Strawberry IPM Newsletter No. 1 – May 23,2014
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2014 STRAWBERRY PEST MANAGEMENT SEASON BEGINS
Red Stele, Root Weevils and Grubs Attack Strawberry Roots
Situation: A much later start to the season this year compared to last! Early strawberry varieties in southern Maine are just starting to show a few open blossoms. Plants that were under row covers and/or plastic mulch are now in full bloom or just beyond. Later varieties and plants in northern Maine are just starting to show flower buds. Moderate winter injury is common in fields this spring, especially in plantings that were not mulched or had mulch blown off the field. Injured plants appear weakened with small, dull colored leaves. Cutting into the crowns will reveal brown discoloration in the internal tissue. To help injured plantings recover, make sure the plants get plenty of water, especially during dry periods, and it may help to apply extra nutrients to encourage root growth and recovery, including nitrogen, calcium, and phosphorus. While we do not recommend heavy nitrogen fertilizer applications in the spring, up to 20 pounds of actual N (e.g. 125 lb. calcium nitrate) may improve early spring growth. Boron is also often applied in the spring to aid in the pollination process and fruit development. Boron is a micro-nutrient, meaning it is only required in very small amounts, and can cause damage to plants if over applied. Typically we recommend one to two pounds of actual boron per acre. A soluble form of boron such as Solubor® (21% boron) is often applied to strawberries in the spring in a foliar spray to assure even distribution across the field.
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 farmstand 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.
We have started scouting strawberry fields for major insect pests at volunteer farms, in Limington, Wells, Cape Elizabeth, Poland Spring, New Gloucester, Dresden, Monmouth, Wayne, and Farmington, and will be reporting our findings through this newsletter on a weekly basis until harvest time.
The best way to manage strawberry pests is to scout your own fields regularly and often. You should start scouting regularly as soon as flower buds emerge from the crown. You should be able to identify the major pests and their damage, and be able to determine if control measures are necessary. Please contact us if you need any help with insect or disease identification.
Strawberry bud weevil or “clipper” is just starting to become active as flower buds emerge from the crown. I found clippers in southern Maine this week, but no damage yet, meaning the overwintering adults are still feeding on pollen, but they’ll soon start laying eggs and clipping flower buds. The clipper is a small weevil, which girdles strawberry flower buds, causing them to dry up and fall off the flower stalk. Scout for damage by counting the number of clipped buds in two feet of row length at five different locations in a field. If the average number of clipped buds per two-foot sample exceeds 1.2, or if live clippers are found, control measures are recommended. Damage is usually first noticed at the edges of the field. Border sprays may be effective in keeping this insect from becoming a problem in larger fields. Fields with a history of clipper problems will typically exceed threshold nearly every year. Insecticide options for clipper include Lorsban®, Brigade®, Bifenture®, Danitol®, Sevin® and PyGanic®.
Tarnished plant bug adults are becoming active in southern Maine, meaning that they will soon be laying eggs. Strawberries are one of their preferred hosts at this time of year. When the eggs begin to hatch, we’ll find the nymphs feeding in the flowers. The nymphs are small, active, yellow-green insects. It is important to scout for them regularly, as they can appear very quickly when the weather gets warmer. Tarnished plant bugs feed on the open strawberry flowers, causing the berries to have seedy ends. To scout for the nymphs shake or tap 30 flower clusters (six clusters in five different locations) over a plate. If four or more of the clusters out of the 30 sampled have any nymphs, control measures should be taken. Be on the alert and scout your fields as soon as blossoms appear. Insecticide options for tarnished plant bug include malathion, Assail®, Brigade®, Bifenture®, Danitol®, and PyGanic®. The grass, hayfields and weeds surrounding a strawberry field may harbor thousands of tarnished plant bugs. For that reason we recommend that you do not mow fields surrounding the strawberries during bloom to prevent tarnished plant bugs from moving into the strawberries from the mowed fields while the berries are in their most susceptible stage.
Cyclamen mites: Plants showing weak growth and yellow, pinkish or blackened, crinkled leaves may be infested with cyclamen mite. Cyclamen mites are very small, smaller than spider mites, 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. Infested plants have shrunken distorted leaves and flower stalks, and produce few, if any, marketable fruit. Miticides such as Kelthane® and Portal® 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.
Two-spotted spider mites have not yet been a problem this spring, but growers with plants under row covers should be alert. This is often where we first find mite problems. Spider mites will reproduce rapidly when warmer weather arrives, so it is important to scout for them regularly. Spider mites feed on the undersides of strawberry leaves, rasping the plant tissue and sucking the sap. Infested leaves will develop yellow flecking and a bronzed appearance. The plants become weakened and stunted. Fields that have had excessive nitrogen fertilizer and/or row covers tend to be most susceptible to mite injury. To scout for mites, collect 60 leaves from various locations in the field and examine the undersides for the presence of mites. Mites are very small – you may need a hand lens to see them. 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).
Root weevil management
Fields that were infested with root weevils last summer should be inspected for grubs this spring. We have found some root weevils in southern Maine and in some coastal fields this week. Infested plants appear week and stunted, usually in somewhat circular patches in a field. 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. A soil drench of Platinum® (thiamethoxam) insecticide during the spring and/or fall when the grubs are active in the soil can provide control. However, Platinum® has a 50 day pre-harvest interval, so it is too late for applications in most fruiting fields this year. Platinum® may also be used as a pre-plant or planting treatment for root weevils. It is not too late to put on an application of nematodes to control the grubs (optimal timing is about mid-May). Two species of nematodes appear to offer the best control of root weevil grubs. Heterorhabditis bacteriophora (Hb) appears to be the best candidate for control of root weevils when the soil temperature is above 60 degrees (‘J-3 Max Hb’ from The Green Spot Ltd., http://greenmethods.com/site/; ‘GrubStake Hb’ from the Integrated Biocontrol Network, http://www.biconet.com/; ‘Larvanem’ from Koppert Biological Systems, http://www.koppertonline.com/).
Nematodes are living organisms and they can be killed if they are misapplied. Order nematodes ahead of time and be ready to apply them through a sprayer or irrigation soon after they arrive. Refrigerate them if you can not apply right away. Do not apply nematodes using a sprayer with a piston pump. Use clean equipment, removing all screens finer than 50-mesh. Apply nematodes in early morning or evening in a high volume of water to already moist soil, pre-irrigating if needed. Apply another ¼ inch of irrigation after application to wash them onto and into the soil. Researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of $100-$200 per acre depending on volume and source. Nematodes tend to work best in heavily infested fields. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven’t taken over the roots.
Once the adults become active in July, bifenthrin (Brigade®) will provide some control if used at the highest labeled rates. The best timing for this spray is at night during the peak feeding activity of adults, before they start laying eggs, or about the time harvest ends.
White grubs: Weak growth noted in fields this spring may also be the result of white grubs feeding on the roots of newer plantings. Grubs were very evident in many fields last summer, as we deal with increasing numbers of Japanese beetles, rose chafers, Asiatic garden beetles and European chafers. The grubs of these beetles will all feed on strawberry roots. They differ from the larvae of black vine weevil and strawberry root weevil in that they have legs and a swollen anterior (rear end), and they tend to be larger. The grubs can be found by pulling up weak plants and sifting through the soil that surrounds the roots. Controlling white grubs once they have become established in a field can be difficult. These tend to be more of a problem in new fields that have been planted following a grass rotation crop, because the adults prefer to lay their eggs in sod. Admire Pro® and Platinum® insecticides are labeled for control of white grubs and should be applied within two hours of irrigation or rainfall to be sure the chemical gets into the root zone. Admire Pro® requires a 14 day to harvest interval, while Platinum® requires a 50 day pre-harvest interval.
Diseases: Bloom is a critical time to protect strawberry fruit against gray mold caused by the fungus Botrytis cinerea, especially when conditions have been damp. Two to three sprays of fungicide during bloom are typically required to provide good protection against this disease. If you tank mix insecticides and fungicides, avoid spraying when bees are active. Botrytis cinerea overwinters on old leaves and plant debris. Fruit infections take place almost exclusively through the flowers, so gray mold control efforts must be focused on the bloom period. If the bloom period is dry and/or good fungicide coverage is maintained, incidence of gray mold at harvest should be low.
There are several excellent fungicide choices for control of gray mold in strawberries. Elevate® (fenhexamid) has good to excellent activity against Botrytis. Captevate® is a pre-mix of captan and fenhexamid and has a broader spectrum of activity than Elevate® alone. Switch® (cyprodinil and fludioxonil), Scala® (pyramethanil) and Pristine® (pyraclostrobin and boscalid) are also excellent products for gray mold control. Topsin M® + captan is also a good fungicide combination, but remember that captan is strictly a protectant and can be washed off by rain or irrigation water. Thiram is similarly effective but also susceptible to wash-off.
The fungicides Cabrio® (pyraclostrobin) and Abound® (azoxystrobin) are NOT suitable for gray mold control, but are effective against anthracnose and other fruit rot and leaf spot diseases. All fungicides mentioned above have a 0-day pre-harvest interval, except Topsin M® (1 day) and thiram (3 days). Remember to alternate fungicides with different modes of action for resistance management purposes.
Red stele root rot
It has been cool and wet this spring, following a wet fall last year, which creates soil conditions suitable for the development of red stele root rot. Be alert for this disease if any fields appear to be weak, stunted or dying. To diagnose red stele, pull up a few plants that look weak and scrape the roots of these plants to see if the center of the root, known as the stele, is rusty red in color, instead of the normal white. Red root cores indicate an infection. Red stele is caused by Phytophthora fragariae, a soil pathogen that infects roots when soils are wet with temperatures around 50°F. The pathogen grows into the roots causing the plants to become weak, stunted and to eventually die. Symptoms are most evident in the spring, and can be mistaken for winter injury. The symptoms often first appear in the most poorly drained portions of a field. Applications of Ridomil Gold®, Alliette® or Phostrol® in the spring or fall when soil temperatures are cool can offer some control of red stele. Some strawberry varieties have resistance to the disease, but the most effective management strategy is to plant only into well-drained soils, and/or plant onto raised beds.
Powdery mildew: This fungus disease often first appears as purple or red blotches on the leaf petioles and flower stems in strawberry fields. Later, the more familiar symptoms of 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 that is characterized by translucent leaf spots that may turn yellow and eventually black. The symptoms start on the lower leaves but may move upwards as bacterial spores are splashed up by rain or irrigation water. Infection of the calyxes may result in blackening of the berry stems and caps. Bacterial angular leaf spot is favored by extended cool, wet weather and nights with temperatures close to freezing. Frequent irrigation for frost protection will encourage the development and spread of the disease, as will extended cool, damp weather. Susceptibility to this disease appears to vary significantly between varieties. Kocide®, which contains copper, can reduce the spread of this disease. Spray applications should start before bloom to prevent spread of the bacteria on the leaves to the berry caps. Application of copper sprays after bloom can result in fruit injury and is not recommended. Hydrogen dioxide (OxiDate®) may also have some activity against angular leaf spot when used on strawberries as part of a gray mold management program.
2013-2014 New England Small Fruit Management Guides are available at Highmoor Farm. The guide contains the latest information on management options for small fruit pests as well as cultural information. Cost of the guide is $10.00 plus $2.69 postage for a total of $12.69. To order this guide, please send your check made payable to UMaine Cooperative Extension mailed to: Highmoor Farm, P.O. Box 179, Monmouth, Maine 04259, atten. Pam St. Peter. For more information, contact Pam St. Peter at 933.2100 or email@example.com.
Copies of the 2014-2015 New England Vegetable Management Guide with a color picture supplement of the important pests and diseases are available from the Cooperative Extension Publications Office, telephone 207.581.3792. Cost of the guide is $25.00 plus $6.38 tax and postage for a total of $31.38.
Vegetable Growers: Expanded Crop Label for Dual Magnum® Herbicide
Maine vegetable growers now are able to use Dual Magnum® on an expanded range of vegetable crops including: asparagus, bell peppers, cabbage, carrots, garden beets, dry bulb onions, green onions, spinach, Swiss chard, and pumpkin. The target weeds for this registration and use are galinsoga and yellow nutsedge. Growers need to go to Syngenta’s web site http://www.farmassist.com/ and agree to a waiver of liability and print off the 24C label. All label instructions will be supplied after the application for use is completed. Once on the FarmAssist web site, click products at top left, then indemnified labels. Create a user name and password, select Dual Magnum®, and the crop. This is ONLY for the product Dual Magnum®, EPA #100-816. It is not for Dual II Magnum® or the generic Dual®/metolachlor products. Rates are about ½ of the normal rate of Dual® on many of these crops, so growers will need to pay attention to that.
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.
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.