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Is The Weather Causing Fruit Drop and Excessive Seeds On Maple Trees?

GARDEN TIPS – written by
Marianne C. Ophardt
WSU Extension Faculty
for the Tri-City Herald, Kennewick, WA Written June 25, 2015

Earlier this month some gardeners noticed that a number of small apples were dropping off their trees and wondered why it was happening. There are three different types of “fruit-drop” that backyard orchardists may observe.

Fruit drop very early in the season is linked to pollination. Apples and pears require cross-pollination for fruit to form. Cross-pollination is the exchange of pollen from the flowers of one variety to the flowers of a different variety of the same type of fruit.

Cross-pollination is needed for fruit development to occur in many tree fruit, like apples and pears. If adequate cross-pollination does not occur, fruit may start to develop but then drop from the tree. This typically happens soon after the flower petals drop. It occurs because there are not enough viable seed within the fruit producing the plant growth regulating chemicals needed for fruit development.

Lack of pollination can be the result of not having a compatible variety nearby to enable cross-pollination, frost, a deficit of bees and other pollinators, or weather conditions that deter bee activity during bloom, such as rain or strong winds.

Apple or pear fruit may also be observed dropping in early summer. This is called “June-drop.”  The drop is usually due to the crop load of the tree. June-drop is a way for the tree to thin itself because it can not support all the fruit that were pollinated and developing on the tree.

This self-thinning allows more of the tree’s carbohydrate resources to go into the development of fruit left on the tree. Backyard fruit growers can avoid an excessive June-drop by thinning or removing extra fruit early in the season, allowing only one fruit per cluster to develop and spacing these an average of six inches apart on the branches. This results in the development of larger fruit instead of many small fruit or considerable fruit loss from June-drop. June-drop may be extraordinarily heavy if late spring weather is hot.

If fruit drop occurs close to harvest, it is called “pre-harvest fruit drop.” This may be caused by a heavy fruit load, high temperatures, wormy fruit, or drought stress.

Local gardeners are also noticing another phenomenon this year, the production of an excessive  amount of seeds on maples and other trees this spring. I was once told that trees produce copious amounts seed like this when stress triggers them to “think” they are dying and driving them to procreate. This is only a partially correct untechnical explanation.

Abnormally large seed crops may be due to heat or drought stress that occurred the previous year, but it may also be due to spring weather the current year. Maples do flower quite early in the spring and their flowers are subject to spring frost damage. Mild spring weather with no killing frosts allows for good pollination and the development of more seeds than in most years.

Scientists have also discovered that some types of trees normally bear heavier seed crops every other year or every few years.  There is even a phenomena called “masting” where some trees, such as oaks, produce massive seed crops on cycles of three to twelve years. This occurs over large regions and is thought to have evolutionary significance within forest ecosystems.

When it comes the abundance of seeds this spring on local maples and other trees, it could be due to the mild spring weather, stress last summer, or cyclical seed bearing… or maybe all three.


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

I love fall. It’s when tart , juicy apples are ready for harvest. Imagine my dismay when the only apple varieties I could easily find when I moved to Washington in 1980 were Red and Golden Delicious. My “apple palate” was developed in the northeast part of the country where apples had more flavor, more tart balanced with sweetness. Red Delicious apples just didn’t measure up for me, but it was the predominant apple found in local orchards and grocery stores.

However, market preferences change with time and the Red Delicious trees in many Washington orchards have been replaced with newer varieties, such as Gala, Fuji and Granny Smith. Within the last several years, even newer varieties, such as Cameo, Honeycrisp, and Pink Lady, have also made an entrance. Soon you may come across SweeTango, one of the newest apple varieties on the market.

SweeTango is hitting market shelves this week in a few big cities, like Seattle. This new variety was developed at the University of Minnesota by the same breeders that developed Honeycrisp. Trademarked by the University of Minnesota, the breeders are hoping SweeTango will be as successful as Honeycrisp, one of SweeTango’s parents..

SweeTango is a blush type apple with a deep red blush over a yellow background. I haven’t had the chance to taste it yet, but it’s reported to be crispy, “juicy and sweet with hints of fall spices, balanced by vibrant acidity.” David Bedford, one of the breeders that developed SweeTango, says it has the “same wonderful crispy texture of Honeycrisp and even more flavor than its parent.” If you don’t find one in Seattle, you’ll probably have to wait until 2011 or 2012 when more SweeTango trees come into production and their fruit becomes available nationwide.

A new apple variety from Minnesota, why not from Washington? After all, Washington state is the top apple producer in the country and at least 45 per cent of the apple varieties in production here are considered passe. Be patient, you will probably see one or more new outstanding varieties being released from WSU within the next year or so.

Traditional apple breeding takes time. Last year in the WSU apple breeding program over 18,000 new hybrid seeds were produced from 18 crosses. Some 20,000 seeds from the crosses made the year before were planted and 14,000 seedling from the 2005 crosses were budded onto dwarfing rootstock. Getting closer to testing and tasting, over 6,200 seedling were planted in evaluation orchards in 2008 and the best selections from earlier trials were propagated for regional trials. They’re also testing “elite” selections in grower trials.

What do breeders look for when developing a new apple? Obviously they want an apple that has super eating quality, one with the right firmness, crispness, juiciness, and a balanced sweet-tart flavor. It must also be attractive with desirable color, size, and appearance. On the production side, a stellar apple variety must bear early, produce well, not be prone to sunburn, and have disease resistance. In addition, it must store well and taste great when it comes out of cold storage. It’s a lot of work, but before long there will also be new unique WSU varieties being released for growing in central Washington.

By the way, my favorite apple varieties are Empire and Ida Red, not usually available in our region, but I am becoming a fan of Cameo, Honeycrisp and Pink Lady.

Published: 9/12/2009 11:37 AM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

I have talked about it before, but a new fruit insect pest is on the brink of becoming a problem in our part of Washington. The insect is called apple maggot. While new to this area, apple maggot isn’t new to me. Before I moved to Washington, I lived in New York state where the apple maggot was a well- established insect pest. It made it impossible to enjoy maggot-free home grown apples and crab apples without numerous pesticide applications.

The adult apple maggot is a fruit fly, not too unlike the cherry fruit fly that attacks cherries in our region. The adult female flies lay their eggs individually in apples and other fruit The key word is “in” fruit. The female fly deposits her eggs below the skin of the fruit, protecting hatching larvae from pesticide sprays to the fruit’s surface. Once an egg hatches into a larva (more correctly a maggot), it starts tunneling through the flesh of the fruit. This tunneling leaves thin brown trails and causes undersized, misshapen dimpled fruit that usually become soft and rotten. Fruit like this is unmarketable for a grower and unappetizing for a backyard grower.

Unlike a number of troublesome fruit and vegetable pests found in gardens and farms of the Columbia Basin, the apple maggot is not a foreign pest. It

s native to eastern North America. Before Europeans arrived and colonized North America, this native insect happily fed on native hawthorns. The apple maggot found a more delectable food source in the cultivated apples the colonists brought with them. As the commercial fruit growing areas moved west in North America, so did the apple maggot.

In 1980 the apple maggot was first discovered in Washington in Clark County, close to Portland, Oregon where it was discovered just a year before. Since that time it has spread up the Interstate 5 corridor and has been detected in 17 western Washington counties. Since the first detection of apple maggot in the state, the Washington State Department of Agriculture (WSDA) has been trying to protect the commercial fruit industry in Washington from the apple maggot. This has involved a voluntary quarantine to keep people from bringing home-grown fruit from infested areas into non-infested areas. You may have noticed signs about the quarantine along state highways.

In addition, they have put out 5,000 to 8,000 apple maggot traps every year to monitor for any new apple maggot infestations. The WSDA also works cooperatively with local county pest boards that have the job of suppressing and eradicating insects and diseases that threaten the commercial fruit industry.

The purpose of today’s column is to alert you that the apple maggot has been found in Benton county this summer! It’s something you should be informed about since home gardeners can unknowingly help this pest graduate into becoming a full-blown pest infestation in our region. Backyard apple, crabapple and hawthorn trees are the most likely potential hosts, but the apple maggot has also been known to attack cherry, pear, plum, and apricot fruit.

Why should you care? The apple maggot poses a significant threat to the apple industry in our area, the state, and the Pacific Northwest. The fruit industry is important to our local and state economy. If the apple maggot gets a stronghold in this area, growers will have difficulty exporting their fruit to other countries. It will also mean growers will need to apply more pesticides to their crops to keep them maggot-free and marketable.

How can we help? Observe the quarantine set up by WSDA. Transporting of apples from infested areas to apple-maggot-free areas of the state is one major way this pest is spread. Don’t plant susceptible hosts, especially apples, crabapples, and hawthorn, in your yards. Remove your trees, if you already have susceptible hosts growing in your landscape or garden and don’t want to apply regular sprays to control pests, such as codling moth, cherry fruit fly, and possibly apple maggot. In fact, you are required by law in Benton and Franklin county to control these pests whether they are infesting a backyard fruit tree or ornamental trees, such as flowering crabapple, flowering cherry, hawthorn, or other susceptible hosts. Help stop this pest before it becomes a serious problem for home gardeners and commercial growers. Fall is a great time to think about removing any worm-infested trees in your landscape and replacing them with trees that won’t pose a threat to the tree fruit industry.

Published: 9/15/2007 2:36 PM


written by

Marianne C. Ophardt

WSU Extension Faculty

for the Tri-City Herald, Kennewick, WA

Recently, I saw a television news report that the crab apples along the driveway at Columbia Basin College were being removed because of concern over an insect called “apple maggot”. If this new pest becomes well established in our area it will have serious implications for our local commercial tree fruit growers, as well as for home gardeners who grow their own backyard apple trees.

It sounds disgusting… maggots in apples? What is it? The name is apt since this pest is a larva, actually a maggot, that attacks apples as well as other fruit trees. Unlike many crop pests that are imported, the apple maggot is native to the eastern regions of North America. Up until the colonists from Europe introduced domesticated apples, the apple maggot’s major host was native hawthorn trees.

A native pest in the Northeast, the apple maggot arrived in the Pacific Northwest in the Portland area in 1979. No doubt it took advantage of the I-5 corridor, as it was soon detected in Clark County, Washington in 1980. It has since spread to 17 western Washington counties and into at least three counties in eastern Washington (Kittitas, Spokane, and Yakima). The adult of the apple maggot is a fly. This allows it to migrate on it’s own, but this natural spread is fairly slow. It’s humans that have greatly accelerated its distribution by bringing apples from backyard trees in infested areas to areas without the pest.

It’s obvious that one way to try to stop, or at least slow down the spread of apple maggot, is to prevent the movement of infested fruit into this area. Short of stopping every vehicle coming from an infested area into a non infested area and checking for fruit, “quarantine” signs have been placed along main highways in our state indicating that homegrown fruit from the infested area should not be transported out of the area. These areas have been quarantined and it’s actually illegal to transport homegrown fruit from a quarantined area to other non-infested parts of the state.

Another way to slow down the distribution of the pest is to discourage new plantings of potential hosts, as well as removal of any potential hosts in the area. This includes apples, along with hawthorns, crab apples, plums, apricots, pears, cherries, and even wild rose hips.

When I worked in New York state over 20 years ago, this insect made it very difficult for home gardeners to grow eatable apples without repeated pesticide sprays through the growing season. The adult apple maggot is a fly, very much like the cherry fruit fly. It lays it eggs singly by making a very tiny puncture in the apple’s skin and inserting an egg beneath the skin. The damage this puncture causes is insignificant. It’s the feeding damage caused by the larvae that hatch from the eggs that creates a problem.

The small larvae (maggots), about one sixteenth of an inch in length when first hatched, tunnel through the apple flesh. These tunnels are quite small, but wind extensively throughout the flesh, making it mushy and brown. The fruit fails to develop properly and will be undersized and dimpled to extremely misshapen. The damaged fruit often drops from the tree early and tends to rot. When finished feeding, the maggots leave the fruit and drop to the ground where they’ll spend the winter in a resting stage in the soil. Adult flies will emerge sometime early the next summer.

Control of apple maggot is difficult, because sprays to the fruit don’t affect the maggots under the skin. To be effective, chemical control must be aimed at killing the adult fly before it lays its eggs under the skin. When it comes to home garden products available to gardeners, this means weekly applications while the flies are present. Commercial growers can control the apple maggot fairly well, but many regions won’t accept apples grown in infested areas. This makes it hard to market their fruit.

Our area has not been identified as having a significant infestation of apple maggot… yet. However, there are concerns that it won’t be long before it is a problem here. We can help delay the onset of apple maggot in several ways. Don’t bring in fruit from infested areas. Don’t plant susceptible fruit tree and ornamental host plants. Remove susceptible host plants from the landscape and replace them with unsusceptible plants.

For more information on the apple maggot and its control in backyard apple trees go to:

Published: 12/16/2006 10:49 AM



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