Nematode Focus: Organic Amendments and Nematicide Impacts

Nematodes, Turfgrass, and Organic Amendments

By Brandon Jones, Graduate Research Assistant, University of Florida and W. T. Crow, PhD, Professor of Nematology, University of Florida

With the exception of a few locations throughout the state, the soils throughout Florida are dominated by high sand content, remnants of a time period when the state was completely inundated by a shallow sea. The white sandy beaches that the state is known for can be found along the majority of the coastline. While tourists travel from all over the world to experience the tranquility of walking barefoot along these sandy coastlines, other organisms which can be economically devastating to turfgrass stands also thrive in these Florida sandy ecosystems. What I am referring to is plant-parasitic nematodes that can be a major problem for sod producers, golf courses, athletic fields, and residential lawns throughout most of Florida. Most people working in the turfgrass industry have a basic understanding of nematodes, along with some knowledge on treating them. For management of these problematic nematodes, the common method is to use pesticides, but it is important to realize there may be other options available.

The use of organic amendments on turfgrass systems has been shown to improve overall health of the plants by counteracting some of the negative properties associated with sandy soils such as decreased water holding capacity, cation exchange capacity and microbial activity. There is some evidence showing a reduction in plant-parasitic nematode numbers with the addition of organic soil amendments, but the data showing a population reduction is largely inconclusive. It’s important for more research to be completed in this area, which is where I come into the story. I am currently working in the landscape nematology lab at the University of Florida and my research is focused on the use of organic amendments on turfgrass.

The project I’m currently working on consists of three separate trials over a period of two years. Two of the trials are topdressing studies and the third trial had amendments incorporated within the soil prior to sprigging. All of the trials are taking place on different bermudagrass cultivars. The amendments being used are Canadian sphagnum peat moss (CSPM), conventionally produced compost, a specific compost product called Comand® Compost, and sand. Many of these treatments are commonly used soil amendments which most people are familiar with. Comand compost is a commercially available product which has been inoculated with specific microorganisms, some of which may be antagonistic toward certain plant-parasitic nematode species. Our objective is the measure the overall effects these different amendments have on turfgrass, so we are collecting data through many different avenues including measuring, root lengths, percent green coverage, thatch depth and of course, plant-parasitic nematode counts.

This project will continue through May 2018 so we are still collecting data. Overall, we are seeing an improvement in turfgrass health among the treatments when compared to the control treatments. The root systems are generally more developed, the percent green coverage is higher and the plant-parasitic nematode populations are lower. However, each of the amendments seem to have their own different benefits. Some may have higher percent green coverage, but higher nematode counts while the other treatment is the opposite.  At this point, it is safe to assume the addition of soil amendments will benefit a turfgrass system, but we’ll need to collect more evidence before any specific recommendation can be made.


Nematicides and Soil Health

By Benjamin D. Waldo, Graduate Research Assistant, University of Florida and W. T. Crow, Professor of Nematology, University of Florida

Not all nematodes are harmful to plants. The vast majority of nematodes in soil are beneficial and contribute to nutrient cycles and soil ecosystem health. Harmful nematodes feed on plants while beneficial nematodes feed on microorganisms in the soil. Microbes help break down organic matter and release nutrients that are bound up in biomass. Beneficial nematodes feed by grazing on microbes such as bacteria and fungi, but also on other nematodes and insects. The grazing feeding behavior stimulates population growth while preventing populations from getting too large and crashing. Soil health can be assessed by analyzing the nematode feeding groups present in soil samples. Stable environments contain a variety of nematodes with different feeding types. Soil with an unhealthy ecosystem is dominated by a few feeding groups with few nematodes high on the food chain that are sensitive to environmental disturbance.

In our study, we found varying effects of nematicides on non-target nematodes. Indemnify had the greatest impact on beneficial nematodes. We found decreases in nematode numbers starting within a few days after the final application, which lasted over eight months. Other researchers have found Indemnify to persist in the soil for an extended period of time. This is beneficial for plant-parasitic nematode management, but it can negatively affect beneficial nematodes and soil health. Divanem, Nimitz and MultiGuard had moderate to low impacts. These three nematicides negatively affected beneficial nematodes a few days after the final treatment, but most of the nematode populations were able to recover after eight months. Nematodes high up the food chain were affected longer than the nematodes lower on the food chain. The active ingredients in Divanem, Nimitz, and Multiguard break down faster in the soil than the active ingredient in Indemnify. The movement rate and susceptibility to microbial decomposition of these nematicides may contribute to the lower impact on beneficial nematodes than Indemnify.

In summary, nematicides affect beneficial nematodes differently. Nematicide selection may have an impact on soil health. Indemnify has long lasting effects on plant-parasitic nematodes in the soil, but these long lasting effects also negatively impact beneficial nematodes. Divanem, Nimitz, and MultiGuard has lower impacts on beneficial nematodes. The effects of these nematicides last weeks to months, but generally recover by eight months. Nematodes at the top of the food chain are affected longer than lower food chain nematodes. This suggests that while some nematodes recover quickly, other nematodes and soil health are impacted potentially for over half a year after nematicide application.