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'musc-mg' ~ electronic advisory from NC Cooperative Extension Service for muscadine growers Contributors to this advisory: Topic: Recent developments in the saga of the 2007 Easter Freeze… The good news and the bad news… First the bad news: While many of the growers with vineyards hit hardest by the 2007 Easter Freeze chose to follow the recommendations to prune their vines back beyond any splits that appeared, we are continuing to witness further splitting of cordons and trunks in these hard hit vineyards, now over three months after the freeze event. And for those growers that chose to wait and see (read: not cut off damaged wood in hopes that the vine might repair itself and support the developing crop), we are now beginning to see cordons collapse and die. These should be removed with winter pruning and a new cordon trained to the wire. The good news is that in vineyards where damaged cordons and trunks were removed, we are seeing quite a bit of growth of healthy shoots and suckers to train as replacements. Many of the replacement trunks are already to the wire and replacement cordons are progressing down the wire. Also good news, we are seeing surprisingly greater fruitfulness than expected on base and latent buds that have broken where fruiting spurs were “fried” by the Easter Freeze. The result is a greater crop load than we anticipated, though still much lower than we would have had otherwise. Crown Gall A recent visit to vineyards in western NC revealed quite a bit of crown gall formation on trunks of young Carlos and Noble vines. Crown gall (Agrobacterium sp.) is a disease caused by a bacterium that causes fleshy, irregularly shaped growths. (These galls are different than the callus we’re seeing running the length of splits in the trunks and cordons of freeze damaged vines – see the pictures of callus and crown gall below as the initial symptoms can be confusing.) Crown gall has the potential to appear in every vineyard but only appears after an injury event, such as cold damage. Unfortunately, after it appears, there’s not much that can be done to stop the gall itself. While a few products are on the market that claim to stop or reverse gall growth, none are known to have any benefit and will probably just be a waste of your money. Figures 1 and 2. Crown gall vs. callus on freeze damaged vines
In the Muscadine Grapes book (see below for ordering information), the authors recommend removing the vines after they decline in vigor and productivity. In this case though, the vines are still too young to start producing, so the grower has two options: wait until the vines deteriorate on their own, or cut the vine (trunk in this case) below the gall and train a new trunk from a sucker or a shoot that breaks below the cut. (For recommendations on retraining cordons or trunks after a severe pruning cut, please see “Allowing Multiple Shoots…” and “Allowing Multiple Suckers…” articles.) Of course, if there’s another cold injury event, the crown gall will probably show up again. Be on the lookout for vine borers… Injuries like crown gall put vines under stress, which attracts borers like shot hole borers, Ambrosia beetles and dogwood borers. Give damaged vines good horticultural care, including care for canker. Thiodan or lorsban sprays directed to the trunks can offer some protection. Borers are more serious in March and April. Hence treatments now would ease the mind but next spring would be more effective. Monitor and trap borers starting in March of next year. Wound dressings may help deter the borers as would removal of seriously affected vines. Continue to check on damaged vines for presence of vine borers (feeding frass [see photo below] or actual borers). Figure 3. Signs of vine borers
Weed Management It is desirable to keep the area between your rows mowed and a weed-free strip underneath the vines for several reasons. Controlling weeds will facilitate air movement (thereby helping to minimize disease pressure), promote worker efficiency and equipment movement, and minimize competition for nutrients and water (which would reduce vine growth and yield). Weeds provide egg-laying sites for grape root borers and interfere with insecticides used to control them. Remember, we want to minimize insect and disease pressure and water stress to freeze-damaged vines. Herbicide use is the most economical means for maintaining a weed-free strip in the vineyard rows. Visit the Muscadine Grape Integrated Management Guide for recommended herbicides and application rates for post-emergence weed control. Remember to protect green tissues from herbicide spray contact with a shield or grow tubes. Propagating Muscadines If you anticipate needing to replace freeze-damaged plants or just want to add a few to an existing planting, you may want to check out the new publication Propagating Muscadines. Now is a good time to take cuttings so you’ll have vines to plant next spring. On the other hand, if you plan to buy your plants, get your orders in soon so they’ll be ready to pick up and plant (after danger of frost has passed) next spring. Muscadine Grapes Book – Ordering Information The 2001 book Muscadine Grapes, by FM Basiouny and DG Himelrick, is a comprehensive source of information on all aspects of the muscadine grape. Written for growers, horticulturists, educators and researchers, this book provides a wealth of information on genetics and breeding, diseases, harvesting, processing and marketing, and much more, and would be a great addition to your bookshelf. It is available at from ASHS Press for $59.95 plus shipping. Announcements
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