Strawberry IPM Newsletter No. 5 — June 6, 2025

MORE RAIN MAKES INCREASES FUNGAL DISEASE THREAT

Fungicide Applications Bloom – Post-Bloom To Control Botrytis, Anthracnose, Powdery Mildew

Situation: A few warm days can make quite a difference! Strawberry growers in southern Maine are starting to see some ripe berries on early varieties and plants grown under row covers. Later varieties are still showing some bloom in central and northern regions of the state. We continue to find adults and nymphs of tarnished plant bugs, and spider mites this week. Continuing damp weather is 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: Mites were present in most fields we’ve scouted. 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: Most fields are now beyond full bloom and the susceptible stage for clipper feeding and bud injury. We have found very few clipped buds or weevils this season, but if you still have late varieties coming into bloom susceptible to injury, scouting should continue.

Tarnished plant bugs: Both adult and nymph stages of tarnished plant bugs are now present in strawberry fields. Populations have been spotty from one location to another and even within a field, so it is well worthwhile to scout your fields for their presence before applying an insecticide. 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®.

Strawberry root weevil: Strawberry root weevils and Black vine weevils begin to emerge and start feeding on strawberry foliage during the harvest season. Look for notching along the leaf edges and the presence of the black or brown snout beetles. The weevils feed mostly at night and spend the daylight hours at the base of the plants under the mulch. They lay eggs at the base of the crowns during the harvest and post-harvest period. The larvae, or grubs, feed on the strawberry plant roots through the fall, overwinter deep in the soil and start feeding again in the spring, causing plants to weaken and die. Badly infested beds should be plowed up as soon after harvest as possible. Bifenthrin (Brigade®) can be applied to kill the adults when they emerge and start to feed on the leaves (usually until mid-late July). Applications should be made at night when the insects are active, and the highest rate of the insecticide should be used. Platinum® can be applied in the fall as a soil drench to control grubs.

Spittlebugs: The first spittlebugs of the season were found this week. The frothy spittle masses appear on the leaf stems (petioles), just below the leaflets. These typically start showing up around bloom. Although these spittlebugs don’t pose a significant threat to the plants, the frothy spittle they cover themselves with creates an annoyance for pickers. Adult spittlebugs are about 1/4 inch long and bright green when they first emerge but later turn dull yellow or brown. Spittlebugs overwinter as eggs and the nymphs emerge in late May. You should start to scout for spittlebugs when the plants are at about 10% bloom. Randomly inspect five one square foot areas per field every week. Spread the leaves and inspect the leaf bases, leaf stems, and flower stems looking for the white, frothy spittle masses. Spittlebugs tend to be a greater problem in weedy fields. Pesticides currently registered for spittlebug control include Provado®, Danitol® and Brigade®.

Potato leafhoppers: Keep a lookout for potato leafhoppers. The potato leafhopper does not overwinter in Maine but must fly in from southern states. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked. Symptoms are often first noticed in new strawberry plantings and may look like herbicide damage. Leafhoppers will also infest older plantings and a variety of vegetables, flowers and fruit crops. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Examine the underside of some injured leaves. Look for small, light green leafhopper nymphs. They are about 1/16 inch long. When touched, they will crawl sideways in a crab-like manner. Controls for potato leafhoppers include Assail®, malathion, carbaryl or Provado®.

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) remains a threat if your field has had standing water during bloom. 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.

Anthracnose fruit rot: As fruit starts to size up and ripen in fields that are wet from recent rains, be on the lookout for this fruit rot. Anthracnose is favored by warm, humid conditions and can spread rapidly under rainy, wet conditions, especially if puddles remain in a field after the rain. Anthracnose appears as black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The fungus is able to multiply on leaves without visible symptoms, which is why it may appear suddenly and widespread in a field. Fungicide products for gray mold may not be effective for anthracnose. Products including Cabrio® and Abound® can provide good control of anthracnose fruit rot.

Powdery Mildew: The weather has been more favorable for the development of powdery mildew 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 fungicide 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®.

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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