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Strawberry IPM Newsletter No. 2 – May 25, 2012

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Clipper and Tarnished Plant Bug Active this Week; Time to Protect for Gray Mold

Note:  Twilight Meeting on June 5 at 5:30 p.m. at Stutzman’s Farm in Sangerville

Situation:  This week I visited strawberry fields in Monmouth, New Gloucester, Minot, Lewiston, Dresden, Livermore Falls, Farmington, Wells, Sanford, North Berwick, and Limington.  Fields in the southern region are generally past full bloom, while fields further north range from early to full bloom.  If the weather holds in a warm pattern, we could be looking at a very early harvest season.  Most fields have seen plenty of rain this week, and growers need to be protecting blossoms and fruit from gray mold infection if it has been more than a week since the last fungicide application.

Strawberry bud weevil or “clipper”:  Although clipper was both present and active in most fields this week, strawberries in the southern part of the state are beyond the stage at which clipper can do significant harm.  Fields further north that still have plants in the flower bud to early bloom stage should be on the lookout for clipper damage and be ready to apply a spray if the damage exceeds the spray threshold of more than one clipped bud per two feet of row length.  Growers should be aware that clipper will also damage raspberry flower buds, especially in years like this when the strawberry buds open early and deprive them of egg laying sites.

Clipper on Strawberry

Clipper on Strawberry, photo by David Handley

Tarnished plant bugs were found in most fields visited this week.  Small, green first instar nymphs are now showing up on blossoms, and overwintering adults are still feeding and laying eggs.  It is important to scout for the nymphs often, as they can show up quickly in warm weather.  For control options, review last week’s issue of this letter or see the 2010-2011 New England Small Fruit Pest Management Guide.

Tarnished Plant Bug Nymph on Strawberry Blossom

Tarnished Plant Bug on Strawberry

Two-spotted spider mites have only been found in a few fields this week, mostly along border rows on older leaves.  None of the fields scouted were over the threshold of 25% or more of leaves infested.  Mites tend to exhibit little growth under wet conditions, so our recent weather has probably kept them in check.  Overwintering adults are now laying eggs and we will start seeing more mites once we get a stretch of warm, dry weather.

Cyclamen mites:  We have seen some plants showing the stunting and crinkled leaves characteristic of cyclamen mite damage.  This has been a problem for some fields during the past two years.  Miticides such as Portal® or Thionex® can offer control, but they must be applied with lots of water (100-200 gals/acre) and a surfactant to get the materials deep into the crown where these very small mites reside.  We will continue to keep a lookout for this pest as it may become more prevalent as the temperatures start to rise.

Cyclamen Mite

Cyclamen Mite Damage on Strawberry Plant, photo by David Handley

White grubs:  We continue to find white grubs feeding on roots under the plants in weak looking fields.  It’s probably too late to successfully control them this spring, but a late summer/early fall soil drench with Admire® or an application of grub killing nematodes could prevent further infestation this fall.  These grubs are the larvae of beetles, most likely Japanese beetles, European chafers or Asiatic garden beetles.  You can scout for grubs by pulling up weak plants and sifting through the soil that surrounded the roots.

White Grub Under Strawberry

White Grub Under Strawberry Plant, photo by David Handley

Diseases:  Many fields have already received a fungicide spray to protect early blossoms from spores of Botrytis cinerea, the fungus that causes gray mold.  If it has been more than a week since the initial application, a second spray should be applied soon.  If the field is just coming into bloom and no fungicide has been applied, now is the time.  Two to three sprays of fungicide during bloom are required to provide good protection against this disease, but if rainfall exceeds more than one inch between sprays and wet conditions are prevalent, additional sprays may be required.  Alternatively, if conditions remain very dry after the second spray, then a third spray may not be necessary.

Leather rot (Phytopthora cactorum) is a threat if you have had wet conditions during bloom, especially if there has been standing water in the field.  Foliar sprays of Aliette®, Agri-Phos® or Phostrol® can provide control.  Sprays should be applied during bloom and fruit development.

Powdery mildew:  No severe symptoms of powdery mildew have been observed yet, but expect to see the problem become more noticeable under warmer, dry conditions.  Look for upward cupping of the leaves and reddish streaking or lesions on the leaf and flower stems.  Consider using a fungicide that will control powdery mildew, such as captan + Topsin-M®, or Pristine® when spraying for gray mold.

Powdery Mildew

Powdery Mildew, photo by David Handley

Anthracnose fruit rot is a potential problem for growers in the coming days as fruit ripens in fields that are wet from irrigation or rain.  This fungus is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation.  In cool seasons, it may appear close to harvest or may not show up at all.  Anthracnose fruit rot is identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them.  The anthracnose fungus can multiply on leaves without visible symptoms, which explains its sometimes sudden appearance in fields.  Fungicides such as Cabrio® and Abound® can provide good control of anthracnose fruit rot.

Anthracnose on Strawberry

Anthracnose on Strawberry, photo by North Carolina State University

Spotted wing drosophila (Drosophila suzukii) is a new pest which is likely to be a concern for late ripening strawberries, day neutral strawberries, fall raspberries and blueberries.  This is a small fruit fly, similar to the type that fly around the over ripe bananas in your kitchen.  However, this species will lay its eggs on fruit before it ripens, resulting in fruit that is contaminated with small white maggots just as it is ready to pick.  As a result, the fruit quickly rots and has no shelf life.  This insect recently came into the U.S.from northern Asia, and caused problems with many berry crops up the east coast last year.  It can complete a generation in under two weeks, with each adult female laying hundreds of eggs.  Therefore, millions of flies can be present soon after the introduction of just a few into a field.  This makes them very difficult to control, and frequently repeated insecticide sprays (3 to 5 times per week) have been needed to prevent infestations once the insect is established in a field.  It is likely that spotted winged drosophila can successfully over winter here, but we suspect that it may not build up to damaging levels until late in the summer.  This could mean that June bearing strawberries will not face a significant threat from it, but later ripening fruit such as day-neutral strawberries, raspberries and blueberries will probably need to be protected.  We will be setting out monitoring traps for spotted winged drosophila in fruit plantings around the state this spring to gather as much information on it as we can, and determine how much of a threat this pest will pose for fruit in Maine.  This will help us develop management strategies for the coming years.  For more information on this new and important pest, and to find instructions on making a simple monitoring trap, and how to identify this from other fruit flies, visit Michigan State University’s Spotted Wing Drosophila website.

Twilight Meeting Reminder:  June 5th, 5:30 p.m. at Stutzman’s Farm, 891 Douty Hill Road in Sangerville. Hold the date!


David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm                                  PestManagement
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.

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