WINETECH Technical Yearbook 2020

A

B

FIGURE 2. Soil samples (3 426) from Nemlab, over a period of three years, rated according to the number of nematodes detected in the samples.

FIGURE 3. A: Ratio of the routine Nemlab samples analysed per rootstock. B: Mean number of ring nematodes isolated from the different rootstocks.

NEMLAB ROUTINE SAMPLE RESULTS

occur in the vineyard environment will disappear, and only C. xenoplax will be left. However, with the application of chemicals, the problem with ring nematodes is only temporarily alleviated in the upper layers of the soil. They can then easily move from the deeper levels of the soil back to the upper treated soil, where, in the absence of competition and natural enemies, they can reproduce more rapidly.

were low to mildly infested, and 46% were high to severely infested (figure 2). The severely infested samples were regarded as infested with >1 000 ring nematode/ 250 g of soil. The highest number of nema- todes found over the three-year period was >6 160, which is extremely high for ring nematodes. The results might, however, have been biased, as the samples might have originated from vineyards with health problems.

province), which were taken from grape- vine-growing areas over a period of three years, were selected for analysis. The se- verity of ring nematode infection was rated, with the different commercial rootstocks being separately analysed. Rating the number of nematodes according to an artificial scale of zero, low-mild and high to severe, indicated that approxi- mately 18% of 3 426 routine samples were found to be without ring nematodes, 36%

The different private diagnostic laborato - ries, during the past decade, have encoun- tered very high numbers of ring nema- todes in the routine samples taken from grapevine that have been analysed for the presence of plant-parasitic nematodes. However, such was not previously proved to be the case. Soil samples (3 250) from Nemlab (Klapmuts, Paarl, Western Cape

WINETECH TECHNICAL YEARBOOK 2020 39