Strawberry IPM Newsletter No. 2 – May 27, 2016

StrawberriesStrawberry IPM Newsletter No. 2 – May 27, 2016

Click on photos to enlarge.

Strawberry Pests Enjoying Early Blooming Fields

Clippers, and Spider Mites Over Threshold this Week

Vegetable and Berry Growers Twilight Meeting
Thursday, June 9, 2016, at 4:00 p.m.
McDougal’s Orchard in Springvale, Maine

While dry weather this spring may reduce worries about gray mold pressure, it is also a concern for fields that have experienced winter injury.  Winter injury damages the plants’ vascular system, reducing the plants’ ability to take up water. Dry conditions make this problem worse as injured plants become drought stressed.  To ease the effects of winter injury, make sure the plants are getting plenty of water; through irrigation if rainfall is lacking. Once fruit has started to develop, strawberry plants should receive one to two inches of water per week. Early varieties are now in bloom in southern Maine, while later varieties have flower buds emerging from the crowns.

Twilight Meeting
The University of Maine Cooperative Extension and the Maine Vegetable and Small Fruit Growers Association will hold a twilight meeting at McDougal’s Orchard in Springvale on Thursday, June 9 at 4:00 p.m. This will be a joint meeting with the Maine State Pomological Society.  Trevor Hardy of Brookdale Farm will be on hand to discuss the latest developments in irrigation equipment for fruit and vegetable growers, and George Hamilton from the University of New Hampshire will be there to talk about good sprayer calibration. We will have an opportunity to tour some of the orchard and berry plantings at the farm, courtesy of Ellen and Jack McAdam, and see some of the new deer-control fencing installed with the help of a federal program.  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. Hold the date! McDougal Orchard is located at 201 Hanson Ridge Road in Springvale Maine.

Clipper Injury
Clipper Injury, Photo by David Handley

Strawberry bud weevil or “clipper” is active in most of the fields we’ve scouted. We are seeing feeding signs on open flowers and clipped buds on early blooming varieties. We expect clippers to become more prevalent as later varieties start coming into bloom. You should start scouting your fields for clipped buds now. Insecticide options for clipper include Lorsban®, Brigade®, Bifenture®, Danitol®, Sevin®, and PyGanic®.

Tarnished plant bug activity has been fairly low so far this season.  We have seen adults in some fields, and found nymphs in about half of the fields, in one case over the spray threshold. The nymphs can be hard to find, especially if the plants are wet. Young nymphs are very small (2 mm), active, yellow-green insects.  It is important to scout for them regularly, as they can appear very quickly. The threshold for nymphs is 4 or more flower clusters infested per 30 sampled. Start scouting any field with open flowers now.  Insecticide options for tarnished plant bug include malathion, Assail®, Brigade®, Bifenture®, Danitol®, and PyGanic®.

Two-spotted Spider Mites
Two-spotted Spider Mites, photo by David Handley

Two-spotted spider mites have been found in most fields this week but were over the threshold only in one field where row covers had been used. Mites typically proliferate under hot, dry conditions, and we often first find them in plantings under row covers.  But any plantings that harbored a high mite population last fall are also likely to see a problem with mites this spring. It is important to scout for mites regularly. If 25% of leaves sampled  (e.g. 15 out of 60) have any mites, a spray should be applied. Chemical control options for two-spotted spider mites include Acramite®, Savey®, Zeal®, Vendex®, Oberon®, Brigade®, Danitol®, Thionex® and JMS Stylet oil® (oils will cause plant injury if used in combination with captan or within 14 days of an application of sulfur).  Be sure to use enough liquid and pressure in the spray to get good coverage on the undersides of the leaves.

Cyclamen mites:  We have seen three fields with light symptoms of cyclamen mite injury this week. Infested plants show weak growth and shrunken, crinkled leaves. These mites are very small and reside in the crown of the strawberry plant, feeding on the developing leaves and flower buds. They are very hard to see, even with magnification. Portal®, Kelthane® or Thionex® can be effective but must be applied in lots of water to be sure that the material is carried down into the crowns where these mites reside. Thionex® will no longer be available for use on strawberries after July of 2016.

White grubs: Grubs have been found in some fields this spring. Infested plants are stunted and often wilt during the heat of the day. 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.

Diseases: As the fields come into bloom it is time to protect the flowers against infection by spores of the gray mold fungus, Botrytis cinerea. Fruit infections take place through the flowers, so gray mold control efforts must be focused on the bloom period. Two to three sprays of fungicide are typically required to provide good protection. The first spray is usually applied at 5-10% bloom, followed by a second application at petal fall. Additional applications may be applied if there is significant rainfall between or following these two sprays.

Leather rot (Phytopthora cactorum) may become a problem in fields where standing water is common during bloom and fruit development, especially if the fields were not mulched last fall. Incidence of leather rot 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®, Agri-Phos® or Phostrol® may be applied during bloom and fruit development to prevent leather rot when there has been excess moisture in a field, especially those with a history of this problem.

Powdery mildew:  We have not yet seen symptoms of this fungus disease in fields. It tends to be more prevalent under warm, humid conditions. It may first appear as purple or red blotches on the leaf and flower stems. Later, upward curling leaves and white, powdery growth on the undersides of the leaves becomes evident. Check your fields for pinkish purple leaf and flower stem lesions as new leaves emerge. Pristine®, Cabrio®, Topsin-M®, captan, Procure®, Torino® and JMS Stylet oil® are registered to control powdery mildew.

Angular Leaf Spot
Bacterial Angular Leaf Spot; photo by David Handley

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. Hydrogen dioxide (OxiDate®) may have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.

David T. Handley, Vegetable and Small Fruit Specialist

Highmoor Farm
P.O. Box 179
Monmouth, ME 04259

Pest Management
491 College Ave.
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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