We announced in a previous newsletter article that we are doing a survey to understand the extent of root-knot nematode (RKN) damage on vegetable crops in Indiana. Among the 18 soil samples from high tunnels of 14 farms, RKNs (juvenile or adult) were found in 13 samples at 9 farms. Only 3 farmers knew RKN was an existing problem at their farms before our survey.
This lack of awareness is not surprising because above-ground symptoms caused by RKN are similar to plant nutrient deficiency. One needs to carefully scout roots for galling to identify RKN problems. The observation of galling also depends on how many roots were recovered from the soil, and the health level of the plants. If the roots have started to decay, one may not notice the galling and can easily overlook the problem. Farmers who grow root vegetables such as carrots may be more likely to notice the problem because roots are the harvested portion (Figure 1).
Figure 1. Root-know nematode damage on a carrot.
Why might root-knot nematodes be a hidden problem in high tunnels? This is because high tunnels used for year-round crop production largely increase soil temperatures inside of the structure throughout the year. Increased temperatures, constant soil moisture, and the fact that excellent RKN hosts are growing year-round make high tunnels an ideal environment for RKN population buildup.
Why is it important to be aware of the potential RKN problem? Compared with other disease or insect problems spread of RKN is limited except for spread by human activities. We will have other articles to discuss how RKN may spread to high tunnels, but being aware of the pathogen is the first step to tackling the problem.
We are continually doing this field survey. If you want to find out if root-knot nematode is a problem at your high tunnel, please contact Wenjing Guan (guan40@purdue.edu) or Dan Egel (egel@purdue.edu). We will arrange a soil nematode test for you.
The project is funded by United States Department of Agriculture National Institute of Food and Agriculture grant no. 2021-51181-35904.