Root-knot nematode (RKN, Meloidogyne spp.) is a major problem in cucurbits such as watermelon, cantaloupe, cucumber, pumpkin, and squash. The reason RKN is problematic lies in their ability to persist for long periods in the soil and their wide host range, which includes more than 2,000 plant species, including crops and weeds. RKN infestations are favored by sandy and well-drained soils. Nematodes can disperse through contaminated water, soil, and infected plants.
Early infection of RKN can result in stunted and chlorotic plants. When nematodes are present in light sandy soils and temperatures are relatively high (above 80°F), plants start wilting (Figure 1). This is due to gall formation in the roots (Figure 2). Galls are formed by the enlarged nematode female bodies with egg masses. When soils are dry and temperatures are high, plants don’t uptake enough water due to the obstruction caused by galling. Plants severely affected by RKN can have reduced yields or die. Occasionally, RKN can form wilt disease complexes with other bacterial and fungal pathogens.
Figure 1. Wilting in a cantaloupe field due to infection with root-knot nematode (Photo by Cesar Escalante).
Figure 2. Root-knot nematode galls on watermelon roots (Courtesy of Dan Egel; originally published in the Southwest Purdue Ag Program website, Vegetable Disease Photos).
Due to the large host range, RKN is difficult to control by crop rotation; however, non-host crops such as grasses (e.g., grain crops or sweet corn) can be used in crop rotation programs for more than three years. This practice can help slow the population growth of nematodes in the soil. The use of certain cover crops has also been suggested. I recommend asking your seed provider for information about cultivars that may present resistance or tolerance to RKN. In some cases, resistant rootstocks have been used to graft cucurbits; however, grafting can represent an extra layer of labor before planting, especially for commercial cucurbit fields.
In the past, the use of fumigants such as methyl bromide showed high efficiency for nematode management; however, these products have been removed from the market due to environmental concerns. Other alternatives for RKN management through pesticides include products such as K-PAM HL (5.8L), Nimitz (4EC), Telone C-17 (L), Telone II (9.85L), VAPAM HL (4.25L), Velum Prime (4.16SC), and Vydate L (2WSL). The appropriate use of these products is described in the 2024 Midwest Vegetable Guide and their respective labels.
I also want to mention a new nematicide called Salibro that was recently launched last year. Its active ingredient is Fluazaindolizine, and it is labeled for use on cucurbits in many states, including Indiana. Conversations with extension specialists and growers suggest it helps manage RKN in cucurbit crops. This product should not be applied by overhead chemigation or aerial spray. Instead, it should be applied directly in the root zone or under the plant’s canopy. I recommend reading the label carefully before using this product, as several application restrictions are listed.
Feel free to contact me if you have any questions or comments or if you’d like to discuss effective practices for managing RKN.
Note:
The use of brand names of specific commercial products herein is solely for educational purposes and does not imply my personal endorsement.
Selected References:
Egel et al. 2022. Diseases of cucumbers, melons, pumpkins, squash, and watermelons. W. H. Elmer et al. (eds.), Handbook of vegetable and herb diseases, Handbook of plant disease management. https://doi.org/10.1007/978-3-030-35512-8_33-1
Egel et al. 2024. Nematodes. Phillips et al. (eds), Midwest vegetable guide 2024. mwveguide.org/guide
Thies. 2017. Root-knot nematodes. Keinath et al. (eds), Compendium of cucurbit diseases and pests. APS Press. St. Paul, MN, USA.