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Gardening Answers Knowledgebase

Plant Answer Line Question

Keywords: Apples--Diseases and pests, Malus domestica

I have a question regarding apple trees and the caterpillars. We have a great apple tree, that I have just noticed has the early nest of these crazy caterpillars that we get around here. Can you help me with the most effective way to get rid of these things before they hatch and start eating our tree???? Is spraying ok for the fruit??


It is possible that your apple tree has an infestation of tent caterpillars, but without seeing the pests, I could not say definitively. If this is what you have, the information below from Washington State University Extension should be of use.

Also, check out Toxic-Free Future's page on managing tent caterpillars. You should be able to prune out the affected part of the tree and dispose of the nest.

Date 2017-03-21
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Plant Answer Line Question

Keywords: Pruning trees, Malus domestica

We have an apple tree in our back yard. Last year it produced more apples then we knew what to do with. We pruned it after last season and then this year was an off year and we only had a few apples. My question is do we need to prune it every year or only after a very productive year? We are very new at this so any pruning tips you have would be great as well!!


Many factors may have affected the fruit production on your apple tree, but the general rules on pruning are to prune young trees very lightly, and old trees more heavily, particularly if they have shown little growth.

Pruning is usually done when the tree is dormant (i.e., winter), but sometimes apples are pruned during the summer growing season (the main reasons to do this would be to improve fruit quality and quantity, to regulate growth and control vigor, and to reduce pest and disease problems. (An excellent resource we have here is Training and Pruning Apple and Pear Trees by C.G. Forshey, American Society for Horticultural Science, c1992.) Another thing to consider is whether your tree is a dwarf, semi-dwarf, or standard apple tree. Pruning differs for each of these.

The following factsheet gives basic guidelines for pruning fruit-bearing trees:

Pruning Apple and Pear Trees from Clemson University Extension

Below are useful webpages about pruning fruit trees, and apples in particular:

Pruning Tree Fruit from WSU Extension

Spring and summer pruning for apples from Oregon State University

We have many great books on this subject in the library if you need additional guidance.

Date 2017-09-27
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Plant Answer Line Question

Keywords: Pruning trees, Malus domestica

Could you provide me with information on pruning Red Gravenstein?


I did not find a simple answer to your question about pruning Red Gravenstein. It seems that pruning is key, however, in controlling whether the tree fruits annually or biennially.

The book The Best Apples to Buy and Grow edited by Beth Hanson (Brooklyn Botanic Garden, 2005) has this to say about the Gravenstein apple: Prune and thin to control its tendency to bear a crop biennially.

From the book Apples for the 21st Century by Warren Manhart (North American Tree Company, 1995):

Classified as a biennial bearer, and understanding of its genetics can lead to getting some apples almost every year. Gravenstein is a triploid with 17 extra chromosomes, which means it is nearly sterile, incapable of very much self-pollination. In pioneer times it was typically planted with the old Tompkins County King, another triploid of fine flavor. The East Malling Research Station near Kent, England suggests that triploid varieties should have pollen from two viable pollenizers to properly set seeded fruit and to pollenize each other as well as the triploid.

The author further discusses not grafting to any rootstock larger than M9, M26, or M& unless you want to harvest fruit 20 feet off the ground.

From a contributor to a discussion on Rainyside Gardeners, a local gardening site:

"We don't have a Gravenstein, but we do have 7 other varieties of apples. Gravenstein bear heavily every other year. They should be pruned annually during dormancy. A simple rule of thumb is, anything that grows straight up or crosses another branch has to go. The straight up growths are called water sprouts, and take energy away from fruit production. Apples need to be thinned. One apple per cluster--remove the rest, save the largest one and pick off all the others. Apples should be at least two inches apart."

The book Training and pruning apple and pear trees by C.G. Forshey, D.C. Elfving, and Robert L. Stebbins (American Society for Horticultural Science, c1992) recommends using the central axis or French axe form for Gravenstein apple trees. Here is a description of this method:
"Vertical Axis. The vertical axis, sometimes called the French axe or the central axis, was developed by J. M. Lespinasse in France, and has performed extremely well throughout North America (Table 1). This system requires leader support to a height of 8 feet to 10 feet above ground and minimal pruning is used to develop a tall conical shape (Fig. 3)."

Another description from the University of California Santa Cruz Agroecology program:

Vertical Axis or French Axe


  • Tree Height -10'-14'
  • Spread at Base - 5'-7'
  • Space between Trees - 5'-6'
  • Tree Density - 500-700 trees/acre
  • Rootstocks - Mark, M9, M26, M7, M106
  • Support - Individual pole or wire trellis
  • Labor Needs - Low; very little pruning; all operations can be done from the ground
  • Cropping - 2-4 years

This system features tall, narrow trees. The aim of this system is to let the tree achieve a natural balance between fruiting and vegetative growth, to reach its ultimate height very quickly (2-3 years), and to come into fruiting early. The vertical axe features almost no pruning in the early years. As with the slender spindle, the aim is to establish a permanent lower tier of branches that are trained to a horizontal position and left long (unpruned). Because the leader is not headed (even at planting), the tree form is very narrow and height is achieved quickly.

Above the lower tier of branches, weak to moderate lateral branches occur randomly. This system also features fruit-bearing on the main leader, which eventually slows tree height, as fruiting is usually more effective than pruning at dwarfing trees. Eventually the leader is pruned into older lateral wood. As the branches in the top part of the tree extend later-ally beyond their desired length of 2-3 feet, they are thinned out or renewed by cutting back to a stub (1-2 buds). The disadvantages of this system are the height of the tree, which requires ladder work, and overly vigorous branches high in the tree, which can shade the lower portions of the tree.

The following article from Alameda County Master Gardeners describes how to prune tip-bearing apples (and pears). This might be of interest to you because Gravenstein is both tip-bearing and spur-bearing.

The Home Orchard Society site has an online forum for submitting questions as well.

Date 2017-05-05
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Plant Answer Line Question

Keywords: Trees--Wounds and injuries, Malus domestica

The bark on our apple tree has split, approximately 24" vertically, revealing the wood of the tree underneath. Is there anything we can do to protect it and help it heal itself? If it were a wound, we'd get stitches for it, but we're afraid to make it worse by wrapping the wrong thing around it.


It is possible your tree's bark split open due to weather extremes (frost cracking or sunscald), or uneven growth. Sometimes it is recommended to score the edges of the split with a sharp tool, but I don't recommend it here because of the length of the split on your tree. Cornell University describes the procedure, however.

According to a following discussion on North American Fruit Explorers, it may be possible to leave split bark to heal on its own.

Missouri Botanical Garden offers the following information on cracks and splits in trunks:

"Cracks and splits in tree trunks are fairly common and may occur for various reasons, but are usually not a significant threat to the tree. Typically, there's not much you can do about them once they occur. They do, however, occasionally signal a serious problem that may eventually kill the tree.
"One of the most common reasons for cracks and splits on tree trunks is frost cracking. Frost cracks occur during cold winter weather. The inner and outer wood in a tree's trunk expands and contract at different rates when temperatures change. When winter temperatures plummet below zero, especially after a sunny day when the tree's trunk has been warmed by the sun's rays, the different expansion rates between the inner and outer wood can cause such a strain in the trunk that a crack develops. Frost cracks occur suddenly, can be several feet long, and are often accompanied by a loud, rifle-shot sound. Frost cracks at a point where the trunk was physically injured in the past.
"Maples and sycamores are very prone to frost cracks. Apples, ornamental crabapples, ash, beech, horse chestnut, and tulip trees are also susceptible. Isolated trees are more subject to frost cracks than trees in groups or in forest settings. Trees growing on poorly drained soils are particularly prone to frost cracks.
"Frost cracks often close during summer, only to re-open in succeeding winters. They do not seriously damage trees, although they do provide openings where certain disease organisms may enter the tree, particularly if the tree is in a weakened condition. Frost cracks are difficult to prevent. Wrapping the trunks with tree wrap paper in fall helps, but is inconvenient to do year after year. Apple growers sometimes white-wash the trunks of apple trees to prevent frost cracks and other winter injury problems, but this is unattractive in landscape settings. The best way to prevent frost cracks is to prevent any injuries to the trunk throughout the tree's life. A professional arborist can bolt frost cracks shut with a technique called lip bolting. Most people simply remove loose bark hanging along the edges of the crack. You should not paint frost cracks or other wounds with tree wound dressing. These materials can trap moisture, causing decay in the trunk."

Date 2017-08-08
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Plant Answer Line Question

Keywords: Pruning, Malus domestica

I have a five-variety dwarf apple tree that is doing well, but seems to be developing a very strong central leader. (I planted it last year.) Is this going to be a problem? I seem to remember hearing that I shouldn't let it do this, but I ca't find any information about how to prune this type of apple tree.


As I suspected, the answer to your pruning question was lurking in the pamphlet I received many years ago with my Raintree Nursery tree order. Here is what they say about "combo fruit trees" and their care:
"Combination fruit trees with several varieties on the same plant can be a fun way to grow lots of varieties in a limited area. They can be somewhat challenging too. Often one or more varieties (branches) will be much more vigorous than others. If this problem isn't carefully addressed, then the tree can become more and more lopsided and the most vigorous varieties will overgrow the others and dominate the tree. Prune back the most vigorous branches upon arrival (if we haven't already done so) to even out the branch lengths. Prune the most vigorous branches back again in the summer to maintain a balance. The most vigorous branches are the most upright. Spread the branches if they are supple enough to spread without breaking. If you keep any upright branches and they are too stiff to spread, cut them back, if possible to the lateral side branches. The combos should be grown as open center trees. On most combo trees, the varieties are named on the plastic label attached to the tree with the bottom budded variety listed first, the second from the bottom listed second and so on. Missing varieties are crossed out on the label."

This image from Missouri State University Extension shows an open center pruning.

Oregon State University Extension has a good general guide by Jeff Olsen to Training and Pruning the Home Orchard.

Date 2017-04-20
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Plant Answer Line Question

Keywords: Malus domestica

My class is planting a tree in honor of our school advisor. Which apples varieties will do best in our area (Olympic Peninsula, WA)?


Washington State University Extension's publication, Apple Cultivars for Puget Sound by Robert Norton (1997, revised edition) has suggestions of some varieties which will succeed in our area. The lists are grouped by type of apple and type of flavor. For your situation, it would make sense to choose a variety which is known for disease resistance. I will include an excerpt from the list below.
Disease-resistant varieties:

  • Pristine: Ripe early to mid August. Clear yellow skin is very attractive. One of the earliest disease resistant varieties, with a refreshing flavor and firm crisp flesh. Moderately tart, holds well on the tree.
  • Williams' Pride: Ripe early to mid August. Attractive red stripe over yellow, good flavor but susceptible to mildew.
  • Chehalis: Ripe early to mid September. Yellow apple with good natural resistance to scab but susceptible to mildew. Thin skin bruises easily. Good dual purpose for fresh eating and sauce but too soft for pies.
  • Prima: Ripe early to mid September.Attractive bright red over yellow, at its best when fresh from the tree but texture softens rapidly in storage. Good mildew resistance.
  • Dayton: Ripe early to mid September. Trees are vigorous and crop well, but may need a year or two in production to reach good quality. Fruit is unattractive dark orange red over yellow. Flesh is crisp, juicy, with sweettart flavor. Stores better than Prima.
  • Liberty: Ripe early to mid October. Attractive, uniform red fruit with good flavor, very similar to Spartan in appearance and quality. Trees are very productive and need effective thinning for good fruit size. Well adapted to western Washington conditions.
  • Enterprise: Ripe mid to late October. Mac type, flavor fair to good, firm, crisp. Moderately productive. Stores well until December, then flavor starts to decline.
  • Belmac: Ripe late October. Late season Mac type, good flavor, firm and crisp. Productive, vigorous trees. Fruits store well until February.

City Fruit, a fruit-growing advice group in Seattle, recommends these varieties:
Akane, Chehalis, Corail, Elstar, Empire, Fiesta, Jonagold, Gravenstein, Honeycrisp, Karmijn De Sonneville (unusually scab prone, but delicious), Liberty, Rubinette, Sansa, Spitzenburg, Sweet Sixteen, and Williams Pride all have had good comments. They have different flavors and characteristics. Apples and Asian Pear-apples are subject to the Apple maggot and codling moth pests.

You may want to make sure there is a designated "tree steward" or volunteer who will maintain the tree over time. Fruit trees need regular care: watering, mulching, pest prevention, pruning. Here is more information:

Date 2016-12-17
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Plant Answer Line Question

Keywords: Malus domestica

I would like to find a site that has a list of tip-bearing apple varieties. It does not have to be comprehensive. Many sites talk about them and mention only a couple.


A search of the North American Fruit Explorers discussion group refers to a list from the USDA Agricultural Information Service which has since been removed from their website. I found an extensive list of tip-bearing and partial tip-bearing apples from Royal Oak Farm Orchard. The list was prepared by Ted Swensen of the Home Orchard Society.

According to Michael Phillips, author of "The Apple Grower" (Chelsea Green, 2005), most apples are spur-bearing or a combination of spur- and tip-bearing; only about 1% of all varieties are solely tip-bearers (such as Cortland and Russet).

Date 2017-04-22
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Plant Answer Line Question

Keywords: food safety, Malus domestica

Is it safe to eat windfall apples if I cut away any sections that look bad? Or should I only use them in cooking?


If you want to err on the side of caution, you should use them neither for fresh eating nor for cooking. There is a toxin produced by fungi called Patulin which may be present in apples which have dropped from the tree and have been lying on the ground, according to a news release from University of Illinois Extension, dated September 21, 2012.

According to the Ontario Ministry of Agriculture, there are ways of diminishing the risk, but the processes involved are more appropriate to commercial apple processors than backyard orchardists. Excerpt:
"Current research suggests that varieties with an open calyx are a greater risk for patulin development within the core of the apple. In such a situation, damage to the fruit is not easily detected [...]

"Patulin is also destroyed by fermentation, which means it is not found in either alcoholic fruit beverages or vinegar produced by fruit juices. Patulin will however survive the pasteurization process if present in the juice."

The website of Food Safety Watch has more information about Patulin.

Date 2017-03-21
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Garden Tip

Keywords: Biofumigation, Quercus alba, Malus sylvestris, Verticillium, Ginkgo biloba, Liquidambar, Katsura, Fraxinus, Pseudotsuga menziesii, Malus domestica

Don't despair if verticillium wilt lives in your garden's soil because there are many resistant plants. A few verticillium-resistant trees include Apple and Crabapple, Mountain Ash, Ginkgo, Sweet Gum, Katsura, Douglas Fir, Arborvitae and White Oak. A long list of susceptible and resistant trees, shrubs, perennials and vegetables.

There is some evidence that broccoli (chopped up new shoots worked into the soil) can act as a soil fumigant, if added to the soil before planting. Studies were done by Krishna Subbarao at University of California, Davis, and showed reduced incidence of wilt in cauliflower crops where broccoli had been planted and its residue added to the soil.

Date: 2007-05-23
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August 01 2017 12:36:01