Vermont Vegetable and Berry News Ė May 23, 2007
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 ext.13, vernon.grubinger@uvm.edu
www.uvm.edu/vtvegandberry

CABBAGE MAGGOT FLIES
(adapted from UMass Extension)

A good indicator of the start of cabbage root maggot flight is blooming of the common weed yellow rocket. Cabbage maggot flies are likely to be found only near their host crop, brassicas. Flies spend the winter as small brown pupae in the soil. Adults emerge in spring and can then travel up to a mile in search of host plants. About 6 to 10 days after the flight of adult flies eggs are laid. Female flies seek out brassica plants to lay eggs at the base of the stem. Cool, moist soil conditions favor survival of the eggs. By late June, if the soil temperatures in the upper ½ to 1 inch are above 100 degrees F then the heat of the soil itself provides control.

When eggs hatch, larvae feed on roots and can cause complete destruction of the root system. In brassica root crops such as turnips, radishes and daikon, feeding tunnels make the root unmarketable. In crops such as broccoli or cauliflower the first sign of a problem is wilting of the plant on sunny days and yellowing of outer leaves. Later, plants collapse, wilt down, and die. If you pull one up you will see that the roots are gone. You may still find the little white maggots feeding, or the small brown, oblong pupae.

Monitoring for adults. Cabbage root maggot flies are rather delicate, hump-backed gray-brown flies, about 5-7 mm long. The flies are attracted to yellow sticky cards, which are inexpensive and easy to use. Attach them with small wire stakes and place near the soil. Itís best to check traps twice weekly, as they often get coated with dust when left out for a whole week. This will tell you when the flight peaks, and when it declines. In cabbage, flight typically declines after mid-May so that some late May or June plantings do not get attacked. You can time your transplanting to try and avoid peak flights, and thus damage.

Monitoring for eggs. To check your field for eggs, look for the 1/8-inch long, torpedo-shaped white eggs that are laid along the stem, or on the soil next to the stem of young transplants. Often eggs are laid in neat rows, or inserted into the soil. They may be under a small clod of dirt near the stem. Eggs may be more abundant in wetter areas of the field. A pencil point helps stir the soil to look for them. Check 25 or more plants, in groups of 2 to 5 plants, scattered around the field. If you have several plantings, scout each planting (it takes about 15 minutes).

If you find more than an average of 1 egg/stem, it is likely to be a damaging population and a banded soil drench may be called for. Conventional growers, see the New England Vegetable Management Guide, on-line at http://www.nevegetable.org/). Organic growers do not have effective insecticide options for this pest so cultural practices are critical.

Floating row covers provide an effective barrier against this pest. Use in a rotated field, as flies overwinter in soil after late season crucifers and could emerge under the cover if the same field has spring brassicas. Replace cover after weeding operations.Crop rotation contributes to keeping populations low. Fall tillage to bury crop residues and to expose over-wintering pupae is also important. If the pest is present in a healthy crop, cultivation that brings soil up around the stem may help encourage formation of adventitious roots from the stem, which can help compensate for root loss due to maggots. Natural enemies in the soil may also help to suppress the population of maggot eggs and larvae.

PLASTIC MULCH AND FERTILIZATION
(adapted from Steve Reiners, Cornell Univ.

If you need to broadcast fertilizer prior to planting, it is relatively easy to figure out how much to apply. If you are using plastic mulch, however, you may be applying more fertilizer than you need. In a typical mulched field, the width of the soil surface covered with mulch is usually three feet.The uncovered area is usually 2 to 3 feet depending on the row spacing. For our example, letís use two feet. Prior to laying plastic you need to add 50 pounds of N and 100 pounds of P and K. Using a 10-20-20 fertilizer you could spread 500 pounds evenly across the acre. But you will be fertilizing the area that is between the rows, an area where crop roots will likely not be feeding but weeds will. If you have the equipment, it is much better to apply the fertilizer only to the area that will be covered with mulch. Since that will be only three feet of every five feet, that means that only 60% of an acre will be used by the crop. You can cut your fertilizer rate to 300 pounds per acre from 500 and still get the same effect. Once this is applied and the plastic is laid, you can use the same calculation to apply fertilizer through the drip system. If you need 20 pounds per acre of N, P, and K and are using a 20-20-20 soluble fertilizer, you will need only 60 pounds of fertilizer rather than 100 pounds. It all comes down to the fertilized-mulched acre. This is the percentage of an acre that is covered by plastic mulch where most of the crop roots will be found. Applying fertilizer based on this will save you money and maintain your crop's quality.

BLUEBERRY SUSCEPTIBILITY TO FROST DAMAGE
(adapted from North Carolina State Univ.)

Growers have asked how the recent cold nights may affect their blueberry crop. Temperatures must drop below 28 degrees F for economic losses to occur on highbush blueberry. The temperature at which freeze injury begins to occur depends on the stage of development from dormant flower buds through young fruit. During the winter, dormant flower buds of highbush blueberries will survive temperatures as low as -20 to -30 degrees F, but as flowerbud swell progresses, cold tolerance decreases. By the time individual flowers begin to protrude from the bud, temperatures below 20 degrees F will begin damaging the most exposed flowers. When corollas have reached half of their full length, temperatures below 25 to 26 degrees F will kill the complete flowers. When the blossoms are open, a temperature of 27 degrees F for more than a few minutes causes damage. Immediately after corolla drop and before the berry begins to swell is the most sensitive stage. A few minutes below 28 degrees F will result in damage. As the berry begins to enlarge, susceptibility is similar to the critical temperature of 28 degrees for open blossoms.

ORGANIC PEST MANAGEMENT WORKSHOP
Tuesday June 12, 2007 from 2-5 pm, River Berry Farm, Fairfax, VT

Join us as we scout for a variety of pests in vegetables, berrries and greenhouse crops on this 50-acre river bottom farm. We'll identify the insects and diseases we find, and discuss organic management options with experienced farmer David Marchant, along with Jon Turmel, entomologist with the VT Agency of Agriculture, and Ann Hazelrigg and Vern Grubinger from University of Vermont Extension. David will demonstrate several different sprayers, large and small, that he uses to apply organic pest control materials, and we'll learn how to calibrate them. Questions? Vern Grubinger 802-257-7967 x13.

Directions: From I 89 take exit 18. take 104 A to rte. 104 go right,  Stay on rte 104 through the center of Fairfax.  Two miles past the blinking light in the center of town take left onto bridge at Fairfax Falls,   cross bridge turn right onto Goose Pond Rd.  Farm is one mile on right. From I-91 take Rte 15 W to Cambridge.  Go Right onto Rte. 104.  Go six miles to Fairfax Falls, turn right onto iron bridge at Falls, cross bridge, turn right onto Goose Pond Rd.  Farm is one mile on right.

ON-FARM COMPOSTING WORKSHOP 101
July 12, 2007, from 9:00-3:30, Highfields Institute West Hill Farm, Hardwick, VT

This workshop involves classroom components, demonstrations on feedstock mixing and
pile formation, and hands-on exercises with an emphasis on recipe development, pile monitoring, and pile management. Our Compost Demonstration and Research Site is a fully functioning farm-scale composting operation where we explore on-farm composting management strategies. Make composting work for your farm by understanding the science of composting and practical methods for managing your operation. Cost: $10 for Farmers, $15 for up to 3 from one farm, $20 for non-farmers. Bring a bag lunch and dress for outdoors. Register by July 2 by calling 802-472-5138 or e-mail: jvh@ezcloud.com

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