We have begun scouting strawberry fields at several volunteer farms for major insect pests, including locations in North Berwick, Wells, Cape Elizabeth, Poland Spring, New Gloucester, Dresden, Litchfield, Wayne, and Farmington.  We will be reporting our findings through this newsletter on a weekly basis until harvest time. You can also get quick access to this information through the Pest Management web page on the Internet at http://pmo.umext.maine.edu.  If you would prefer to receive this message via e-mail, please give us a call at 933-2100 or send an e-mail message to: dhandley@umext.maine.edu.

The best way to manage strawberry pests is to scout your own fields regularly and often.  You should be able to identify the major pests and their damage, and be able to determine if controls measures are necessary.  To properly scout your fields you may want a copy of the Strawberry Production Guide for the Northeast, Midwest and Eastern Canada. This contains detailed information on strawberry pest identification and monitoring, and also provides information on all other aspects of strawberry production, including varieties, planting systems, nutrition, marketing and more.  It may be purchased for $48.00 per copy. Copies of the 2003-2004 New England Small Fruit Pest Management Guide are still available.  This guide offers the latest recommendations for pest management in all small fruit crops, including registered chemical and non-chemical alternatives. The cost is $6.00.  These publications can be ordered from the University of Maine Cooperative Extension at Highmoor Farm, P.O. Box 179, Monmouth, ME 04259-0179.   Checks should be made payable to Cooperative Extension.

Situation:  A cold, open winter, with winds that blew the mulch off of many plantings, has left many fields with significant winter injury (see article below).  Older beds, and those in more exposed locations have been hardest hit.  Growers have reported that Cabot and Mira varieties seem to have been especially susceptible.  Although a cool start to the spring delayed early growth in most areas, subsequent warm weather has pushed plants along in recent weeks.  Many fields in southern and central Maine are in early bloom, with only late varieties still in the bud stage.  Fields that were under rowcovers are at or just past full bloom.  Only a few fields have shown any frost injury, and the overall damage has been very light. 

Strawberry bud weevil or "clipper" is now active in strawberry fields where flower buds are emerging from the crown. We have found significant clipper injury in Poland Spring, New Gloucester and Wells this week, indicating that these insects are likely to be active in any fields where flower buds are present. The clipper is a small weevil, which girdles strawberry flower buds causing them to dry up and fall off the flower stalk.  The damage should be scouted for 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 1.3, or if one or more 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 throughout the field.  Fields with a history of clipper problems can be expected to exceed threshold nearly every year. 

Tarnished plant bugs are just starting to become active.  We have seen a few adults and small nymphs (immature) in several fields. Adult plant bugs are still laying eggs, so we expect to see more nymphs soon. The nymphs are small, active, yellow-green insects. It is important to scout for the nymphs regularly, as they can show up quickly in warm weather. Tarnished plant bugs feed on the open strawberry flowers, causing the berries to have seedy ends.  To scout for this insect shake 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 now!

Twospotted spider mites have been found in a few fields this week, but we expect them to become more prevalent once the temperatures get higher.  Mites have been over threshold in Poland Spring and Wells this week, mostly in fields that were under row covers.   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 rowcovers 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. Predatory mites, such as 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. 

Diseases: Many strawberry plantings are now coming into the bloom stage.  Bloom is a critical time to protect the fruit against fungus diseases, including gray mold.  Two to three sprays of fungicide during bloom will usually provide good protection against this disease. If you tank mix insecticides and fungicides, avoid spraying when bees are active.  Leather rot and leaf spot may also become an issue at this time, and may require different materials to provide good control.  The recent changes in fungicide registrations have provided strawberry growers with a wider range of materials to choose from.  An article from Annemiek Schilder of Michigan State University is included below to offer some help in deciding which materials may be best for your situation. 

What Fungicide do I Choose for Disease Control in Strawberries?

Annemiek Schilder, Michigan State University

There are more choices for disease control in strawberries than ever before. This can be a rather bewildering experience, as growers have to consider the disease control spectrum, efficacy ratings and cost per acre for each product. This article aims to help strawberry growers in the decision-making process by outlining unique aspects of several strawberry diseases, characteristics of the newer fungicides, and by suggesting several possible fungicide programs. A few notes on specific diseases:

1) Control of leaf diseases, such as common leaf spot, scorch, Phomopsis leaf blight and angular leaf spot may only be needed on susceptible cultivars. Some leaf diseases can spread to the berries (e.g., phomopsis can also cause a fruit rot), or berry caps (angular leaf spot and scorch). If these have been a problem in the past, start fungicide sprays before bloom.

2) Leather rot (Phytopthora cactorum) is best controlled by growing strawberries in well-drained soil and by applying straw mulch between the rows to prevent the berries from touching the soil (where the fungus resides) and prevent soil from splashing up onto the berries. If there still is a problem, use Ridomil Gold or Aliette for control. Some phosphorous acid products such as Agri-Phos (similar to Aliette) may also work, but have not been evaluated on strawberries in Michigan. Spray during bloom and fruit  development. 

3) Angular leaf spot is a bacterial disease that is characterized by translucent leaf spots and blackening of the berry caps. It is favored by cool, wet weather and nights with temperatures close to freezing. The bacteria are spread by rain splash or by irrigation water. Copper (e.g., Kocide, Cuprofix, Bordeaux, etc.) is the only chemical that works against this disease. Some labels suggest adding lime as a safener to reduce the risk of crop injury. In susceptible varieties, start spray applications before bloom to prevent multiplication of the bacteria on the leaves before they jump to the berry caps.

4) Botrytis gray mold, the predominant fruit rot in most areas where strawberries are grown, primarily enters the berries through the blossoms, which means that chemical control should be focused on the bloom period. The Botrytis fungus can produce numerous spores on dead leaves and other plant matter and spreads easily by wind. Make sure to protect the king blooms especially, since these provide the largest berries. The other period for control is pre-harvest, since Botrytis can spread rapidly from infected berries to ripe and overripe berries. Pre-harvest sprays reduce post-harvest rots and increase shelf life of the berries.

5) Most other fruit rots, including anthracnose, tend infect the berries somewhat later in the season, i.e., during the green fruit or ripening stage. Anthracnose fruit rot is favored by warm, humid conditions and can spread rapidly during rains or frequent irrigation. In cool seasons, it tends to appear closer harvest or may not show up at all. Anthracnose fruit rot can be identified by black sunken lesions with wet, orange (and sometimes gray) spore masses in them. The anthracnose fungus is able to multiply on the leaves without visible symptoms, which may explain its sometimes widespread and sudden appearance in fields. 

New fungicide characteristics (prices are estimates for comparative purposes only and may vary depending on the supplier and quantity purchased). Please follow label directions carefully before use.

Pristineâ (pyraclostrobin and boscalid) contains a strobilurin and an analid active ingredient. This fungicide is a very broad-spectrum material and has excellent activity against leaf spots, powdery mildew, and fruit rots, including Botrytis gray mold. It is surface-systemic (i.e., it is somewhat mobile within the wax layer on the plant surface) and has limited back action. The fungicide gets rainfast quickly. The label rate is 18-23.5 oz/acre (approximate cost: $32-$42/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Cabrioâ (pyraclostrobin) is a strobilurin-type fungicide with excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots. However, it does not provide much control of Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 12-14 oz/acre (approximate cost: $16-$18/acre). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Quadrisâ (azoxystrobin – this product will be sold under the name Abound in future) is also a strobilurin-type fungicide with good to excellent broad-spectrum activity against leaf spots, powdery mildew and fruit rots. It does not have much activity against Botrytis gray mold. It is surface-systemic and has limited back action. The fungicide gets rainfast quickly. The label rate is 6.2-15.4 fl oz/acre (approximate cost: $12-$30/acre; $24 at the 12-oz rate). The number of applications is restricted for fungicide resistance management. PHI=0 days.

Elevateâ (fenhexamid) is a fungicide with a new chemistry that has excellent activity against Botrytis gray mold. While fenhexamid has some systemic activity, it should be used as a preventative fungicide. The fungicide gets rainfast quickly. Can be used to alternate with fungicides in other chemical classes. The label rate is 1.5 lb/acre (approximate cost: $41/acre). PHI=0 days.

Captevateâ (fenhexamid and captan) is a pre-mix of Elevate and Captan. It has excellent activity against Botrytis as well as moderate to good activity against anthracnose and other leaf spot and fruit rot diseases. This formulation appears to perform a bit better than a tank mix of Elevate and Captan. The label rate is 3.5-5.25 lb/acre (approximate cost: $42-$63/acre). At the high rate, the dose is equivalent to 1.5 lb Elevate and 5 lb Captan. The PHI=0 days.

Switchâ (cyprodinil and fludioxonil) is a mixture of a systemic and protectant active ingredient (both are new chemistries). Switch has excellent activity against Botrytis gray mold and moderate to good activity against anthracnose and scorch. The label rate is 11-14 oz/acre (approximate cost: $39-$50/acre). PHI=0 days.

Older fungicides such as Topsin Mâ, Captan, Thiram, Sulfur, etc. remain effective disease control tools. The approximate prices per acre: Topsin M $16/acre; Captan $13/acre; Thiram $8/acre; Sulfur $1-2/acre; and copper formulations: $3 to $4/acre.

Suggested fungicide programs These programs will provide simultaneous control of foliar diseases, Botrytis gray mold and other fruit rots. Other combinations are possible. If angular leaf spot control is needed, add a copper product. If leather rot control is needed, apply Ridomil Gold or Aliette.

(Source: Michigan Fruit Crop Advisory Team Alert, Vol. 19, No. 3, May 4, 2004)

Pre-bloom	Bloom	Green berry	Pre-harvest	Approx. cost per acre	Comments
Topsin M + Captan	Pristine	Cabrio or Quadris	Elevate (0-day PHI)	$130-140	Under high disease pressure
Topsin M + Captan	Captevate	Cabrio or Quadris	Pristine (0-day PHI)	$130-140	Under high disease pressure
Topsin M + Captan	Switch	Cabrio or Quadris	Elevate (0-day PHI)	$130-140	Under high disease pressure
Captan	Switch	Cabrio	Topsin M + Captan (1-day PHI)	$100-110	Under moderate to high disease pressure
Captan	Thiram	Cabrio	Thiram (3-day PHI)	$50	Under low to moderate disease pressure
	Thiram	Thiram	Captan (0-day PHI)	$30	Under low disease pressure

Root Weevil Management

From info supplied by Richard Cowles, CT Agricultural Experiment. Station; Peter Shearer, Rutgers Cooperative Extension; and others  

Despite the hard winter, we have observed some plantings of strawberries infested with the grubs of black vine weevil and strawberry root weevil this spring.  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; ‘GrubStake HB’ from Integrated Biocontrol Systems; ‘Larvanem’ from Koppert Biologicals). Beneficial nematodes can also be applied in late summer (August 15 - September 1), and in that case, Steinernema feltiae (‘Nemasys’ from Griffin Greenhouse Supply, ‘Gnat Not’ from Integrated Biological Control Systems, ‘Entonem’ from Koppert Biological) should be considered in northern locations since it tolerates cooler soil temperatures and completes its life cycle quickly.

Once the grubs begin to pupate (usually early June) nematodes should not be applied, because they do not attack the adult (beetle) stage.  Once the adults become active 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 1 week before harvest ends.  Neem-based products containing azadiractin (such as Aza-Direct) may be acceptable for organic production, and while neem will not kill the adults it can disrupt egg-laying if applied at high rates at least twice.

Although bifenthrin claims to kill spider mites, many twospotted spider mite populations are resistant to pyrethroids. Spraying this product or other pyrethroids usually exacerbates spider mite problems by selectively killing off predatory mites. Growers challenged with black vine weevil problems should plan well ahead, and use horticultural oil (SunSpray UltraFine Oil) early in the growing season. If applied with an airblast mist blower, oil can be inexpensive, effective, and non-toxic to predatory mites. This strategy can then reduce the risk of spider mite problems later. Be sure to use oil about 2 weeks before any Captan sprays, because the two products are extremely phytotoxic. Alternatively, Brigade may be applied with oil 2 to 3 days after mowing the foliage during renovation.  This approach should jointly control spider mites and root weevil adults.  

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, refrigerating if delay is necessary. 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 Ľ inch of irrigation after application to wash them onto and into the soil. Although references suggest rates of several billion nematodes per acre, I found researchers and suppliers recommended 250 (if banded in the row) to 500 million per acre, at a cost of about $100 to 200 acre depending on volume and source. Ironically, nematodes probably work best in the worst weevil-infested fields. High populations of weevil larvae allow explosive growth in nematode populations, while low populations of larvae may not permit efficient nematode reproduction. Strawberry plants can recover their vigor remarkably well if crown feeding has not occurred and diseases haven’t taken over the roots. 

Root weevils cannot fly, so they infest new plantings by wandering into fields from surrounding weedy and woodland vegetation, or in large numbers from recently plowed, infested strawberry plantings. Even plantings several hundred feet away can become generally infested as a result of mass migration from plowed fields. A good rotation program with substantial distance between strawberry fields can help to manage root weevils. Also, when turning under old, infested strawberry plantings, it is critical to leave a row or two at the perimeter of the field as a trap crop to protect other plantings. Adult weevils will be intercepted in these rows before they leave the field and thus lay their eggs where the larvae will not do any damage. At the end of the season the trap rows should be turned under prior to planting winter rye. Do not spray the trap rows as this may repel weevils and result in more migration to other fields. 

Some Beneficial Nematode Suppliers:

The Green Spot: 603-942-8925 or www.shopgreenmethods.com 

Griffin Greenhouse Supplies: 978-851-4346 or www.griffins.com

Integrated Biological Control Systems: 888-793-4227 or www.goodbug-shop.com

Koppert Biologicals: 800-928-8827 or www.koppert.com

Winter Injury in Strawberries?

Many growers are reporting moderate to severe winter injury in their fields this spring.  A very cold winter with little snow cover and lots of wind has clearly taken its toll.  Despite the fact that strawberries are an important and successful crop here in Maine, they are not particularly hardy plants.  Most varieties will experience cold injury at temperatures of 10° to 15°F, which are not uncommon during a typical Maine winter.  However, the combination of mulch and snow cover usually provides adequate protection during the winter, keeping the temperature around the plants within tolerable limits, even when air temperatures drop well below injurious levels.   However, if mulch coverage is poor, due to removal by wind, animals or other factors, and/or there is a lack of adequate snow cover during the coldest periods of the winter, then cold temperature injury could be a problem.  

To assess suspected winter injury in a strawberry planting, plants can be sampled throughout a field, noting different varieties and landscape features, such as elevation, lack of mulch coverage, etc.  Examine the crowns and roots for color.  Beneath the protective brown or black dead layer, there should be healthy, firm, white tissue.  Slice the crowns lengthwise to examine the interior tissue.  Brown discoloration at the base of the crown indicates a mild but significant level of injury.  The degree of injury increases as the amount of browning extends toward the top of the crown and gets darker in color.  If the tissue is killed all the way to the top of the crown, including the leaf and flower buds, plant death is very likely, but this rare.  Strawberry plants usually survive milder injury, but even slight browning in the crowns often leads to reduced plant vigor and yield.  

You can help alleviate the symptoms of winter-injured plants by applying a light dose of nitrogen to the plants.  This can help stimulate new root growth and leaves, improving the plants ability to support larger fruit and thus improving yield.  Approximately fifteen to twenty pounds of actual nitrogen (e.g. 100 pounds of calcium nitrate) applied in the spring as growth starts can stimulate new growth, without causing excessive foliage growth that can encourage mites and fruit rot. 

Tarnished Plant Bug Scouting Review

Monitoring for tarnished plant bug in strawberry fields should begin just prior to bloom. Nymphs are sampled by shaking flower clusters over a white surface (e.g. a paper or plastic plate).  The shaking causes nymphs to fall out of the flower cluster making it possible to count them.  At least 30 flower clusters should be sampled evenly across the field.  For example, if you stop at 10 locations, sample 3 clusters per location.  If the average number of nymphs per cluster exceeds 0.25 before 10% bloom, or more than 4 clusters are infested with nymphs (regardless of how many), then an insecticide application should be made. Monitoring this way should be carried out at least once a week during the bloom period in a “V” or “X”-shaped sampling pattern across each field.  If tarnished plant bug nymphs are not found until mid to late bloom the control threshold can be raised to 0.50 nymphs per flower cluster, and sprays can be delayed until just post-bloom.

A sequential sampling method for monitoring tarnished plant bug has also been developed and can save scouting time if nymph populations are especially low or high.  Using the table below, scout as many blossoms as is necessary to determine if control is required.  For example, after scouting 15 blossoms check the table to see if a decision can be made.  If no nymphs have been found no control is needed.  Under the low threshold (2% injury allowed), if 3 or more nymphs have been found, a control should be applied.  If you choose to use the high threshold (4% injury allowed), and tolerate more injury, than a control should not be applied until 5 or more nymphs are found.  If one or two nymphs are found, scouting should continue, i.e. examine five more clusters and move down the chart to 20 clusters examined.  Continue scouting until the table provides a control or no control decision for the number of infested flowers.