Strawberry IPM Newsletter No. 2 — May 22, 2026
Strawberry Bloom in Southern Maine
Insect and Mite Populations Low
Situation
A few warm days have advanced strawberry development across the state. Early varieties are coming into bloom, and plants that were under rowcovers are now at or just beyond full bloom. Plant growth has been slow and weak in some fields, due to the cool start to the season, some winter injury, and last summer’s drought. Spring fertilizer applications, water and warmer temperatures should improve growth over the next week.
Spring Fertilizers: Heavy nitrogen applications in the spring are not recommended. High nitrogen levels will encourage excessive vegetative growth and soft fruit, which can increase pest problems including spider mites and gray mold. Depending upon soil type and history, 15 to 30 lb. of actual nitrogen per acre applied in the spring is adequate to promote good early growth. If you haven’t yet applied nitrogen, an application of Calcium nitrate (15.5% N) 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) when the flower buds emerge from the crowns.
Two-spotted spider mites: Mites have been present in most fields, but in relatively low numbers, with only one field over the recommended management threshold of 25% of leaves infested. Continue to scout for mites regularly as populations can build very quickly under warm, dry conditions. 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).
Strawberry bud weevil: Clipper is just starting to get active in strawberry fields. We have found both the insect and some damage this week, but not yet over the recommended management threshold. 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. Once the plants are in full bloom, with the primary and secondary blossoms open, clippers can no longer cause significant damage. Insecticide options for clippers include Brigade®, Bifenture®, Danitol®, Sevin XLR Plus® and PyGanic®.
Tarnished plant bugs: To date we have only found one adult tarnished plant bug in the strawberry fields and no nymphs. No fields are over the management threshold, so no sprays have been recommended. Adults usually appear shortly after bloom begins and 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®.
White grubs: Grubs have been found in some fields this week. Infested plants are stunted and often wilt during the heat of the day. Pulling up infested plants will show the roots have been eaten an inch or so below the soil line. The grubs can be found by sifting through the soil under the plants. These grubs are the larvae of Japanese beetle, European chafer and Asiatic garden beetle. They have legs and a swollen anterior (rear end). Admire Pro can be applied for control of white grubs in the spring. It should be applied within two hours of irrigation or rainfall to be sure the chemical gets into the root zone, and it requires a 14-day pre- harvest interval.
Gray Mold: As more strawberry fields come into bloom, preventive management of gray mold should be a priority. Two to three sprays of fungicide during bloom are typically required to provide good protection. Fungicide choices for control of gray mold in strawberries include: Topsin M® + captan, 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.
Angular leaf spot is a bacterial disease characterized by small water-soaked spots on the leaves, which may turn yellow or black. The symptoms start on the lower leaves but spread throughout the foliage when spores are splashed up by rain or irrigation water. Infections can cause blackening of the berry stems and caps. This disease is favored by extended cool, wet weather with night temperatures close to freezing. Irrigating fields for frost protection encourages development and spread of the disease. Although we have not yet seen angular leaf spot in any fields this season, growers who have been irrigating for frost control should be on alert for symptoms. Hydrogen dioxide (OxiDate®) may have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.
If you have questions about the Newsletter, please give us a call at 207.933.2100 or send an e-mail to: 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 4, at 5:30 pm at Clark’s Farm, 65 Boynton Schoolhouse Rd., Jefferson. The Farm boasts PYO strawberries and a wide variety of vegetables sold through their Farm Market.
New England Small Fruit Management Guide
A new edition of this guide is in the works and should be available soon. In the meantime, you can access the latest information through the online version. Visit the New England Small Fruit Management Guide for more detailed pest information.
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
Monmouth, ME 04259
207.933.2100
Pest Management
17 Godfrey Drive
Orono, ME 04473
1.800.287.0279
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