Stop the bot: grapevines, fungus and fungicides

Grapevines Photo by Christine und Hagen Graf CC BY 2.0

When it comes to grapes, people think of fresh table grapes, grape juice, jam, jelly, raisins and, of course, wine! However, these fruit products on your table take more than just a grape to make. Behind the pictures of vines dripping with ripe grapes and their tasty products, there are some important challenges which need to be dealt with step by step.

Vineyards during winter periods Photo by (Elba) Dave Shewmaker CC BY-NC-ND 2.0

In all major grape-growing countries, one of the most destructive diseases are grapevines trunk diseases caused by various fungal groups named botryosphaeriaceous (bot) species. The diversity of these fungal species makes it more complicated for disease diagnosis and the creation of control strategies. 

In New Zealand, a range of fungi species can cause dieback and canker in grapevines and other woods host (typically Neofusicoccum australe, N. luteum, N. parvum and Diplodia mutila). When infected, the upper parts of the grapevine’s trunk will start to limit growth and development. First symptoms are noticed in older vines, around five years old, although the infection usually begins in younger vines. These fungi survive through winter periods on dead wood within a dormant structure called pycnidium.

But how do these pathogens invade the plant? 

The answer is plant wounds. Grapevines require trimming and pruning to remove excess wood for the next season’s growth and also to produce more fruit. However, during rainy periods, the spores are released from pycnidium, penetrate the tissue through pruning wounds and damage the vine’s vascular system. Therefore, wounds protection tends is a solution to reduce the disease severity on the grapevines.

Pruning vines Photo by Stefano Lubiana CC BY 2.0

There are a huge number of fungicides in use to control the wood disease caused by bot species. Which fungicides should we use? And how effective they are? Unfortunately, no fungicides had been evaluated against the pathogens in New Zealand until a study by Lincoln University staff, Nicholas Amponsah, Eirian Jones, Hayley Ridgway and Marlene Jaspers, that tested the effect of fungicides on mycelium growth, and conidia germination of three botryosphaeriaceous species (N. australe, N. luteum and D. mutila) in New Zealand grapevines.

The Lincoln scientists observed the growth of pathogens treated by different fungicides in the laboratory. They found that nine out of 14 tested fungicides showed the ability to inhibit the mycelial growth of three pathogens. These fungicides, from most to least effective were: carbendazim, flusilazole, thiophanate methyl, tebuconazole, iprodione, fenarimol, procymidone, mancozeb and chlorothalonil. Carbendazim, iprodione, mancozeb and flusilazole were most effective in potted vines. However, in the vineyard, the most effective fungicides were flusilazole, carbendazim, tebuconazole and thiophanate methyl. 

Identifying the effective fungicides to apply at each particular stage of grapevines growing (e.g. potted vine or in the vineyards) will allow grapevine growers to select the most appropriate fungicides and reduce the amount of redundant control. 

Vineyard in the Coromandel Peninsula, New Zealand. Photo by Chris Gin CC BY-NC-ND 2.0

To be successful in the control of bot diseases, the use of fungicide applications alone may not fully effective. Not only do we need to understand the life cycle of the grapevines, but the research teams also recommended that grapevines wounds should be protected with the above fungicides after trimming and pruning. Avoiding pruning during or directly after rainfall is also recommended, as the spores can be released by rain-splash. Combining cultural methods and chemical applications will provide effective control of the grapevines disease.

Delayed management may cost a lot of money, time, and delicious grapes. That’s why I recommend that, to stop the bot, disease prevention is better than cure.

Patanun Kanjanamaneesathian is a postgraduate student in the Master of Science. She wrote this article as part of her assessment for ECOL 608 Research Methods in Ecology.

Reference: Amponsah, N., Jones, E., Ridgway, H., & Jaspers, M. (2012). Evaluation of fungicides for the management of Botryosphaeria dieback diseases of grapevines. Pest Management Science, 68(5), 676-683.

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