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Strawberry IPM Newsletter No. 4 – June 8, 2012

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For full page print version, please see link at the bottom.  Click on photos to enlarge.


Watch for Fungus Diseases:  Gray Mold, Powdery Mildew

Situation:  Access to fields has remained limited this week.  Heavy rains have kept the fields muddy, and soaking wet plants are difficult to scout for insects and mites.  We visited fields in North Berwick, Wells, Cape Elizabeth, Monmouth, New Gloucester, Minot, Lewiston, Wales, Dresden and Livermore Falls.  There is some light harvesting going on in early varieties, and later varieties are sizing up, with a few late blossoms still showing.  Day neutral varieties grown on plastic mulch are now coming into full harvest.  The early start predicted for the season keeps getting pushed back by the recent cool, wet weather.  We are seeing many fields with pale or mildly yellowing leaves.  This is most likely a symptom of the prolonged cool, cloudy conditions, but may also be related to mild magnesium deficiencies related to the high rainfall.

Strawberry bud weevil or “clipper”:  Fields are now beyond the stage at which clipper can do significant harm, and activity was fairly low this week.

Tarnished plant bugs were only found in a few of the fields scouted this week, as the cool, wet weather continues to slow their development and activity.  Only one field in Cape Elizabeth was over the recommended spray threshold of 4 out of 30 flower clusters scouted having nymphs present.  Keep scouting for the nymphs, because they may appear quickly when things dry out, and the feeding remains a threat past petal fall.

Large Tarnished Plant Bug Nymph

Two-spotted spider mites continue to be found in strawberry fields this week, with several fields exceeding the threshold of 25% of sampled leaves infested.  This is somewhat surprising, given the extended wet weather, and suggests that populations will increase rapidly once conditions become warmer and drier.  Chemical control options for two-spotted spider mites include Acramite®, Savey®, Zeal®, Vendex®, Oberon®, Brigade®, Danitol®, Thionex® and JMS Stylet oil ® (oils will cause plant injury if used in combination with captan or within 14 days of an application of sulfur).  Pay close attention to harvest intervals for these products as the fruit begins to ripen.

Two-spotted Spider Mites

Two-spotted Spider Mites, photo by David Handley

Spittlebugs:  We continue to find spittlebug masses in fields this week, so it looks as though their populations may be high this year.  The spittle masses are a nuisance for the pickers, so if you haven’t yet checked your fields, now is the time.  Pesticides registered for spittlebug control include Provado®, Thionex®, Danitol® and Brigade®.

Sap beetles can be a problem on ripening fruit.  The 1/8 inch long, dark brown beetles chew small holes in ripening fruit, similar to slug injury.  They may be seen in the holes they’ve chewed into ripe fruit, but often drop to the ground when disturbed.  The best management strategy for sap beetles is good sanitation.  Keep the field free of overripe fruit by picking often and thoroughly. Insecticide sprays for this pest can be effective, but should be a last resort during the harvest period.  Brigade®, Assail®, Dibrom® and PyGanic® are registered for control of sap beetles with pre-harvest intervals ranging from 12 to 24 hours.  Read the product label carefully for this and other application instructions and restrictions.

Sap Beetle

Sap Beetle, photo by New York State Agricultural Experiment Station

Strawberry rootworm (not root weevil) adults and feeding injury have been found on strawberry leaves in some fields this spring.  The adult stage of this insect is a small (1/8”) dark brown beetle.  The beetles feed on strawberry leaves during the spring and late summer, causing numerous small holes in the leaves.  The adults in fields now will soon lay eggs.  The larvae are small grubs that feed on the roots of strawberry plants, causing them to be stunted and weak.  If these beetles and/or feeding injury is prevalent in a field, a treatment is recommended.  Sevin 50WP® is registered for control of this pest, and sprays targeted at other insect pests at this time may also control rootworm.  Strawberry rootworm should not be confused with root weevil, a larger insect that causes much more serious damage when present in a field.

Strawberry Rootworm

Strawberry Rootworm Beetle, phot by David Handley

Diseases:  Fungicide applications that were made prior to the heavy rainfall last week are most likely no longer effective, and thus another application will be needed to protect developing fruit and foliage from the common fungus diseases.  The highest concern is for gray mold, which could be a major problem in fields because of the extended wet conditions.  An effective fungicide for gray mold such as Switch®, Scala®, Elevate® or Pristine® should be applied if more than one inch of rain has fallen since your last application.  Bear in mind that while these products are very good for controlling gray mold, only Pristine® will also provide control of foliar diseases as well, so use an additional product effective on foliar diseases, if needed.

Leather rot (Phytopthora cactorum) may start to show up as fruit begins to ripen.  Look for fruit with a dull pink or purplish appearance.  The fruit is also tough, with very bad flavor.  Conditions have been very conducive to the development of leather rot.  Foliar sprays of Aliette®, Agri-Phos® or Phostrol® can provide good control of this disease.

Anthracnose fruit rot is still a concern because of the recent wet weather.  Infections on the fruit start as brown patches, eventually turning black.  Whole fruit may suddenly turn soft or dry up to blackened mummies.  Effective fungicides include Cabrio® and Abound®.

Anthracnose on Strawberry

Anthracnose on Strawberry, photo by North Carolina State University

Powdery mildew:  Symptoms of powdery mildew have been showing up in many fields this week, but have mostly been mild.  One field had discoloration of the fruit stems and caps in addition to severe leaf cupping, and a fungicide was recommended.  Abound®, captan, Pristine®, Cabrio® and Topsin-M® are registered for control of powdery mildew.

Powdery Mildew

Powdery Mildew, photo by David Handley

Leaf spot infections were more common in strawberry fields this week.  The spots usually appear on older leaves first, as small purple or red spots with white centers.  Spots may coalesce to turn the leaves purple and necrotic,   leading to the death of the leaf and weakening of the plant.  Fungicides registered for leaf spots include captan, Topsin-M®, Syllit®, Cabrio®, Nova® and Pristine®.

Leaf Spot on Strawberry Plant

Leaf Spot, photo by David Handley

Birds, specifically cedar waxwings have been moving into fields to feed on ripening fruit.  Waxwings often destroy many of the early ripening fruit, despite our best efforts to scare them off.  Only by keeping a near constant presence in the field and eliminating roosting sites can you reduce the damage.  Usually, they are discouraged once the fields start to be regularly harvested and customers are present.  Songbirds are protected by law and should not be killed.  However, permits may be issued for killing birds by the U.S. Fish and Wildlife Service if they receive a recommendation for such a permit from the Maine Wildlife Services Office (part of the USDA Animal and Plant Health Inspection Service) in Augusta, along with an application from the grower.  There is a $50 fee for the application, and it may take over a month for the permit to be processed.  However, the permit is good for one year; so if you have problems this season, you may consider applying for a permit this winter, which would allow you an option to kill birds, if necessary, next season.  The Wildlife Damage Office has recommendations for managing birds in crops, and also has some control options available through their office.  For more information on permits or bird control contact the office in Augusta at 207.629.5181.  The office is located in the Capital West Business Center at 79 Leighton Road in Augusta.

Cedar Waxwing

Cedar Waxwing, photo by Cornell University


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                                  Pest Management
P.O. Box179                                      491 College Ave
Monmouth,ME 04259                        Orono,ME 04473
207.933.2100                                    1.800.287.0279

Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture Cooperating.  Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment.  A Member of the University of Maine System.

Where brand names or company names are used it is for the reader’s information.  No endorsement is implied nor is any discrimination intended against other products with similar ingredients.  Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.

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