Armillaria root disease (also known as oak root fungus) is a chronic problem on grapevines and has been known in California since at least the 1880’s (Gardner & Raabe, 1963). Despite the long history of this disease on grapevines, published research on disease progression in vineyards and control treatments for grapevines is scant. The purpose of our research is to gain an understanding of how oak root fungus infects grapevines and spreads within vineyards with the ultimate goal of developing a reliable management plan for control of Armillaria root disease. Armillaria mellea does not enter vineyards by wind-blown spores. Inoculum is present belowground in the form of infected roots. Removing all roots from the soil would likely ensure permanent control of root disease, but this is a difficult, and unrealistic, task. Pre-plant chemical treatments, such as soil-fumigation with methyl-bromide or sodium tetrathiocarbonate (formulated as Enzone, Entek), are temporarily effective; they often succeed in killing some of the inoculum. Unless fumigant reaches all underground inoculum, permanent control will not be achieved. Based on the lack of effective chemical controls and the frequency of A. mellea on the roots of native hosts, resistant rootstocks may provide long-term control of Armillaria root disease in vineyards. We have two screening experiments in progress that include 20 different rootstocks. Rootstocks that experience less mortality, such as 11 OR and Freedom, tend to exhibit defense responses, such as formation of callus tissue, or escape infection altogether more frequently than rootstocks that experience more mortality, such as Riparia Gloire or 039-16. Although final results for both experiments will not be gathered until Fall 2000, preliminary data show that some rootstocks are more tolerant of infection than others. Tolerance of infection may achieve control of root disease by decreasing the rate at which the fungus spreads on individual root systems which, in turn, allows infected vines to produce new, healthy roots in order to provide their shoots with an adequate supply of water. Decreasing growth of existing infections also provides less “food” for the fungus and, therefor, less energy to cause new infections. Our research on the epidemiology of Armillaria root disease in a Sonoma County vineyard over two growing seasons has provided valuable information on symptom development, replant success, and rate of spread of existing disease centers (clusters of dead/dying vines) in a meter-by-meter planting. In terms of symptoms, we found that most vines that succumbed to root disease developed symptoms in late August and died a few weeks later. However, 88%of the vines we observed with symptoms in 1998 are still alive, suggesting that appearance of symptoms is rarely followed by immediate death. The large replanting effort that was undertaken in this vineyard in 1995 is still promising; of the 191 replants, only 9 have died. Existing disease centers are spreading; of the 54 vines that died in 1999, 28 neighbored vines that died in 1998. Isolates of A. mellea collected from new disease centers were identified as the same fungal individual identified in existing centers.
/wp-content/uploads/2017/09/AFV-Header-Logo.png 0 0 AVF /wp-content/uploads/2017/09/AFV-Header-Logo.png AVF1999-10-18 09:43:462017-10-18 09:44:23Studies in the Biology and Control of Armillaria Root Disease of Grapevines