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'musc-mg' ~ electronic advisory from NC Cooperative Extension Service for muscadine growers
Vol. 4 No. 2
April 10, 2008
Contributors to this advisory:
Connie Fisk, Muscadine Extension Associate, Dept. of Horticultural Science, NCSU
Bill Cline, Extension Plant Pathologist, Dept. of Plant Pathology, NCSU
Hannah Burrack, Extension Specialist, Dept. of Entomology, NCSU
Topics in this issue:
*Impending cold weather
*Botryosphaeria and vine dieback
*Cutworms on muscadines
Impending cold weather
I’ve been hearing some concern about the extended weather forecast showing temperatures dropping into the 30s in the next couple of weeks. Three reasons to relax: 1) the vines are just starting to break bud and are not nearly as far along as they were last year at this time, 2) based on what we learned from damage following the 2007 Easter Freeze, the critical temperature appears to be 24-25 ºF and even if the primary bud is damaged muscadines have several back-ups (secondary, base and latent buds), and 3) we don’t have any proven protective measures for muscadines (so there’s not much you can do and worrying certainly won’t help). Keep in mind that what we experienced last year was a rare event and muscadine vines are very resilient.
Botryosphaeria and vine dieback
The plant pathogenic fungus Botryosphaeria is likely to cause an increase in grape vine dieback in 2008, due to cordon and trunk injury that occurred during the Easter freeze in April of 2007. The disease appears as a rapid dieback of cordons or entire vines, and dieback may occur at any time during the year. A cross section of the infected stem often shows a wedge of discolored wood (see pictures).
Botryosphaeria is a wound-infecting pathogen found in pruning wounds and other injuries. It is widespread and common -- even healthy plants will often have some dead wood or pruning stubs that are colonized by this fungus. Fortunately most infections do not result in disease or death, because the plant is able to "wall off" the infected area.
Messy wounds or large "amputations" take longer to heal and are more difficult for the plant to wall off. Such wounds are likely starting points for the infections that lead to dieback or death. The plant may be infected for weeks or months without showing signs of disease, then die suddenly when stressed by drought or a heavy crop load.
Fungicide sprays and wound-sealing compounds are generally not very effective against dieback. There is some benefit to pruning to remove infections by cutting back to healthy wood.
This disease is usually diagnosed by field symptoms, but if needed, growers can send samples to NCSU for diagnosis. Your county extension agent can tell you how to send samples to the Plant Disease and Insect Clinic in Raleigh, or to Bill Cine at the NCSU Horticultural Crops Research Station in Castle Hayne. Fresh, whole samples with the trunk/crown/root in one piece are best, but the fungus can also be recovered from symptomatic trunk sections or stem pieces. Samples for diagnosis should have both green (healthy) and brown (dying) portions.
Cutworms on muscadines
The following information was put together in response to a recent call about cutworms on muscadine vines. It’s not common in North Carolina but is something to be aware of in case you’re trying to diagnose mysterious damage on your vines.
Have you observed insect damage on buds or new growth? Cutworms could potentially be the culprit. If you think this may be the case, before treating you should go out at night to confirm that cutworms are causing the damage and not something else. Cutworms found at night or day curl into a tight ball when disturbed. Depending upon the species, they may be present in ground cover or under loose bark during the day. Cutworms only feed at night, so if you have high numbers and associated damage, you should be able to see them feeding after dark. Visit the University of California webpage at http://www.ipm.ucdavis.edu/PMG/P/I-LP-PSAU-CD.001.html for a photo of a cutworm feeding on a Vitis vinifera bud.
Sampling should be pretty extensive, because cutworm populations are clumped, so looking at a few random vines could miss populations. A good place to start would be where you have seen populations at ground level. In V. vinifera in California, they recommend treating when 4% of buds are damaged, but this threshold was developed across varieties, including those which may have relatively fruitful secondary buds. In these cases, the vines can compensate for early season damage through the secondary buds. I would not rely on this compensation in muscadines and would tend to be more conservative if you observe damage.
Culturally, if you know you have a cutworm problem, you should avoid weed control measures until after bud swell, because this could drive the cutworms up into the plants
If cutworm damage is observed, there are several control options. Sevin (carbaryl), Lannate (methomyl), and Deligate (spinetoram) are conventional options, and Entrust (spinosad) is an organic material. If you decide to treat, consult Hannah Burrack, NCSU Extension Entomologist, for rate information. If mites have been a problem in the past, avoid using carbaryl or methomyl, because these materials can harm mite predators. All of these materials are hard on bees as well and should not be applied when bees are foraging.
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 meeting will start at the Johnston County Cooperative Extension Office and include an overnight bus tour of 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 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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