Strawberry IPM Newsletter No. 5 – June 7, 2013
For full page print version, please see link at the bottom. Click on photos to enlarge.
Situation: A stretch of fair weather has moved strawberry development along at a more normal pace over the past few days. The heat and storms of last weekend do not appear to have caused any serious issues in strawberry fields we visited. Leaf spot and tarnished plant bugs were the most common problems seen. Harvest is getting underway in some fields that were under row covers this spring. Most fields are now beyond full bloom and most growers are predicting a “normal” opening date for their pick-your-own fields. Overall, most fields appeared very good this week and the crop looks quite promising.
Diseases: The risk of gray mold infection remains very high, with significant rainfall predicted over the next few days. It is important to keep blossoms and fruit protected with fungicides under wet conditions. If the last application occurred over a week ago, or more than one inch of rain has fallen since the last application, an additional fungicide spray should be considered.
Anthracnose fruit rot also remains a threat as tropical storms often create the wet fields and high temperatures that are conducive to the development of this fruit rot. It may be best to use a fungicide product that offers control of both gray mold and anthracnose, such as Pristine® or Cabrio®.
Leather rot (Phytopthora cactorum) could also appear in fields if standing water is prevalent for an extended time following heavy rains. Aliette®, Agri-Phos® or Phostrol® applied during fruit development can help prevent leather rot when the risk of this disease is high.
Powdery mildew is just starting to appear in some fields this week. This was encouraged by recent warmer weather. Leaves that are cupping upward are the most notable symptom for this fungus disease, and you may also see red streaking on leaf and flower stems. We anticipate that powdery mildew will become more prevalent soon, because it prefers warm, humid conditions. Fungicides for gray mold that also offer control of powdery mildew include Topsin-M® and Pristine®.
Leaf spot/leaf blight infections were noticed in most fields we scouted this week. Leaf spot or leaf blight, caused by the fungus Phomopsis obscurans, was the most common problem. This disease usually appears on mature leaves as small purple or red spots with white or brown centers. Over time the spots may coalesce into a larger lesion, and give the leaf a burned appearance. The disease can spread onto the fruit stems and calyxes, giving them an unattractive reddish-brown discoloration. Leaf scorch is caused by a different fungus, and has been less common this spring. The spots are smaller and don’t have the white or brown centers. The spots often coalesce to turn the leaves purple and necrotic. Strawberry varieties vary greatly in their susceptibility to leaf spot and leaf scorch, with many having at least some resistance. However, under high disease pressure, many will show some symptoms. Fungicides registered for leaf spots include captan, Topsin-M®, Syllit®, Cabrio®, Rally® and Pristine®.
Tarnished plant bug populations were significantly higher in many fields this week. Half of the fields we scouted were over the control threshold for plant bug nymphs and sprays were recommended. At this time we are finding mostly very small, green, first and second instar nymphs. They can be distinguished from similarly colored aphids because they are much more active, and will run rapidly when disturbed. The nymphs and adults are feeding on flowers and developing fruit and will cause the berries to have hard, seedy ends and other malformations. Products registered for control of tarnished plant bug include Assail®, Thionex®, Malathion®, Brigade®, Danitol® and PyGanic®.
Strawberry bud weevil or “clipper” injury has been noted in several fields this week and we found more live clippers than in any previous scouting trips this year. However, most of the injury was to lower order (late, small) flower buds, so the economic significance of the potential fruit loss is minimal, and no sprays were recommended. If your fields still have late varieties in early bloom, you should continue scouting for clipper and apply controls if significant damage is noted to the buds. Be aware the clippers will move on to raspberries and blackberries and clip off their buds, once the strawberries have come into bloom.
Two-spotted spider mites were found in most locations this week but, with the exception of one field, were well below the control threshold. The predicted wet weather will probably slow further spider mite development, at least temporarily; but we still anticipate that populations will rise when hotter, drier weather arrives.
Sap beetles have been found in two fields this week while scouting for tarnished plant bug. This is not cause for alarm yet, but growers should be aware that they are present and keep an eye out for damage as the berries start to ripen. The 1/8 inch long, dark brown beetles chew small holes in ripening fruit, similar to slug injury. They may be seen in the holes they’ve chewed into ripe fruit, but often drop to the ground when disturbed. The best management strategy for sap beetles is good sanitation. Keep the field free of overripe fruit by picking often and thoroughly. Insecticide sprays for this pest can be effective, but should be a last resort during the harvest period. Assail®, Brigade®, Dibrom® and PyGanic® are registered for control of sap beetles with pre-harvest intervals ranging from 12 to 24 hours. Read the product label carefully for this and other application instructions and restrictions.
Birds, specifically cedar waxwings, will soon be moving into fields to feed on ripening fruit. Waxwings often destroy many of the early ripening fruit, despite our best efforts to scare them off. Only by keeping a near constant presence in the field and eliminating roosting sites can you reduce the damage. Feeding is reduced once the fields start to be regularly harvested and customers are present.
Songbirds are protected by law and should not be killed. However, permits may be issued for killing birds by the U.S. Fish and Wildlife Service if they receive a recommendation for such a permit from the Maine Wildlife Services Office (part of the USDA Animal and Plant Health Inspection Service) in Augusta, along with an application from the grower. There is a $50 fee for the application, and it may take over a month for the permit to be processed. The permit is good for one year, so if you have problems this season, consider applying for a permit this winter, to give you the option to kill birds, if necessary, next season. The Wildlife Damage Office has recommendations for managing birds in crops, and some control options available through their office. For more information call the office in Augusta at 207.629.5181. The office is located in the Capital West Business Center at 79 Leighton Road in Augusta.
Hold the date: Highmoor Farm Fruit and Vegetable Growers Field Day July 31, 2013.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm Pest Management
P.O. Box 179 491 College Avenue
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.
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Image Description: Strawberries
Image Description: Leaf Spot on Strawberry Plant
Image Description: First Instar Tarnished Plant Bug Nymph
Image Description: Clipper on Strawberry