Taking an environmentally sensitive approach to pest management
Many apple cultivars that are popular in Missouri are harvested in September and October. Harvesting apples at the “right time” will enhance and preserve the flavor and quality of the fruit. For example, fruit harvested too early is small in size with hard flesh and will taste starchy. In contrast, over mature fruit will have a dark, dull color with greasy peel and will taste starchy or have off flavors.
Several factors affect the harvest date. The fewer the number of apples on a tree, the more rapid fruit matures, resulting in an earlier harvest date. A heavy crop load will delay the harvest date. Also, high levels of nitrogen generally delays red color development, and induces flesh softening and early fruit drop. However, the most important factor influencing the harvest is temperature throughout the growing season. Apple harvest is slightly delayed this year with the usually cool temperatures. Apple cultivars vary in their response to temperature. For example, cultivars such as ‘Jonagold’ and ‘Honeycrisp’ favor cool northern climates. Thus, fruit of these cultivars grown in New York tends to be firmer with enhanced red blush on the peel as compared to that grown in warmer, southern climates. Also, ‘Red Delicious’ fruit is a brighter red color and is more elongated in shape, with the typical five points on the bottom of each apple when night temperatures are cool. In many years, ‘Red Delicious’ apples produced in Missouri tend to have a brownish-red, dull peel color and the fruits have a round shape due to high night temperatures often exceeding 80ºF during August and September.
The “right time” to harvest depends on the intended use. For homeowners, apples can be left on the tree longer than those harvested for a retail or wholesale market. When apples are left on the tree longer, they are sweeter and softer than fruit picked earlier. Also, the storage life of later-harvested fruit is shorter than that picked earlier. Fruit that is to shipped long distance must be harvested earlier, when fruits are firmer and less susceptible to bruising during transport.
There are several ways to determine the proper time of harvest. First, nursery catalogues will often list the days to maturity, which is the number of days from peak bloom to harvest. Alternatively, catalogues often have charts that present a range of harvest dates based on location. Another indicator of apple maturity and harvest is peel color. Peel color changes from green to yellow as the fruit matures and is ready for harvest. For apples that are primarily red in color, often the shift in color can be evaluated by looking for the color change on the side of the apple that has not been exposed to sunlight. However, because of the influence of nitrogen on color, other indicators, such as flesh firmness, and sugar and starch content should be used in conjunction with change in peel color to determine the proper time of harvest. Most commercial growers use instruments, such as a penetrometer to measure the firmness of the flesh and a refractometer to assess sugar content. Hard ‘Red Delicious’ fruit will measure 16.5 pounds, while ripe fruit will measure 8 pounds, and over-ripe will be less than or equal to 7 pounds. The refractometer measures soluble solids (i.e., sugars) and values are listed as degrees Brix. Apple cultivars vary in soluble solid content at harvest. ‘Fuji’ apples are normally very sweet and will have high Brix values (>18), while Red Delicious will be lower. In fact, industry standards in some states require ‘Red Delicious’ and ‘Golden Delicious’ apples to have minimum Brix values of 10 and 11, respectively, at harvest. Iodine tests are also used by commercial growers in some states to determine the time of harvest. For example, if half the area of the flesh is stained by an iodine solution, then it is ready for cold storage. With less flesh area staining, the fruit is more mature. Because of the toxicity of iodine to humans and animals, this test is not recommended for homeowners. While these instruments and iodine testing are useful, homeowners can evaluate firmness and sugar and starch content by tasting the fruit. When the peel color starts to change from green to yellow, pick two fruit on opposite sides of the tree at about shoulder height. As you bite into the fruit, assess the flesh firmness and note the sweetness and absence of starchy flavors. If starchy flavors are detected, sample the fruit 5 to 7 days later and taste them again. When the taste of the fruit is acceptable to your palate, harvest the apples, refrigerate them immediately, and savor your fruit in the following days.
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REVISED: August 1, 2012