Strawberry IPM Newsletter No. 1 — April 17, 2025

2025 STRAWBERRY PEST MANAGEMENT SEASON BEGINS

Vegetable and Berry Growers Twilight Meeting at Belanger’s Farm, Lewiston, June 5, 5:30 p.m.

Situation: March was slightly warmer than average this spring, but April has been very cool and damp, keeping strawberry plants dormant in matted row plantings under straw mulch. It is now time to uncover the strawberries, if you haven’t already done so, as long as the forecast is not predicting temperatures below about 25ºF. Removal of the mulch has been difficult in most fields due to late snowstorms and very wet soils. Although it is generally desirable to remove winter mulch early in the spring to stimulate new growth and push flower bud development, strawberries typically won’t start to grow until soil temperatures are at least 40ºF. Leaving the mulch on too long after conditions are warmer will result in delayed bloom, lower yields and reduced plant vigor. Plants in most fields probably haven’t started to grow yet, and removing the mulch at this later date shouldn’t have much impact on growth and yield. For plants under rowcovers, if you put more than one layer of fabric over the plants (e.g. 0.6-1.25 oz.), one layer can be removed to improve light penetration, while the second is left on to contain heat and stimulate growth. Remove the remaining cover just before bloom to allow pollinators to work the blossoms. If only one layer (1.25 oz or less) was used, it can remain on until bloom begins. If a heavier material was used for winter protection, consider removing it and applying a lighter cover to allow better light penetration.

Winter injury: Plants may be victims of winter injury if they appear weak or dead: especially in more exposed parts of a field, where mulch was not applied or where mulch was displaced by wind or animals. This is caused by freezing of the tissue in the crown of the plants, and 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 as they start to grow and set fruit, and apply nutrients to encourage root growth and flower development. These should include nitrogen, calcium, and phosphorus. However, heavy nitrogen fertilizer applications are not recommended in the spring, but up to 20 pounds of actual N (e.g. 125 lb. calcium nitrate) may improve early growth.

Spring weed management: Herbicides available for spring applications in strawberries are very limited due to concerns about plant injury and harvest intervals. Devrinol® is registered for use in the spring and can be very effective on annual grasses and some broadleaf weeds, but only has pre-emergent activity, i.e. will not control weeds already emerged. Dacthal (DCPA) is no longer registered for use and should not be applied. Remaining stocks of Dacthal must be properly disposed of. Contact the Maine Board of Pesticide Control for information on collection of obsolete pesticides. There are other herbicide options for strawberries in the spring that 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®.

Two-spotted spider mites: One of the first problems often encountered on strawberries once the new foliage starts to emerge is spider mites. Mites overwinter on the plants and will start to feed on the undersides of the leaves under warm, dry conditions. This can occur very early on plantings under rowcovers or in high tunnels. Scout for mites regularly once the plants begin to grow. Spider mites are mostly found on the undersides of strawberry leaves. Infested leaves will develop yellow flecking and a bronzed appearance, and 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).

Cyclamen mites: If your planting had indications of cyclamen mite damage last season, begin looking for injury as soon as new growth begins. Infested plants show weak growth and shrunken, crinkled leaves. These mites are very small 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. Portal® miticide can be effective, but must be applied in lots of water to be sure that the material is carried down into the crowns where these mites reside.

Red stele root rot: With the wet conditions this spring, growers should be on alert for this root rot if any fields 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 early spring for control of red stele. 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 the disease, but the most effective management strategy is to plant only into well-drained soils, and/or plant onto raised beds.

We will begin scouting strawberry fields for overwintering insect pests and disease issues in a few weeks. The results of our strawberry scouting will be reported through this newsletter until harvest time. You can also get quick access to this information through the UMaine Pest Management web page. If you have questions about the Newsletter, please give us a call at 933.2100 or send an e-mail message to me at: david.handley@maine.edu.

Spring Growers’ Twilight Meeting

The Maine Vegetable & Small Fruit Growers Association will be having a Spring Twilight Meeting on Thursday, June 5, at 5:30 pm at Belanger’s Farm, 262 Cotton Road in Lewiston. The Belanger’s grow a wide variety of vegetables for the wholesale market and strawberries for both wholesale and PYO. They have recently invested in new packing and storage facilities.

2024-2025 New England Small Fruit Management Guides

A printed version of the new edition of the Guide is available through our office. The cost of the Guide is $25, including shipping. You can request a copy by sending a check made out to “UMaine Cooperative Extension” to our address below.

Free access to the latest edition of the Guide is also available online on the New England Small Fruit Management Guide webpage.

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.

 

Sincerely,

David T. Handley
Vegetable & Small Fruit Specialist

Highmoor Farm
P.O. Box 179
52 U.S. Route 202
Monmouth, ME 04259
207.933.2100

UMaine Cooperative Extension Diagnostic and Research Lab
Pest Management Unit
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279

Where brand 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 products assume all associated risks.

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