What Is It? | Facts in Depth | For the Professional Diagnostician
Garlic Bloat Nematode
Bulbs initially are slightly discolored and as the disease progresses, the bulbs become very dark in color and begin to decay. Eventually, they get very soft and exhibit cracking. The basal plate also can be easily separated with slightly reduced roots.
Above ground symptoms of bloat nematode infections include leaf splitting, stunting, curled or twisted leaves, stem softening/collapse and leaf swelling. Eventually, the plants exhibit pre-mature defoliation.
The bloat nematode, Ditylenchus dipsaci, can survive long periods of time in a dried, suspended state. Mating is required for reproduction with this particular nematode. After fertilization by the males, mature females can lay up to 10 eggs per day for 20 to 50 days. Under favorable conditions, the second stage juveniles hatch from their eggs and undergo two more molts. At this stage, they are infective and can survive desiccation. With water present, these juveniles can move limited distances to feed on young plant parts, but rarely feed on the roots. Extensive bulb damage caused by feeding creates wounds for secondary pathogens. The juveniles mature and differentiate into mature males and females. The life cycle of this nematode can be completed in 19 to 23 days.
Favorable Environmental Conditions
These nematodes can rapidly increase in population under ideal conditions of warm, moist soils. Nematodes also spread by rain and irrigation.
Often Confused With
- Fusarium basal rot – Advanced infections of bloat nematode cause severe discoloration and rotting of the base of the bulb, which resembles symptoms of Fusarium basal rot. Fusarium basal rot is often a secondary infection to bloat nematode. Some differences between the two diseases are that Fusarium turns the bulbs pink and the roots are completely decayed, while the roots are usually intact with bloat nematode.
Monitor for discoloration, distortion, and pre-mature drop of foliage in plant clusters, which enlarge as the pathogen spreads from plant to plant after periods of rain or wetness.
Currently, there is no threshold information available for bloat nematode on garlic.
- Start with nematode-free seed – Using nematode-free planting material is the best management strategy for preventing disease by preventing pathogen introduction. This particular nematode has been found to survive in bulbs used as seed, so it is critical that pathogen-free planting material is obtained from trusted sources.
- Rotating with non-host crops – Rotation with non-Allium species is an important aspect of management of bloat nematode. If bloat nematode is a problem, garlic should be grown in a 5 year rotation.
- Use hot water treatments – Hot water treatments can be used to reduce bloat nematode in questionable planting material. The following three-stage hot water treatment is recommended: dip cloves in 38° C water for 30-45 minutes, then in 49° C water for 20 minutes with a final soak in 18-22 ° C water for 10-20 minutes immediately prior to planting.
- Use Chemical management – Chemical management options are available for managing bloat nematode. Nematicides can be used to reduce nematode populations in severely infested fields. See the Midwest Vegetable Production Guide (OSU Extension Bulletin 948) for nematicide recommendations.