Strawberry IPM Newsletter No. 4 — May 30, 2025

TARNISHED PLANT BUG ACTIVE IN SOUTHERN MAINE

Two-Spotted Spider Mite Populations Over Threshold in Some Fields

Situation: Strawberry development continues to be slow, due to the mostly cool, damp weather. Some early varieties that were under rowcovers are beyond petal fall and may be ready for harvest in about two weeks if the weather improves. Fields continue to look good overall, and bloom is very strong in fields that escaped winter injury or root rot issues. We have found adults and nymphs of tarnished plant bugs, and spider mites have reached control thresholds in some fields this week. There is no frost predicted in the near-term forecast, but growers in the north should remain ready to protect through bloom. The dominant damp, cool weather continues to be ideal for the development of fungal diseases, including Botrytis gray mold, leather rot and anthracnose. Growers with bloom in their fields should be applying preventive fungicide sprays through petal fall.

Two-spotted spider mites: Despite the cool weather, we continue to find mites in nearly all fields we’ve scouted, with populations varying from just a few to being well over the spray threshold of 25% of leaves infested. We recommend that you continue scouting for mites right up to harvest. Once harvest is over and the beds are renovated, you should scout for mites again in the late summer to early fall and be ready to apply a miticide to prevent high overwintering populations from infesting the fields next spring.

Strawberry bud weevil: Early fields are now beyond full bloom and the susceptible stage for clipper feeding and bud injury. To date we have found very few clipped buds or weevils in the fields, but later varieties just coming into bloom are still susceptible to injury, so scouting fields that are not yet at full bloom should continue. Clippers can often be found within the flower clusters, laying eggs and feeding on pollen.

Tarnished plant bugs: We found both adult and first instar nymphs of tarnished plant bugs in several fields this week, indicating that this insect is active in strawberry fields. Adults are now laying eggs in the flower stalks and leaf petioles. Both the adults and nymphs feed on the developing flowers, causing the fruit to become “cat faced”, with hard, seedy tips. It is important to scout for tarnished plant bugs regularly, as they often appear suddenly in a field. The threshold for plant bug nymphs is four or more flower clusters infested per 30 sampled. Tap flower clusters over a plate or tray to knock nymphs off. Insecticide options for tarnished plant bugs include malathion, Assail®, Brigade®, Bifenture®, Dibrom®, Danitol®, Closer® and PyGanic®.

Cyclamen Mites: I continue to find pockets of cyclamen mite injury in fields. Infested plants show weak growth and shrunken, crinkled leaves. Cyclamen 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. At this point, it may be best to delay miticide applications until after renovation, following leaf mowing, to improve coverage down in the crowns.

Diseases: The weather has been very conducive to the development of fruit rots, especially Botrytis gray mold. Two to three fungicide sprays are recommended during bloom, one as bloom starts and a second at full bloom. Additional sprays should be applied if weather conditions, e.g. an inch or more of rain has fallen, occur that would stimulate infection.

Leather rot (Phytopthora cactorum): If your field has had standing water during bloom, you should be concerned about the possibility of leather rot infection of the flowers and developing fruit. Fungicides applied for control of Botrytis gray mold are generally not effective against the leather rot organism. Foliar sprays of Aliette®, Prophyt® or Phostrol® applied during bloom are most effective against this disease.

Strawberry leaf spot: This fungal disease is characterized by small purple spots with white centers on the leaves. The symptoms are often first visible on the older, lower leaves. We have seen leaf spot in most of the plantings we scouted this week. If you see leaf spot in your field, you should consider using a fungicide that will provide control as part of your spray program for gray mold. Products such as Captan®, Luna Sensation®, Mervion® and Pristine® have activity on both diseases.

Powdery Mildew: We found a couple of fields with low levels of powdery mildew on foliage this week. The symptoms of this disease include upward curling of the leaves, purple or reddish blotches on the petioles, and the white, powdery fungus on the undersides of the leaves. These infections will weaken plants and can reduce yield the following year. When selecting a fungide for Botrytis fruit rot, use a material that is also effective against powdery mildew such as Captan, Topsin-M®, Pristine®, or Cabrio®, or tank mix the gray mold product with a good powdery mildew product such as Quintec® or Procure®.

Slugs may be a problem in some fields this season. Moist conditions encourage the presence of these mollusks. Slugs usually feed at night, leaving large holes and tunnels in ripening fruit. Baits such as Deadline® and Sluggo® offer some control of slugs but should be used prior to fruit ripening. Pay close attention to label instructions and precautions. Baits should also be applied to the fields in mid-September if slugs have been a problem, to reduce egg-laying.

Grass control in strawberry fields: Controlling perennial grasses in strawberry beds can be challenging. Poast®, Select 2EC® and Selectmax® 0.97EC are registered to control emerged grasses in strawberries. Often more than one application is needed to obtain satisfactory control. All of these products require the addition of a crop oil concentrate to the spray. It is important to note that these products can cause significant injury to strawberry plants if they are applied on hot, humid days, or if high temperatures occur within one or two days of application. Poast® should not be applied within 7 days of harvest. Select® and Selectmax® should not be applied within 4 days of harvest. Follow all product label instructions.

Cornell Berry Diagnostic Tool: Cornell University has an online key to help you diagnose problems you find in your berry plantings. By following the descriptive key of symptoms through the site, the tool can often help accurately identify the problem and offer management options. Visit the Cornell Berry Diagnostic Tool webpage.

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.

You can also get quick access to this information through the UMaine Highmoor Farm news blog or the UMaine Pest Management web page.

 

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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