Strawberry IPM Newsletter No. 1 – May 17, 2019


Strawberry IPM Newsletter No. 1 – May 17, 2019
Click on photos to enlarge.


Twilight Meeting Thursday, June 6, Maxwell Farm, Cape Elizabeth

A lot of rain, not much sun and cool temperatures have characterized this spring so far. This follows a fall that abruptly ended in early November with snow and cold temperatures, leaving many strawberry fields with no winter mulch or fall applied herbicides to control spring weeds. As a result, there is plenty of potential for winter injury to strawberry plants and for red stele root rot to be problematic in fields with poor drainage and/or susceptible varieties.

We will begin scouting strawberry fields for major insect pests next week, and will be working with volunteer farms in Wells, Limington, Cape Elizabeth, Minot, New Gloucester, Dresden, Monmouth, Wayne, and Farmington. The results of our scouting will be reported through this newsletter and blog on a weekly basis until harvest time. You can also get quick access to this information through the UMaine Pest Management web page at If you would prefer to receive this newsletter via email, please give us a call at 933.2100 or send an email message to:

Dark brown internal tissue on strawberry plant with winter injury..
Winter injury on strawberry plant, photo by David Handley.

Winter injury: Plants that appear weak, or dead, especially in more exposed parts of a field or where mulch was not applied, or has been displaced by wind or animals, may be victims of winter injury. This is caused by freezing of the tissue in the crown of the plants or can be diagnosed by cutting into the crowns of the strawberry plants. The internal tissue will show dark brown discoloration. To reduce the impact of winter injury, make sure the plants get plenty of water, and apply nutrients to encourage root growth and flower development, including nitrogen, calcium, and phosphorus. Heavy nitrogen fertilizer applications in the spring are not recommended, but up to 20 pounds of actual N (e.g. 125 lb. calcium nitrate) may improve early spring growth.

Spring Weed Management:  Many growers were not able to make their typical dormant fall herbicide applications due to the early snowfall. Herbicides available for spring applications are much more limited due to concerns about plant injury and harvest intervals. Dacthal® and Devrinol® herbicides are registered for use in the spring and can be very effective on annual grasses and some broadleaf weeds, but only have pre-emergent activity, i.e. will not control weeds already emerged. Other herbicides have some post emergent activity but may only be applied with a shielded sprayer to the areas between the plant rows, not directly over the plants, or injury is likely to occur. These materials include Chateau®, Prowl H2O®, Satellite Hydrocap®, and Aim®.

Red Stele Symptoms on Strawberry Plant
Red Stele Symptoms on Strawberry Plant; photo by David Handley

Red stele root rot
Spring conditions have been very conducive to red stele development, so you should be alert for this root rot and check any fields that appear to be weak, stunted or dying. To diagnose red stele, pull up a few plants that look weak and scrape the roots of these plants to see if the center of the root, known as the stele, is rusty red in color, instead of the normal white. The red color would indicate an infection. Red stele is caused by Phytophthora fragariae, a soil pathogen that infects roots when soils are wet with temperatures around 50°F. The pathogen grows into the roots causing the plants to become weak, stunted and to eventually die. Symptoms are most evident in the spring, and can be mistaken for winter injury. Ridomil Gold®, Alliette® or Phostrol® are fungicides that can be applied in the late fall or early spring for control of red stele. Spring applications in fields that have any history of red stele are recommended this year, due to the extended period of potential infection. In newly planted beds, RootShield® may be applied as a pre-plant root dip to help prevent infections. Many varieties have some level of resistance to this disease, but the most effective management strategy is to plant only into well-drained soils, and/or plant onto raised beds.

Strawberry bud weevil or “clipper” will soon become active as flower buds begin to emerge. The clipper is a small weevil, which girdles strawberry flower buds, causing them to dry up and fall off the flower stalk. Scout for damage by counting the number of clipped buds in two feet of row length at five different locations in a field. If the average number of clipped buds per two-foot sample exceeds 1.2, or if live clippers are found, control measures are recommended. Damage is usually first noticed at the edges of the field. Border sprays may be effective in keeping this insect from becoming a problem in larger fields. Fields with a history of clipper problems will typically exceed threshold nearly every year. Insecticide options for clipper include Lorsban®, Brigade®, Sevin® and PyGanic®.

Tarnished plant bugs will also soon be active and begin laying eggs in strawberry leaf and flower stems. Once the eggs start to hatch, the nymphs will begin feeding in the flowers. The nymphs are small, active, yellow-green insects. They can appear very quickly in warm weather, so it is important to scout for them regularly. Tarnished plant bugs feed on open strawberry flowers and young fruit, causing the berries to have seedy ends. To scout for the nymphs, tap or shake 30 flower clusters (six clusters in five different locations) over a plate. If four or more of the clusters out of the 30 sampled have any nymphs, control measures should be taken. Be on the alert and scout your fields as soon as open flowers appear! Insecticide options for tarnished plant bug include Assail®, Brigade®, Danitol®, Dibrom®, and PyGanic®.

Cyclamen mites:  Plants showing weak growth and yellow, pinkish or blackened, crinkled leaves may be infested with cyclamen mite. These mites are very small, smaller than spider mites, and reside in the crown of the strawberry plant feeding on the developing leaves and flower buds. They are very hard to see, even with magnification. Infested plants have shrunken distorted leaves and flower stalks, and produce few, if any, marketable fruit. The miticide Portal® can be effective, but must be applied in lots of water and a spreader adjuvant to be sure that the material is carried down into the crowns where these mites reside.

Two-spotted spider mites can be a problem in the spring, especially for plants under row covers. However, the cool temperatures, rain and extended cloud cover will likely delay their emergence this spring. Mites reproduce rapidly when warm weather arrives, so it is important to scout for them regularly. Spider mites mostly feed on the undersides of strawberry leaves, rasping the plant tissue and sucking the sap. Infested leaves will develop yellow flecking and a bronzed appearance. The plants become weakened and stunted. Fields that have had excessive nitrogen fertilizer and/or row covers tend to be most susceptible to mite injury. To scout for mites, collect 60 leaves from various locations in the field and examine the undersides for the presence of mites. Mites are very small – you may need a hand lens to see them. Chemical control options for two-spotted spider mites include Acramite®, Portal®, Nealta® Savey®, Zeal®, Vendex®, Oberon®, Brigade®, Danitol® and JMS Stylet Oil® (oils will cause plant injury if used in combination with captan or within 14 days of an application of sulfur).

Root weevil management
Fields that were infested with root weevils last summer should be inspected for grubs this spring. Infested plants appear weak and stunted, usually in somewhat circular patches in a field. Digging under the plants will reveal small (1/4”-1/2”) crescent-shaped legless grubs. Typically, the grubs begin to pupate when the plants are in bloom. A soil drench of Platinum® (thiamethoxam) insecticide during the spring and/or fall when the grubs are active in the soil can provide control. However, Platinum® has a 50 day pre-harvest interval, so it is too late for applications in most fruiting fields this year. Platinum® may also be used as a pre-plant or planting treatment for root weevils. It is not too late to put on an application of nematodes to control the grubs (optimal timing is mid-late May). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees, and is available from Green Methods, the Integrated Biocontrol Network, and Koppert Biological Systems.

Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another 1/4 inch of irrigation after application to wash them onto and into the soil. Researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of $100-$200 per acre depending on volume and source. Nematodes tend to work best in heavily infested fields. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven’t taken over the roots.

Once the adults become active in July, bifenthrin (Brigade®) will provide some control if used at the highest labeled rates. The best timing for this spray is at night during the peak feeding activity of adults, before they start laying eggs, or about the time harvest ends.

White grubs:  Weak growth noted in fields this spring may also be the result of white grubs feeding on the roots of newer plantings. These grubs are the larvae of beetles, including European chafer and Asiatic garden beetle. They differ from the larvae of black vine weevil and strawberry root weevil in that they have legs and a swollen anterior (rear end), and they tend to be larger. Their feeding weakens the plants by reducing the number of roots. The grubs can be found by pulling up weak plants and sifting through the soil that surrounded the roots. Controlling white grubs once they have become established in a field can be difficult. These tend to be more of a problem in new fields that have been planted following a grass rotation crop, because the adults prefer to lay their eggs in sod. Admire Pro® and Platinum® insecticides are labeled for control of white grubs and should be applied within two hours of irrigation or rainfall to be sure the chemical gets into the root zone. Admire Pro® requires a 14 day to harvest interval, while Platinum® requires a 50-day pre-harvest interval.

Diseases:  Once flower buds start to open, bloom is a critical time to protect strawberry fruit against gray mold caused by the fungus Botrytis cinerea, especially when conditions have been damp. Two to three sprays of fungicide during bloom are typically required to provide good protection against this disease. Botrytis cinerea overwinters on old leaves and plant debris. Fruit infections take place almost exclusively through the flowers, so gray mold control efforts must be focused on the bloom period. If the bloom period is dry and/or good fungicide coverage is maintained, incidence of gray mold at harvest should be low.

There are several excellent fungicide choices for control of gray mold in strawberries. Elevate® (fenhexamid) has good to excellent activity against Botrytis. Captevate® is a pre-mix of captan and fenhexamid and has a broader spectrum of activity than Elevate® alone. Switch® (cyprodinil and fludioxonil), Scala® (pyramethanil) and Pristine® (pyraclostrobin and boscalid) are also excellent products for gray mold control. Topsin M® + captan is also a good fungicide combination, but remember that captan is strictly a protectant and can be washed off by rain or irrigation water. Thiram is similarly effective but also susceptible to wash-off.

The fungicides Cabrio® (pyraclostrobin) and Abound® (azoxystrobin) are NOT suitable for gray mold control, but are effective against anthracnose and other fruit rot and leaf spot diseases. All fungicides mentioned above have a 0-day pre-harvest interval, except Topsin M® (1 day) and thiram (3 days). Remember to alternate fungicides with different modes of action for resistance management purposes.

Angular leaf spot is a bacterial disease that is characterized by translucent leaf spots that may turn yellow and eventually black. The symptoms tend to start on the lower leaves but may move upwards as bacterial spores are splashed up by rain or irrigation water. Infection of the calyxes may result in a blackening of the berry stems and caps, reducing their marketability. Bacterial angular leaf spot is favored by extended cool, wet weather and nights with temperatures close to freezing. Frequent irrigation for frost protection can greatly encourage the development and spread of the disease, as will extended cool, damp weather. Susceptibility to this disease appears to vary significantly between varieties. The copper-containing material Kocide®, can reduce the spread of this disease. Start spray applications before bloom to prevent multiplication of the bacteria on the leaves before they jump to the berry caps. Application of copper sprays after bloom can result in fruit injury and is not recommended. Hydrogen dioxide (OxiDate®) may also have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.

Other Berries:
Raspberries are showing significant winter injury in many fields, with tip dieback showing as the buds begin to expand. Further injury may become apparent once the floricanes start to flower and emerged lateral branches wilt and die due to damaged vascular tissue.

Highbush blueberries are showing some winter injury on last year’s growth. This appears as a dark brown or black discoloration on the shoots. The damage is usually limited to growth above the snowline. The cool, wet weather has initiated the release of mummy berry spores from the overwintering mummies. Expect infection periods to continue over the next few weeks, anytime there is a significant moisture event (rain, mist, fog). Protectant fungicides for mummy berry should be applied once the flower buds have begun to expand. Registered materials include Indar®, Orbit®, and Quilt Excel®.

2019-2020 New England Small Fruit Management Guides will soon be available from UMaine Cooperative Extension. We anticipate an early June delivery date for the updated edition of this guide. Members of the Maine Vegetable & Small Fruit Growers Association will receive a free copy. The guide contains the latest information on management options for small fruit pests as well as cultural information. You can also access the guide on the UMass Cooperative Extension website.

The best way to manage strawberry pests is to scout your own fields regularly and often. You should begin to scout as soon as flower buds emerge from the crowns and continue to monitor the plantings one or two times per week up until harvest. You should be able to identify the major pests and their damage, and be able to determine if control measures are necessary.

Service Animals vs. Food Safety in Pick-Your-Own Fields
A question that often arises for pick-your-own berry growers regarding the new FSMA Produce Safety Rule is whether customers’ service animals can be allowed into the fields. Service Animals On U-Pick Farms is a new publication from the University of Georgia Extension, designed to help growers address having service animals on their farms. The publication reviews applicable Americans with Disabilities Act (ADA) policies and outlines what this may mean for farms with U-Pick operations, roadside stands, on-site restaurants, and other venues that are open to the general public. Click here to download the publication free as a PDF file. For more information regarding the Produce Safety Rule and how it applies to your farm visit the Produce Safety Alliance Website.

Twilight Meeting Thursday June 6th will be held at the Maxwell Farms strawberry fields, 527 Ocean House Road, Cape Elizabeth. Bill & Lois Bamford will host this meeting and tour us through some of their strawberry fields within sight of Casco Bay. The farm has a long history in Cape Elizabeth, and has had to adapt to changing markets and a rapidly growing population surrounding the production fields. We will also get an update on the berry pest situation around the state. There will also be a Respirator Fit Test available. The meeting will run from 5:00 p.m. to 7:00 p.m.

Participants wearing respirators at a respirator fit test.
Participants at a respirator fit test, photo by Jason Lilley.

Respirator Fit Test at Twilight Meeting on June 6
Worker Protection Standard new rules require that all pesticide applicators that use products requiring respirator use MUST have a respirator fit test. To use products that require just a dust respirator (N95 TC-84), those respirators must still be fit tested. Time slots for fit tests are 30 minutes long and will take place 5:00 p.m. to 7:00 p.m. during the Twilight Meeting at Maxwell Farms. Participants must preregister and must have a medical evaluation prior to the testing. Contact Lisa Turner at  to preregister. More details to follow. Hope to see you on the Cape!


David T. Handley
Vegetable and Small Fruit Specialist

Highmoor Farm                      UMaine Extension Diagnostic
P.O. Box 179                            Research Lab, Pest Mgmt. Unit
52 U.S. Route 202                   17 Godfrey Drive
Monmouth, ME  04259          Orono, ME  04473
207.933.2100                          1.800.287.0279

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 products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these producers assume all associated risks.

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