Strawberry IPM Newsletter
July 26, 2007
Renovation and Weed Management Issue
Bed renovation should begin as soon after harvest as possible. Early renovation allows more time for runner plant development, leading to larger crowns and more flower buds for next year. Early renovation also improves weed management by tilling in many weeds before they go to seed, and can help with insect and foliar disease control by interfering with life cycles at a critical stage of development.
Strawberry Bed Renovation Review
The first step in the bed renovation process is to determine which beds should be carried over for another year and which should be plowed be down and put into a crop rotation. Beds that do not appear to have suffered much from winter injury, had good production, and a good plant stand with no major weed, insect or disease problems should be carried over for another year. Beds that do not meet these criteria should be plowed down and seeded to a suitable cover crop to reduce weed, insect and disease problems that have developed and to increase soil organic matter content. If you intend to fumigate this fall, plow down the cover crop at least two weeks prior to the application to allow the plant residue to break down. Fumigation should be done before the average soil temperature at a depth of six inches falls below 50ºF. Ideally, beds that are plowed down should be rotated out of strawberries for at least three years. If properly managed, crop rotation will greatly reduce pest problems and improve the vigor and longevity of strawberry beds without the need for soil fumigation.
Renovating a strawberry bed is basically a thinning process to promote healthy new growth that can support a heavy crop next spring. While some of the general renovation scheme may need to be modified for individual situations, all beds should undergo the following steps once harvest is complete.
1. Broadleaf Weed Control: If perennial broadleaf weeds such as dandelion, shepherd’s purse, daisy or goldenrod are a problem and/or a high population of annual broadleaf weeds such as lambsquarter, sorrel or pigweed are present, hand-pull as many as possible, especially within the plant rows, and/or apply 2,4-D amine (Formula 40®).
2. Leaf Mowing: Four to five days following the 2,4-D application (or immediately if 2,4-D was not applied) mow off the leaves of the strawberries about 1 1/2 inches above the crowns. If the planting is weak or under drought stress, it is recommended that this step of the renovation process be skipped this year.
3. Fertilization: Apply 40 to 60 pounds of actual nitrogen per acre (use the higher rate on sandy soils and fields where growth has been weak). Phosphorus and potassium applications should be made according to soil test recommendations. Soil testing kits and information are available from your county Cooperative Extension office.
4. Plant Thinning: For the single matted row system, strawberry plant rows should not be any wider than 24 inches. After mowing off the leaves, till the sides of the rows to narrow the beds back to a width of 12 to 18 inches. Use the wider setting for varieties that tend to throw few runners or any fields experiencing drought stress. Set the tiller so that it incorporates the mowed leaves and spreads about one inch of soil over the remaining crowns at the same time. This will reduce leaf disease and mite problems, and help stimulate new root growth on the remaining plants.
5. Pre-emergent Weed Control: To control annual weeds, apply terbacil (Sinbar® 80WP) according to label directions (2 to 6 oz. per acre). Be sure to follow all label precautions. To avoid plant injury, do not use terbacil if you do not intend to mow off the leaves. Napropamide (Devrinol®) or DCPA (Dacthal®) may be used as an alternative to terbacil at this time, as described below. If you are not using herbicides, regular cultivation, before weeds are more than 2” tall, will be needed throughout the summer.
6. Subsoiling: Soil compaction caused by tractor and picker traffic in the field can cause soil drainage problems and interfere with good root development. Using a subsoiling blade between the rows will break up compacted layers of soil and improve water infiltration. Subsoiling is best done late in the renovation sequence to prevent interference from straw and crop residues.
7. Irrigation: To encourage rapid plant growth and get the most out of your fertilizers and herbicides irrigate the beds regularly. Strawberries will grow best if they receive 1 1/2 inches of water per week during the growing season.
Don't forget your plants once these renovation steps are completed. Check the strawberry fields regularly during the summer for pest problems. Finding and managing problems early can prevent major problems next spring. Pay close attention to the following items:
Nutrition: Following the application of 40 to 60 pounds of actual nitrogen at renovation, another 20 pounds of nitrogen may be applied in mid-late August to stimulate flower bud development. One way to determine the nutrient status of strawberry plants during the summer is to have a leaf tissue analysis done. Tissue analysis offers a view of what is happening within the plant, and can spot any nutrient deficiencies. In combination with regular soil tests, tissue analysis will provide a complete picture of a field's fertilizer needs. For more information about tissue analysis contact: Analytical Lab, 407 Deering Hall, University of Maine, Orono, ME 04469-5722, Telephone: 581-2945.
Diseases: Foliar diseases should be monitored in your fields by regularly examining leaves. We have seen all of the common leaf diseases in fields this spring and expect that they will continue to be a problem through the summer. The most common summer diseases are powdery mildew, leaf spot and leaf scorch. Fungicides available for these diseases include Captan, Topsin-M®, Cabrio®, Pristine® and Abound®. See the 2006 New England Small Fruit Pest Management Guide for detailed descriptions of these diseases and their management.
Insects: If black vine weevils or strawberry root weevils are a problem in a strawberry field that you would like to carry over, bifenthrin (Brigade®) can be applied when adult feeding is noticed (usually until mid-late July). Look for notching along the leaf edges and the presence of the black or brown snout beetles. Applications should be made at night when these insects are active, and the highest rate of the insecticide should be used. Parasitic nematodes such as Heterorhabditis bacteriophora or Steinernema feltiae should be applied to provide control of root weevil grubs in late August. The latter species is more tolerant of cool soil temperatures. Nematodes require specialized handling and application. Contact us or talk with one of the suppliers for more details. See the New England Pest Management Guide for sources.
Strawberry rootworm (not root weevil) is a small (1/8") dark brown to black beetle, which feeds on strawberry foliage, causing it to look skeletonized. The small larvae feed on strawberry roots, further weakening the plant. Adult feeding damage on the leaves usually occurs in late July through August. Heavy rootworm feeding can weaken strawberry plants so control should be considered when injury is noticed.
Keep a lookout for potato leafhoppers, which can weaken strawberry plants and spread disease. Potato leafhopper does not over winter in Maine, but must fly in from southern states. These small, bullet-shaped insects feed on plant sap from the undersides of leaves, causing the leaves to become curled, stunted and yellow-streaked. Symptoms are often first noticed new strawberry plantings, but leafhoppers will also infest older plantings and a variety of vegetables, flowers and fruit crops. To scout for leafhoppers, brush the leaves of the plants with your hand. The small, whitish adults can be seen flying off the plant. Examine the underside of some injured leaves. Look for small, light green leafhopper nymphs. They are about 1/16th inch long. When touched, they will crawl sideways in a crab-like manner. To control potato leafhoppers on strawberries, malathion, carbaryl or Provado® can be used. See the New England Small Fruit Pest Management Guide for details on the use of these products.
Mites: Two-spotted spider mites can become problems during the summer. Continue to take leaf samples for spider mites after renovation. If more than 25% of a 60 leaf sample has mites, controls should be applied. Summer is an ideal time to use predatory mites to control pest mites, because they prefer warmer temperatures, and there is less likelihood of an insecticide spray application that would kill them. Amblyseius fallacis, can provide good control of two spotted spider mites when they are released at a rate of about 10,000 mites per acre. Predator mite releases should only be made after a spider mite infestation has been found in the field. Releasing predators into a clean field will often result in them dying, due to a lack of food. For sources of predatory mites call (916) 324-4100 and ask for a copy of the guide Suppliers of Beneficial Organisms in North America, or go to the internet web page:
http://www.cdpr.ca.gov/docs/ipminov/bensuppl.htm.
Cyclamen mites: Plants showing weak growth and yellow, crinkled leaves may be infested with cyclamen mite. Cyclamen mites are very small and reside down in the crown of the strawberry plant feeding on the developing leaves. They are very hard to see, even with magnification. Miticides such as Thionex® or Kelthane® can be effective, but must be applied in lots of water to be sure that the material is carried down into the crowns. If you suspect you have this problem give us a call.
Weeds: Weeds tend to become a big problem during the summer because they are often forgotten among all the other demands on our time and because of a lack of good chemical control options. However, the importance of good weed management should not be underestimated. Keeping weeds under control this summer will prevent a heavy infestation next spring. Here’s a summary of weed control options for strawberries:
1. Cultivation: Following renovation, cultivation between strawberry rows can provide effective temporary control of annual weeds. Several types of cultivators are available which will work well in strawberry beds. Cultivators can also be used to help sweep runners into the plant rows.
2. DCPA (Dacthal®): A pre-emergent herbicide used in the early spring, late fall or after renovation. It offers good, short-term control of some annual broadleaf weeds and grasses. It is weak on ragweed, galinsoga, smartweed, shepherd's purse and mustard. Its action will be improved if worked into the soil by irrigation or light cultivation, and it tends to work best in lighter, warmer soils. This may be used as an alternative to terbacil or napropamide when there is a high risk of plant injury from those products.
3. Napropamide (Devrinol®): A pre-emergent herbicide which provides good control of annual grasses, volunteer grains and some broadleaf weeds. Typically applied just before mulching in the fall. Split applications have become popular due to the loss of other pre-emergent herbicides, e.g. half maximum rate application after renovation or in late summer after desired daughter plants have rooted, and a second half maximum rate application once the strawberry plants are dormant. Napropamide should be activated by irrigation, rainfall or light cultivation within 24 hours of application. Repeated long-term use of this material, i.e. with no crop rotation, may eventually result in poor daughter plant establishment, due to rooting inhibition.
4. Terbacil (Sinbar®): An effective pre-emergent herbicide with some post-emergent activity, which should be applied at renovation time, after mowing and tilling the beds, but before new growth begins. A second application can be made in late fall, after the plants are dormant. No more than 6 oz. may be applied in a single application, and no more than 8 oz. may be applied one season. An example of one season's use could be 5 oz. applied at renovation and 3 oz. applied in the late fall, the latter in addition to napropamide or DCPA. Terbacil can cause injury to strawberry plants. It is important to determine appropriate rates for each location.
5. Sethoxydim (Poast®): A post-emergent herbicide for control of actively growing grasses. It will not control broadleaf weeds. It should not be applied when grasses are under stress, e.g. drought, or on unusually hot, humid days. Do not use sethoxydim within six weeks of a terbacil (Sinbar) application to avoid leaf injury. Sethoxydim should be used in combination with a crop oil concentrate. Do not tank mix with 2, 4-D.
6. Clethodim (Arrow®, Prism®, Select®): A post-emergent herbicide, similar in activity to Poast, for control of actively growing grasses. It will not control broadleaf weeds. It should not be applied when grasses are under stress, e.g. drought, or on unusually hot, humid days. Clethodim should be used in combination with a crop oil concentrate.
7. Paraquat (Gramoxone Max®): A contact herbicide for post-emergent control of most annual weeds and suppression of many perennial weeds. Paraquat will injure or kill strawberries, so applications are made between rows only, with a sprayer shielded to protect the strawberries. It should be used in combination with a nonionic surfactant. Paraquat should not be applied within 21 days of harvest or more than three times in one season.
8. Pelargonic Acid (Scythe®): A contact herbicide for post-emergent control of most annual weeds and suppression of many perennial weeds. Scythe will injure or kill strawberries, so applications are made between rows only, with a sprayer shielded to protect the strawberries. This product has a relatively low toxicity and no residual soil activity. It has a strong, unpleasant odor
9. 2,4-D amine (Formula 40, Amine 4): A post-emergent herbicide effective on most broadleaf perennial weeds. It will not control grasses, nor offer any pre-emergent control. 2,4-D should be applied immediately after harvest is complete if emerged broadleaf weeds are a problem. After application, the bed should be left undisturbed for three to five days, before mowing the leaves off the plants. This allows time for the material to be taken in by the weeds. This material can also be used when the plants are dormant (late fall or early spring) to control winter annuals and biennials. Such applications have been of minimal benefit in northern New England, and sometimes result in injury to the strawberries. Do not tank mix 2,4-D with Sethoxydim (Poast®).
10. Flumloxazin (Chateau®): A pre-emergent herbicide for control of broadleaf weeds, including dandelion and shepherd’s purse. For use in the fall when plants are dormant for control of weeds the following spring.
The use of herbicides alone rarely gives complete weed control. Some hand weeding will be necessary. Regularly scout your fields for weeds, noting "hot spots" and weed species that may require special attention. To provide good weed control throughout the life of a strawberry bed, growers should concentrate on crop rotation and good pre-plant weed control.
Visit the New England Small Fruit Pest Management Guide on-line for more detailed pest information at: www.umass.edu/fruitadvisor.
David T. Handley
Vegetable & Small Fruit Specialist
Highmoor Farm
P.O. Box 179
Monmouth, ME 04259
(207) 933-2100
Pest Management Office
491 College Ave
Orono, ME 04473
1-800-287-0279
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this newsletter please call 207-933-2100 to discuss your needs.
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