MN Fruit & Vegetable IPM News - Vol. 1, No. 9

Believe it or not, plant physiology is a very interesting subject! Strawberry growers incorporate many aspects of plant physiology into their crop production practices, especially at renovation time. Here are three basic concepts in plant physiology that relate to how the strawberry responds to management practices at renovation.

Source sink concept : Strawberry plant parts, such as leaves, roots, crowns, runners, flowers and fruit act as energy providers (source), or energy users (sinks). Some parts (i.e. crowns), may switch from being energy users to energy providers, depending on the time of year. Competition for energy can occur between plants and within plants. When plants are too close together, they compete with each other for resources. You can expect yield per plant, and average berry size, to be reduced. In a matted row system, optimum plant density is somewhere around 6-8 plants per square foot of row. This is just a ballpark number and depends on variety, soil type, etc.

Competition for resources within the plant occurs too. For example, flowering and fruiting processes compete with runner development. Runner development can compete with crown formation. Crowns can compete with each other. As a result, older, multi-crowned plants tend to produce smaller fruit. The optimum number of crowns in a strawberry plant is different for different cultivars. Growers using the plasticulture system usually aim for 4-6 crowns per plant. During renovation of matted row plantings, growers use various methods to adjust plant density. Narrowing the rows back to 8-12 inches is the most common practice. Yields can be increased if narrower rows are combined with closer row spacings. The stand may be thinned during mowing or a light raking, which removes weakly rooted plants. Rows can be narrowed to one side so that original mother plants are eventually cut out. Or, a cultivator tooth can be used to cut out older plants in the middle of the row.

Root physiology : Strawberry plants must produce new roots to remain productive. Primary roots penetrate the soil and anchor the plant. Fibrous secondary roots form on the primary roots. These white roots mine the soil for nutrients and water and are frequently regenerated in a healthy plant. The root system of a strawberry plant is similar to that of an African violet. As the plant grows taller, it initiates new leaves. Older leaves at the base of the plant drop off. New primary roots develop where the old leaves fall off. These roots will not elongate unless they are in contact with moist soil. Root formation tends to take place when the plant is non-fruiting, and when soil temperatures are cool. Renovation can encourage new root development if rows are narrowed with a rototiller and a small amount of soil is added to the middle of the row. This encourages new roots to form at the base of the crown. Otherwise, as the plant grows older, the crown extends upward, grows out of the soil, fails to develop new roots, and is more exposed to winter injury.

Environmental interactions : In most Junebearing cultivars, cooler temperatures and shorter day lengths cause the plant to initiate flower buds for next year’s crop. Different cultivars respond differently to these environmental triggers. Defining the exact conditions that cause fruit bud initiation to occur is like shooting at a moving target. It is generally believed the process begins as daylengths shorten to less than 14 hours. Flower initiation probably continues until cold temperatures cause plants to go dormant. These factors affect the timing of renovation practices.

It is important to have a vigorous healthy plant in place when flower bud initiation begins. Nitrogen is often applied in early August to give plants a boost. Herbicides such as

2,4-D and Lontrel are not recommended after mid-August because we assume these interfere with flower bud initiation. In northern regions, where summer days are longer, and frost comes earlier, growers may choose not to mow off strawberry plants as part of the renovation process. Mowing can be helpful in terms of reducing pest populations and encouraging new vegetative growth. It is not essential however, and should not be done if plants don’t have time to grow back by mid-August. Plant physiology affects renovation practices in many ways. Growers who understand strawberry plant physiology can use this knowledge at renovation time and manipulate their plants to produce better crops.

*Article published in the All Ontario Berry Grower (Vol. 00, No. 2, June 2000).

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ACKNOWLEDGEMENTS

Co-Editors: Bill Hutchison, Department of Entomology, University of Minnesota, hutch002@umn.edu
Jeanne Ciborowski, Minnesota Department of Agriculture, Ag. Resources Division,jeanne.ciborowski@state.mn.us
Suzanne Wold-Burkness, Department of Entomology, University of Minnesota, woldx018@umn.edu

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., Tuesday 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/default.htm

Partial funding for this publication is provided through partnership agreements with the Minnesota Fruit and Vegetable Growers Association and the United States Department of Agriculture – Risk Management Agency (RMA) and the RMA Community Outreach and Assistance Partnership Program. These institutions are equal opportunity providers.

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References 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.

Last Revised July 12, 2004.
The University, including the Minnesota Extension Service, is an equal opportunity educator and employer. ©1999-2004 Minnesota Extension Service, University of Minnesota. All rights reserved. Contact copyright@extension.umn.edu for information on reproduction or use of this material.