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STRAWBERRY PESTS NOW ACTIVE DESPITE COOL, WET WEATHER
Clippers, Tarnished Plant Bugs, Spider Mites Found in Fields this Week
Vegetable and Berry Growers Twilight Meeting
Wednesday, June 11, 2014 at 5:30 p.m.
Fairwinds Farm, Bowdoinham, Maine
Situation: Continued cool wet weather has kept strawberry development at a relatively slow pace. Fields in southern to mid-state Maine are coming into full bloom for early varieties, while late varieties are just starting to show a few primary blossoms. The time from bloom to harvest is approximately three weeks, but may take a little longer under extended cool conditions. Most fields we visited this week showed some moderate winter injury. Weak plants, especially in areas where the mulch was thin, show browning within the crown tissue, indicative of freeze damage.
The University of Maine Cooperative Extension and the Maine Vegetable and Small Fruit Growers Association will hold a twilight meeting at Fairwinds Farm in Bowdoinham on Wednesday, June 11 at 5:30 p.m. Pete and Cathy Karonis grow 10 acres of strawberries and approximately 40 acres of mixed vegetables in fields along the Kennebec River and have a farm stand and greenhouses in Topsham. They will host a tour of their strawberry, raspberry and vegetable plantings, 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. 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. Damage so far is very light, suggesting that the adults are feeding on pollen and mating, but they will very soon start laying eggs and clipping buds. If you haven’t yet been looking for clipped buds, now is the time. Insecticide options for clipper include Lorsban®, Brigade®, Bifenture®, Danitol®, Sevin® and PyGanic®.
Tarnished plant bug nymphs were found in most of the fields we scouted this week. 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. Only one field was over the threshold (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 were over the threshold (25% of leaves infested) in one location this week. This is surprising given how cold and wet 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. 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).
Cyclamen mites: One two-year old field showed 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.
Root weevil management
Plants damaged by root weevils should become more obvious in the coming days as the fields dry out and the grubs become more active. We have not found any additional fields infested since our reports of two fields last week. Infested plants appear weak and stunted, and may wilt during hot days. Digging under the plants will reveal small (1/4”-1/2”) crescent-shaped legless grubs. Typically, the grubs begin to pupate when the plants are in bloom. Once the adults become active in July, bifenthrin (Brigade®) will provide some control if used at the highest labeled rates.
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. Two to three sprays of fungicide during bloom are typically required to provide good protection against this disease. Remember that fruit infections take place through the flowers, so gray mold control efforts must be focused on the bloom period.
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.
Anthracnose fruit rot is a potential problem when fruit ripens in fields that are wet from irrigation or rain. This fungus disease is favored by warm, humid conditions and can spread rapidly during rains or when fields are irrigated with overhead sprinklers. In cool seasons, it may appear close to harvest or may not show up at all. Anthracnose fruit rot is identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The fungus can survive and multiply on leaves without visible symptoms, appearing suddenly as a fruit rot when the conditions are right. Fungicides such as Cabrio® and Abound® can provide good control of anthracnose.
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 was found in one field this week. This 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 also have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.
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.
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