MN Fruit & Vegetable IPM News - Vol. 2, No. 7

When used properly, leaf analysis provides the most reliable method to determine fertilizer needs for established orchards. Soil tests should be used prior to planting to determine lime requirements and phosphorus, potassium and magnesium levels. In established orchards, however, soil tests are primarily used as a supplement to leaf analysis information.

Many factors affect the nutrient composition of leaves. Soil moisture, soil texture/structure, native soil fertility, and fertilizer practices have direct effects on nutrient uptake. Crop load, variety, rootstock, disease and insect incidence, weather conditions, and cultural practices such as weed control and pruning can also alter leaf nutrient composition. Whenever possible, consideration of these factors should be taken into account when interpreting leaf analysis results. Fertilizer application is often necessary to provide optimum levels and balance of nutrients for plant growth, but fertilizer cannot make up for poor insect and disease control or correct problems like severe damage due to winter injury.

The basis behind leaf analysis is that optimum ranges exist for the level of each nutrient in the leaf and maximum quality/yields occur when nutrients are maintained within these ranges. If the level of a nutrient falls outside of its optimum range, corrective measures should be taken. The table below provides nutrient concentration levels indicative of deficient, optimum, or excessive conditions for 11 essential elements in apple leaves of bearing trees.

Recommended Procedures for Sampling and Handling Apple Leaves

Obtaining a representative sample is important to avoid misleading results and erroneous interpretations. Even the best-equipped laboratory cannot make up for a poorly collected or improperly handled sample. Optimum nutrient ranges are based on leaves sampled at a specific maturity level and collected at a specific period during the growing season. The following instructions should be used as a guide for proper leaf sampling and handling procedures:

Leaf samples should be collected between July 15 and August 15.
At least 4-6 trees should be selected for sample collection. Trees not typical of the orchard should be avoided.
Trees should be of the same age, variety, and rootstock, growing on a relatively uniform soil of the same fertility. If these conditions are not met, the orchard should be divided into uniform blocks that are sampled separately.
Leaves from the middle of the current year’s terminal shoot growth should be selected. Spur leaves should be avoided. Collect both the leaf blade and its attached petiole (leaf stalk).
Collect a total of 60-100 leaves (about 10-15 leaves per tree), 4-6 feet from the ground, from shoots spaced around the tree. Do not pick more than 2 leaves from any one shoot. Leaves showing insect, disease, or mechanical damage should not be selected for sampling.
If you are trying to diagnose specific leaf symptoms, send in two samples – one from trees showing the symptom and one from trees not showing the symptoms.
If leaves are dusty or dirty, they can be rinsed in distilled or deionized water. Do not let leaves soak in water, because nutrients will leach out. Dried leaves should not be washed.
Place leaves in a clean paper bag and dry at room temperature or send immediately to a laboratory. Do not use plastic bags unless samples have been previously dried.

The University of Minnesota Research Analytical Laboratory (phone: 612-625-3101) offers tissue testing services for a fee. An information sheet along with current prices can be found at the following web site:

http://ral.coafes.umn.edu/Forms/DIAGNOSTIC%20PLANT2003a.pdf

A number of private laboratories also offer tissue testing services. Contact your Extension Office or fertilizer dealer for information about commercial laboratories in your area or look in the Yellow Pages under “laboratories”.

Interpretations for Nutrient Levels in Bearing Apple Trees (sampled between July 15 and August 15)
Nutrient	Deficient (below)	Optimum (within)	Excessive (above)
Nitrogen (%)	1.80	1.90 - 2.30	2.40
Phosphorus (%)	0.08	0.09 - 0.40	--
Potassium(%)	1.00	1.20 - 1.80	1.90
Calcium (%)	0.70	0.80 - 1.60	--
Magnesium (%)	0.20	0.25 - 0.45	0.55
Sulfur (%)	--	0.20 - 0.40	--
Manganese (ppm)	20	25 - 135	200
Boron (ppm)	25	30 - 50	70
Copper (ppm)	4	6 - 12	50
Zinc (ppm)	15	20 - 50	100
Iron (ppm)	45	50 - 200	300

Note: If pesticides containing copper, zinc, or manganese were sprayed on the trees, then concentrations of these elements may be much higher in the leaf tissue. This is usually not a cause for concern, because most of the sprayed elements are on the leaf surface.

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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 Jeanne Ciborowski, 651-297-3217, jeanne.ciborowski@state.mn.us , MDA, 90 W. Plato Blvd., St. Paul, MN 55107-2094. 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: www.mda.state.mn.us/biocon/fruitreports/

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.

DISCLAIMER

Reference to products in this publication is not intended to be an endorsement to the exclusion of others which may have similar uses. Any person using products listed in this publication assumes full responsibility for their use in accordance with current manufacturer directions.

The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2005 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.