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Strawberry IPM Newsletter No. 3 – June 1, 2012

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Insect Pressure Light; More Rain Ahead: Protect for Gray Mold

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

Situation:  Heavy rains limited how many fields we could scout this week, but we managed to visit strawberry fields in Monmouth, New Gloucester, Minot, Lewiston, Wales, and Livermore Falls.  Early varieties are mostly past bloom, with some pink fruit showing.  Day neutral varieties grown on plastic mulch are now starting to be harvested.  Later varieties are in full to late bloom.  It is still looking like an early start to the season, although the cool, wet weather forecast for the next week will likely slow things down.  Growers will need to continue protecting blossoms and fruit from gray mold infection and be on the lookout for leather rot or anthracnose fruit rot because of all the recent rainfall.

Strawberry bud weevil or “clipper”:  Nearly all fields we visited are well beyond the stage at which clipper can do significant harm, although clipper was still present and active in some fields.  Northern fields may still have late varieties with susceptible flower buds, in which case scouting for damage should continue.  Remember that clipper will also damage raspberry and blackberry flower buds.  We have seen clippers in most raspberry plantings that we’ve been through this week.

Clipper Injury

Tarnished plant bugs were found in some of the fields scouted this week.  We found adults and small nymphs, but numbers were generally low, probably due to all the rain, which can slow their development and activity.  Keep scouting for the nymphs, because they may appear quickly when things dry out, and the feeding remains a threat even past petal fall.

First Instar Tarnished Plant Bug Nymph

First Instar Tarnished Plant Bug Nymph, Photo by David Handley

Two-spotted spider mites have been found in more fields and in higher numbers this week, although none of the fields have reached the threshold of 25% or more of leaves infested.  Mite development has probably been hindered by recent rainfall, but expect populations to increase rapidly once conditions become warmer and drier.

Two-spotted Spider Mites

Two-spotted Spider Mites, photo by Michigan State University

Cyclamen mites:  We found cyclamen mites in two more fields this week, with some plants showing fairly severe leaf crinkling and yellow streaking.  The symptoms can be mistaken for herbicide injury.  If you suspect your plants have cyclamen mites, give us a call or send us a plant sample (whole plant) for analysis.

Spittlebugs:  We have found a few spittlebug masses in fields this week.  Frothy spittle masses on the leaf and flower stems usually show up around bloom.  Spittlebugs don’t pose a significant threat to the plants, but the spittle masses are a nuisance for the pickers.  Spittlebugs overwinter as eggs and the nymphs emerge in late May.  Scouting for spittlebugs should start when the plants are at 10% bloom.  Randomly inspect five, one square foot areas per field every week.  Spread the leaves and inspect the crowns, leaf bases, leaf stems, and flower stems looking for the frothy spittle masses.  Small, yellow-orange nymphs will be under the spittle.  If the average number of spittle masses is more than two per foot, a treatment may be warranted.  Spittlebugs tend to be a greater problem in weedy fields. Pesticides currently registered for spittlebug control include Provado®, Thionex®, Danitol® and Brigade®.


Spittlebug, photo by David Handley

Diseases:  Most fields have now had at least one fungicide spray to protect blossoms against gray mold.  If it has been more than a week since the last application or more than one inch of rain has fallen on the field, another spray should be applied soon.  Two to three sprays of fungicide are usually needed during bloom to provide adequate control of gray mold, but when rainfall exceeds one inch between sprays additional coverage is needed.  However, when conditions are dry after the second spray, further applications are often not necessary.

Gray Mold on Strawberries

Gray Mold on Strawberries, photo by James Dill

Leather rot (Phytopthora cactorum) continues to be a threat this spring because many fields have experienced extended periods with standing water between the rows.  These conditions are very conducive to the development of leather rot.  Foliar sprays during bloom and fruit development of Aliette®, Agri-Phos® or Phostrol® can provide good control of this disease.

Powdery mildew:  No severe symptoms of powdery mildew have been observed yet, but we’re starting to see a little more leaf rolling in fields suggesting that this disease may become more evident once temperatures start to rise.  Upward cupping of the leaves and reddish streaking or lesions on the leaf and flower stems are the most obvious symptoms of this disease.  White, powdery growth on the undersides of the leaves will appear as the disease develops further.

Anthracnose fruit rot remains a threat due to the recent wet weather and warm temperatures; especially for plantings using plastic mulch, which provides a good environment for the development and spread of the fungus.  Effective fungicides include Cabrio® and Abound®.

How much nitrogen fertilizer should I use?
Nitrogen is an essential component in the synthesis of amino acids and proteins in the plant.  As a fertilizer, it stimulates vegetative growth, such as leaves, petioles and shoots.  Heavy applications are not recommended in the springtime because excess vegetative growth at this time will result in dense leaf canopy that will cover developing fruit, keeping it in a dark, cool wet micro-climate, and encouraging the development of fruit rot such as gray mold.  In a matted row system, the majority of nitrogen fertilizer should be applied during the summer months, following harvest when new leaf and shoot (runner) growth is needed to re-establish good planting vigor for next year’s crop.

During the planting year (assuming the general fertility and condition of the soil is good), a strawberry planting should receive 20 to 40 pounds of actual nitrogen per acre incorporated into the soil prior to planting.  Another 30 pounds should be applied in late June to early July, and a final 20 pounds can be applied in late August to early September.  Each of these applications corresponds to periods of growth in the plants.  Calcium nitrate [Ca(NO3)2, 15% N] is the recommended source of nitrogen in new plantings because it is readily available, not volatile, and also provides calcium.

For established beds, only 10-20 pounds of actual nitrogen, if any, should be applied in the spring.  As part of the renovation process following harvest, 50 to 70 pounds of nitrogen per acre should be applied to the planting, followed by 20 to 30 pounds in late August to early September.  Recent studies have shown that this later summer application of nitrogen has significant positive impact on yield and growth the following year, so be sure not to forget it as the summer starts to wane.

Vegetable & Berry Growers Twilight Meeting
We hope to see you next Tuesday night, June 5th, 5:30 p.m. at Stutzman’s Farm, 891 Douty Hill Road in Sangerville for a growers twilight meeting and tour of this innovative farm.  Hold the date!


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.

Any person with a disability who needs accommodations for this program should contact Pam St. Peter at 207.933.2100 or TDD 1.800.287.8957 to discuss their needs at least 7 days in advance.

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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