Eric Sideman's Pest Report
June 2, 2003

(View List Of All 2003 Pest Reports)

WARNING - The word frost is in the forecast for low valleys for tonight. See the frost protection guidelines under strawberries below.

ENTRUST

Entrust is a new organic, NOP-approved formulation of SpinTor, a well-known conventional insecticide. Its active ingredient is Spinosad, a compound derived from cultured soil fungus organisms (a process similar to the production of Bt products).

Entrust is effective against and labeled for many insects on a wide range of crops. For instance: asparagus beetle larvae on the ferns; maggot, caterpillar, and thrips pests on berries; caterpillars and thrips on cole crops and cucurbits; sweet corn caterpillars; Colorado potato beetle, caterpillars, thrips, and leafminers on solanaceae; caterpillars, thrips, and leafminers on leafy greens and root crops; and apple maggot, cherry fruit fly, leafminers and caterpillars on stone and pome fruit. See the label for details.

Entrust has also been shown to be effective against brassica flea beetles when used against other pests on those crops, though it is not labeled for flea beetles.

It is important not to use Entrust on a continual basis, to avoid building up resistance within pest populations. So, other products and pest control methods should be alternated with Entrust sprays.

Entrust comes in one pound bags. They are not cheap--$329 per pound. But a pound treats 5-16 acres at typical rates. I was told that it keeps well in a sealed plastic bag.

One supplier of Entrust in the East is UAP here in Maine (795 6640).

Though Entrust is toxic to a fairly broad range of pests, it is considered to be easy on many common beneficials. The label says it is toxic to bees for 3 hours after application. Mammalian toxicity is very low.

(Modified from a report by Brian Caldwell. He and I and OMRI are working together on a SARE project to train Extension folks about organic materials and we have done a lot of "looking-into" Entrust)
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STRAWBERRIES

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, Farmington and Dresden 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. except there is not much organic growers can do. On a small scale, clipped buds should be collected and removed from the field and destroyed. On a large scale, rotation is the only organic approach and so a high number of clipped buds is a sign that it is time to rotate out of that field. 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. So far only fields in Poland Spring and Dresden have been over threshold for tarnished plant bug. 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! BUT, organic growers have not material that has been shown effective. Organic growers can reduce pressure by managing fields around strawberries. Do not mow during strawberry flowering or you will send the pest into the strawberry field looking for food. Keep fields around strawberries mowed short at other times to limit TPB populations.

Two-spotted 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. If 15 or more of the 60 leaves (i.e. 25%) have any mites on them some control measure is recommended. Organic growers usually do not have mite problems. There are beneficial mites that can be released to control the two spotted mite. Call the Greenspot in NH for information (603 942 8925).

Frost Protection in Strawberries

Strawberry growers can ensure a full crop of berries only if they exert some influence on temperature during the year. Temperature control is especially

important during the winter and early spring when flowers are susceptible to frost. Of all the factors that negatively affect strawberry production, frost can be the most serious. Frost can eliminate an entire crop almost instantaneously. Strawberries often bloom before the last frost free date, and if a frost occurs during or just prior to bloom, significant losses can result. The strawberry flower opens toward the sky, and this configuration makes the flower particularly susceptible to frost damage from radiational cooling. A black (rather than yellow) flower center indicates that frost damage has occurred.

Strawberry growers occasionally delay the removal of straw mulch in spring to delay bloom and avoid frost. Research has demonstrated, however, that this practice also results in reduced yields. Also, applying straw between the rows just prior to bloom will insulate the soil from the air. This will increase the incidence of frost injury as solar radiation will not be absorbed by the soil and re-radiated at night. If additional straw is to be applied between the rows in spring, delay its application for as long as possible before fruit set.

Overhead irrigation is frequently used for frost control because flowers must be kept wet during a freeze in order to provide protection. As long as liquid water is present on the flower, the temperature of the ice will remain at 32F because the transition from liquid to ice releases heat. Strawberry flowers are not injured until their temperature falls below 28F. This 4 degree margin allows the strawberry grower to completely cover a field with ice and yet receive no injury from frost. However, if insufficient water is applied to a field during a freeze event, more injury can occur than if no water was applied.

Several principles are responsible for the ability of ice to protect strawberry flowers from injury. First, although pure water freezes at 32F, the liquid in the strawberry plant is really a solution of sugar and salt. This depresses the freezing point to below 32F. Also, ice crystals need nucleators to allow them to form initially. Certain bacteria serve as nucleators. Sometimes, in strawberry flowers, the bacteria that allow ice to form are absent, allowing the freezing point to be lowered. The temperature of the applied water is usually greater than the temperature of the plants, so this serves to warm the flowers before heat is lost to the air. As long as liquid water is continually applied to the plants, the temperature under the ice will not fall below 32F. When one gallon of water freezes into ice, 1172 BTUs of heat are released.

Several factors affect the amount of water that is required to provide for frost protection, and the timing of application. At a minimum, apply water at 0.1 - 0.15 in/hr with a fast rotating head (1 cycle/min.) Water must be applied continuously to be effective. A water source of 45 - 60 gal/min-acre is required to provide this amount of water. Choose nozzle sizes to deliver the amount of water required to provide protection under typical spring conditions in your location.

Under windy conditions, heat is lost from the water at a faster rate, so more water is required to provide frost protection. For every gallon of water that evaporates, 7760 BTUs are lost. The application date then depends on both air temperature and wind speed Under windy conditions, there is less chance of flower temperatures falling below that of the air because of the mixing of air that occurs at the boundary of the flower. Winds are beneficial if the temperature stays above the critical freezing point, but detrimental if the temperature approaches the critical point. Less evaporation (and cooling) will occur on a still, humid night. Under extremely windy conditions, it may be best not to irrigate because the heat lost to evaporation can be greater than the heat released from freezing.

Stage of development: Strawberry flowers are most sensitive to frost injury immediately before and during opening. At this stage, temperatures lower than 28F likely will injure them. However, when strawberry flowers are in tight clusters as when emerging from the crown, they will tolerate temperatures as low as 22F. Likewise, once the fruit begins to develop, temperatures lower than 26F may be tolerated for short period.

The length of time that plants are exposed to cold temperatures prior to frost also influences injury. Plants exposed to a period of cold temperatures before a frost are more tolerant than those exposed to warm weather. A freeze event following a period of warm weather is most detrimental.

Flower temperature: The temperature of all flowers in a field is not the same. Flowers under leaves may not be as cold as others, and those near the soil generally will be warmer than those higher on the plant. On a clear night, the temperature of a strawberry flower can be lower than the surrounding air. Radiational cooling allows heat to be lost from leaves and flowers faster than it accumulates through conduction from the surrounding air.

Soil also retains heat during the day and releases heat at night. It is possible that on a calm, cloudy night, the air temperature can be below freezing yet the flowers can be warm. Wet, dark soil has better heat retaining properties than dry, light-colored soil.

Using row covers: Row covers modify the influence of wind, evaporative cooling, radiational cooling, and convection. Because wind velocity is less under a row cover, less heat will be removed from the soil and less evaporative cooling will occur. Also, relative humidity will be higher under a row cover, reducing heat loss from evaporation. In addition, convective and radiational heat loss is reduced because of the physical barrier provided by the cover. Plant temperature under a cover may eventually equal that of the air, but this equilibration takes longer than with uncovered plants. In other words, row covers do not provide you with additional degrees of protection, but they do buy time on a cold night as flower temperatures will fall less rapidly inside a cover. Often the temperatures fall so slowly under a row cover that irrigation is not needed. If irrigation is required, less water is.needed to provide the same degree of frost protection under a row cover. Water can be applied directly over the row covers to protect the flowers inside.

Turning on the water: Since cold air falls to the lowest spot in the field, a thermometer should be located here. Place it in the aisle at the level of the flowers, exposed to the sky, and away from plants. Air temperature measured at this level can be quite different from the temperature recorded on a thermometer at the back of the house. The dewpoint temperature measured in the evening is often a good indication of how low the temperature will drop on a clear night, and is related to the relative humidity. Air temperature will fall less if the humidity is high.

If the air is very dry (a low dewpoint), evaporative cooling will occur when water is first applied to the plants, so irrigation must be started at a relatively warm temperature. Most local weathermen can provide the current dewpoint, or it can be obtained from World Wide Web-based weather information services. If the air temperature falls below 34F on a clear, calm night, especially before 3 A.M., it would be wise to start irrigating since flower temperatures could be several degrees colder (Table 2). On the other hand, if conditions are cloudy, it may not be necessary to start irrigation until the temperature approaches 31F. If conditions are windy or the air is dry, and irrigation is not turned on until the temperature approaches 31F, then damage can occur due to a drop in temperature when the water first contacts the blossom and evaporation occurs. Therefore, the range in air temperatures which indicates the need for irrigation at flowering is normally between 31 and 34F, depending on cloud cover, wind speed and humidity, but can be as high as 40F. Admittedly, these numbers are conservative. Flowers can tolerate colder temperatures for short periods of time, and irrigation may not be needed if the sun is about to rise.

Obviously, one does not want to irrigate too soon since pumping is expensive, and excess water in the field can cause disease problems.

Turning off the water: Once irrigation begins, it should not be shut off until the sun comes out in the morning and the ice begins to slough off the plants, or until the ice begins to melt without the applied water.

Rules of Thumb

2. Use small diameter nozzles (1/16 - 3/16 in. diameter)

3. A 30 X 30 ft. staggered spacing of nozzles is preferable

4. Use metal sprinklers to minimize icing

5. Minimum rotation of once per minute

(Source: New York Berry News, Vol 2., No. 4. April 16, 2003)

The Scoop on Black Vine Weevil Control in Strawberries

The larvae of several kinds of root weevils can cause serious damage to strawberry roots, leading to reduced yield and in at least one case this year in southern Vermont the complete demise of a previously healthy field. Black vine weevil (BVW) is probably more common than strawberry root weevil or rough strawberry root weevil in New England. The life cycle and management of these weevils are the same. Their larvae are whitish, crescent-shaped larvae and * to1/2 inch long with no legs. Adults emerge and feed from May through August, laying eggs as late as October that hatch and overwinter as larvae. Adult feeding causes characteristic scalloping or notching of the leaf edges, but rarely does this cause economic damage.

(Feeding on the interior of the leaf, causing holes, is caused by Asiatic garden beetles or Japanese beetles.)

Adults weevils hide in the crowns during the day and feed at night. They are not easy to kill with insecticides so a better strategy is to kill the larvae with applications of beneficial nematodes. If adults are numerous (i.e. more than 50 out of 100 leaves sampled across the field have notching) then a spray may be warranted.

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.

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.

The key to successful use of beneficial nematodes is sufficient time for multiplication of the nematodes in hosts (weevil larvae) and dispersal of nematodes throughout the soil. Early- to mid-May application has given excellent results, especially when the numbers of larvae of the next weevil generation are evaluated in the autumn. Research in CT, NJ and elsewhere has shown that the appropriate nematode species properly applied can effectively infect and suppress weevil populations. 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 so quickly. Other beneficial nematodes may also control weevils but these 2 species were most commonly found established in CT strawberry fields. There is no point in applying beneficial nematodes in early or mid-summer since few larvae are present.

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 * 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. Green Spot says their formulation requires lower numbers of nematodes but the cost ends up about the same. 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 (Mention of pesticides and biological controls is for information purposes only; no endorsement of materials or brands is intended. Always read and follow instructions on the label.)

(Modified from the strawberry report from David T. Handley Vegetable & Small Fruit Specialist)

CUTWORMS

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)