In this Issue:
VEGETABLE NEWS
A RISK MANAGEMENT AGENCY FACT SHEET
APPLE NEWS
Summer Pruning
STRAWBERRY NEWS
White Grubs in Blueberries and Strawberries
Please Note: the next newsletter will be published August 11.
| Vol 3 No. 9 | July 21, 2006 |
Summer Pruning
Article reprinted, with permission, from the Vermont Apple Newsletter, July 1, 1998, by M. Elena Garcia
Summer pruning differs from dormant pruning in that the leaves that are actively producing carbohydrates are removed. When these leaves are removed, the resources that were used to produce these leaves, such as carbohydrates and nitrogen are also removed. An effect of this removal will be a reduction in growth as measured by the net dry matter accumulation for that year, and depending on the type of cut, the timing, and severity, the trees may not be able to overcome this reduction in dry matter accumulation which may result in yield reductions. In addition, pruning while the tree is growing interferes with other physiological functions such as flower bud formation because it disrupts the production and movement of hormones.
So, why is summer pruning a recommended practice for many orchards? Summer pruning is really unnecessary if the orchard is managed correctly. Generally, well-structured trees that are properly dormant pruned do not require any summer pruning other than the removal of water sprouts that grow in the canopy's interior. Also, in trees with a very light crop, summer pruning may not be cost effective. However, if you are concerned about problems associated with low light penetration into the canopy then summer pruning should be an option to consider. For example, research on 'McIntosh' has shown that summer pruning can significantly improve the crop value by improving fruit color, especially in a season with poor coloring weather near harvest.
Reasons for summer pruning:
To improve fruit color and quality
The red color development in apples is due to formation of red pigments, anthocyanins. The synthesis of these pigments occurs when light shines directly on the fruit. Summer pruning can be used very effectively to improve light penetration into the canopy thus increasing fruit color in ‘poor coloring' varieties. Besides color improvement, summer pruning has been shown to improve fruit calcium content, thus, reducing the incidence of such disorders as bitter pit of apple.
To regulate growth and control vigor
Summer pruning can be used on young trees to encourage leader development and direct growth into the permanent scaffold structure. It can be used to alleviate temporary problems with crowding in high-density orchards. Summer pruning may or may not reduce vegetative vigor depending on type of cut, the timing, and severity. The control of vigor in trees should be accomplished by training, dormant pruning, regulation of fruiting and soil water and fertility programs.
To reduce pests and disease problems
Vigorous growing shoots such as water sprouts of some cultivars are susceptible to fire blight infections. The woolly apple aphid often colonizes the bases of actively growing water sprouts. Research at UMass has shown that summer pruning consistently reduced the incidence of flyspeck on apple fruit by approximately 50% in each of 2 years in trees where no fungicides were applied.
Table 1 summarizes the effects of summer pruning on tree size, growth, and fruiting.
Timing of summer pruning:
Early summer pruning (generally not recommended)
It is done before terminal bud formation. Generally induces some regrowth which can be detrimental because it alters the leaf to fruit ratio. Ways in which early summer pruning can have negative effects include loss of buds, reduced flower bud formation, delayed hardening, there may be decreases in fruit size and/or soluble solids content, and some trees may require more pruning during the dormant season.
After terminal bud formation
This is the time summer pruning is recommended, which corresponds to late July and early August. At this time the trees have entered physiological dormancy, and will generally not respond with renewed growth. It has the effect of reducing total leaf area. However, the total accumulation of carbohydrates does not decrease because the leaves found deep in the interior of the canopy are now exposed to increased light levels, stimulating their photosynthetic output.
Type and severity of cut:
Complete removal of vigorous water sprouts by thinning cuts. Fruiting branches that have too much vigorous growth can be headed-back to just above the fruiting cluster, and should be removed during dormant pruning. Upturned branches can be thinned to a lateral branch.
Tips to help you with your summer pruning:
The preferred time during the season is late July through August. Remember, the earlier summer pruning is performed, the more regrowth that will occur during the summer. In addition, early summer pruning can lead to decreases in fruit size and lower soluble solids content.
To generate fruiting wood on bare scaffold branches, select shoots that are as horizontal as possible, that have a good crotch angle, and that will provide a well spaced (12” to 18”) canopy along the length of the canopy branch. Prune these shoots to about 18”.
About 90% of the cuts should be on the current season's growth and two-year old wood. Start by pruning the upper third of the tree. This will create pathways for the sunlight to penetrate into the interior of the canopy. Do not summer prune trees with moderate to low vigor. Spend only 5 to 10 minutes per tree.
In conclusion, because of the complex interactions of summer-pruning timing, severity, and types of cuts with the physiological processes of the plant, summer pruning should be used only for specific purposes and with certain limitations. It should be closely supervised to reduce severe crop damage and losses. One should work towards the goals of not having to summer prune at all by placing the emphasis on well-designed tree structure.
The above information should be used as a general guide for effects of summer pruning. Remember that the response to summer pruning varies with timing, and the type and severity of pruning.
ACKNOWLEDGEMENTS
Co-Editors: Bill Hutchison (hutch002@umn.edu), Department of Entomology, University of Minnesota, Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Management and Development Division, and Suzanne Wold-Burkness (woldx018@umn.edu), Department of Entomology, University of Minnesota
The Newsletter is published weekly from May through August, cooperatively, by the Minnesota Department of Agriculture (MDA) and the University of Minnesota (U of MN). Reports are posted on the U of MN and MDA web sites on Fridays. If you have suggestions and/or comments, please send your contributions by 4 p.m., Wednesday to Jean Ciborowski, 651-201-6217, jeanne.ciborowski@state.mn.us, MDA, 625 Robert St. North, St. Paul, MN 55155-2538. You can access the Newsletter at the U of MN web site in htm format at: www.vegedge.umn.edu/MNFruit&VegNews/mnindex.htm and at the MDA web site in pdf format at: http://www.mda.state.mn.us/ipm/ipmnews/
Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association (MFVGA) and the United States Department of Agriculture – Risk Management Agency (RMA). These institutions are equal opportunity providers.
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