Strawberry IPM Newsletter No. 2 — May 9, 2025
STRAWBERRY BLOOM BEGINS IN SOUTHERN MAINE
No Insect Problems Yet, Spider Mites Found Everywhere; Bloom Sprays Should Target Gray Mold
Situation: Early strawberries under rowcovers have just started to bloom in the southern part of the state. Overall, fields look good, some slightly ahead of average development for this time. As expected, there is evidence of winter injury, especially in exposed sites, and places where the winter mulch was thin or had been blown off. There has also been deer damage evident in some fields. It’s still early for most insect pests, but expected warmer weather next week is likely to bring about increased activity. Growers seeing bloom beginning in their fields should begin applying preventive fungicide sprays for gray mold.
Two-spotted spider mites: We have found mites in most fields we’ve scouted this week. These are overwintered adults that are now laying eggs. Populations are below control threshold but will increase rapidly with the arrival of warmer, drier weather. You should begin to scout for mites now, especially on plantings that are under rowcovers, because they will reproduce earlier in that protected environment. To scout for mites, collect 60 leaves from various locations in the field and examine the undersides for the presence of mites. If 15 or more leaves have any mites (25%), a control should be applied. Chemical control options for two-spotted spider mites include Acramite®, Portal®, Nealta® Savey®, Zeal®, Vendex®, Oberon®, Brigade®, Danitol®.
Strawberry bud weevil: We have not yet found any bud damage from “clippers”, and most fields are not yet in the highly susceptible early bloom stage. Once fields start showing a few open blossoms, begin scouting for clipped buds. Small holes in the petals of opening flowers indicates clipper feeding. Clippers can often be found within the flower clusters, laying eggs and feeding on pollen. The control threshold for clipper injury is more than 1.2 clipped buds per two feet of row. Clipper damage is often most common in later blooming varieties. Insecticide options for clippers include Brigade®, Bifenture®, Danitol®, Sevin XLR Plus® and PyGanic®.
Tarnished plant bugs: We haven’t seen any adults or nymphs in strawberry fields yet. Adults usually appear when the first flowers appear and begin to lay eggs in the flower stalks and leaf petioles. Once the flowers begin to open, it is important to scout for tarnished plant bugs regularly, as they may appear very quickly with warmer, drier weather. The threshold for plant bug nymphs is 4 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®.
Diseases: Early bloom fungicide sprays are recommended to protect strawberry fruit against gray mold, especially when conditions have been damp. Two to three sprays of fungicide during bloom are typically required to provide good protection. Most fruit infection takes place through the flowers, so control efforts should take place during bloom. Fungicide choices for control of gray mold in strawberries include: Topsin M® + captan, Elevate®, Captevate®, Switch®, Scala® and Pristine®. Remember to alternate fungicides with different modes of action for resistance management purposes.
Leather rot (Phytopthora cactorum) can become a problem in fields where standing water is common during bloom and fruit development, especially if the fields were not mulched last fall. Leather rot infections can be reduced by applying straw mulch between the rows to prevent berries from touching the soil and reducing soil splashing onto the berries. Foliar sprays of Aliette®, Prophyt® or Phostrol® applied during bloom will help prevent leather rot.
Leaf Spot is a fungal disease characterized by small purple spots with white centers on the leaves. The symptoms are often first visible on the older, lower leaves. 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.
Slugs may be a problem this season. Moist conditions and mulch encourage the presence of these mollusks. Slugs usually feed at night, leaving large holes in the leaves and tunnels in the ripening fruit. Baits such as Deadline® and Sluggo® offer some control, 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 for next year’s generation.
Deer: Feeding damage by deer has been observed in several fields this spring. Rows of plants look weak or dead and have few, if any leaves, although the root system may look healthy. When deer feed on plants during the winter the plants often die, as they are exposed and the crowns are damaged. By the time the mulch is removed, the plants will just look dead, and any evidence left by the deer has been washed away. Deer will also feed in the spring, eating leaves and sometimes damaging crowns. If deer are a problem in your area, it is best to fence the planting before they start feeding in it. Temporary electric fences are usually adequate if set up correctly and in a timely manner. Always contact your local game warden before you consider dispatching any animals.
Spring Fertilizers: Rains this spring may have growers concerned about fertility levels in the soil. Heavy nitrogen applications in the spring are not recommended at this time to prevent excessive vegetative growth and soft fruit, which encourage pest problems including spider mites and gray mold. Depending upon soil type and history, 15 to 30 lb. of actual nitrogen per acre is adequate to promote good early growth. However, if your soils are light and prone to leaching, early nitrogen applications may not have been taken up by the plants. Plants that have yellow or reddish color and short petioles (leaf stems) may benefit from a light nitrogen application. If you have already applied nitrogen this spring, keep the supplemental rate low (10-20 lb.) If you haven’t applied nitrogen, a heavier application may be more effective (20-30 lb.). Calcium nitrate (15.5% Ca) is a good source of available nitrogen and also supplies calcium, which can be helpful in fruit development. Boron applications in the spring are also helpful to promote good pollination and early fruit development. However, boron in high amounts can be toxic to the plants. One to two pounds of actual boron per acre is adequate to meet the needs of strawberry plants, often applied as a foliar spray of Solubor (20% B).
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
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