Towards practical application of Verticillium isaacii Vt305 to control Verticillium wilt of cauliflower : exploring complementary biocontrol strategies

Verticillium wilt is one of the most important diseases of cauliflower and can lead to serious economic losses. In this study, two complementary strategies were explored to employ the antagonistic capacity of Verticillium isaacii towards Verticillium wilt of cauliflower. The first strategy focused on introducing V. isaacii Vt305 by artificial inoculation of cauliflower plantlets at the nursery stage. Two inoculum types (spores and microsclerotia of V. isaacii Vt305) and different concentrations of microsclerotia were tested in greenhouse and field trials. Seed treatment with 500 microsclerotia seed(-1) led to a satisfying biocontrol level of Verticillium wilt. In addition, the PHYTO-DRIP(R) system was successful in delivering the microsclerotia to cauliflower seeds. The second strategy relied on the stimulation of the natural V. isaacii populations by rotating cauliflower with green manures and potato. Four green manure crops and potato were tested during multiple field experiments. Although these crops seemed to stimulate the V. isaacii soil population, this increase did not result in a control effect on Verticillium wilt of cauliflower in the short term. Importantly, our results indicate that the use of green manures is compatible with the application of V. isaacii Vt305 as biocontrol agent of Verticillium wilt in cauliflower

Soil activity and persistence of rimsulfuron to maize and selected grasses

When subjected to rimsulfuron in bioassay experiments [small pot test method; sandy loam soil; preplant herbicide incorporation (PPI); calculation of ED,, for shoot fresh weight], several gramineous species, including both crops and weeds, displayed a highly differential response. Highly sensitive species include the weedy Poa annua and the cultivated Poa pratensis and Festuca rubra. Echinochloa crus-galli, the ryegrasses (Lolium multiflorum and L. perenne) and Alopecurus myosuroides have only moderate to low sensitivity whereas maize behaves as a tolerant species. However, maize root weight is a much more sensitive response variable compared to shoot weight and, based on the degree of inhibition at the root level caused by rimsulfuron PPI, maize might be classified as a moderately sensitive species. In bioassay experiments with Lolium perenne, a relatively small increase in soil pH resulted in a significantly higher herbicidal activity of soil-applied rimsulfuron