The bulb and stem nematode (Ditylenchus dipsaci), is a major pest of garlic that has destroyed hundreds of acres of garlic in Canada over the past decade. The nematodes survive in the soil as well as in garlic cloves that are being used to plant subsequent crops. Cloves with low numbers of nematodes are asymptomatic , and it may not be until the third or fourth year of growing the crop that rot is observed just above the basal plate (Figure 1).
Female nematodes can lay up to 500 eggs during their lifespan and can start producing eggs in as few as 19 days at an average temperature of 15°C. The fourth juvenile life stage of the nematode can resist dry environments and freezing temperatures allowing it to survive the winter in cloves or soil (Yuksel, 1960).
Symptoms of the stem and bulb nematode include premature senescence prior to harvest and the yellowing of the lower leaves moving upwards. As the root plate rots, infected plants can be easily pulled, and the plants appear to have no roots attached. Symptoms can be easily confused with Fusarium basal rot. Garlic infected by a subspecies of Fusarium oxysporum are also easily pulled, but some roots typically remain attached to the bulb. Both stem and bulb nematodes and Fusarium oxysporum f. sp. capae can colonize the bulb at the same time.
The best management practice is preventing the introduction of nematodes into the crop. Testing planting stock for stem and bulb nematode prior to planting is the most effective way to avoid this pest. Bulbs can be submitted to a pest diagnostic lab qualified for nematode extraction, identification and count. Soil from fields prior to planting can also be sampled. Stem and bulb nematodes are most prevalent in the top 5 cm (2 inches) of the soil profile (Blauel et al., 2021). Avoid allowing samples to dry out and keep in a cool place prior to submitting to the lab. Submit soil samples within two days of sampling to help avoid false negatives. Before planting, growers should consider sending their poorest looking cloves to determine whether stem and bulb nematode is present in their planting stock.
Many growers have started clean, with nematode and virus-freed roundels from the Garlic Growers Association of Ontario / SPUD Unit or planted bulbils in nematode-free soil. Both strategies can result in a nematode-free crop that can be multiplied and phased into production in 2-4 seasons. These methods are effective at reducing the pathogens present in the crop, but it can take several years to reach the number of plants desired. In addition, it takes careful planning to avoid contamination from infested fields.
Once stem and bulb nematodes are present in the crop, it is difficult to manage. The Ditylenchus nematode genus has an extensive host range that includes over 450 plant species (Mckenry and Roberts, 1985). According to studies conducted at the University of Guelph and University of Manitoba, the specific nematode species that is found in to infect garlic in Canada reproduces well in alfalfa, peas, beans, and onion. Crops that reduce the population of stem and bulb nematode after garlic include soybean, wheat, canola, corn, barley, potato, carrot, and lettuce (Hajihassani et al., 2016; Ives 2019). Once the bulb and stem nematode is introduced to a field, utilizing a four-year crop rotation with a non-susceptible crop can help suppress this nematode.
A hot water treatment (soak) of cloves at 49°C for 20 minutes prior to planting has shown to be an effective method of suppressing nematodes; but it can be difficult to implement. Temperatures below 49°C may not kill the nematodes, and temperatures above 50°C may damage the germination rate of the planting stock.
It’s also important to prevent soil moving from infested fields to a nematode-free field. Clean machinery, boots, tools and other equipment of all soil between fields to help prevent nematodes from establishing in a new field.
Several crop protection products have been evaluated for their potential to manage this nematode in Canada. Multiple field trials conducted by the University of Guelph and OMAFRA have shown fluopyram (FRAC group 7) to be effective at reducing nematode levels thus improving yields.
Trials conducted by Ives in 2016 and 2017 showed a drench application of fluopyram to infested planted stock in muck or mineral soil significantly decreased nematode survival resulting in a greater marketable yield compared to other treatments. Work conducted by Celetti in 2017 and 2018 showed fluopyram drenched over infested planting stock in open furrows resulted in reduced nematode damage, fewer nematodes in the harvested bulbs, and marketable bulbs when harvested the following year. In a trial conducted by Blauel et al., in 2019, a fluopyram drench provided a significant increase in the percent marketability and yield in planting stock that had both low and high levels of nematodes.
Velum Prime (fluopyram) has since been recently registered on garlic via the Minor Use Program for the management of stem and bulb nematode. This registration is the result of an URMULE submission and as of March 10, 2022, the PMRA has approved a use pattern of Velum Prime on garlic as outlined below. This product provides a new management strategy that will be useful for managing nematode populations in lightly infested planting stock, or on planting stock that was harvested from a field with a history of stem and bulb nematode. This label expansion was made possible due to past work conducted by Michael Celetti, Lilieth Ives, Mary Ruth McDonald and Jim Chaput.
Summary;
- Always test new planting stock for stem and bulb nematode by sending a sample to a lab prior to planting
- Obtain clean seed roundels from the Garlic Growers Association of Ontario / SPUD unit or plant bulbils in nematode-free soil
- Implement a four-year crop rotation using non-hosts to stem and bulb nematode
- Clean machinery prior from nematode-infested fields prior to entering a new field
- Rogue out symptomatic plants throughout the growing season
- When Velum Prime is applied as a soil application for control of stem and bulb nematode, use another FRAC mode of action (not a group 7) for the first foliar fungicide application of the season, if applicable
| Pest Suppressed | Rate | PHI | Use Information |
| Stem and bulb nematode (Ditylenchus dipsaci) | 500 mL/ha or 3.75 mL / 100 m row (based on 75 cm row spacing) | 30 days | One application at planting in the fall or in the spring. Spray specified dosage in a 10-15 cm band in-furrow at planting and cover with soil. For best results, direct the in-furrow spray to the seed and soil. Apply in 50-300 L of water per hectare. |
Blauel, T., Celetti, M.J., Jordan, K.S., and McDonald, M.R. 2021. Optimizing methods to sample and quantify stem and bulb nematode, Ditylenchus dipsaci, in garlic, Allium sativum, field soil. Canadian Journal of Plant Pathology. In press.
Blauel, T., Vander Kooi, K., and McDonald, M.R. 2019. Evaluation of nematicides for control of stem and bulb nematode in garlic, 2018-2019. 42-44.
Celetti, M.J., and Cranmer, T.J. 2017. Effect of drenching Velum Prime, Agri-Mek SC and Vive-ABA over rows planted with garlic cloves cv. Music infested with stem and bulb nematode on plant stand, yield, nematode damage and nematode populations in the bulbs at harvest in 2017. 15-16.
Hajihassani, A., Tenuta, M., and Gulden, R.H. 2016. Host Preference and Seedborne Transmission of Ditylenchus weischeri and D. dipsaci on select pulse and non-pulse crops grown in the Canadian prairies. Plant Disease. 100:1087-1092.
Ives, L. 2019. Epidemiology and Management of Stem and Bulb Nematode. M.Sc. thesis, University of Guelph, Guelph, Ontario, Canada.
McKenry, M. V., and Roberts, P. A. 1985. Phytonematology Study Guide Publication 4045. University of California, Division of Agriculture and Natural Resources. 1-56.
Yuksel, H., 1960. Observations on the life-cycle of Ditylenchus dipaci on onion seedlings. Nematologica 5:289-296.
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