| | Roguing | Insect management | Irrigation
Return to the Guide to Commercial Potato Production on the Canadian Prairies..
Disease prevention (Also Disease management)
In seed potato production it is imperative to maintain disease within levels tolerated by the certification system. Failure to achieve the tolerated disease levels will result in either the downgrading or rejection of specific seed lots or in certain cases the rejection of the entire farm from certification. Bacterial ring rot is the
most devastating disease since its presence will result in the rejection of the total farm.
Disease standards for certified seed potatoes
| Disease and varietal mixture | E1 | E2 | E3 | E4 | FD | Cert |
| PSTV | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Ring rot | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 | 0.0 |
| Total all viruses | 0.0 | 0.1 | 0.2 | 0.3 | 0.5 | 2.0 |
| Total Blackleg and wilts | 0.1 | 0.2 | 0.3 | 0.5 | 1.0 | 2.0 |
| Varietal mixtures | 0.0 | 0.0 | 0.0 | 0.1 | 0.2 | 0.5 |
Nuclear and Pre-elite class seed have a 0.0% tolerance for all diseases on final inspection.
Many disease pathogens are normally present in potato production areas. Consequently, there is a constant potential for the introduction of these pathogens into a seed crop. The seed grower must be constantly aware of the potential sources of disease introduction, the mechanisms of disease spread and the methods of preventing disease introduction. Grower reputation is built upon preventing or minimizing disease introduction and spread in the seed crop.
Preventing disease contamination of seed lots is the main objective of seed potato production. Disease contamination can occur from four sources:
- The parent seed used to produce the crop.
- The equipment and storage used in potato production and handling.
- The soil used to produce the crop.
- Insects transmitting disease from other potatoes in the crop production area.
Seed source
Many disease problems in a seed operation can be traced indirectly and sometimes directly to purchased seed. This is especially true with bacterial ring rot, although leaf roll and mosaic viruses are also frequently problems in purchased seed. Purchase seed from experienced growers who have a reputation for producing quality, disease free seed.
Equipment contamination
Contaminated potato handling equipment is an important source of disease introduction and spread. Ring rot bacteria can contaminate equipment used in fieldwork or potato handling and potato structures through contact with diseased material. Dormant ring rot bacteria can survive several years in a desiccated state on the surfaces of equipment or storage structures. For these reasons, seed growers are discouraged from purchasing used equipment or from sharing equipment with other producers. If this type of equipment is used it must be thoroughly cleaned of dirt and debris with a high-pressure washer then disinfected under the supervision of a seed inspector. Parts with the potential to harbor disease inoculum such as the sponge or soft rubber rollers used on seed cutters, should be replaced.
When equipment is in need of a cleanup, the seed potato growers must use proper sanitation procedures and apply them rigorously. Sanitation consists of cleaning and disinfecting all equipment, storage, tools and pallet boxes that contact the seed potatoes. Since most disinfectants are inactivated by soil and plant debris, it is essential that this material be removed by thoroughly cleaning the equipment with a pressure washer or steam cleaner before the disinfectant is applied. The seed storage and all equipment coming in contact with the seed lot should be disinfected with a quaternary ammonium compound such as Ag-Services Incorporated General Storage Disinfectant, Bardak 2210 Disinfectant Sanitizer, or DMR-23 Disinfectant. Surfaces must remain wet for at least 10 minutes for the disinfectant to destroy disease organisms.
Field borne diseases
Certain potato diseases can survive from season to season in the field. Depending on the type of pathogen, it may survive in the resting form either in the soil or in potato plant debris, or in a living form in surviving potato tubers. On occasion, diseased tubers survive the winter and grow the following spring as diseased volunteer plants. These volunteer potatoes are a source of contamination for the current season crops. Most seed potato producers practice a three to four year rotation to minimize soil disease problems. Fields with a previous history of bacterial ring rot infection should not be used for potato production for a minimum of two years, and during those two years volunteer potato plants must be eliminated.
Growing seed potatoes in a commercial production area
Sucking and chewing insects carry many viral diseases of potatoes. For example, aphids transmit potato leaf roll and mosaic viruses from plant to plant. Aphids become infected with the virus while feeding on diseased plants and are capable of transmitting the virus to healthy seed plants. Attempts to control aphids in the seed fields may fail to prevent disease introduction. A virus-infected aphid may feed on a potato plant leaf and introduce the virus into the plant before it succumbs to an insecticide; however, insecticides do prevent disease transmission from continuing unchecked.
Seed growers who are producing in commercial production areas with the associated greater risk of disease inoculum should attempt to isolate their seed fields from potential sources of contamination. If that option is not available, then the grower should attempt to control viruliforous (virus-infected) aphids in the source field before winged aphids migrate to seed fields, spreading virus to the seed crop. If the seed field already has virus-infected plants then the application of pesticides will help prevent spread within the field. Planting seed with low or zero incidence of virus as reported by a post-harvest test, and limiting the number of seed generations produced in areas of commercial production will help to limit virus spread within seed crops. Roguing all infected plants as early as possible prevents in field spread by aphids.
Roguing
The purpose of roguing is to:
- Remove plants of a variety different from that planted in the field
- Remove diseased plants that will produce diseased seed tubers or which represent inoculum sources for disease spread within the field
- Ensure the seed field passes inspection.
Although roguing is a common practice in seed potato production it is only practical when the field is contaminated with a very low incidence of an off variety or diseased plants that are easily distinguishable. When rouging, remove plants, seed piece and daughter tubers from the field.
The process of roguing requires:
- Experienced individuals, who are capable of recognizing the symptoms of the important potato diseases
- Appropriate timing
- Environmental conditions which contribute to the expression of visible disease symptoms.
- In addition, roguing is costly, as the field may have to be walked several times to remove the off variety or diseased plants.
Roguing for viral diseases is best done prior to flowering and during overcast weather.
Although roguing is considered to be a valuable tool in the maintenance of seed quality, it is rarely completely effective. Only those plants that are manifesting visually recognizable symptoms can be rogued. Symptom expression can be influenced by many factors including environmental conditions and varietal characteristics. In addition, not all pathogen-infected plants (even those from seed pieces cut from the same tuber) express disease symptoms to the same degree or at the same stage of growth. The end result is that much of the roguing is conducted to provide a visually clean field that will satisfy the seed certification specifications.
Tuber-unit planting is a tool that has been used to improve the effectiveness of the roguing process. All seed pieces cut from a single tuber are manually fed into a planting mechanism, which places them consecutively in a low. A gap is sometimes left between the seed pieces generated from different tubers. If the plants originating from any of the seed pieces cut from a single tuber express symptoms of disease, then all the seed pieces cut from the tuber are removed from the field. This ensures that all seed is removed from the field even if only one piece is manifesting symptoms of disease or has characteristics of a foreign variety. Since tuber-unit planting is slow and very labor intensive, its use is limited to small plots of high value seed. This practice was a regulatory requirement for the first and second field generations of seed. Regulatory amendments approved in May 2002, resulted in the removal of this requirement from seed regulations, due to cost, and time consideration, relative to industry benefits. However, it is considered an important management tool for seed growers, particularly when a grower has concerns for the level of virus that may be present in seed planted.
Insect Management
Certain types of aphids and leafhoppers have the potential to both introduce and spread viral diseases within a seed crop. Controlling the populations of these insects by the application of insecticides at planting or after crop emergence will reduce, but not completely eliminate, problems with insect-borne disease. Seed growers should monitor insect populations and if possible, plan on vine killing before insect numbers increase beyond acceptable levels. Isolation and planting clean seed will also reduce the risk of insects spreading disease within the seed crop.
Irrigation (Also see Irrigation Management)
A continuous supply of an adequate amount of moisture via timely rainfall or irrigation is crucial for maximizing yields and quality of seed potatoes. Adequate moisture at tuber set is particularly important as it encourages setting of a large number of tubers and controls or reduces the severity of common scab. Over-irrigation increases susceptibility to late blight, blackleg, powdery scab and tuber rots. The wheels on wheel-move and centre pivot irrigation systems may contribute to the transmission of some viral or bacterial diseases within the field.
Written by Dennis Lidgett |
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