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EARLY FIELDS GETTING READY FOR HARVEST
Tarnished Plant Bugs, Spider Mites and Leaf Diseases Active
Situation: Strawberry development continues to be slow, as we can’t seem to string together more than a couple of warm days before the cool damp weather creeps back in. Despite the clouds, many fields are starting to get a bit dry; although rain predicted for this weekend may bring those fields some needed moisture. Overall, most fields look very good, with good plant vigor and fairly heavy bloom. Turn out for our twilight meeting at Fairwinds Farm in Bowdoinham was very good, and we thank Pete and Cathy Karonis for their hospitality. Many of the strawberry growers there were hoping to start picking next week and perhaps opening for pick-your-own next weekend. It looks like we’ll have a good crop for July 4th.
Strawberry bud weevil or “clipper” is very active in late flowering varieties and raspberries this week. Most early and mid-season varieties are now beyond the point at which clippers can cause significant damage. Two fields scouted this week were over threshold for clipped buds. Remember that clippers will move onto raspberries to clip flower buds after strawberry bloom.
Tarnished plant bug nymphs are present in most fields this week, but in most cases were not over the threshold of 4 flower clusters infested with nymphs out of 30 sampled. Most of the nymphs found were still in the very small, bright yellow-green phase. It is important to keep scouting for nymphs through the bloom period and into the green fruit stage because feeding damage can still occur, causing misshapen, seedy berries.
Two-spotted spider mites were present in most fields scouted this week but, with one exception, they were well under the threshold of 25% of leaves infested. Cool, damp weather generally keeps mite populations in check naturally, but they can increase rapidly under hot, dry conditions, so it is important to keep scouting for them.
Cyclamen mites: We continue to find fields with cyclamen mite infestations. Usually symptoms are first noticed in beds that are two or three years old. Infested plants show weak growth and yellow, crinkled leaves. The flower stems are small and short and the petals are deformed and sometimes look pink. The symptoms can be confused with winter injury, herbicide injury or virus infection. Cyclamen mites reside on undeveloped leaves and flower clusters down within the crown of the strawberry plants, and can be very hard to see, even with magnification. Miticide applications must be applied with lots of water (40-100 gals./acre) to be sure that the material reaches the mites.
Sap beetles sometimes become a problem when fruit starts 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. Brigade®, Assail® 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.
Slugs may also start feeding on strawberries as they start to ripen. Moist conditions and mulch encourage the presence of slugs. They feed at night, leaving large holes and tunnels in ripening fruit and shiny slime trails on the leaves. Baits such as Deadline® and Sluggo® offer some control of slugs, and should be used prior to fruit ripening. Avoid contacting the developing fruit with the bait. Pay close attention to label instructions and precautions. Slugs overwinter in the egg stage, so baits applied to the fields in mid-September can effectively reduce egg-laying.
Diseases: Many fields are now past the most susceptible bloom stage for primary infection by Botrytis spores. Fungicides applied during bloom should provide adequate protection against gray mold unless fields get lots of rain post-bloom. If more than one inch of rain has fallen since your last fungicide application, it is likely that the fruit are no longer protected, and another application may be warranted.
Leather rot (Phytopthora cactorum): Most fields have dried out very well over the past week, reducing the chance of leather rot infections. If you have standing water in your fields during the bloom or early fruit development period, you may want to consider a fungicide application to prevent leather rot. Remember that fungicides applied for gray mold are generally not effective for leather rot. Aliette®, Agri-Phos® or Phostro® are considered most effective.
Powdery mildew: Warmer, humid weather has increased the symptoms of powdery mildew in fields this week. Many plants are starting to show red streaks on the leaf and flower stems, upward curling leaves, and white, powdery growth on the leaf undersides. Keep an eye out for leaf cupping in your fields and, if you need to apply another fungicide for gray mold, add a material that will also provide control of powdery mildew, such as Pristine®, Topsin-M®, or captan.
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 has also been noted in a couple of fields. 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®.
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 keep them at bay. They are often discouraged once people start to occupy the fields much of the day to harvest. Cedar waxwings are songbirds and are protected by law. They should not be killed. However, the U.S. Fish and Wildlife Service may issue permits for killing birds 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. However, the permit is good for one year; so if you have problems this season, you may consider applying for a permit this winter, which would allow you the option to kill birds, if necessary, next season. The Wildlife Damage Office has recommendations for managing birds in crops, and also has some control options available through their office. For more information on permits or bird control contact the office in Augusta at 207.629.5181. The office is located in the Capital West Business Center, 79 Leighton Road in Augusta.
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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