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Lesson Plan: Overview
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Throughout the year, various threats to all or parts of the cranberry plant may translate to a less than optimal crop. One key aspect of the grower’s role is to anticipate these threats, monitor the bog and its environment, and take action when necessary. Sometimes, the action is relatively simple—such as turning on sprinklers at the right time—but the decision-making behind it is complex. In springtime, for example, there is no one temperature that signifies that a frost will threaten the bog. Instead, the tender buds—which are vulnerable to damage by frost—have different temperature tolerances based on how far they have developed. The more advanced they are, the less tolerant they are of cold (and so they must be protected at higher temperatures). Growers must know what is happening on the bog and the overall development of the buds in order to identify when dropping temperatures pose a problem. In addition to the bud development stage, other factors determine risk of damage, including location and variety: Location: Temperature on the planted area of the bog is critical, as opposed to the temperature of upland areas. For example, the lower areas of the bog in which the vine is planted can be subject to temperatures ten or more degree Fahrenheit colder than the upland areas. Special monitoring is therefore required. Variety of cranberry: While all buds become more sensitive to lower temperatures as they develop, different varieties are at risk of injury at different temperatures. In addition, different phases in development also determine each variety’s particular temperature sensitivity. To manage a threat, growers spray the bogs with water for the duration of the intolerable temperatures (a few hours, a day, etc.). Although at first it may seem counterintuitive to spray water on the plant—after all, it will freeze —this is effective because as water freezes, the ice-water system stays at a constant temperature: 32 degrees Fahrenheit. Thus, the constant water bath provides a buffer from even colder temperatures. In addition, the ice itself is a wind barrier, creating a second protection for the plant. It may seem a good idea to regularly spray the plants with water so that growers need not monitor temperatures. In fact, this is not the case. Too much water, especially in the spring, can foster disease and pest growth. Also, water is a precious resource and must be managed carefully. It is of prime importance, therefore, for growers to know if and it is truly necessary to spray water on the plants. They must realize when the temperature is a definite threat to the buds. Growers must use their knowledge of the bud’s development, weather forecasts, and a bit of foresight to determine the trigger temperature at which they will turn on the water. Usually, this is about 3-5 degrees Fahrenheit higher than the minimum temperature the buds can tolerate at their given stage of development. If all goes well, the buds make it through this vulnerable time. If, however, there is damage, it can be recognized by plant color as well as actual bud condition. Walking the bogs is an integral part of keeping tabs on what’s happening, so that growers can adapt to the on-site, in-the-moment conditions.
Note: For additional detail, please review the information in the Exploring Cranberries Web resources listed for this lesson.
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