Plant Health and Fungal Protection in Ecological Viticulture

An ecological vineyard is a complex living system where the grower actively tries to encourage the self regulation of the ecosystem and the health of this organism.

One of the primary interests in ecological viticulture is to grow healthy and disease resistant plants. Most of the widely used cultivars do not bear the quality of resistance to fungal infection.With the help of plant health enhancing products which are accepted by bio gro standards, and with the correct soil-and plant management the regulation of fungal diseases through the induction and enhancement of the plant's own defence mechanisms,can be approached.This does not involve the application of toxic compounds to plants.All the plant growing and plant caring steps with their methods of interrow -and undervine planting,herbal leys,green manuring,mulching,soil melioration,compost applications,choice of suitable varieties and rootstocks,training and pruning techniques,try to enhance the health and quality of the vine and its fruit.Plant resistance can be induced in general and in specific ways. The cuticula and the stomata can be strengthened to create a physical barrier for the fungal spores to enter the inside of the plant cells. Also,the infection pressure can be reduced by applying naturally occurring resistance elicitors (e.can trigger a response to plant pathogens) such as yeast cell membrane and certain etheric oils which are rich in saponines (soaping agents),and which act as a dispersing agent with spore germination inhibiting and antibiotic qualities; and flavonglycosides such as quercetin which give a waxy coating to the leaves. The efficacy of botanical extracts usually depends not only on one active ingredient but on the diversity and the synergy of the various ingredients. Only as a last resort,biological fungicides(copper,sulfur,limesulfur) are to be used to manage fungal problems.Cu accumulates in the soil and is inhibiting earthworm population. Sulphur and limesulphur harm the predatory mite T.pyri and can be phytotoxic,especially on young plants and in spring weather conditions with wide fluctuations of cold and warm temperatures.

The fungal diseases downy mildew (Peronospora viticola), powdery mildew (Oidium tuckeri) and Botrytis cinerea in grape vines,their disease cycles,their symptoms,identification characteristics and possible plant protection schemes in ecological viticulture,i.e. plant health enhancing measures to develop the plants resistance to the infection with these pathogens , shall be discussed in this report.

Peronospora or Plasmopara viticola-downy mildew

May affect all green parts of the vine such as leaf,tip,flower cluster,stalk and young fruit. The infected fruit is unmarketable,its taste is altered. The fungi survive as oospores in the soil or as mycelium in the seeds. The infected plants produce sporangia on their lower surface of the leaves and shed their spores onto other parts of the vine and on new plants. The infection of P.viticola becomes first apparent on the foliage by brightening of the affected tissue. Oval or cylindrical areas of varying sizes and looking like oily blotches develop on infected leaves and stalks in a yellowish to brown colour on the upper surface of the leaves. After the appearance of the oily blotches a humid/warm climate triggers an outburst of a white mycelium on the lower surface of the leaves. On the older leaves yellow lesions occur. The now developed summer sporangia get dispersed by wind onto other parts of the vine and lead to a secondary infection with the next rain. Infected flower clusters discolour yellowish brown and wither. The greatest damage done by the fungus is the infection of the cluster of young berries and the stalks. Berries up to pea- size are covered by white mycelium.Infected berries then discolour to a violet blue and shrivel to a leathery tissue.

Conditions for infection

a) Determination of the date of primary infection:
Spores (oospores) germinate in spring ,once soil humidity is sufficient and a daytime minimum temperature of 8 degree Celsius is reached. Now the oospores develop a hyphae with one single sporangia attached to it and are called ascospores. For a successful primary infection the oospores have to complete their cycle and have to be splashed onto the leaves by heavy rain.The leaf size has to be 2cm or more (during and after 3-leaf stade) and free water has to be present for at least 6 hours for a primary infection.

b) Incubation period:
The period from infection to the ocurrence of the first symptoms of the fungal disease (oily blotches) is called incubation period. According to G.Hill a certain ripening factor is added to the medium daytime temperature and summed up every day. As soon as the total sum reaches 100, the incubation period is over. A medium daytime temperature(MDT) of 7 degree C has a factor 5,a MDT of 10 degree C a factor 6,a MDT of 14 degree C a factor 10,a MDT of 16 degree C a factor 13 and a MDT of 20 a factor 20.

c) Conditions for sporulation:
According to Blaeser and Hill Plasmapora viticola has to meet certain criteria to trigger sporulation on the adaxial surface of the leaves :

• 4 hours of continuous wet foliage
• relative humidity of >95%
• temperature at the beginning of the wetness/darkness period >12.5 degree C
• medium temperature during the outbreak period from 10pm-5am >10 degree C
• darkness from 10pm -5am

Besides the purely climatic factors,the metabolic processes in the vine play an important role in the ocurrence of the infection with the fungal pathogens. During the night,both starch and proteins in the vine have reached their highest degree of solubility. This causes an increase of sugar in relation to undissolved starch. The proportion of soluble nitrogen and phosphorus undergo an increase.
According to Pantanelli , sporulation and infection get assisted by soluble N-and P components. Higher nighttime temperatures cause an increase of protein decomposition to soluble amino acids,and of starch to sugars and CO2,and an increase in sporulation intensity.

d) Calculation of the infection potential:
Assume that a primary infection ususally leads to 50 to 100 oily blotches/ha. These infection centres can produce a multitude of new infections according to temperature during the wetness/darkness periods. During the course of the vegetation period new infection cycles can ocurr again and again. With heavy rainfall,thunderstorms and rising temperature the infection can increase to up to 500 oily blotches/ha. The 50 to 100 oily blotches of the primary infection are to be multiplied with the appropriate multiplication factor and added to the already existing oily blotches. At a temperature of 11.0 degree C the multiplication factor (MF) is 1.2;at 12 degree C the MF is 1.7;at 13 degree C it is 2.24,at 14 degree C it is 2.85,at 15 degree C-3.7,at 16 degree C-4.85, at 17 degree C-6.63,at 17.5 degree C-10.0.

In ecological viticulture the economical threshhold is 1000 oily blotches/ha. To prevent further damage the use of a copper fungicide is recommended from this point of time. At the same time it is necessary to use preventative and plant health enhancing or plant strengthening means to lower the reinfection potential. Vine management using partial leaf plucking in the bunch zone,removal of water shoots,double-and stunted wood,groundtouching wood and pruning for adequate aeration and drying off is advised. Interrow-and undervine planting of herbal leys (lowgrowing species under vines) combined with a stem hight of at least 700mm reduces the infection potential and the splash intensity of raindrops. Another preventative measure is the spreading of well ripened compost and the application of an equisetum arvense (horsetail) spray,as it increases the activity of antagonists in the soil which control the germinating pathogen spores.

Effective microorganisms (EM) in the compost produce plant hormones,beneficial bioactive substances and antioxidants,while solubilising nutrients. The metabolic byproducts of the Ems catalyse an energy shift within the ecosystem,which creates a healthier environment for the vines. A healthier environment in turn makes the plants healthier,more resistent to disease and less attractive to damaging insects.High populations of beneficial microorganisms which occur in the ecosystem, over time also exclude pathogenic microorganisms and nematodes.Beneficial micro-organisms create esters which deter insects. EM include antioxidising and purification microorgs known as photosynthetic bacteria.For their survival and proliferation it is essential that the soil has been adequately nourished and is not saturated with actively oxidising substances,mainly pesticides (herbicides) and highly soluble salt fertilisers. As soon as ideal germination conditions of the winterspores of Peronospora exist (soil humidity, soil-and air temperature), and the danger of a primary infection is given,two preflowering spray applications of plant health enhancers are recommended. With higher rainfall rates >50mm/24h and higher temperature the application of Cu,limesulfur or sodiumbicarbonate as toxic fungicides are to be applied. For monitoring the infection potential and for calculating the incubation period, a weather station including a thermometer,a thermohygrograph and a leaf wetness recorder are needed.

Powdery mildew (Oidium tuckeri)

Symptoms:

Soon after sprouting the mycelium grows between the bud scales on the young wood which retards in development. The leaves curl and get covered by a whitish coating. In December the mycelium appears on both sides of the leaves (indicator shoots) which have to be pruned and removed from the vineyard. Infected clusters fall off,early infected grapes dry out,peasized grapes rupture (the grape skin hardens while the fruit pulp is still growing). With late infection the leaves and the grapes are coated with a greyish mycelium.

Conditions of infection-Biology of the pathogen

Oidium tuckeri overwinters as a mycelium between the bud scales. After budbreak it grows on the green parts of the vine and develops conidia which can lead to continuous reinfection. The infection and conidia development can occur on both sides of the leaves. Oidium t. can penetrate through the cuticula into all vine organs. Conditions of an infection with Oidium t. are quite different to the ones of Peronspora. A relative Air humidity of >80% is sufficient for the infection process,no dripping water is required. Optimum conditions are humid,warm days and cool,clear nights (anticyclones). The incubation period takes 7-14 days according to temperature. The conidia germinate already at 5 degree C and develop optimally at 20 degree C. For prevention of Oidium t. the same management methods apply as for Peronospora.

Botrytis cinerea

All green parts of the plant can be infected. B.can develop throughout the year in favourable Infection conditions. In spring with humid and cool weather the fungus covers the buds and young wood with a grey coating. It infects the flower clusters which turn brown and break off. Wounds from pruning or mechanical abrasion are colonised rapidly by the fungi. Damage can be of abiotic (hail,leafplucking) or biotic (wasp,leafroller,grass grub beetle) nature. If the fungus infects unripe berries it will lead to damaging bunch rot. At veraison from 25 degree Oechsle,the intrinsic resistance of the vine decreases and the danger of infection increases rapidly. B. infection can also lead to stem rot where infected parts discolour greenishbrown,turn brittle and the grapes don't ripen. Riesling is especially prone for stem rot. Plenty of aeration of the leaves and bunches is essential for B. prevention. See management of P. and O. for cultural management.

During the flowering period the interrow growth is to be kept low by using a roller or by cutting alternate rows. All undervine growth has to be kept low. Leafplucking of parts of the bunch area after petal fall helps to harden off the plants. A harmonious nutrient supply with the help of interrow planting,organic fertiliser and humus (well ripened compost) application prevents high nitrogen supply phases and too much vigour.

Plant protection with plant health enhancers/plant strengthening agents

Fungal infections can be prevented by timely applications of plant health enhancing agents which can induce general or specific resistance to pathogens into the vines. A mechanical resistance is achieved by hardening the epidermis and cuticula by incorporating silica into the plant tissue. Active resistance can be induced with phytoncides which are secondary contents of plants which regulate and control plant metabolism,protect against pathogens and enhance the health of the plant (Haller,Klingauf). Phytoncides are also factors for natural immunity in the plant realm. They are seen as preinfectional resistancy factors. Volatile sulphur compounds,so called Alkylsulfides have been isolated from onion and garlic (Vistanen). In nasturtium plants Benzylthioglycosides can be found which are a preliminary stage of Benzyl-isothiocyanate,the most active biocidal mustard seed oil in the plant realm.

The phytoncides can trigger defence mechanisms by the formation of phytoalexines which in return prevent and stem the spread of pathogens. Phytoalexines can be characterised as plant specific protectants against penetrating microorganisms,primarily fungi. The Phytoalexines are induced by elicitors. The triggering stimulus can be brought about by the chemical active substances (phytoncides) inherent in the plants extracts. Another possibility are cinnamon acid derivatives and flavonoids,such as quercetin which create a waxy protection layer on the leaf surface. By application of these waxy lipoid substances a strengthening of the epidermis and the cuticula is caused,similar to the one caused by silicic acid. Sodium silicate which is derived by melting quartz sand with soda is a product with good sticking qualities and its high pH-value (up to 13) changes the milieu on the foliage to the disadvantage of the pathogens. As a sprouting application it provides a protective coating to the leaves and on the wood and knocks off wintereggs of harmful insects and fungal spores by suffocating them. Sodium silicate works even better once combined with plant extracts,sulphur-and copper products and has added value with its synergism. Plant extracts contain various active ingredients which are used in preventative plant protection. The etheric oils,resins and balms have antiputrefying qualities. Tannins increase the resistance of Vitis vinifera against Botrytis c. The use of pomace or marc as a soil conditioner causes the vine to take up the humified tanning agents and phenolic carbon acids and synthesizes them into defence substances (Graefe). These defence substances seem to have a direct fungicidal effect against Peronospora.

In biodynamic viticulture management, special preparations which enhance and support vital processes of the whole vine plant,above and below ground,are being used. These are the plant-care preparations: cow-horn-manure and cow-horn-silica.They mesh in with plant growth in an organizing way. They help in forming the special character of the vine and they balance extremes of any kind. They also enhance the existing forces of nature.Plant health processes are influenced positively by activating beneficial soil microbial and fungal life,by enhancing fruit quality(colour,aroma,taste,shelf life)and by reducing the susceptibility to pathogens (Pfeiffer 91, Casera 96).

Additionally, special compost preparations made of yarrow,stinging nettle, oak bark, dandelion and valerian,are used to improve compost and humus qualities. These are directing the composting process towards fermentation instead of decomposition.

Grateful acknowledgement is made to Dr.Uwe Hofmann of Eco-Consult Geisenheim/Germany, for his assistance in preparing this article.