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From the Crop Update of 3/28/2001

Cultural Practices - Dr. Terry Bates

Phylloxera:    Greg English-Loeb and I have been looking at the effect of phylloxera on Concord biology over the past couple seasons. Phylloxera is a grapevine pest that attacks different species of grapevines in different ways. Evolutionary scientists theorize that certain grapevine species developed a tolerance to phylloxera through co-evolution. Meaning, way back in history when phylloxera ancestors started to attack wild grapevines, some grapevines could survive the phylloxera attack and live to reproduce while other grapevines simply died out. Survival of the fittest (as Darwin would say) in this case went to the vines that could bend but not break under phylloxera pressure. This is the definition of tolerance as opposed to resistance.

Phylloxera tolerance comes in different forms. With some grapevines, phylloxera attacks the fine roots of the vine and weakens the root system but does not attack the leaves or kill the vine. Concord is a good example of this. In other grapevines, phylloxera attacks the leaves but not the roots. Some of the wild Eastern US grapevines like V. riparia and V. rupestris fall into this category. Rootstocks like 3309C that come from these wild vines have phylloxera free root systems but phylloxera susceptible leaves.

V. vinifera grapevines did not co-evolve with phylloxera; therefore, tolerance was never selected for (in an evolutionary sense). So when phylloxera was introduced into Europe and California, it attacked the vinifera roots and killed the vines. The solution to this problem was to graft the vinifera shoots onto rootstocks that were not attacked by phylloxera. Grafting vinifera is essential in vineyard soils where phylloxera is present.

So what does all of this have to do with Concord production in NY? Isn't Concord tolerant to phylloxera? Isn't the whole industry own-rooted? Isn't it expensive to replant on a rootstock? All fair questions.

As you have heard me say many times before, a healthy root system that does its job in water and nutrient uptake is the key to adequate vine size. Adequate vine size is the key to optimal yield and quality. Poor soil pH is a stress on Concord roots for nutrient uptake. Poor weed control is a stress on Concord roots for water absorption. Phylloxera is also a stress on Concord roots because it inhibits the absorptive surface area of the root system. Furthermore, work at UC Davis has shown that phylloxera injury also provides sites of root fungal infection that can have a secondary negative effect on grape roots. Understanding the degree of impact phylloxera has on Concord production is the first step in combating the root stress.

One way to deal with phylloxera on Concord is to graft Concord onto a phylloxera resistant rootstock like 3309C. Dr. Shaulis did just that back in the 1950's and it gave him bigger Concord vines with little other inputs like fertilizer or weed control. The big healthy phylloxera-free root system gives the vine all it needs on the Fredonia lab site - sometimes the vine size it too big. The other way to deal with phylloxera is to leave Concord on its own root system (a weaker root system) and give the roots what they need through more intensive management. Past and Current research on fertilization, soil pH, weed management, etc. all look at giving Concord roots adequate water and nutrients to grow a vine of adequate vine size. Phylloxera is just another 'aphid in the ointment' that we must deal with and not ignore.

As you all know and may experience, not all vineyard sites are very good and adequate vine size may be difficult to achieve even with intensive management. Rootstocks may be a tool for boosting vine growth on these sites. Dr. Peter Cousins and I are starting a new experiment that looks at several rootstocks on both Concord and Niagara on two soil types. Before you rule out rootstocks as a tool, remember that Dr. Shaulis deemed rootstocks 'essential' for Concord replant sites back in 1974.