'musc-mg' ~ electronic advisory from NC Cooperative Extension Service for muscadine growers
Vol. 3 No. 5
July 27, 2007

Contributors to this advisory:
Connie Fisk, Muscadine Extension Associate, Dept. of Horticultural Science, NCSU
Bill Cline, Extension Plant Pathologist, Dept. of Plant Pathology, NCSU
Wayne Mitchem, Extension Associate – Vineyard Weed Management, Dept. of Horticultural Science, NCSU
Ken Sorensen, Emeritus Professor, Dept. of Entomology, NCSU

Topics in this issue:
*Current Acreage Estimates – Please send updates for your county
*Re-training damaged vines
*Diseases of leaves and fruit
*Spotlight on common purslane
*Identification and management of grape root borers

Current Acreage Estimates – Please send updates for your county

The current acreage estimates for muscadine production in NC are here.  Every time I speak I’m told that the numbers are way off and I recently heard that NCDA is actually reporting a decrease in muscadine acreage (which I can’t believe), so I need your help in keeping the acreage estimates as accurate as possible.  I’ve heard back from most of the County Extension Agents, but even they don’t always have the most up-to-date figures.  So, if you’re a grower, please look at the acreage for your county and let me know if changes need to be made to the acreage or number of growers in your county (connie_fisk@ncsu.edu).  For this estimate we’re interested in all commercial acreage, even if it’s a quarter acre of fresh market varieties.  Thanks! 

Re-training Damaged Vines

We have been in the field a lot this year looking at damaged vines, many from the freeze that hit the SE in April, but also from crown gall as a result of cold damage, and from lightning damage and herbicide injury.  These events cause significant damage, especially to young vines, and how affected growers choose to react will determine the long-term health of their vineyards.  For vines with girdled, galled, or cracked trunks the best course of action is to cut the trunk below the damage and train a sucker or shoot that breaks below the cut to be your new trunk.  Growers that want to wait and see if the vine pulls through are just postponing the inevitable – the damaged vines will eventually decline.  It would be better to remove the damaged wood this year and get started re-training.  For recommendations on re-training vines damaged by freeze, crown gall, lightning damage, etc. please see the “Allowing Multiple Shoots…” and “Allowing Multiple Suckers…” articles.

Diseases of leaves and fruit

On farm visits this week we began to see higher incidence of disease symptoms on leaves and fruit. Angular leaf spot is appearing on unsprayed vines, and small black scab-like lesions on fruit, caused by the black rot fungus, are also becoming evident. Now is a good time to assess how well your foliar fungicide program is working. If you are dissatisfied with the level of disease control achieved, consider starting sprays earlier in 2008. Remember, by the time diseases become visible, much of the damage that will occur that season has already gotten started. To be effective, fungicidal sprays must be applied prior to the appearance of symptoms! It may also help to improve coverage by modifying your sprayer, or you may wish to alternate to a fungicide with a different mode of action.

Whether you apply fungicide sprays from now until harvest should be dictated by historical levels of fruit rot diseases in your field. Vineyards with low historical disease incidence may opt to discontinue fungicide sprays, while those with a history of fruit rot problems should plan to make one or two more spray applications. Some other general rules that may help in decision-making: 1) Fungicides applied in early season (from bloom to mid-summer) are more effective than those applied from now until harvest, 2) Fruit rot diseases are more severe in wet years, 3) Fresh-market cultivars are usually more susceptible to fruit rots than are wine cultivars, and 4) Bronze-colored cultivars are more susceptible to rots than dark ones.  If you are unsure which fungal pathogen is causing the spots on your leaves and/or fruit and want to know what to do about it in the future, please see the article, Muscadine Grape Diseases and Their Control, by Bill Cline.

Spotlight on common purslane

There are many weeds in the vineyard this time of year that cause growers grief.  One I’ve been getting a lot of questions about lately is purslane.  Read on for how to identify it and what to do about it if it is a problem in your vineyard. 

Identification: Common purslane is a prostrate growing plant that has very succulent fleshy leaves and stems (see http://www.ppws.vt.edu/scott/weed_id/porol.htm).  It is a summer annual and is adapted to poor, compacted soils as well as drought conditions.  Common purslane is a common weed in gardens, horticultural crops and agronomic crops. 

Seedling plants have fleshy green stems that can become maroon over time.  Leaves are opposite or nearly opposite and have the shape of a raindrop.  The leaves are very thick, waxy and succulent.  Common purslane flowers are yellow. 

There are a number of purslane species found in NC and throughout the world.  All of them have the same succulent, waxy appearance although leaf shape and the presence or absence of hairs and flower color may change.

Control: Common purslane is susceptible to most preeemergence herbicides used in vineyards, therefore the first step in controlling it is a good preemergence  herbicide program with simazine + oryzalin (Surflan and others) or Chateau.  It is more difficult to control postemergence however glyphosate is fairly effective while paraquat provides poor postemergence control.

The other side of the story: Purslane isn’t all bad.  People from various cultures around the world praise the virtues of purslane and use it in soups and salads, among other things.  You can find several recipes on the internet; perform a Google Search for “purslane recipe” and you’ll be amazed at the diversity of uses for this “herb.”  If you’re really interested (what better way to diversify your farm stand offerings than to sell something that already grows everywhere) Frances Robinson wrote a 70 page book in 1999 called “Purslane: The Incredible, Edible Weed” (it even comes with a packet of seeds in case you don’t have enough already growing on your farm – did you know that a single plant can produce up to 52,300 seeds?). Purslane leaves are reported to have five times the Omega-3 fatty acid found in spinach and are also high in vitamins C and E and beta-carotene.  So next time you find purslane growing somewhere you don’t want it, hand-pull it and use its succulent leaves in your next entrée – that’ll teach it!

Identification and management of grape root borers

Adult grape root borers emerge from pupal casings at the soil line during July and August.  You will see shed pupal skins near the base of vines if you have an infestation.  Adult grape root borers resemble wasps, but are much more sluggish.  Adults will mate and the females can lay up to 500 eggs on weeds, leaves, and the base of grapevines during their 7 day life.  During egg laying they can easily be approached and killed.  The eggs hatch in about 15 days and enter the soil in search of roots.  Once the borer finds a root it will burrow into it and if damage is extensive you will begin to see leaf discoloration and wilting, loss of vigor and productivity, and eventually vine death.

There are many natural enemies of the grape root borer including barn swallows, mockingbirds, crested fly catchers, larvae of fireflies, a number of fungi, and a species of nematodes.  Vineyard surveillance during July and August can result in reduced infestation through elimination of adult females.  If your vineyard is known to have grape root borers and you want to try to control them chemically, you can apply Lorsban 4E at the rate of 4.5 pints in 100 gallons of water.  Apply the diluted mixture to the soil at the base of each vine once each year, 35 days before harvest.  The solution should not touch the fruit or foliage.  Providing a physical barrier (such as plastic, bark mulch, Leno cloth, or ridges of soil placed around the base of vines) may also provide grape root borer control by inhibiting adult emergence.

If you have a particularly troublesome disease, weed, or insect in your vineyard that you would like to see in a musc-mg spotlight, please email connie_fisk@ncsu.edu

Upcoming Events

• Don’t miss the 34th Annual NC Muscadine Grape Association Annual Meeting, Trade Show, and Bus Tour August 2 and 3, 2007.  Visit http://www.ncmuscadine.org for complete details.  (One pesticide credit available for each day of this meeting.)
• Mark your calendar: Muscadine Field Day, September 12, 2007 at the Castle Hayne Research Station.  Details to come in August.
• Planning is underway for the 3rd annual North Carolina Muscadine Harvest Festival at the Duplin Commons Agribusiness Center.  Plan on joining us for educational seminars, wine tasting, and live music Sept 28-29.  See http://www.muscadineharvestfestival.com for details.

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