Attempts to Eradicate Phylloxera

Gallicolae are rarely seen on European or grafted vines, and for that reason the full cycle of the phylloxera is seldorm completed. On the other hand, the radicolae can perpetuate themselves indefinitely, causing debility, and ultimately the death of such vines that are vulnerable to them. They produce lesions which result in abnormal growth of the part attacked and also allow other parasites to get in, such as fungi and bacteria.

Eventually the whole of the root beneath the lesion is separated from the remainder of the vine and dies. The gallicolae, when they do appear, are relatively harmless, though they cause some damage through feeding on the sap. When phylloxera attacks a vine, for the first year or two there is no sign at all of its existence in the vineyard. If anything, the yield of grapes increases slightly. The debility is only noticed after the phylloxera has taken a firm hold of the vine.

This may happen in two or three years, or it can take as many as eight. Then the damage begins to take effect: the tendrils are less well-developed, the shoots are thin and short, and bunches of grapes are small. Even so, the contrast is not great, but the phylloxera has taken hold and the vine is doomed. The next year, the same symptoms are seen, but they are more marked. By the following year, the vine is clearly drying up and preparing to die.

Phylloxerae travel from vine to vine through the ground or over its surface, particularly when helped by wind or rain. The sexuparae, in particular, can be blown to quite distant vineyards. They can also be spread by vineyard tools, machinery, and clothing. Although many attempts have been made to exter­minate them, none have been successful. The most drastic and dramatic remedy was to flood the vineyards during the winter, but this could only be done in suitable geographical areas and was quite out of the question in Jerez.

Viala proposed a remedy involving human urine, but this proved worse than the phyl­loxera. Eloy Martinez attempted to electrocute the pests, but his experiments were equally futile. Fumigation of the roots and soil with carbon disulphide, organic acids, and arsenic compounds has been tried with limited success, but it has been found impossible to control phylloxera on a large scale. The problem has been to find some form of soil insecticide that does not cause more mischief than it cures, by leaving undesirable residues in the vine.

Moreover, it is doubtful whether any systemic insecticide (which is absorbed into the plant sap to attack the pest from within) could operate successfully against phylloxera, as the parasite produces galls which deaden the plant tissues and reduce sap flow just where jt would be required. In fact there is no known remedy, and the only solution is to pull up all the vines and replant with American stocks that resist attack. This, however, does not cure the plague, but merely renders it innocuous.

When phylloxera attacks a vine, for the first year or two there is no sign of its existence in the vineyard. If anything, the yield of grapes increases slightly. The debility is only noticed after the phylloxera has taken a firm hold of the vine.