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Vineyard Terrorist Gets New Foot In The Door
C.A. de Klerk, ARC Infruitec-Nietvoorbij, Stellenbosch
(Translation from Afrikaans)
Vineyards are forever being terrorised by a whole range of pests and diseases. In the majority of cases, however, there are good defence mechanisms in the form of chemical and other control measures.
An insect terrorist which practically forced the entire viticultural industry in South Africa onto its knees in the early 1900s by destroying numerous vineyards and causing large-scale bankruptcies, is a very small plant louse with the well-known name "phylloxera". At the time, the use of phylloxera-resistant rootstocks undoubtedly saved the viticultural industry from certain demise, but this terrorist was not exterminated and remains a looming threat.

Fig. 1 Phylloxera can be observed with the naked eye.

Over the past few years there has been large-scale expansion in the viticultural industry, causing a shortage of propagation material, rootstocks in particular. The bigger demand also resulted in a price hike for grafted vines. As a result, large-scale plantings of ungrafted vines are currently taking place. This is a wonderful situation and opportunity for the omnipresent phylloxera terrorist to revive, once again to cause large-scale destruction and bankruptcies.

Fig. 2 Round galls are formed on the reverse side of leaves.

With this article, ARC Infruitec-Nietvoorbij would like to equip the viticultural producer with more information about phylloxera and in the interest of the industries extend a serious warning that new plantings should not be undertaken with ungrafted vines.
Phylloxera multiplies like weeds
This insect pest has a very interesting and impressive life cycle:

It is a small plant louse which occurs above as well as below the soil surface;
It attacks the roots as well as the leaves of vines;
Wingless as well as winged stages occur in the life cycle;
The damage caused has various symptoms;
The most important aspect is that the insect multiplies incredibly fast, like weeds.

Fig. 3 Phylloxera multiplies inside the galls.

The subterranean cycle consists of females laying eggs, from which larvae are hatched. The larvae in turn develop into females and reproduction occurs without males. Each female can produce up to 60 eggs and 10 generations can occur within one year. Theoretically one female can therefore generate millions of new terrorists in the course of one season.
In autumn some of the larvae change into hibernating larvae, while others develop into a winged form. The winged form lays eggs of two sizes, generating males as well as females. After mating, eggs are laid on the trunk of the vine, where they hibernate. In the next spring these eggs hatch and larvae move to the leaves, where a cycle similar to that on the roots occurs. In autumn the larvae move again from the leaves to the soil. Two cycles, on the roots as well as the leaves, therefore take place concurrently, causing serious damage to the vine.
Deadly cancers are caused

Fig. 4 Thickenings and hooked galls are caused on fine roots.

Phylloxera have long, sucking mouth parts that are stuck into the plant tissue when they feed. On the leaves, galls are formed on the reverse side with a small opening on the top surface. As the phylloxera breed and multiplies, the entire leaf is soon covered with these galls, the leaf withers and dies. The name phylloxera means "dry leaf". In South Africa we are very fortunate, however, in that leaf galls seldom develop; if so, they occur only in certain circumstances on the leaves of rootstocks.
On fine roots, the growth points in particular, hooked galls are formed, the roots stop growing and rot. On older roots, round galls are formed that also rot in time. In the case of ungrafted vines especially, the entire root system can be destroyed by these cancers in 3 to 4 years' time.
Galls on the roots are clearly discernible during the growing season, while above ground symptoms show as poor growth only. The poor growth usually occurs in patches in a vineyard block, increasing gradually as the insect spreads.
Everyone has this problem

Fig. 5 Phylloxera populations are reduced if vineyards are covered with water for long periods.

Phylloxera is indigenous to the USA, where it was discovered in 1854 and whence it spread to Europe on American cultivars that were exported at the time for their increased resistance to oidium. From there it spread throughout the world and currently occurs in practically all viticultural countries. The insect has a history of 115 years in South Africa and occurs in all viticultural areas throughout the country. As a result of the world-wide distribution, damage and poor control measures, phylloxera is generally considered the most important insect pests of vines.
A few countries such as Chile and large parts of Australia are still phylloxera free, but for them it is likewise a huge dilemma and an ongoing struggle to keep the terrorist at bay.
Remedies have never been developed
No chemical substance against phylloxera has been found that may be applied in existing vineyards in an economic and environmentally friendly fashion. Taking into account that this pest has been the number one terrorist in vineyards world-wide for more than a century, it is a remarkable record for this tiny plant louse. There are two explanations for this state of affairs. The insect may occur very deep in the soil, as deep as the vine's roots are able to penetrate, and it multiplies extremely quickly. Soil fumigation and contact substances do not readily penetrate that deep and systemic substances usually move upwards and not downwards in the plant. Deeply rooted infestations are therefore not sufficiently eradicated, multiplying again quickly to pest populations.
What can the producer do to protect himself?

Fig. 6 Resistance of rootstocks to phylloxera is not equally good.

Apart from using phylloxera resistant rootstocks, very little can be done to solve the problem. Research and experience have shown that there are only two very risky possibilities of reducing the population build-up and/or distribution. It is a well-known fact that the effect of phylloxera is less dramatic in sandy soils. In heavy soils, small cracks are formed which create wonderful "avenues" for the moving larvae, thus progressing from one vine to the next. In sandy soils their movement is restricted in that they are stuck in one spot, "spinning" like a car in sand. The sand content must be high, however, and surveys have indicated that no phylloxera occurs in soils of which the medium and fine sand content exceeds 65%. It remains an open question, nevertheless, whether vines will perform economically in such soil types.
Drowning of the insect is a possibility, but water has to cover the entire surface for at least three months. In cultivated areas along rivers it often happens that vineyards are flooded for long periods. This helps to reduce the insect population, but it builds up again to pest populations in one or two seasons.
The only solution world-wide is resistant rootstocks
The only practical method of keeping this destructive pest under control is to graft cultivars onto phylloxera-resistant rootstocks. Grafted vines must therefore be planted instead of vines that have not been grafted.
Even so, the pest persists in terrorising vines, the reason being that no rootstock is absolutely resistant (immune) to phylloxera under all circumstances. All rootstocks display a certain degree of resistance to the ravages of phylloxera. The resistance of some rootstocks consists only of tolerance to phylloxera. These vines can therefore bear a high population without harmful consequences, while creating a high source of infection for surrounding vineyards. Some rootstocks may initially offer good resistance, but within 6-8 years the terrorist gets the better of them as well.
Another remarkable characteristic of phylloxera is that there are various biological strains, also in South Africa. A rootstock which shows good resistance to phylloxera in one area (e.g. the Boland), may show poor resistance in another area (e.g. Olifants River).
Which rootstock must be used?
The choice of a rootstock with regard to phylloxera resistance is in itself a difficult decision. This is further complicated in that rootstocks differ considerably with regard to other characteristics, such as resistance to drought, wet and saline conditions, nematodes, crown-gall and phytophthora.
Planting a vineyard is an expensive investment that has to pay dividends for 20 to 25 years. Expert advice regarding the specific rootstock for the particular situation should therefore be obtained in advance.
Make it difficult for the terrorist
Although there is no instant solution to control phylloxera, the problem can be drastically reduced with good management. The premise here is that the stronger the growth of the plant, the better its resistance to the onslaught. All aspects of viticulture should therefore be managed optimally. Use the optimum rootstock and take precautions for optimum cultivar choice, soil preparation and tillage, planting, fertilisation, irrigation, pruning, canopy and crop management, pest and disease control, etc. The smallest and weakest game always fall prey to the lions!
What approach should be followed against this terrorist?
From the above it is clear that the phylloxera terrorist has been with us for a very long time and will remain a potential danger for many years. The producer can take out the following insurance:

Use the best rootstock-scion combination for your specific conditions;
Only use certified propagation material;
Apply the most appropriate viticultural practices;
Obtain expert advice before implementing any action;
Propagation of ungrafted vines should not be considered under any circumstances, regardless of the cost and availability of grafted material. Wait another year, even two, until optimum combinations can be obtained;
Plantings of ungrafted material will definitely give the phylloxera terrorist yet another advantage which will endanger your own economic prosperity and that of your neighbours.

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