Strawberry IPM Newsletter No. 2 – May 20, 2015
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Strawberry Pests Off to a Slow Start
No Clippers, Tarnished Plant Bugs or Spider Mites Over Threshold this Week
Vegetable and Berry Growers Twilight Meeting
Thursday, June 11, 2015 at 5:30 p.m.
Snell’s Family Farm, Buxton, Maine
Situation: It’s too hot, no wait, it’s too cold. Great swings in temperature have been the feature this spring as we bounce from days in the 80’s to days in the 40’s, but as far as strawberry plant development is concerned most fields are about where they should be for this point in the season. Early varieties are coming into bloom, while later varieties now have flower buds emerging from the crowns. Some inland locations have had to protect buds from frost, and may have to again over the next week; while more southern and coastal sites have, so far, not had serious frost threats. The most common complaint among growers is the lack of rain. While groundwater levels are still in good shape for irrigation, dry fields can lead to stressed plants and nutrient deficiencies, which result in poor fruit size and quality. Once the fruit have started to develop, strawberry plants should receive one to two inches of water per week to prevent a rapid decline in fruit size after the first picking.
The University of Maine Cooperative Extension and the Maine Vegetable and Small Fruit Growers Association will hold a twilight meeting at Snell’s Family Farm in Buxton on Thursday, June 11 at 5:30 p.m. John, Ramona and Carolyn Snell, as well as other family members, grow mixed vegetables, apples, bedding plants, cut flowers, and raspberries. They sell their produce at their farm stand and at local farmers markets in addition to operating a large Community Supported Agriculture (CSA) program. 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. Hold the date! We’ll give driving directions soon.
Strawberry bud weevil or “clipper” is now active in most of the fields we’ve scouted. But so far all we have seen is feeding signs on a few open primary flowers, no clipped buds, suggesting that the adults are now just feeding on pollen and mating. However, they will very soon start laying eggs and girdling flower buds. Given these signs, you should now start looking for clipped buds. Insecticide options for clipper include Lorsban®, Brigade®, Bifenture®, Danitol®, Sevin® and PyGanic®.
Tarnished plant bug activity has been very low so far this season. We have had reports of a few adults spotted in the field, but we have not yet found any nymphs, which are the more damaging stage of this insect. 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 have only been found in one location this week. This is surprising given how dry it has been. Mites typically proliferate under hot, dry conditions, and we often first find them in plantings under row covers. But plantings that harbored a high mite population last fall are also likely to see a problem with mites in the spring. Spider mites will reproduce rapidly under warmer temperatures, so it is important to scout for them 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 two fields with light symptoms of cyclamen mite injury this week. Infested plants show weak growth and yellow, 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: There have been calls regarding white grubs in turf this week, so we should expect that we may also see injury in strawberry beds. Infested plants are stunted and often wilt during the heat of the day. These grubs are the larvae of the 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 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
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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