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CLIPPER IS ACTIVE ON LATE-BLOOMING VARIETIES
Powdery Mildew Infecting Many Fields
Situation: Early varieties and plants that were under row covers in southern Maine are now just past bloom, with primary flowers starting to size into green fruit. Later varieties are mostly in bloom this week. The mix of hot and cold weather recently has made it challenging to predict when the crop will be ready, but it still looks as though it may only be a day or two behind a “normal” season. Insect activity in strawberry fields has increased in the past week, most notably strawberry bud weevil or clipper. Powdery mildew continues to be an issue in many fields, and cool weather may encourage the development of bacterial angular leaf spot.
Strawberry bud weevil or “clipper”: Although we have seen increased clipper activity in most of the fields scouted this week, many fields in southern Maine are beyond the growth stage (blossoms in bud stage) where clipper poses a threat. Once beds are in full bloom, clipper will not be able to cause economic harm. However, fields not yet in full bloom should continue to be scouted. Three fields were over the control threshold of 1.3 or more buds clipped per 2 foot of row length this week.
Tarnished plant bugs continue to be relatively scarce in the fields scouted this week. While we still have not found nymphs in most of the fields scouted, we did find them in some fields, and one field was over the threshold of 4 or more infested flower clusters per 30 sampled. Warmer weather will likely bring about an increase in tarnished plant bug activity in the coming days, and strawberry flowers can remain susceptible to feeding injury even after petal fall. Products registered for controlling tarnished plant bug include Brigade®, Danitol®, Malathion®, Thionex® and PyGanic®. Bees and other pollinators are also active in your fields now, so apply pesticides at night when they are less active and use materials that pose the least threat to pollinators. See page 115 of the 2010-2011 New England Small Fruit Pest Management Guide for more information (http://www.umass.edu/fruitadvisor/pdf/2010NESmallFruitGuide.pdf).
Two-spotted spider mites: In spite of a few warm days, the mostly cool, damp conditions appear to be keeping spider mites in check. Most fields had no mites in our samples and those that had mites were well below the spray threshold of 25% of leaves infested. Warmer weather will stimulate mite activity, so it is important to keep scouting in the coming weeks.
Spittlebugs: We have been finding spittlebug masses in some strawberry beds this week. The frothy spittle masses are found on the leaf stems (petioles), just below the leaflets, usually showing up around bloom. Although spittlebugs don’t pose a significant threat to the plants, the frothy spittle masses create an annoyance for pickers. Spittlebugs overwinter as eggs and the nymphs emerge in late May. Start scouting for spittlebugs when the plants are at about 10% bloom. Randomly inspect five one-square foot areas per field every week. On hot, dry days the spittle masses may be at the base of the plants, so spread the leaves and inspect the crowns, leaf bases, leaf stems, and flower stems looking for the frothy spittle masses. The small, yellow-orange nymphs will be under the spittle. If the average number of spittle masses is more than two per square foot, a treatment may be warranted. Spittlebugs tend to be a greater problem in weedy fields. Pesticides currently registered for spittlebug control include Provado®, Thionex®, Danitol® and Brigade®.
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.
Diseases: Most early fields are at the stage for a second application of fungicide to protect against gray mold. Later blooming fields may now be ready for their first application. Two to three sprays are generally required to provide good protection against Botrytis. However, if rainfall exceeds more than one inch between sprays and wet conditions are prevalent, additional sprays may be required.
Powdery mildew: We continue to find powdery mildew symptoms in nearly all fields scouted this week. Conditions have apparently been just wet and warm enough to encourage its development in susceptible varieties. Leaf cupping, purple leaf and flower stem lesions are being seen on many plants. Mildew infections weaken plants and can reduce yield the following year. Some varieties are more susceptible than others, for example Annapolis and Sable are quite susceptible, while Jewel, Mira and Mesabe are thought to be resistant. Captan, Topsin-M®, Pristine®, Cabrio®, Quintec®, Procure® and Rally® are presently registered to control powdery mildew.
Bacterial angular leaf spot: We have not yet found plants with symptoms of angular leaf spot (Xanthomonas fragariae) this spring, but the cool wet conditions may encourage this disease if it is present in your field. Angular leaf spot is a bacterial disease characterized by small, translucent or “water-soaked” leaf spots that occur between the veins. The spots coalesce, turn yellow, reddish and eventually black. The symptoms start on the lower leaves and move up as bacterial spores are splashed by rain or irrigation water. Infection of the calyxes may also occur, resulting in blackened berry stems and caps. Irrigation for frost protection can encourage the development of this disease, although watering has not been needed yet for frost this spring. Copper-containing chemicals, such as Kocide®, Cuprofix®, and Bordeaux are the only materials that have some effect on this disease. Some labels suggest adding lime as a “safener” to reduce the risk of crop injury. Spray applications need to begin before bloom to prevent spread of bacteria on the leaves before they spread to berry caps. Application of copper sprays after bloom can result in fruit injury and is not recommended. Therefore, most fields are now past the stage where copper should be considered. Recent research suggests that hydrogen dioxide (OxiDate®) may also have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.
Don’t Forget: Twilight Meeting in Lewiston on June 8
The University of Maine Cooperative Extension and the Maine Vegetable and Small Fruit Growers Association are sponsoring a growers meeting at R. Belanger & Sons Farm in Lewiston on Wednesday, June 8th at 5:30 p.m. Come tour the new packing and storing facility, get a look at look at early vegetables and discuss the strawberry season ahead. One pesticide applicator re-certification credit will be available. Belanger and Sons Farm is located at 262 Cotton Road in Lewiston. Directions:
From the north: On the Maine Turnpike I-95, take Exit 80 toward Rt. 196/Lewiston. Merge right onto Alfred Plourde Pkwy. Take ramp onto Rt. 196, E. Lisbon St., then slight right onto Pleasant St., then slight left onto Commercial St. Travel 2 miles on Ferry Rd. Turn left onto Cotton Rd. The farm is on the left.
From the south: On the Maine Turnpike I-95, take Exit 80 toward Rt. 196/Lewiston. Turn right onto Alfred Plourde Pkwy. Turn left onto River Rd. and travel 2 miles. Continue onto Ferry Rd., then turn right onto Cotton Rd. The farm is on the left.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management
P.O. Box 179 491 College Ave
Monmouth, ME 04259 Orono, ME 04473
Maine Cooperative Extension, the Land Grant University of the state of Maine and the U.S. Department of Agriculture Cooperating. Cooperative Extension and other agencies of the U.S.D.A. provide equal opportunities in programs and employment. A Member of the University of Maine System.
Where brand names or company names are used it is for the reader’s information. No endorsement is implied nor is any discrimination intended against other products with similar ingredients. Always consult product labels for rates, application instructions and safety precautions. Users of these products assume all associated risks.
Any person with a disability who needs accommodations for this program should contact Pam St. Peter at 207.933.2100 to discuss their needs at least 7 days in advance.