Strawberry IPM Newsletter No. 3 – May 28, 2015
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Strawberry Insect Pests Now Active
Clippers, Tarnished Plant Bugs and Spider Mites Over Threshold this Week
Vegetable and Berry Growers Twilight Meeting
Thursday, June 11, 2015 at 5:30 p.m.
Snell Family Farm, 1000 River Road, Buxton, Maine 04093
Situation: Broad swings in temperature continue to characterize the weather, from unusually hot days to a surprise freeze in some inland towns last weekend. Conditions also remain dry, and while that is good for reducing the chance of fungal diseases, the plants will need water soon to help size up the berries. Early varieties are at full bloom or slightly beyond in much of the state, while later varieties are now coming into bloom. Some fields may have experienced frost or freeze damage late last week as night temperatures fell dramatically, in spite of fairly windy conditions.
Strawberry bud weevil or “clipper” activity is increasing in some of the fields we’ve scouted. Clipped buds on later varieties are becoming apparent and were over the threshold (more than 1.2 clipped buds per two feet of row) in one location this week. Scout for clipped buds now in fields just coming into bloom. Once a field is in full bloom, clipper is no longer a significant threat. Insecticide options for clipper include Lorsban®, Brigade®, Bifenture®, Danitol®, Sevin® and PyGanic®.
Tarnished plant bug activity has increased this week. We are now finding the small, yellow-green immature bugs, or nymphs, in the flower clusters. These will feed on the receptacle of the flowers, causing the fruit to have seedy ends, or “catfacing”. The nymphs are very small (2 mm) at this time and can be hard to see. It is important to scout any flowering fields for them now, as they can spread very quickly. The threshold for nymphs is 4 or more flower clusters infested per 30 sampled. Insecticide options for tarnished plant bug include malathion, Assail®, Brigade®, Bifenture®, Danitol®, and PyGanic®.
Two-spotted spider mites are building up in some fields, which is to be expected when we have extended warm, dry weather. Two fields have been over the control threshold of 25% or more of leaves infested. Mites will reproduce rapidly if warm conditions continue, so it is important to scout for them regularly. Chemical control options for two-spotted spider mites include Acramite®, Savey®, Zeal®, Vendex®, Oberon®, Brigade®, Danitol®, and Thionex®. Be sure to use enough liquid and pressure in the spray to get good coverage on the undersides of the leaves.
Root Weevils: Two fields with a history of strawberry root weevil problems have had some grub activity this week. Infested plants look weak, and often wilt. There are no chemical controls registered for use within the harvest period at this point. Parasitic nematodes may be applied, but need high moisture conditions to become established and provide effective control. See the New England Small Fruit Management Guide for details.
Strawberry rootworm (not root weevil) adults and feeding injury have been found on strawberry leaves in some fields this spring. The adult stage of this insect is a small (1/8”) dark brown beetle. The beetles feed on strawberry leaves during the spring and late summer, causing numerous small holes in the leaves. The adults in fields now will soon lay eggs. The larvae are small grubs that feed on the roots of strawberry plants, causing them to be stunted and weak. If these beetles and/or feeding injury is prevalent in a field, a treatment is recommended. Sevin 50WP® is registered for control of this pest, and sprays targeted at other insect pests at this time may also control rootworm. Avoid spraying insecticides, especially Sevin 50WP®, during bloom, as it is highly toxic to many pollinating insects. Strawberry rootworm should not be confused with root weevil, a larger insect that causes much more serious damage when present in a field.
Spittlebugs: The frothy spittle masses on the leaf and flower stems from spittlebugs usually show up around bloom. Spittlebugs don’t pose a significant threat to the plants, but the spittle masses are a nuisance for pickers. Spittlebugs overwinter as eggs and the nymphs emerge in late May. Scouting for spittlebugs should start when the plants are at 10% bloom. Randomly inspect five, one square foot areas per field every week. Spread the leaves and inspect the crowns, leaf bases, leaf stems, and flower stems looking for the frothy spittle masses. Small, yellow-orange nymphs will be under the spittle. If the average number of spittle masses is more than two per 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®.
Diseases: Fields in bloom should be protected against infection by spores of the gray mold fungus, Botrytis cinerea. Although the present dry conditions will likely reduce disease pressure this spring, fungicides need to be applied as protectants in case a significant moisture event occurs, causing a sudden release of fungal spores. Registered products include Topsin-M®, captan, Elevate®, Thiram®, Pristine®, Scala® and Switch®. See the New England Small Fruit Management Guide for details.
Powdery mildew: This foliar disease is now starting to show up on susceptible varieties. It may first appear as purple or red blotches on the leaf and flower stems. The most prominent symptom is an upward curling of the leaves and white, powdery growth on the undersides. Check your fields for leaf cupping now. Some, but not all, of the fungicide products registered for gray mold will also provide control of powdery mildew. Pristine®, Cabrio®, Topsin-M®, captan, Procure®, Torino® and JMS Stylet Oil® are registered to control powdery mildew.
Leaf spot infections are becoming more common in strawberry fields this week. The spots usually appear on older leaves first, as small purple or red spots with white centers. Leaf scorch may also be seen. The spots are smaller in the case of scorch, and lack the white centers. Spots may coalesce to turn the leaves purple and brown, leading to the death of the leaf and weakening of the plant. Many strawberry varieties have at least partial resistance to leaf spot and leaf scorch. Fungicides registered for leaf spots include captan, Topsin-M®, Cabrio®, and Pristine®.
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 seven days of harvest. Select® and Selectmax® should not be applied within 4 days of harvest. Follow all product label instructions.
Reminder: Twilight Meeting
The University of Maine Cooperative Extension and the Maine Vegetable and Small Fruit Growers Association will hold a twilight meeting at the Snell Family Farm, 1000 River Road, Buxton, ME 04093 on Thursday, June 11 at 5:30 p.m. The Snell’s will host a tour of their farmstand, greenhouses and vegetable fields and describe their growing and marketing practices. In addition, we’ll discuss the upcoming season and pest management issues facing vegetable and berry growers this year. We anticipate that one pesticide applicator recertification credit will be awarded for the meeting.
David T. Handley, Vegetable and Small Fruit Specialist
P.O. Box 179
Monmouth, ME 04259
491 College Avenue
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.
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