Right along with pumpkins, there’s nothing that seems more symbolic of the fall harvest season than apples. It’s no secret that Washington apples are known throughout the world for their beauty and crunch. In fact, more than two-thirds of all apples grown in the United States for fresh eating come from the 162,000 acres of apple orchards nestled in the eastern foothills of Washington State. In 2013, the state apple crop destined for the fresh market is estimated at 120 million bushels! There are no harvest machines to pick apples, which means that each of the nearly 12 billion apples harvested is hand picked by an estimated 35,000 to 45,000 pickers. If you put all of the Washington State apples picked in a year side-by-side, they would circle the earth 29 times.
Eating fresh apples is good for you. The average U.S. consumer eats about 16 pounds of fresh apples a year, about one apple per week. A new national survey of 1,021 household shoppers across the nation conducted by the U.S. Apple Association shows people think of apples as the next super fruit. It is an accessible, value-priced, nutritional energy source on par with blueberries and pomegranates.
Although apples are not grown as a commercial crop here in our coastal area, most home gardeners have at least one, or, more often, several apple tree varieties which they savor for fresh eating. There’s nothing more disgusting however, than finding the proverbial worm in the apple. Unfortunately, both apple maggots and codling moth are common pests in home orchards throughout Western Washington. Although neither of these pests is strictly a worm, their larvae are responsible for the majority of damage to local apples. It’s important to know the difference between these two pests, to be able to recognize the insects, and to understand how to manage their invasive behavior.
The larvae of the codling moth are pinkish or cream-colored “worms”, which have distinct black or dark brown heads and six claw-like legs. Codling moth larvae tunnel straight to the core of an apple where they actively feed, often leaving granular, brown excrement around the entry holes that look like sawdust.
Apple maggots on the other hand, are white, headless and legless and worm-like. Fruit infested with apple maggots has a mushy, brown appearance, but the core is left untouched. The apple maggot is the juvenile stage of a fly that emerges during early summer, mates and lays eggs. It doesn’t look like a common fly because it has distinct black and white striped markings on the wings. When laying each egg, the female makes a tiny puncture in the fruit and inserts the egg just below the skin. This initial fruit damage is easily overlooked, but eventually leads to fruit dimpling. The eggs hatch in three to seven days as small, cylindrical, cream-colored larvae known as maggots. The maggots lack legs and visible head capsules, but have dark mouth parts that protrude from tapered heads. As apple maggots tunnel through the apple flesh, they leave characteristic winding brown trails that are best seen when the fruit is cut open. The first indication that a backyard apple tree is infested with apple maggot occurs when the homeowner discovers these brown trails in fruit at harvest. Fruit damaged by apple maggot becomes soft, rotten and often drops from the tree.
The traditional approach to protecting apples from apple maggot has been spraying backyard trees with organophosphate insecticides. Since the apple maggot spends most of its life within the fruit or buried in the soil, the insecticides must be timed to coincide with adult fly activity. One practical and effective way to monitor apple maggot flies is to hang yellow, rectangular sticky traps in your tree. The yellow color attracts flies over short distances and the flies become trapped by the sticky substance.
Public concern about the misuse and over use of pesticides has led to the removal of most organophosphate insecticides, like Diazinon, from homeowners’ use. One product homeowners may consider using for apple maggot and codling moth control is kaolin clay (sold as Surround, Surround at Home and other trade names). Kaolin products will suppress a broad range of insect pests that feed on apple leaves and apple fruit, including both codling moth and leaf rollers. Organic apple enthusiasts have found success in preventing insect pests by “bagging” apples early in the growing season. Paper or cloth bags are placed around individual fruit and stapled shut at the stem end of the apple. The bags act as physical barriers to prevent insect damage to the fruit.
The best thing home orchard enthusiasts can do to reduce both apple maggot and codling moths in next year’s crop is to pick up and place in plastic bags all infested fruit (windfalls) to prevent these two notorious pests from overwintering. Infested fruit should not be placed in the compost pile.
Q: Last year, our apple tree was just loaded. This year, it has a very light crop. What caused this?
Occasionally certain fruit trees, such as apples, bear heavily one year and sparsely the next. This is called “biennial bearing”. The spring-flowering buds of most hardy fruit trees have actually been formed during the previous summer. Therefore, an especially heavy crop one year may prevent adequate bud formation for the following year.
Biennial bearing is difficult to alter or correct. However, you can induce a return to normal yearly fruit production by early and heavy thinning of the fruit during the year in which the trees are producing their large yield.
This column is printed as a service of the Washington State University Extension Office at Elma. Donald D. Tapio is the regional gardening and farming specialist for Grays Harbor and Pacific counties. He can be reached at (360) 482-2934 or email@example.com.