'musc-mg' ~ electronic advisory from NC Cooperative Extension Service for muscadine growers
Vol. 4 No. 3
May 15, 2008

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

Topics in this issue:
*Tissue Testing
*Grapes Dropping Off Before Maturity
*Bermudagrass: A Perennial Problem
*Insect and Disease Pests During Establishment
*2008 Survey of Muscadine Grape Acreage in North Carolina

Tissue Testing
It is important to take tissue samples every year to monitor the fertility of your muscadine vines.  Ideally this is done once in mid-May or any time before bloom and again in the second or third week of June.  The May test is primarily to assess the need to apply boron while the June test will help you determine whether or not your vineyard requires a late-June application of nitrogen.  The tissue sample should contain 12 to 15 leaves of one cultivar that are representative of the entire vineyard.  The leaves should be opposite flower/berry clusters.  Don’t pull leaf samples from shoots with no flowers or newly set berries. You should choose the third to fifth leaves back from the growing point, immediately twist off the petiole, and place the leaves in a paper bag or envelope.  Sampling paperwork can be obtained at your County Extension Office or on the NCDA&CS website.  Send the samples to the NCDA – Agronomic Division in Raleigh for analysis along with a $5 fee per sample.  The results are typically available via their website within a few days. 

Recommended nutrient levels are:

Grapes Dropping Off Before Maturity
Muscadine growers (especially homeowners) often call their local Extension Agent to find causes for poor yield. They usually say that for the past several years they've seen good fruit set, but that the grapes drop off the vines once they get about the size of a pearl. There are several possible causes:

1.  Poor fruit set is a common complaint on backyard vines, but almost unheard of in well-managed commercial vineyards with known cultivars.  This suggests that the problem is cultural.  A common cause of low yields in backyards is thin, weak growth caused by lack of proper pruning, or by competition from nearby trees.  Home vines are often grown on an overhead trellis, and may not be pruned correctly (or at all).  Such vines are very productive when young (around years 4-7), but eventually become a mass of thin, unproductive wood due to lack of pruning.

2.  Some heirloom vines are low producers.  We have been collecting cuttings from old vines at abandoned homestead sites in southeastern NC.  Some of these old clones produce very little fruit, even with the best of care.  If the vine has been passed down for generations, there is a chance it is inherently low-yielding.

3.  Some fungal pathogens (powdery mildew, bitter rot) can attack flowers and fruit at an early stage, causing poor set or fruit drop.  Look for a white "haze" on the surface of young berries (powdery mildew), or black spots, streaks, or shriveling of flower clusters and small fruit.  Near harvest, bitter rot can also cause drop of large green berries.

4.  Insects may feed directly on flowers and small berries.  Look for Japanese beetles and June beetles feeding on flower clusters.

5.  Stink bugs can cause severe fruit drop on muscadines.  Developing berries punctured by stink bugs drop off without any obvious injury visible on the surface, but will have one or more dead, brown seeds when cut open in cross-section.  Stink bug damage occurs when grapes are sizing but before the seeds harden.

6.  Poor pollination can surely occur due to adverse weather, but is rarely reported from commercial vineyards in NC.  Dry weather (drought stress) has been implicated in fruit drop on muscadines.

7.  Something called 'dry calyptra' has been reported from Georgia on female-flowered vines.  The calyptra is the cap that covers the individual flowers, and if it does not fall off, that flower cannot be pollinated (resulting in poor fruit set). This isn't a problem in self-fertile cultivars because they are often pollinated before, or as, the cap is falling off.

8.  Some cultivars are female-flowered and must have a pollinator in order to set fruit.  Unless there just happens to be a wild male vine in the woods nearby, pollination will not occur on a female vine (i.e., no fruit) unless a perfect-flowered cultivar (like 'Carlos' or 'Noble') is planted close by. This is often the culprit when a productive vine stops producing after development removes surrounding woods.

9. Boron deficiency may also result in poor fruit set. Visible symptoms generally do not appear until the vine is critically deficient in this micronutrient, so foliar analysis is important in monitoring boron status (see above for information on NCDA&CS tissue testing).  For mature vineyards, a common recommendation has been to apply 5 pounds per acre of Borax (10 percent) every 2 years or spray annually with 1 pound per 100 gallons of water of Solubor (20 percent) just before bloom. For mature backyard vines 2 Tablespoons of Borax can be mixed in with the fertilizer and spread over a 20 ft x 20 ft square around each vine every 2 to 3 years, before bloom.  Boron deficiency is more likely on sandy soils with high pH.  Excessive boron causes injury; do not exceed boron recommendations.

Bermudagrass: A Perennial Problem
Controlling bermudagrass is a considerable challenge but one worth accepting.  Bermudagrass is very competitive and will reduce the growth of young plants as well as fruit yields in mature plantings of grape, apple, peach, blueberry, and blackberry crops.  The good news is bermudagrass can be controlled in perennial fruit crops with Poast, Fusilade, or clethodim (Select, SelectMax, Intensity, and others). 

Application timing is critical to successful bermudagrass control.  An initial application should be applied to bermudagrass having 4 to 6” of new growth.  A second application will be necessary when regrowth occurs.  The second application and its timing are critical to successful control.  The bermudagrass must have recovered from the initial herbicide application before applying the second application.  Growers often ask how long should I wait after the first application before making the second application and there is no specific answer to that except to say the time frame can vary.  Factors affecting regrowth include soil moisture at the time of application, rainfall events after the application, and temperature.  The common mistake made with the second application is failing to apply it or applying it too soon. 

The table below provides herbicide rate range and crop restriction information pertaining to non-bearing uses as well as PHI information for each of the herbicides mentioned above.  On each of these product labels there is detailed information regarding bermudagrass control.  In addition to bermudagrass these products control johnsongrass and annual grass weeds like large crabgrass, fall panicum, goosegrass, and others.  If you have questions regarding the use of these products contact the local agent with the Cooperative Extension Service in your county.

Insect and Disease Pests During Establishment
New muscadine acreage is being established across North Carolina in 2008. Calls and emails from new growers concerned about insects and diseases are flooding our voicemails and email inboxes, but there isn't much to control for during establishment, with the exception of weeds. Growers should devote their time to training the vines' permanent framework and making sure to provide adequate irrigation.

Here are some pest management tips to keep in mind when establishing a muscadine vineyard:

1. During the 2 to 3 years required for establishment, few insects or diseases are usually encountered.  However, Japanese beetles can be a fairly severe problem.  They do not persist over the entire growing season but normally feed over a 4- to 6-week period and can be sprayed for as needed.  Japanese beetles feed on grass roots and may emerge in large numbers on land that was previously a well-established pasture.  If the vineyard is to be established in an old pasture, make an extra effort to kill grass during the growing season preceding planting.  Sprays and/or cultivation are effective methods for eliminating grass.  Consult the North Carolina Agricultural Chemicals Manual or your local Cooperative Extension agent for specific recommendations.

2. Growers inclined toward sustainable agriculture may be willing to accept a greater level of foliar damage.  Pheromone traps are commercially available for attracting Japanese beetles. Yes, I said "attracting", therefore do not hang them in the vineyard - hang them out in the woods.  Another possibility is application of milky spore disease which may help to control the grub stage.  This will also help to get rid of moles in the yard by eliminating the grubs they feed on.

3. Grape root borer is not a threat during the first 3 years.  Apparently the borer requires some degree of shade for successful establishment in a vineyard.

4. Symptoms of black rot may appear on the leaves of muscadines during the establishment period, but since no fruit is usually present and infections are not usually severe, sprays are not usually necessary.

2008 Survey of Muscadine Grape Acreage in North Carolina
(Surveys were mailed out in mid-April. If you did not receive one, you are probably not on our mailing list or we have an incorrect address for you. Please print off a copy of the survey here.)

North Carolina’s muscadine grape industry is growing.  In order to meet the needs of the industry statewide we need an accurate estimate of acreage and cultivars in production and any additional plantings that you anticipate in the next few years.  Please take a few minutes to fill out the survey and return it to Connie Fisk, Extension Associate – Muscadine Grapes, NC State University, Duplin County Cooperative Extension, PO Box 949, Kenansville, NC 28349.

All information collected will be confidential.  However, if you would like your information shared with the North Carolina Muscadine Grape Association or potential muscadine grape buyers please check the box at the bottom of the survey marked “yes” and sign and date the form.

Thank you for taking the time to respond to the survey.  The information collected will help adjust programming and influence the path of muscadine research, breeding and marketing efforts in North Carolina.  If you have any questions or comments please feel free to contact Connie by email (connie_fisk@ncsu.edu) or phone (910-296-2143).

Upcoming Events

• Mark your calendar for the 35th Annual NC Muscadine Grape Association Annual Meeting, Trade Show, and Bus Tour July 31 and August 1, 2007.  The tour will leave from Williamston, NC both Thursday and Friday, visiting vineyards and wineries in the northeast corner of North Carolina.  You don’t want to miss this fun-filled educational event.  More details to come in late May.
• Planning is underway for the 4th Annual North Carolina Muscadine Festival at the Duplin Commons Agribusiness Center.  Plan on joining us for educational seminars, wine tasting, and live music Saturday, September 27.  Visit http://www.muscadineharvestfestival.com for details.

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