Effective management of PVY is requiring changes to seed certification procedures and grower practices. As with other potato viruses, the best management method for PVY is to avoid introduction of the virus to your fields. Once the virus has been detected, steps must be taken to avoid spreading it on your farm. There are three main strategies for managing PVY in potatoes. Use an integrated approach with the following practices for the best results.
- Avoid introduction of PVY onto your farm
- Manage inoculum levels in the field
- Reduce on-farm spread of PVY by aphids
- Use resistant cultivars strategically
Avoid introduction of PVY onto your farm.
Don’t plant the problem! -Purchase the best certified seed potatoes. This is the absolute best defense any grower can have against PVY! As previously mentioned, virus infections in plants cannot be cured. Once a plant is infected it stays infected for life and virus is easily transmitted to progeny tubers in most cultivars. Therefore, the best defense against virus disease is minimizing exposure or being resistant to infection. While Seed Certification programs remain the primary defense against PVY, their job has gotten more complicated by the factors mentioned above that have been primarily responsible for the resurgence of PVY in the US potato crop. Seed certification has relied primarily on visual inspection of the crop to determine virus levels both during the growing season and in the post-harvest grow-outs of samples of tubers from each seed lot entered into the certification process. In recent years, seed certification programs have increased the amount of lab testing of plants from the field and post-harvest tests to improve the reliability of virus incidence estimates.
Select seed based on post-harvest estimates of virus incidence rather than the estimates from summer inspections. The summer inspection data can provide information on how much virus was planted, but it does not always accurately estimate how much virus is in the harvested seed due to asymptomatic late season infections and the mild/transient nature of symptoms in the growing season due to virus strain and cultivar characteristics. Also, the buyer should ask for information on how virus incidence was determined, e.g. visual inspection, lab testing. Also, it is important to ask for the number of plants or tubers that were observed or tested from the seed lot to determine virus. The reliability and precision of the estimate is significantly influenced by the sample size. (For more information see % Disease Estimation and Sample Size Tools).
Obtain PHT estimates based on lab testing vs visual assessment (PVY). Lab testing is more accurate due to mild or non-existent foliar symptoms typical of some cultivars/PVY strains.
Find out how many tubers were observed or tested for PVY to generate the PHT estimate. Larger sample sizes allow for the detection of virus at lower levels and are more accurate but are often not feasible. Be aware that the PHT only provides an estimate of the virus in a seed lot and that this estimate has an associated standard deviation that is not typically reported
Don’t plant seed potatoes with symptoms of virus-caused tuber necrosis. Inspect the seed you purchase for lesions and necrosis. Destroy affected seed and keep it out of your fields.
Avoid compost from contaminated sources outside your farm. Ensure these materials do not originate from potato debris or cull piles.
Manage inoculum levels on your farm.
Practice a strict on-farm sanitation protocol. All cutting and planting equipment should be disinfested before coming in contact with seed as well as between seed lots. PVY can be mechanically transmitted from an infected plant to a healthy plant via plant sap on hands and tools. Several commercial disinfectants are available. Make sure these are allowable for use in your growing region. For more information please see Cleaning and Disinfecting Potato Equipment and Storage Facilities.
Destroy overwintering sources of PVY. Properly destroy cull piles according to established guidelines as infected tubers will produce sprouts that can serve as a source of PVY. Because they are cull piles, there is a greater chance the culled tubers harbor PVY, as well as other potato viruses, late blight, etc. Cull piles pose a very large risk to the potato farm and this risk is controllable. In some states, laws mandate the destruction of cull piles. For more information please see Cull and Waste Potato Management.
Rogue volunteer potatoes early in the season.Roguing means the removal and destruction of unwanted potato plants, often growing as volunteer potatoes from the previous year’s crop. This practice eliminates potential sources of inoculum before it can be spread.
Rogue infected plants throughout the season. Infected plants serve as sources as inoculum so should be removed on a regular basis.
Destroy weed hosts throughout the season. Some common weed hosts of PVY include the nighshades, pigweed, lambsquarters and purslane.
Do not plant seed potato fields near fields of other Solanaceous crops. These include other potato fields, tomato, eggplant, pepper, tomatillo, tobacco, groundcherry and petunia.
Reduce on-farm spread by aphid vectors of PVY.
Isolate seed fields from commercial production. Commercial fields are often a source of PVY because management is not cost-effective.
Do not plant seed potato fields near fields of other Solanaceous crops such as tomato, eggplants, pepper, tomatillo, tobacco, ground cherry and petunia. These crops can be a source of PVY as management is not cost-effective.
Use border crops to surround high-valued seed lots. Border crops can “cleanse” PVY from aphid sytlets (mouthparts) before the aphids find the potatoes. Borders consist of plants, or crop species, that cannot support infection of PVY. The non-host border is planted around small, early-generation seed lots, <0.2 ha field size, with fallow land around the outside of the border and no skips within the crop-plus-border area. The border buffers the potato seed lot from the in-flight of aphids, because the aphids usually land at the interface between fallow ground and green crop. For more information on border crops see Management of Potato Virus Y (PVY) in Wisconsin Seed Production.
Time planting and top kill to avoid aphid flights. Prevent late-season virus infection by planting and top-killing seed potato fields early. This precludes the colonization of potatoes by late-season, migrating aphid populations. For example, the soybean aphid tends to move into potatoes as soybean fields surpass certain growth stages (R5 stage and beyond).
Spraying for colonizing aphids may reduce spread of PVY within the field under some circumstances. Spray only when scouting indicates aphid populations are above threshold levels. Critical factors affecting efficacy are timing, aphid species, choice of chemical and coverage. The green peach aphid, potato aphid, and buckthorn aphid will colonize and reproduce on potato and are efficient vectors of PVY. Systemic insecticides applied at planting are effective in reducing within field spread of virus by colonizing aphids, however, they lose efficacy mid-season and have been implicated in off target effects on beneficial species such as ladybugs as well as bees. Remember – most vectors of PVY do not colonize potato and their ability to transmit PVY to the plant will not be affected by systemic insecticides.
Spraying for immigrating winged aphids (colonizing or non-colonizing) is NOT effective in controlling the spread of PVY into a field. As noted in the aphid section, PVY can be acquired and inoculated within seconds of an aphid feeding or probing. This can happen before an insecticide has a chance to kill or deter the aphid. This holds true for both standard insecticides such as organophosphates as well as newer anti-feedant compounds.
Anti-feedant compounds may help control spread of PVY by colonizing aphids. However, they are not effective in controlling immigrating aphids because they do not work quickly enough. Anti-feedant compounds include Fulfill and Beleaf.
Mineral oils may reduce the spread of PVY by interfering with aphids’ interest and ability to puncture the leaf surface but do not protect the underside of the leaf and need to be sprayed often. Unless your sprayer covers all surfaces it will not be effective. These oils must be applied frequently to cover new growth and oil dilution due to rain or irrigation. These oils include JMS Stylet Oil and Aphoil. Check your states pesticide regulations to be sure these chemicals are allowed.
More information: Aphid Vectors of PVY.
Use resistant cultivars strategically.
It’s important to understand the classification of resistance which includes tolerance, field resistance, partial or strain-specific resistance and immunity. The level of resistance to PVY strains has been characterized for many potato cultivars and further testing is ongoing (see table below). Plant immune cultivars whenever possible and avoid planting tolerant cultivars in close proximity to fields with susceptible cultivars.
- Immunity: Immune plants do not support virus infection and are resistant to all strains of PVY. While there are known resistance genes that confer durable resistance to all PVY strains tested, they have not been widely used by breeding programs until recently. There are few commercially available immune cultivars in the US, e.g. Eva and Payette Russet. Plant immune cultivars whenever possible.
- Partial or strain-specific resistance: Potato cultivars will often have reduced levels of virus, will restrict movement of virus within the plant, will develop a necrotic (cell death) response that walls off and kills the infected plant tissues, or will express a combination of these traits. All of these reactions tend to reduce, slow, or limit the spread of virus within a field or to plants in adjacent fields and to progeny tubers. Many US cultivars possess this type of resistance, but the resistance is, for the most part, specific for PVYO. PVYO is becoming less prevalent in the US and this type of resistance is a major factor in the strain shift observed over the past decade (see figure below). With few exceptions this resistance in not effective against the emerging strains of PVY.
- Field resistance: These are cultivars that can be infected under experimental conditions, but that generally stay heathy in the field. This may be attributed to plants that are less attractive to aphids or that possess mature plant resistance, i.e. older plants are not as susceptible to infection. Onset of mature plant resistance can vary and can be PVY strain-specific.
- Tolerance: Tolerant cultivars are the Typhoid Mary’s of potatoes. They are easily infected at all stages of growth and virus is easily transferred to progeny tubers, but the plants rarely show any symptoms. Yield can be significantly affected. While these cultivars may be a good option when grown in isolation, when infected with PVY, they are an excellent source of virus for aphids to acquire and move to adjoining or nearby fields. Therefore, avoid planting tolerant cultivars in close proximity to fields with susceptible cultivars. Shepody, Russet Norkotah, Silverton Russet and Cal White are examples of tolerant cultivars. An updated list is maintained at the Oregon Seed Certification Service under Variety Information then click Latent Variety List. The susceptibility of some common North American potato varieties is provided in Table 1, below.
Table 1. Potato cultivar PVY foliar and tuber symptoms (data source Gray, Whitworth 2018)
* PVY resistant varieties, plant did not become infected after inoculation
…….. Not tested/planted
PVY Cultivars – PVY Foliar and Tuber Symptoms.pdf
