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Situation: A few berries are starting to be picked this week and an early field that was under row cover may open for harvest this weekend. It appears that the season will open on about its normal date, although anxious customers have been calling and hoping to get into fields early. We are still scouting for tarnished plant bug and spider mites in late blooming fields, although pest levels have remained mostly quite low this week. As we move into the harvest season, its time to keep an eye out for other pests, including slugs, sap beetles and birds, which are as eager to enjoy the ripening fruit as your paying customers.
Strawberry bud weevil or “clipper”: Most fields in southern Maine are well beyond the stage when clipper could pose a significant threat. However, if you have very late blooming varieties or you are far enough north that many of the plants still have unopened buds, you should continue to scout for clipper damage. One field was over threshold this week but the damage was occurring on small, tertiary and quaternary buds, with the primary and secondary already opened and undamaged, so the payoff of applying a spray was questionable.
Reminder to Raspberry Growers: Strawberry clipper will move onto raspberry buds after strawberry bloom. Check raspberry flower clusters for clipped buds and live clippers. Insecticide sprays to control raspberry fruit worm adults, which are also active at this time, should provide some control of clipper as well. Products registered for clipper on raspberries include Brigade®, Sevin XLR Plus® and Aza-Direct®.
Tarnished plant bugs were again few and far between in fields this week. We have seen a few nymphs in southern Maine fields, but not enough to exceed the control threshold. Fields still in bloom should continue to be scouted for tarnished plant bugs nymphs until petal fall. Remember that this insect can also be a significant problem on day-neutral strawberry varieties, which flower and fruit in the late summer and fall. This is when the insect is at its peak population, so feeding pressure on the crop can be intense. Pay close attention to days to harvest restrictions on any insecticide used for tarnished plant bugs on day-neutral varieties, because often you will have to protect flowers at the same time as the fruit is ripening.
Two-spotted spider mites: Strawberry fields continue to be relatively free of spider mites this spring. Only two fields scouted this week showed the presence of mites, and only one of those was above the threshold of 25% of leaves infested. Should we get a warmer, dryer stretch of weather mite populations could bounce up, so it is important to keep scouting right up until harvest.
Sap beetles are sometimes a problem as we start harvesting berries. 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.
Diseases: Fields with ripening fruit should have received the needed two to three bloom sprays for protection against gray mold by now. Fields still in the bloom to late bloom stage may need a final spray to protect the blossoms from infection by spores, especially if they have been through some of the recent rain shower activity.
Powdery mildew: This appears to be the most prevalent disease in strawberry fields this year. Leaf cupping, reddening of leaf stems and fruit stems, and white, powdery fungal growth on the undersides of leaves has been seen to some degree in nearly every field. Good growing conditions for the fungus have made it challenging to keep in check. If you still have a bloom fungicide spray that should be applied, consider using a material that will also help control powdery mildew, such as captan, Topsin-M® or Pristine®.
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 (‘Darselect’ is quite susceptible to this). The spots are smaller in the case of scorch, and lack the white centers. Spots may coalesce to turn the leaves purple and necrotic, 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®, Syllit®, Cabrio®, Nova® and Pristine®.
Anthracnose fruit rot: As fruit starts to ripen in fields that are wet from recent rain, be on the lookout for this fruit rot. Anthracnose is favored by warm, humid conditions and can spread rapidly under rainy, wet conditions, especially if puddles remain in a field after the rain. Anthracnose appears as black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The fungus is able to multiply on leaves without visible symptoms, which is why it may appear suddenly and widespread in a field. Fungicides such as Cabrio® and Abound® can provide good control of anthracnose fruit rot.
Birds, specifically cedar waxwings will be moving into fields to start feeding on ripe fruit, if they haven’t already. These birds can 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. Usually, they are discouraged 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. 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 an 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 at 79 Leighton Road in Augusta.
Hold the Date!
Highmoor Farm Field Day, Thursday, July 21, 2011.
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.
Any person with a disability who needs accommodations for this program should contact Pam St. Peter at 207.933.2100 to discuss their needs at least 7 days in advance.
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.
Image Description: Print Friendly
Image Description: Strawberries
Image Description: Large Tarnished Plant Bug Nymph
Image Description: Tarnished Plant Bug Injury
Image Description: Two-spotted Spider Mites
Image Description: Sap Beetle
Image Description: Gray Mold on Strawberries
Image Description: Leaf Spot
Image Description: Anthracnose on Strawberry
Image Description: Cedar Waxwing
Image Description: Bird Damage on Strawberry