THESIS OF DOCTORAL (PhD) DISSERTATION

Transcription

1 THESIS OF DOCTORAL (PhD) DISSERTATION VESZPRÉM UNIVERSITY GEORGIKON FACULTY OF AGRICULTURE CROP PRODUCTION AND HORTICULTURAL SCIENCES DOCTORAL SCHOOL Consultant: Dr. habil. GÉZA FISCHL university professor THE ROLE OF ENVIRONMENTAL CONDITIONS IN THE DYNAMICS OF EPIDEMICS OF UNCINULA NECATOR (SCHW.) BURR. Prepared by: ISTVÁN FÜZI Keszthely 2003

2 1 1. Background and research objectives Grapevine powdery mildew is one of the plant diseases of highest economic importance in Hungary. Research in the biology and overwintering of the pathogen, as well as in the ecological conditions of primary infection has become more intensive all over the world in the past two decades. The sexual form of the fungus and its epidemic role have especially got in the centre of interest. Studies have been published one after the other from America through Europe to Australia about the occurrence of the cleistothecial form of the fungus, the production and overwintering of fruiting bodies and the primary infection initiated by the ascospores released by them. Before and parallel with these investigations, some researchers conducted intensive studies on the epidemic role of mycelium overwintering in the buds and determined frost resistance of hyphae. In Hungary Lehoczky et al. started research to reveal the role of the cleistothecial form in epidemics, but the promising work stopped with the death of János Lehoczky (1993). Regular epidemics of grapevine powdery mildew provoking heavy losses in the first part of the 1990s, followed by the sudden decrease of their severity in 1996 pointed out that we know rather little about the disease process and the environmental conditions influencing it, and we should obviously revise and widen our knowledge. I have been dealing with grapevine powdery mildew since Being a student of the post-graduate education in plant protection at the University of Pannon Agricultural University (PATE), I prepared my thesis on complex plant protection in vineyards. From 1989 I carried out efficacy trials at the Plant Protection and Soil Conservation Station of County Tolna with new fungicides to control powdery mildew and to work out a management programme against the disease. During the evaluation and processing of these trials, especially regarding dynamics of epidemics, I frequently came across inconsistencies that I could not explain on the bases of my knowledge and the Hungarian literature data available that time. It was the main reason why I began to thoroughly study the dynamics of epidemics of grapevine powdery mildew and the biology of the fungus causing the disease. Therefore in 1997 I applied for the doctoral programme of PATE titled The effect of environmental conditions on the resistance to fungal diseases within the Theoretical bases of integrated pest management methods, in the frame of which I have dedicated myself to studying the role of environmental conditions on the dynamics of epidemics of Uncinula necator. 1

3 2 I set the following objectives for my studies: 1. Surveying the incidence of the overwintering forms of Uncinula necator in the wine-growing region of Szekszárd 2. Study on the susceptibility of the leaves and bunches of the common grapevine cultivars to powdery mildew 3. Study of cleistothecium production of Uncinula necator, analysis of the environmental conditions influencing the process 4. Study of the epidemiological role of antagonists parasitising powdery mildew fungus 5. Analysis of the annual and in-season epidemic curves of Uncinula necator in the wine-growing region of Szekszárd 6. Study of fungicide spray programmes to prevent powdery mildew epidemics in vineyards 2

4 Study areas and sampling sites 2. Materials and methods I have made observations on the dynamics of epidemics of Uncinula necator in the wine-growing region of Szekszárd since They mainly based on small- and large-plot fungicide trials where natural increase of pathogen populations could be monitored in the untreated control plots. I began studies on the cleistothecial form in I involved 14 vineyards of different cultural operations, nutrient supply and plant protection in the survey. I investigated the dominance conditions of the two overwintering forms, dynamics of epidemics of Uncinula necator, the relationship of infection level and production of cleistothecia, as well as level of parasitism of cleistothecia in all vineyards. A vineyard at Görögszó growing 4200 stocks of the variety Nosztori Riesling has been of major consideration, being an excellent site for studying both (cleistothecial and mycelial) overwintering forms of the pathogen due to the extremely high susceptibility of the variety to powdery mildew. I established several small-plot trials in this vineyard to get information on the effect of weather conditions and fungicide spray programmes on the production of cleistothecia by the fungus and the level of parasitism. In this trial I compared efficacy of four fungicides: Discus DF (50% kresoxim-methyl), Quadris (250 g/l azoxystrobin), Topas 100 EC (100 g/l penconazole) and Topas 100 EC + Karathane LC (350 g/l dinocap) in controlling powdery mildew. I applied the fungicides at the rate indicated in the label in both years, six times consecutively between flowers separating and the beginning of veraison. I studied the role of the primary inoculum in the epidemiology also in this vineyard at Görögszó between 1996 and 1998 at sampling sites duly separated from each other and left untreated for different periods (one, two or three years). I studied the role of the production site in the epidemiology in three vineyards of different exposure but growing the same varieties. I obtained data on the susceptibility of varieties in a vineyard of the Research Institute of Viticulture and Oenology of the Ministry of Agriculture and Rural Development at Pécs between 1997 and In the vineyard with high trellis (Moser) system I designated 10 varieties grown in Hungary in large areas. The varieties were managed under similar conditions and powdery mildew was controlled by applying fungicides 9-10 times a year. 3

5 Determination of infection level Since 1994 I have surveyed incidence of flag shoots indicating bud infection in all the vineyards involved in the study. I read symptoms on 500 stocks in each vineyard, except for the one growing Nosztori Riesling where every stock was examined, three times between bud burst and flowering. I surveyed level of foliar and fruit infections various times during the season in order to monitor dynamics of epidemics of Uncinula necator. Field assessment was made by estimating infection level on 50 leaves and fruits in small plots and 100 ones in larger vineyards and at the sampling sites of the variety study area. The randomly selected leaves were examined on the adaxial surface and where symptoms could be assessed, also on the abaxial surface. I assessed colonization rate of powdery mildew on the adaxial surface of leaves collected for cleistothecial studies, 30 leaves per small plot and 50 ones in larger vineyards and the variety study area Sampling and microscopic examination of samples Leaf samples were generally taken in the middle of October (also several times before it for studying the process of cleistothecium development) in order to survey the amount, maturity and parasitism of cleistothecia. Samples were taken randomly, 30 fully developed leaves in small plots and 50 ones in larger vineyards and at the sampling sites of the variety study area, equally from both sides of the grapevine rows. After a short storage at +1 o C or +2 o C, 5 discs of 1.13 cm 2 surface were excised from each leaf approximately from the same places, and the number of cleistothecia was counted both on the adaxial and abaxial surfaces, using a stereomicroscope at 30x magnification. I grouped the cleistothecia in four categories such as immature, semi-mature, mature and parasitised. I calculated the average of the obtained data on colonisation rate of Uncinula necator and the number of cleistothecia for each sample and referred the number of cleistothecia to 1 cm 2 leaf surface or a grapevine stock. In doubtful cases I checked parasitism using light microscopy. In 1997 I estimated the number of cleistothecia on bunches in a single vineyard (at Görögszó, in cv. Nosztori Riesling), using a similar method. On sampling sites where cleistothecia were produced in high numbers and with an even distribution on the berries, I took 1 bunch from each of 12 stocks before vintage. After a short storage, I cut discs of

6 5 cm 2 surface from the skin of each of 5 berries per bunch using a disc cutter, and counted the number of fruiting bodies in each category. Where cleistothecia were produced in low numbers and with an uneven distribution on the bunches, I washed them off with a wetting agent to filter paper funnels. I counted the number of mature cleistothecia remained on the bottom of the funnel using a stereomicroscope at 30x magnification. In spring 1997, before pruning I collected 100 canes of about 50 cm length from a few sampling sites of the vineyard with Nosztori Riesling grapes at Görögszó, and counted the number of cleistothecia using a stereomicroscope at 30x magnification Estimating canopy surface area of grapevine stocks For better use in practice, I referred the obtained data to one stock. For this, I designated 10 relatively regular stocks in different varieties of six vineyards with umbrella training system in autumn 1997 before leaf fall. I measured the whole leaf surface of these stocks and calculated the average of the obtained data Morphological study of the ascospores of the fungus I examined morphological maturity of ascospores in the cleistothecia by light microscopy studies at a magnification of 200x Meteorological observations I used the data of the meteorological station of the Plant Protection and Soil Conservation Station of CouQW\7ROQD6]HNV]iUG.HVHO\ for analysing weather conditions. I measured daily rainfall in the particular vineyards during the season. VL~W 2.7. Processing and evaluation of data I processed and evaluated data with Excel 97 software. I used the same programme package (Excel 97) for determining the polynomial function describing the relation between powdery mildew infection and 5

7 6 production of cleistothecia and the closeness of correlation. I calculated the average and the standard error of the average for the results of the years regarding susceptibility to powdery mildew of the studied grapevine varieties and production of cleistothecia of Uncinula necator in the particular varieties. I used analysis of variance and Fischer test for the statistical analysis of fungicide treatments. 6

8 7 3. Results 3.1. Incidence of the overwintering forms of the fungus and its importance in the vineyards of the wine growing area of Szekszárd I regularly found flag shoots indicating mycelial overwintering of Uncinula necator only in one of the fourteen studied vineyards, at Görögszó growing Nosztori Riesling grapes. These diseased shoots emerged from certain buds of canes heavily infected by powdery mildew, which had been affected by the pathogen early in the previous year. In 1996 and 1997 flag shoots were not found even in the Nosztori Riesling vineyard due to the hard winter before the season in both years. In these two winters temperature fell below the degree 13 o C, critical for overwintering hyphae. Incidence of flag shoots in 1994 and 1995 was rather high, they were shown on % of the stocks, however from 1998 on, this value has reduced to a very low level ( %). Flag shoots generally emerged from buds farther from the base of the cane (buds 5-10). The earliest start of infection by ascospores of Uncinula necator was observed also in the Nosztori Riesling vineyard at Görögszó. I found the scattered, tiny powdery mildew spots indicating it on the abaxial surface of leaves close to the stock between 12 May and 27 June, at different dates in the particular years. Symptoms appeared on bunches 2-4 weeks after observing them on the leaves; they could be caused by both primary (ascospores) and secondary (conidia) infections. The increase in rate of colonisation started even later on the adaxial surface of leaves. The first immature cleistothecia appeared days after observing the first symptoms of infection by ascospores (in July) in the untreated plots of the vineyard; first on the abaxial surface of the leaves, soon on the bunches and finally on the adaxial surface. Maturing process was short, it took days. Fruiting bodies appeared in all the studied vineyards if rate of colonisation of Uncinula necator on the leaves was over 1%. Their incidence in areas receiving intensive fungicide spray programmes restricted mostly to the adaxial surface of the leaves, while in neglected vineyards cleistothecia were produced also on the abaxial surface of leaves and on berries. 7

9 Process of producing cleistothecia of the fungus I monitored the changing number of cleistothecia in time at Görögszó in the Nosztori Riesling vineyard in In the untreated plots of the vineyard, presumably due to the difference between light and moisture conditions, the rate of colonisation of the pathogen increased first on the abaxial surface, then on the berries, finally (from August) on the adaxial surface of the leaves. In plots of the same vineyard sprayed till early August it is the common practice in Hungary the fungus could not significantly affect the abaxial surface of leaves and the berries due to the protective effect of fungicides (susceptibility of bunches stopped at veraison). On the adaxial surface of the leaves, remaining susceptible until leaf fall, first cleistothecia were produced after vintage, in the second part of September, and their number, in parallel with the raising level of infection, continuously increased until early October, reached its maximum (about cleistothecia/stock), while after it only the continued maturation could be observed. This process took place similarly in vineyards sprayed with efficient fungicides every year. A close correlation was observed between infection level on the adaxial surface of the leaves before leaf fall and the number of the produced cleistothecia every year between 1997 and 2001 (R 2 values for the five years were: 0.89; 0.95; 0.93; 0.90 and 0.74, respectively). The number of cleistothecia per grapevine stock was in the order of magnitude of hundred thousand for the average infection level of 5-20% and reached some millions for 25-50% rate of colonisation. Relationship between level of infection and number of cleistothecia could be well described by polynomial function Parasitism of cleistothecia The hyperparasitic fungi Ampelomyces spp. were present on all the 9 designated areas during the four-year long study between 1997 and 2000 on the colonies of Uncinula necator, and parasitised its cleistothecia. These mycoparasites did not appear in any of the studied vineyards in 1997; between 1998 and 2000 on certain surveyed areas in all the three years, while in other ones only in one or two years. I found the first parasitised powdery mildew colonies on the leaves in late August early September. Level of parasitism was much higher on the adaxial than on the abaxial surface of the leaves. Hyperparasites were present in 19 samples out of the 8

10 9 36 ones collected during the four years (incidence of 53%). This ratio was 11% for the abaxial surface of the leaves (i.e. in 4 of the 36 samples). Average level of parasitism of the cleistothecia on the adaxial and abaxial surfaces of the leaves was 8.3% and 0.8%, respectively. Incidence of cleistothecia parasitised by Ampelomyces spp. increased together with colonisation rate of Uncinula necator on the grapevine leaves. The higher the level of foliar powdery mildew was, the lower the proportion of immature cleistothecia and in parallel, the higher that of the parasitised ones were. The highest ratio of parasitised cleistothecia was recorded on leaves with 50-80% colonisation rate of Uncinula necator. 3.4 Environmental conditions influencing the production and parasitism of cleistothecia Weather conditions had a significant effect on the production and parasitism of fruiting bodies. The highest number of cleistothecia was produced on the foliage of grapes in the year (1999) when summer was mainly humid and rainy and autumn was mostly dry and warm. In the years with abundant rain in late summer and autumn (1998 and 1999), the number and ratio of parasitised cleistothecia were significantly higher than in the dry years (1997 and 2000). Comparing the same varieties of three production sites, I concluded that conditions were more favourable for the infection and cleistothecium production of Uncinula necator in vineyards at higher altitudes. In the study conducted at Pécs the rank of varieties in susceptibility was similar on the leaves in all the three years. Susceptibility of cv. Kékoportó (Blauer Portugieser) was by far the highest of all the varieties. It was followed by three varieties with similar susceptibility: Kadarka, Kékfrankos (Blaufränkisch) and Leányka (Mädchentraube). No considerable difference in susceptibility was shown on the further six varieties Olaszrizling (Italian Riesling), Piros tramini (Red Traminer), Muscat Ottonel, Chardonnay, Rizlingszilváni (Müller thurgau) and Cabernet sauvignon. Colonisation rate of Uncinula necator on the particular varieties showed a close correlation with the number of produced cleistothecia, while it was less close with the level of their parasitism. In 1998 when level of parasitism was high, the number of cleistothecia parasitised by Ampelomyces spp. was the highest on the foliage of Kékoportó grapes (16.1 cleistothecia/cm 2 ), while the ratio in proportion to the total number of cleistothecia was the biggest on cv. Leányka (55 %). 9

11 10 Fruits, except for cvs Kadarka and Kékoportó, were little affected by powdery mildew due to regular fungicide treatments. Comparing the leaf and bunch susceptibility of the particular varieties, there was a considerable difference on Kékoportó and especially on Kékfrankos plants which seemed to be relatively more susceptible than the other varieties due to such trait of their foliage. The efficient fungicide spray programme in summer significantly influenced dynamics of epidemics of Uncinula necator, it had an effect even on foliar powdery mildew in autumn, and via it on the production of cleistothecia and their parasitism by Ampelomyces spp. The efficacy of fungicides compared to each other and also on the particular organs of the plant (fruit and leaf) was considerably different. Best results were obtained on leaves and bunches by kresoxim-methyl in both years. Azoxystrobin proved to be much more efficient on bunches than on leaves, while it was the contrary with penconazole. Efficacy of penconazole conspicuously improved when used in mixture with dinocap Importance of primary inoculum in the epidemiology of Uncinula necator In 1997-ben, considering that I did not count the number of cleistothecia in 1996, I tried to estimate from foliar powdery mildew in the previous year and the number of cleistothecia present on the canes in spring before pruning how the amount of inoculum produced in the previous year affected infection level in the current year. In 1996 I found conspicuous fruit and foliar powdery mildew in the untreated plot of a single vineyard (at Görögszó in cv. Nosztori Riesling). Foliar infection of 41.3% in late August indicated that the number of produced cleistothecia exceeded one million per grapevine stock and they certainly reached maturity. In spring 1997 it was the only production site where I found cleistothecia (with morphologically mature ascospores) on the canes. Later, leaving the plot untreated again, it was similarly the single place of all the vineyards involved in the study where severe damage on the berries could be observed. I designated another untreated plot in this vineyard in a part which received an intensive fungicide spray programme in the previous year. I compared the two untreated plots for fruit powdery mildew seven times in 1997, and I always found big differences between them, though with a decreasing extent. The average rate of colonisation of the cluster surface was by four hundred times higher at the first assessment and nine times 10

12 11 higher in the last one in the plot untreated for two years than in the one left untreated only in one season (1997). This spectacular experiment was the result of basically two factors: the very big difference in the primary inoculum (ascospores) and due to the interrupted endemism, the low infection pressure characteristic of the whole wine-growing region during these two years of the study. I continued this experiment in I left untreated the plots not sprayed for the previous one or two seasons. I designated a third untreated plot between them at a place that received an intensive fungicide spray programme in both previous years. In autumn 1997 there were considerable differences among the three plots in the number and maturity of cleistothecia: fruiting bodies appeared later and therefore began to mature later in the plot treated in both seasons before this trial than in the ones left untreated for one or two years. In 1998 these differences were obviously seen at the first assessments of infection level, but they decreased with time, and finally they almost completely disappeared. All this means that in this vineyard at Görögszó the number (158,000) of mature cleistothecia per stock produced in autumn 1997 contained so high volume of inoculum (ascospores), the part of which, remaining for spring 1998 was enough for provoking local epidemics in the plot treated in both seasons before Effect of environmental conditions on the dynamics of epidemics of Uncinula necator Uncinula necator was considered the most important pathogen of grapevine provoking endemic epidemics in the wine-growing region of Szekszárd till the middle of 1990s. Most severe epidemics took place in 1994 when heavy losses were recorded in certain vineyards in spite of the strict pest management programmes. In 1996 however, endemism decreased to a minimum level and increased only slowly after it, while it reached the initial level by It is obvious that weather conditions had the highest impact on epidemic situation. However, it is not enough to analyse meteorological data recorded during only the actual period of fruit infection in order to understand relationships. It is clear, as the dynamics of epidemics of Uncinula necator is influenced by the environmental conditions affecting each overwintering and infecting forms of the fungus (cleistothecium, mycelium. ascospore and conidium). Epidemic curves of the pathogen in the particular years can be evaluated only by considering all these, changes in 11

13 12 the economic importance of grapevine powdery mildew occurred in the 90s can be explained only by that. In the wine-growing region of Szekszárd the period between flowering and berry touch of grapevine is generally warm and humid enough for the increase of conidia of Uncinula necator. In summer, as three climates (Mediterranean, ocean and continental) have effect in the region, the amount of rainfall is rather varying, but it influences in-season epidemic curve of the fungus during the time of fruit infection less than the amount of primary inoculum. It practically means that if primary inoculum is lacking, damage on berries cannot be significant even if weather conditions during fruit infection is very conducive to the disease. On the other hand, if high volume of inoculum is available, meteorological conditions cannot be so adverse to prevent the outbreak of local epidemics of the fungus. Susceptibility of varieties is a key factor in the annual and in-season epidemic curves of Uncinula necator. In addition to the susceptibility of bunches, that of the leaves has also a significant role in such trait of the varieties. In vineyards with intensive fungicide spray programmes, production of cleistothecia takes place in autumn on the leaves, mainly on their adaxial surface. Therefore, leaf susceptibility has a significant effect partly on the amount of primary inoculum, and partly as the disease process mainly starts on the abaxial surface of the leaves on the severity of primary infection in spring. It influences the future infection pressure on bunches. The hyperparasitic fungi Ampelomyces spp. do not have a direct role in influencing fruit infection because they appear at the end of the growing season in the vineyards when bunches are already ontogenetically resistant to powdery mildew. However, they take part in suppressing production of cleistothecia and parasitising them, which have an impact on next year s primary inoculum. The more rainy late summer and autumn are, the higher their importance is because their dissemination is subject to humid conditions. The most efficient means of influencing dynamics of epidemics of Uncinula necator is undoubtedly chemical control. In practice fruit protection has the priority, namely the prevention of losses from affected berries that provides protection only for that part of the season when bunches are in a susceptible state. However, foliar infection in autumn and production of cleistothecia on the leaves can be considerably reduced even under such conditions, especially by using fungicides of long-term effect (kresoxim-methyl). 12

14 Forecasting of grapevine powdery mildew As dissemination of conidia and ascospores of Uncinula necator is restricted, the amount of primary inoculum produced in a vineyard has a decisive role in influencing in-season epidemic curve of the pathogen. Survey data on the infection level of the particular vineyards, completed with meteorological observations and local experience can be well used in long-term forecasting of powdery mildew. Examination of the leaves at the end of the season in especially important as it supplies information on the likelihood of next year s infection by ascospores. For instance, in autumn 1997 economic threshold was hundred thousand of mature cleistothecia per grapevine stock that could lead to the outbreak of local epidemics in the particular vineyards in It is obvious, however that this threshold is not constant, as level of parasitism, washing-off, overwintering and ascospore release of cleistothecia change year by year, depending on meteorological and other conditions. As the production of cleistothecia is closely related to infection level, even only the latter one can supply useful information for the practice. Considering that the amount of primary inoculum has more influence on fruit damage caused by powdery mildew than weather conditions during the susceptible period of the bunches, the short-term forecasts that do not take the origin, volume and overwintering of the inoculum into consideration, involve a lot of mistakes. In epidemic situations they often expose vineyards to excessive risks, while in the lack of inoculum they recommend unnecessary treatments, loading them excessively. I studied efficacy of the Galati Vitis computer-aided forecasting program at the Plant Protection and Soil Conservation Station of County Tolna between 1993 and The program gave a relatively accurate forecast in 1993 and 1995 out of the 5 studied seasons. In 1994, the year of the most severe epidemics, the vineyards most exposed to powdery mildew were affected by the pathogen earlier than it was predicted by Galati. In 1996 there was no severe outbreak, however the earliest epidemics with the heaviest losses should have taken place that time according to the prediction of the program. There was a similar experience in Based on all these, it can be concluded that the weakest point of the Galati program in forecasting powdery mildew was the negative prediction. Its primary reason is that the program considers only the first two of the three conditions necessary for the occurrence of epidemics (i.e. host plant, environmental conditions and pathogen), while it does not take pathogen (primary inoculum) into account. 13

15 14 4. New research results 1. I surveyed the incidence of the two overwintering forms of the fungus causing grapevine powdery mildew in the vineyards of the wine-growing region of Szekszárd. I concluded that the occurrence of the cleistothecial form was general, while that of the mycelial one was sporadic (it could not be observed in any of the studied years in most of the vineyards). This fact is decisive in working out the control strategy to prevent the disease. 2. I developed a new method for counting the number of cleistothecia of Uncinula necator produced on the leaves and bunches. 3. I concluded that production of cleistothecia of Uncinula necator follows infection level of powdery mildew in space and time. There is a close correlation between the colonisation rate of the fungus and the number of produced cleistothecia (the higher the colonisation rate is, the more number of fruiting bodies are produced). The intensity of cleistothecium production depends on how favourable the environmental conditions are for the infection by Uncinula necator. 4. In Hungary I published the first data on parasitism of the cleistothecia of Uncinula necator by Ampelomyces spp. I concluded that level of parasitism of cleistothecia is highly influenced by colonisation rate of Uncinula necator and weather conditions. Level of parasitism rises with the increasing colonisation rate, being the highest on leaves with 60-80% colonisation rate. I found a positive correlation between level of parasitism and the volume of rainfall during late summer and autumn months. Furthermore I concluded that the ratio of parasitised cleistothecia on the adaxial surface of leaves colonised by Uncinula necator was significantly higher than on the abaxial surface. In Hungary Ampelomyces species have a role in the epidemiology of the pathogen by decreasing the volume of the overwintering inoculum (ascospores). 5. I evaluated bunch and leaf susceptibility of the particular grapevine varieties. I concluded that it was also important to be aware of leaf susceptibility, because cleistothecia containing ascospores are mainly produced on the leaves in vineyards receiving an intensive 14

16 15 fungicide spray programme. The leaf and bunch susceptibility of certain grapevine varieties may be considerably different (e.g. the leaves of cv. Kékfrankos, so common in Hungary are more susceptible to powdery mildew than its berries). 6. I concluded that chemical control targeted to prevent fruit infection may considerably reduce also leaf infection in autumn and by that, the production of cleistothecia by applying certain fungicides (e.g. kresoxim-methyl). Regular use of fungicides influences (may reduce or even may increase) parasitism of Uncinula necator cleistothecia by Ampelomyces spp. Level of parasitism can be decreased if the applied fungicide prevents a more severe outbreak till the end of the season, necessary for higher level of parasitism. However, parasitism can increase if the fungicide only delays powdery mildew attack on the foliage, thus preventing early production and maturing of cleistothecia, and giving way to the disease only if populations of Ampelomyces spp. have started growing. 7. I analysed the conditions influencing the epidemic curve in each of the past 12 years using meteorological, varietal and pathological observations. I concluded that the volume of primary inoculum was more important in the dynamics of epidemics affecting fruits than weather conditions during fruit infection. However, weather has a significant effect on the volume of primary inoculum by having impact on the whole life cycle of Uncinula necator (production and wash-off of cleistothecia, overwintering and colonisation of buds, fruits and leaves). Altogether, though meteorological conditions play a significant part in the dynamics of epidemics of Uncinula necator, their role in directly influencing fruit infection cannot be considered the most important one. 15

17 16 5. Recommendations Nation-wide surveys carried out by the Plant Protection and Soil Conservation Service in 2001 also confirmed that the cleistothecial form has the decisive role among the two overwintering forms throughout the country. Considering that this fact has a significant impact in the control of the disease, it would be desirable to widely inform grapevine growers and extension specialists about the recent results. As environmental conditions favouring infection by ascospores and conidia are different, the short-term forecasting systems, taking only the meteorological conditions of infection by conidia into consideration, should be modified by all means. Reliable forecasting inevitably requires information on the state of primary inoculum. It needs in-season and annual epidemic curves of the fungus and up-to-date knowledge on the environmental conditions influencing them. When working out the chemical treatments to prevent grapevine powdery mildew, it is reasonable to develop a programme which, in addition to an efficient fruit protection, considerably reduces leaf infection in autumn and by that, production of cleistothecia. The application of certain mechanical methods may be useful to complete chemical control: - removal of severely diseased bunches, being important means of carrying cleistothecia, as soon as possible during cultural operations, - where mycelial overwintering is frequent, short spur pruning is recommended (avoid long cane pruning), - careful execution of cultural operations to allow good penetration of pesticides in the airy canopy. In spite of the obtained results, I deem it important for the future to survey all the major grapevine varieties grown in Hungary for leaf and bunch susceptibility to powdery mildew, ascospore release of the fungus and to continue studies on overwintering of cleistothecia in Hungary. 16

18 17 6. Scientific publications in the field of the dissertation 1. Füzi, I. (1999): Az Uncinula necator (Schw.) Burr. kleisztotéciumos DODNMiQDN HO IRUGXOiVD pv D NOHLV]WRWpFLXPNpS] GpV IRO\DPDWD D GpO- GXQiQW~OLV] O OWHWYpQyekben. Növényvédelem, 35: Füzi, I. $ V] O OLV]WKDUPDW NOHLV]WRWpFLXPRV DODNMiQDN járványtani szerepe a szekszárdi borvidéken. Növényvédelem, 35: Füzi, I. $ V] O OLV]WKDUPDW NOHLV]WRWpFLXPRV DODNMiQDN MHOHQW VpJH0DJ\DURrszágon. Növényvédelem, 37: Füzi, I. $] LG MiUiV D IDMWD pv D NpPLDL Q YpQ\YpGHOHP KDWiVD az Uncinula necator (Schw.) Burr. kleisztotéciumainak Ampelomyces spp. általi parazitáltságára. Növényvédelem, 38: Füzi, I. (2003): Natural parasitism of Uncinula necator cleistothecia by Ampelomyces hyperparasites fungi in the south western vineyards of Hungary. Acta Phytopathologica et Entomologica Hungarica, 38 (1-2): Publications in popular science 1. Vörös, G. és Füzi, I. (1 6] O YpGHOHP D 6KHOO WHFKQROyJLiMiYDO Agrofórum, 2 (5): Füzi, I. $ V]HUNRPELQiFLyN pv D] LG ]twpv MHOHQW VpJH D V] O OLV]WKDUPDW V]LV]WHPLNXV EORNNROiViEDQ,QWHJUiOW 7HUPHV]WpV D Kertészetben 15., Budapest, Füzi, I. pv 9 U V * 7ROQDL V] O N Vigyázat, lisztharmat! 0DJ\DU0H] JD]GDViJ

19 18 4. Füzi, I. $ V] O EHWHJVpJHN 7ROQiEDQ -ben. Agrofórum, 5 (11): Füzi, I. (J\ OLV]WKDUPDWPHQWHV HV]WHQG D V]Hkszárdi borvidéken. Integrált Termesztés a Kertészetben 17., Budapest, Füzi, I. (1996): A 95- V V] O SHURQRV]SyUD-járvány tanulságai a szekszárdi borvidéken. Agrofórum, 7 (5): Füzi, I. (1997): Nem volt lisztharmat a szekszárdi borvidéken. Kertészet pv6] OpV]HW Füzi, I. 9LVV]DYRQXOyEDQ D V] O OLV]WKDUPDW" *\DNRUODWL Agrofórum, 8 (7): Füzi, I. )XQJLFLGHV YpGHNH]pV KDWiVD D V] O OLV]WKDUPDW NOHLV]WRWpFLXPNpS] GpVpUH,QWHJUiOW 7HUPHV]WpV D.HUtészeti és Szántóföldi Kultúrákban 20., Budapest, Füzi, I. ÒM PHJYLOiJtWiVEDQ D V] O OLV]WKDUPDW *\DNRUODWL Agrofórum, 10 (6): Füzi, I. (2001): Újra csúcson a lisztharmat. Növényvédelmi Tanácsok, 10 (április): Lectures given in the field of the dissertation 1. Füzi, I., Brenner, L. és Lehel, Z. (1994): Újdonság: a Topas 100 EC V] O EHQ pv DOPiEDQ 1 YpQ\YpGHOPL )yuxp.hv]wkho\ (O DGiVRN összefoglalói, Gabi, G. és Füzi, I. (1995): A "GALATI" sziptwyjpshv HO UHMHO] módszer alkalmazásának tapasztalatai a szekszárdi borvidéken. 1 YpQ\YpGHOPL)yUXP.HV]WKHO\(O DGiVRN VV]HIRJODOyL 18

20 19 3. Füzi, I. $ V] O SHURQRV]SyUD HOOHQL YpGHNH]pV WDSDV]WDODWDL 1995-ben a szekszárdi borvidéken. Növényvédelmi Fórum '96,.HV]WKHO\(O DGiVRN VV]HIRJODOyL 4. Füzi, I. 6] O ERWULWLV]-járványok tanulságai a '90-es években. 1 YpQ\YpGHOPL)yUXP.HV]WKHO\(O DGiVRN VV]HIRJODOyL 5. Füzi, I.$GDOpNRNDV] O OLV]WKDUPDWUncinula necator /Schw./ Burr.) járvány- és kórtünettanához. 43. Növényvédelmi Tudományos 1DSRN%XGDSHVW(O DGiVRN VV]HIRJODOyL 6. Füzi, I. pv *DEL * $ SULPHU LQRNXOXP MHOHQW VpJH D V] O OLV]WKDUPDW MiUYiQ\GLQDPikájában. Növényvédelmi Fórum '98,.HV]WKHO\(O DGiVRN VV]HIRJODOyL 7. Füzi, I. és Fischl, G. (1998): Uncinula necator (Schw.) Burr. kleisztotéciumképzésének sajátosságai. 44. Növényvédelmi 7XGRPiQ\RV1DSRN%XGDSHVW(O DGások összefoglalói, Füzi, I. (1999): Ampelomyces spp. +LSHUSDUD]LWD JRPEiN HO IRUGXOiVD V] O OLV]WKDUPDW-kolóniákon. 45. Növényvédelmi Tudományos Napok, %XGDSHVW(O DGiVRN VV]HIRJODOyL 9. Füzi, I. (2000): Feketerothadás károsítása a szekszárdi borvidék V] O OWHWYpQ\HLEHQ ;.HV]WKHO\L 1 YpQ\YpGHOPL )yuxp.hv]wkho\(o DGiVRN VV]HIRJODOyL Publications in foreign language 1. Füzi, I. (1995): Fungicides against diseases of pea, Pisum sativum L., in Hungary. Pesticide Science, 45: Füzi, I. (1997): Control of leaf rust of winter wheat, Triticum aestivum, in Hungary. Pesticide Science, 49: