MN Fruit & Vegetable IPM News - Vol. 2, No. 4

(Reprinted with the Author’s permission – First appeared in: MI State University Fruit Crop Advisory Team Alert, Vol. 19, No. 3, May 4, 2004, http://www.ipm.msu.edu/CAT04_frt/F05-04-04.htm#5)

There are more choices for disease control in strawberries than ever before. This can be a rather bewildering experience, as growers have to consider the disease control spectrum, efficacy ratings, and cost per acre for each product. This article aims to help strawberry growers in the decision-making process by outlining unique aspects of several strawberry diseases and characteristics of the newer fungicides. A few notes on specific diseases:

1) Control of leaf diseases, such as common leaf spot, scorch, Phomopsis leaf blight and angular leaf spot may only be needed on susceptible cultivars. Some leaf diseases can spread to the berries (e.g., Phomopsis can also cause a fruit rot), or berry caps (angular leaf spot and scorch). If these have been a problem in the past, start fungicide sprays before bloom.

2) Leather rot (Phytopthora cactorum) is best controlled by growing strawberries in well-drained soil and by applying straw mulch between the rows to prevent the berries from touching the soil (where the fungus resides) and prevent soil from splashing up onto the berries. If there still is a problem, use Ridomil Gold or Aliette for control. Some phosphorous acid products such as Agri-Phos (similar to Aliette) may also work, but have not been evaluated on strawberries in Michigan. Spray during bloom and fruit development.

3) Angular leaf spot is a bacterial disease that is characterized by translucent leaf spots and blackening of the berry caps. It is favored by cool, wet weather and nights with temperatures close to freezing. The bacteria are spread by rain splash or by irrigation water. Copper (e.g., Kocide, Cuprofix, Bordeaux, etc.) is the only chemical that works against this disease. Some labels suggest adding lime as a safener to reduce the risk of crop injury. In susceptible varieties, start spray applications before bloom to prevent multiplication of the bacteria on the leaves before they jump to the berry caps.

4) Botrytis gray mold, the predominant fruit rot in most areas where strawberries are grown, primarily enters the berries through the blossoms, which means that chemical control should be focused on the bloom period. The Botrytis fungus can produce numerous spores on dead leaves and other plant matter and spreads easily by wind. Make sure to protect the king blooms especially, since these provide the largest berries. The other period for control is pre-harvest, since Botrytis can spread rapidly from infected berries to ripe and overripe berries. Pre-harvest sprays reduce post-harvest rots and increase shelf life of the berries.

5) Most other fruit rots, including anthracnose, tend to infect the berries somewhat later in the season, i.e., during the green fruit or ripening stage. Anthracnose fruit rot is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation. In cool seasons, it tends to appear closer harvest or may not show up at all. Anthracnose fruit rot can be identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The anthracnose fungus is able to multiply on the leaves without visible symptoms, which may explain its sometimes widespread and sudden appearance in fields.

New fungicide characteristics (2004 prices are estimates for comparative purposes only and may vary depending on the supplier and quantity purchased). Please follow label directions carefully before use.

Pristine (pyraclostrobin and boscalid) contains a strobilurin and an analid active ingredient. This fungicide is a very broad-spectrum material and has excellent activity against leaf spots, powdery mildew, and fruit rots, including Botrytis gray mold. It is surface-systemic (i.e., it is somewhat mobile within the wax layer on the plant surface) and has limited back action. The fungicide gets rainfast quickly. The label rate is 18-23.5 oz/acre (approximate cost: $32-$42/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Cabrio (pyraclostrobin) is a strobilurin-type fungicide with excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots . However, it does not provide much control of Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 12-14 oz/acre (approximate cost: $16-$18/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Quadris (azoxystrobin – this product will be sold under the name Abound in future) is also a strobilurin-type fungicide with good to excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots. It does not have much activity against Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 6.2-15.4 fl oz/acre (approximate cost: $12-$30/acre; $24 at the 12-oz rate). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Elevate (fenhexamid) is a fungicide with a new chemistry that has excellent activity against Botrytis gray mold. While fenhexamid has some systemic activity, it should be used as a preventative fungicide. The fungicide gets rainfast quickly. It can be used to alternate with fungicides in other chemical classes. The label rate is 1.5 lb/acre (approximate cost: $41/acre). PHI=0 days.

Captevate (fenhexamid and captan) is a pre-mix of Elevate and Captan. It has excellent activity against Botrytis as well as moderate to good activity against anthracnose and other leaf spot and fruit rot diseases. This formulation appears to perform a bit better than a tank mix of Elevate and Captan. The label rate is 3.5-5.25 lb/acre (approximate cost: $42-$63/acre) . At the high rate, the dose is equivalent to 1.5 lb Elevate and 5 lb Captan. The PHI=0 days.

Switch (cyprodinil and fludioxonil) is a mixture of a systemic and protectant active ingredient (both are new chemistries). Switch has excellent activity against Botrytis gray mold and moderate to good activity against anthracnose and scorch. The label rate is 11-14 oz/acre (approximate cost: $39-$50/acre). PHI=0 days.

Older fungicides such as Topsin M, Captan, Thiram, Sulfur, etc. remain effective disease control tools. The approximate prices per acre: Topsin M $16/acre; Captan $13/acre; Thiram $8/acre; Sulfur $1-2/acre; and copper formulations: $3 to $4/acre.

Another product labeled in 2005 for Botrytis is Scala (pyrimethanil). The label rate is 18 oz/acre. PHI=1 day.

(NOTE: Pesticides named are still current. Pesticide labels can change however, so always check to make sure that the pesticide is currently labeled and read the label carefully. The label is the final authority on how you may legally use any pesticide.)

More information is also available in “ Integrated Pest Management Manual for Minnesota Strawberry Fields"

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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.