Measurement and evaluation of the effects of soil factors on ring nematode (Criconemoides xenoplax)

The objective of this project was three-fold: (1) to determine if soil factors such as soil texture and pH have any effect on ring nematode (Criconemoides xenoplax) (RN); (2) determine the vertical distribution of RN in soil for different crops; and (3) determine if RN populations exhibit seasonal fluctuations.

Samples received at ARC Infruitec-Nietvoorbij’s nematode diagnostic service and at Nemlab were selected for their RN numbers:  either classified as “low” (< 250 RN/250 cm^-3 soil) or “high” (> 1 000 RN/250 cm^-3 soil).  Seventy-two samples were thus selected, representing all the major fruit and vine areas of the Western Cape, and also the Lower Orange River.

Soil from these samples was analysed for five different soil fractions, namely coarse sand, medium sand, fine sand, loam, and clay.

Our results show that the different soil fractions had no effect on RN numbers and that high RN numbers occurred in all types of soil, both sandy and clayey type soils.

The results also showed that pH values ranging between 4.5 – 7.0 had no effect on RN numbers.

To determine the vertical distribution of RN and also if seasonal fluctuations occur, a vineyard and a nectarine orchard was sampled in January, April, July, and October.  Samples were taken at 20 cm intervals down to 1 m deep.  Although RN numbers decreased below 60 cm depth, their numbers were still high enough at the 80-100 cm depth to cause serious damage.  No seasonal fluctuations were observed.

The outcome of this project was:

1. This study confirms that soil fractions do not affect RN numbers;
2. Although almost 50% of the RN population present in a plant’s root zone occurs in the top 40 cm soil, damaging high levels can occur to at least 1 m deep, posing a serious problem for effective nematode control. These high nematode numbers below the zone that can be effectively fumigated provide a source for re-infecting replanted vineyards and orchards;
3. Seasonal fluctuations do not occur, therefore samples for diagnostic analysis can be taken at any time of the year.