disease and insect control and potentially reduce the number of annual pesticide applications needed in Florida blueberries. On the other hand, when applied incorrectly, Dormex can result in flower bud injury, excessive fruit thinning and yield reductions. Also, potential users should be aware that Dormex is classified as a restricted use pesticide. Extreme caution should be used when handling and applying this material and ALL LABEL DIRECTIONS SHOULD FOLLOWED EXACTLY.

Para acceder al paper completo clickear

Fuente Univerisad de Florida y LATINBERRIES

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