Introduction

In our previous Michigan State University Extension article, “Combating root-knot nematodes in daylilies: Experimental results – Part 1,” we explored pre-plant dipping practices to best control northern root knot nematodes (Meloidogyne hapla). To recap, northern root knot nematodes are detrimental to many crops in Michigan, including bare-root ornamentals like daylilies, and can cause significant economic losses. Daylilies are typically a three-year crop and fumigation can be an effective management tool in reducing nematodes in the first year of production. However, in the subsequent years of that production cycle, fumigants cannot be reapplied thereby allowing northern root knot nematode populations to reestablish and infest the plants. Our first trials explored root dipping practices to combat northern root knot nematodes, and we have since begun exploring fumigant alternatives that can be reapplied each year of production.

In 2018, a field trial was established with ‘Going Bananas’ daylilies to test nematicides and composts (Table 1) compared to an untreated and fumigated control over the course of the three-year production cycle. We monitored plant growth and nematode populations in roots and soil.

Results

In July (mid-season) of both 2018 and 2019, 1 gram of roots was collected from three plants within each plot and stained to determine the number of northern root knot nematode galls. In 2018, northern root knot nematode galls were fairly abundant. The fewest number of galls was observed in the Soil Steaming, TerraClean 5.0 and Fumigated treatments (Figure 1). In 2019, however, nematode counts plummeted across all treatments, thus all treatments were similar in terms of northern root knot nematode counts within roots (Figure 1).

Despite having the fewest number of galls in 2018, the plants within the fumigant treated plots were consistently much shorter than all the other treated plants (Figure 2). Indemnify, both as a drench and root dip, resulted in plants with the greatest growth in 2018 and 2019 (Figure 2). Although Indemnify did not result in the lowest northern root knot nematode counts, we speculate that combining this product with another nematicide, such as TerraClean 5.0, could result in significant reductions in northern root knot nematodes and improved plant growth.

It is important to note that Indemnify is not yet available for ornamental use but is in the labeling process. This year in 2020, the trial is in the third and final year of production and we will continue to monitor plant growth and nematode populations. At harvest in October, we will complete a cost-benefit analysis for each treatment compared to fumigation.

Conclusion

We have identified promising treatments to combat northern root knot nematodes in bare-root ornamental production including Indemnify (dip and drench), TerraClean 5.0 and Soil Steaming. Soil Steaming, although effective, is currently limited by technology in a field setting. Should an efficient method for application become available, it could be exceptionally effective at controlling nematodes. We will continue to monitor these treatments through the production cycle, so stay tuned for updates.

Before making nematode management decisions, understand the nematodes within your field. For more information and instructions on soil sampling, please visit the MSU Plant & Pest Diagnostics website.