Vermont Vegetable and Berry News – April 25, 2006
Compiled by Vern Grubinger, University of Vermont Extension
(802) 257-7967 ext.13,

(adapted from NY Berry News)

Strawberries: Straw mulch should be removed as soon as the strawberry plants begin to grow. Prepare equipment for frost protection now so you won’t be caught off guard once flowering begins. Keep in mind a freeze event flowing a period of warm weather is most detrimental. Strawberry flowers can get frost injury at temperatures less than 28°F. However, when strawberry flowers are in tight clusters they can tolerate temps as low as 22°F. Before the temperature reaches the critical level, flowers should be protected with irrigation, causing water to freeze which gives off heat and prevents a further drop temperature. Applying floating row covers to berry plants in the spring can increase yields, accelerate plant development, and protect against moderately fluctuating spring temperatures. But because they speed early-season development row covers can also make flowers more vulnerable to frost injury. Scout the fields for disease. If there is evidence of excessive leaf spot, leaf scorch, or leaf blight on the leaves you may want to plan to apply fungicides. (See the New England small fruit pest management guide for options, including copper for organic growers.)

Raspberries: Pruning should be completed by budbreak if possible. Remove dead and diseased canes, and take out weaker canes to allow thick, healthy ones to thrive. Aim for about 4-5 canes per sq. ft, but this is not always possible. Apply nitrogen fertilizer; a general rate of 50 lb N/acre on one-year-old plants, 75lbs N/acre two year old or older plants. Apply at budbreak in one application or split between budbreak and June. Prepare trellis systems while vegetative growth is minimal. I prefer to tip my longer canes back by about 20% so I don’t need a trellis. Consider cane disease control. If warranted, apply a delayed dormant spray of lime sulfur at budbreak, when buds show ¼ to ½ inch green. Spraying after that can cause leaf burn.

Blueberries:  Pruning should be completed by the end of April if possible. Remove old, diseased canes at ground level, detail prune to remove twiggy wood, thin out canes to provide adequate sunlight. Leaves need 30% of full sunlight for good fruit production. The goal is to have 10 to 20 healthy canes varying in age and height. Maintain clean paths in between rows to decrease insect populations. Apply nitrogen fertilizers. Split the total quantity of nitrogen into two applications, one at flowering and one in June. For mature plantings, a good all purpose mix is 1000 lbs of ammonium sulfate or urea per acre. Use the ammonium sulfate where pH over 5.0. However, it is far better to fertilize based on last year’s tissue test results! Consider springtime disease control. Plants are susceptible to mummyberry infestations from green tip through full bloom. Indar provides best control for primary infections. Cane diseases can be reduced by applications of lime sulfur, when plants are still dormant.

(adapted from Long Island Fruit and Vegetable Update)

When it’s time to cut seed, warm it to 55 to 60 degrees before handling. This minimizes bruising, which can lead to seed rot. Before cutting thoroughly wash and disinfest all equipment. Quaternary ammonium compounds, sodium hypochlorite (household bleach) and calcium hypochlorite are effective disinfectants, but less so if soil or organic matter is not removed from surfaces before treatment. Cleaning equipment in between cutting different seed lots/varieties may seem to be a waste of time, but it can prevent spreading disease from one seed lot to another, and it may not be obvious that one seed lot has a disease problem. Planting practices that help avoid seed decay in the field include: plant into warm, well-drained soil to promote fast emergence; plant shallow; and lightly cultivate to break up compacted soil, as this increases temperature and oxygen levels around the seed, speeding plant establishment.

(adapted from Rutgers Cooperative Extension)

Sudangrass and sorghum-Sudangrass hybrids are annual warm season grasses that make excellent summer cover crops. They are heat and drought tolerant, and winterkill with the first hard frost. They can grow from 6 to 8 feet tall, producing large amounts of biomass, helping to maintain soil organic matter. All that growth requires nitrogen, and the extensive root systems of these crops are good at taking it up, preventing leaching. The N in the crop tissues can become available to subsequent crops as the residue decomposes.

When seeded densely, these crops can serve as smother crops, helping to suppress weeds. The book Managing Cover Crops Profitably recommends seeding rates of 35 lb/acre if drilled, 40-50 lb/acre if broadcast. Seeding depth should be 0.5 to 1.5 inches: you can plant shallow in heavier soils, but sow more deeply in sandy soils. The crop should be planted after the threat of frost in spring and before July 15 to allow for maximum growth. Planting with less than six weeks until frost will result in unsatisfactory dry matter production. Warm soil temperatures, over 60°F, are required for germination.

Planting with a seed drill into a well-prepared seedbed will result in a better stand and requires less seed than broadcasting followed by light tillage. Although row spacing does not affect yield, narrow rows are better for cover cropping. A good stand is important for dry matter production and weed suppression. Make sure that soil pH is between 6 and 7, then apply 40 to 60 lb/acre of nitrogen at planting to ensure plant establishment and stimulate plant development.  In some soils, especially sandy soils, topdressing with an additional 25 to 50 lb of nitrogen after mowing will improve growth.

Mowing can be used to increase the extensive root system of these crops. Repeated mowing also causes the root system to penetrate deeper, helping to loosen compacted soil. Mowing can be done several times during the season depending on rainfall and management. Mowing is necessary to encourage tillering, increase vegetative growth, prevent seed head formation, and get maximum dry matter production. Without mowing the crop can become unmanageable and hard seed may be set that will produce volunteer weeds in subsequent crops. When the crop is approximately 18 to 36 inches tall it should be mowed, chopped, or flailed. The plants should not be clipped too closely (less than 8 inches) or they may weaken or die. Frequency of mowing will depend on seasonal environmental conditions and fertility. At the end of the growing season the crop should be mowed again, just prior to a killing frost. Green crop residue from young plants decomposes quickly. However, residues from older, larger plants decompose slowly due to their high carbon to nitrogen ratio.

Some studies suggest these crops can be used to suppress certain species of nematodes, as a result of the release of nematicidal compounds during decomposition. For this purpose, it is important to finely chop and incorporate top growth into the soil when still it is still green and before a killing frost, then run a cultipacker across the field to firm the soil.

Prussic acid poisoning is a concern if you plan on feeding these crops to livestock. The danger of poisoning is highest in the early growth stages and following a light frost. Do not pasture livestock until the crop is 18 to 24 inches tall, rotating pastures to prevent grazing of young regrowth, and removing livestock if new shoots develop after a partial kill by frost. Hay should be made when the grass is in the boot stage. Poisoning of horses has been reported; they should not be allowed to graze Sudangrass or sorghum-Sudangrass hybrids, and they should never be fed the hay.

Scout your Sudangrass and sorghum-Sudangrass fields for aphids. Sugars in the plant can attract aphids. Aphids can transmit plant diseases and may need to be controlled if they are a potential problem for nearby crops.

Wednesday May 9th, 4:00 pm, Plainfield VT

Richard Wiswall and Sally Colman run Cate farm, where they have 7 greenhouses that produce greenhouse tomatoes, other vegetables, bedding plants, flowers and herbs. Over the past few years they have made many innovations, including the installation of homemade bottom-watering benches, a trolley system for transporting trays between houses, and modifying all their oil furnaces to run on biodiesel that is made on the farm from local waste vegetable oil. Recently, Wiz also converted a G cultivating tractor to run on batteries. Directions: take Interstate 89 to exit 8, get off the ramp onto Route 2 headed
east, go nine miles, towards Plainfield. Look for a big log building (Plainfield Hardware) on the left, about 1/4 mile before turning left onto Coburn Rd. (Coming from the east on Route 2 Coburn Rd. is one mile after Plainfield, on the right.) Go one mile on Coburn Road, through covered bridge, to Cate Farm Rd. on the right. The farm is 1/4 mile up on the left. For more info or if questions, contact Vern Grubinger.


June 12 – River Berry Farm, Fairfax VT
July 30 – Edgewater Farm, Plainfield NH