Strategies

Tactics

• Hot water dips, e.g. banana rhizomes for protection from Radopholus spp.
• Chemical dips

Nursery Certification Program

Role of California Department of Food and Agriculture Division of Plant Industry

Designated Pest Status Ratings for Nematodes in California:

• A=13
• B=3
• C=15
• D=56
• Q=4
• X=6

The Golden Nematode Act and associated quarantines provide an excellent example of regulatory activities to control the spread of a nematode.

C. Increase in carrying capacity.

• nature of organisms
• probability of spread, etc.
• nature of damage
• how is education best accomplished - lectures, television, radio, newspaper, farm press?
• consider examples.

• water, wind;  irrigation systems - re-use of tail water, e.g., Aswan Dam reclaimed areas. Use of settling ponds for water drawn from rivers.
• machinery and equipment;  commercial harvesters, applicators;  used, contaminated, soybean equipment  probably contributed to spread of Heterodera glycines in the US. 
• dumping tare soil associated with harvested root crops.
• vectoring of Bursaphelenchus spp. by insects.
• movement by animals;  G.C. Martin fed roots with Meloidogyne incognita to cattle and  rodents.  Viable eggs survived digestive tract.  
• movement by birds;  new polders in Netherlands reclaimed from ocean and apparently infested with plant-feeding nematodes by migratory birds. 

Rate of Spread of Plant-Feeding Nematodes

The rate of movement of nematodes in soil from a point source would be quite slow if dependent only on their own activity. Active movement might be around 3 to 5 feet per year, and probably would only occur if there was food available within that radius. However, significant movement of nematodes is generated by natural and anthropogenic forces. 

Nematodes with stages that are resistant to desiccation may be spread widely and for long distances in blowing dust.  Wind spread of cysts of Heterodera avenae across desert regions between cereal production areas has been measured in Australia (Meagher et al).

Nematodes are readily and rapidly spread throughout a field, and among fields, by irrigation water, run-off, engineered drainage systems, and flood water. 

They are also rapidly spread around a field by tillage operations and land leveling (Thomason, Roberts and others). Such activities would generate broadcast distribution essentially instantaneously.

Many nematodes, particularly endoparasites are consumed in plant material by birds and other animals (Martin). They successfully survive passage through the digestive tract and become point-source infestations along migration patterns or within territorial boundaries. Their introduction into the New Polder region of the Netherlands after reclamation of land from the sea has been associated with migratory birds. 

Movement from field to field also occurs with contaminated soil adhering to vehicles and custom tillage and harvesting equipment. Consider the potential for nematodes being spread from field to field on the tires of tomato trailers and tomato harvesters that are currently swarming over Solano and Yolo counties. 

Movement of the soybean cyst nematode (Heterodera glycines) in the Midwest has been associated with the purchase of used equipment from established soybean areas for use in new areas of production.

Such spread results in single or multiple point-source infestations in a new field and, left undisturbed, might take several years to become evident. However, tillage and water movement are the norm. In the irrigated agriculture of California there may be 9 to 11 separate tillage operations conducted in a field after harvest of a crop in late summer to prepare it for the new crop in the spring. 

Consider the spread of water across fields in winter rainfall areas where compacted layers and decline of soil structure, resulting from intensive tillage, diminish porosity and water infiltration. 

Further, consider the frequency of furrow irrigation during the summer crop. There is enormous movement of soil and its resident organisms within a field in a single year. Spread throughout a field from a point-source infestation will probably occur in one or two years under conventional production practices in annual crops in California.

The most important determinant of rate of spread in agriculture is the movement of infested plants. That underlies the rationale for the existence of the CDFA Nematode Exclusion Division. 

Especially important is the import of plant material that will be used to propagate nursery stock, and the subsequent distribution of that nursery stock. Sale and movement of infested nursery stock, seed or turf 
immediately spreads the nematode pest to uninfested areas and distributes it throughout the planting site. Again, spread throughout the field is instantaneous. 

The pattern of distribution among fields is probably most intense closer to the nursery but, depending on the area serviced, may be statewide or even across state boundaries.

So, in summary, the most significant determinants of the rate of spread of nematodes are not the innate activity of the organisms but somewhat unpredictable effects of physical conditions, cultural operations, and topography, and market patterns. 

Spread Potential of Some Example Nematodes

1.  Belonolaimus longicaudatus

• Irrigation runoff into neighboring intensive agriculture.
• Movement with golf equipment.
• Potential for movement in turf if the nematode becomes established in turf nurseries.
• Wide host range of nematode: food source highly probable at new location.

2. Radopholus similis

• Endoparasite of subtropical and tropical plants. 
• Easily distributed widely in planting stock from nurseries.

3. Rotylenchulus reniformis

• Wide host range of tropical and subtropical plants, including many ornamentals that are distributed commercially.
• Cotton is a major host.
• Resistant to desiccation.

4. Aphelenchoides besseyi

• Easily distributed with seed, so always associated with its host.
• Resistant to desiccation.
• Sampling and detection problem in seed lots or harvested grain.

5. Globodera rostochiensis

• Eggs protected by a cyst and resistant to desiccation.
• Easily distributed with seed potatoes.
• Easily moved on farm equipment, custom harvesters, animals, etc.
• Very long-term survival in absence of hosts.