Using Crop Rotation to Regulate the Pest Ditylenchus dipsaci in Arable and Vegetable Farming

The stem nematode Ditylenchus dipsaci causes damage to field crops. The pest attacks many different host plants. We examined these plants’ susceptibility to D. dispaci and, based on our findings, recommend crop rotation.

Ditylenchus dipsaci is a plant-parasitic nematode. Nematodes are important pathogens affecting the farming sector. There are no effective means of direct control. The globally occurring stem nematode D. dipsaci has over 500 host plants and more than 30 races with different host plant preferences. The nematodes penetrate the stem and can cause hypocotyl swelling, stunted leaves, and lateral bud formation. Seedlings can often die as a result (Fig. 1).

Host plants tested for infectivity and virulence against D. dipsaci

In Switzerland, nematicides are no longer authorised for direct control. In order to be able to continue crop cultivation in soils contaminated with D. dipsaci despite their wide range of host plants, the adaptation of crop rotations is a possible approach to controlling the nematodes. To this end, D. dipsaci populations were analysed for their infectivity and virulence towards crop plants. Infectivity was tested based on the number of nematodes that had penetrated the plant: In vivo eight to twelve days after nematode inoculation and in microplots at BBCH 11 (first true leaf unfolded) in the dyed seedlings. To determine virulence, the number of reproduced nematodes in the plants was determined at 60 days after first inoculation in vivo, and at around 90 days after sowing in the microplots. Given varying levels of damage in different geographical areas, four different regional populations were tested in vivo. In the follow-up microplot trial, the Seeland population from Switzerland was also analysed for Pf/Pi (ratio of final to initial population levels) in the soil.

No differences between populations from different geographical areas

Comparison of the infectivity and virulence of the four D. dipsaci populations from Seeland (CH), Rhineland (DE), Franconia (DE) and Aisne (F) showed no significant differences in vivo. The Swiss population from Seeland showed the highest virulence.

Highest virulence towards peas, maize, sugar beet and onions

The in vivo trials showed significant highest D. dipsaci infectivity in leeks, onions and maize. The strongest virulence was seen in maize and peas, with significant differences to the other crops tested. In the microplots, peas, leeks and onions were most strongly infected, with peas displaying the highest D. dipsaci virulence. Infectivity and virulence were low towards garlic, hemp, celery, carrot, sorghum, Tagetes, head lettuce and wheat. In addition to the high virulence found in peas, the Pf/Pi ratio revealed the significant highest multiplication rate of D. dipsaci in peas.