Flower borders help reduce mosaic in Russet Norkotahs

In recent years, there has been an increased interest in improving soil health through changing traditional agricultural practices. One way to accomplish this is to increase overall species diversity in agricultural ecosystems. Having diversity in plant species can improve crop health in other areas as well. In 2014, a flower mix used as a crop border was found to be effective at reducing the spread of mosaic (primarily caused by PVY) in the highly susceptible potato variety, Russet Norkotah sel. 8.

In 2015, a study was conducted at the San Luis Valley Research Center which evaluated the use of a companion crop, planted with a potato crop, to determine whether or not this would reduce the spread of mosaic in potatoes. In this study, the change in mosaic levels in a potato crop was evaluated under four different scenarios with and without the use of a companion crop: 1. no insecticides were applied, 2. no insectides applied + flowers as a border, 3. insectides applied, and 4. insectides applied to the crop that was adjacent to a plot of potatoes with a flower border. Russet Norkotah sel. 3 seed with a mosaic level of 2% was evaluated under these four scenarios, with and without a companion crop. Plants were visually evaluated for mosaic levels two times in the summer and a sample was also collected at harvest and sent to Hawaii to evaluate the spread of mosaic.

Results from this study indicate that the use of a companion crop can, in some cases, reduce the spread of mosaic more than just using a border of flowers alone. There was not a statistical difference between mosaic levels in the potatoes when no insecticides were used vs. when a flowering border was used. However, when a companion crop was used in combination with the flower border, there was a reduction of mosaic levels when compared with the plot that did not have insecticides applied. There was not always a reduction in mosaic levels when a companion crop was used for each of the four scenarios, but there was never a statistical increase in mosaic when the companion crop was planted with the potatoes. This indicates that the use of a companion crop could help in managing mosaic caused by PVY.

There are a couple of reasons why increasing plant diversity in a potato crop might have an effect on the spread of mosaic. PVY and other potato viruses that cause mosaic are spread by infected aphids feeding on potato plants, similar to mosquitos infected with malaria spreading the disease to humans. A diverse mix of plant species attracts a variety of natural predators to aphids, such as lacewings and ladybugs. The feeding on aphids by their natural predators would reduce aphid population numbers, which would also reduce the potential spread of mosaic. Another reason for the reduction in mosaic levels might be that the plant species used in the flower mix and companion crop mix are not hosts for viruses affecting potatoes. Potato viruses that cause mosaic are non-persistent, meaning that an aphid will lose the virus it is carrying if it feeds on a non-host plant species. The greater the number of non-host plant species in or near a potato crop increases the likelihood that an aphid will feed on a non-host plant, rather than a potato plant. If an aphid infected with a potato virus feeds on a non-host plant, it will lose the virus before it feeds on a potato plant, thereby preventing the spread of mosaic.

PVY is a potato disease that has recently increased in severity in the San Luis Valley and across North America. The management of this, and other mosaic causing viruses, can be very difficult when raising susceptible potato varieties like Russet Norkotah. The use of alternative management strategies, like using flowering border crops and companion crops, provide additional tools the potato farmer can use to manage the spread of this disease. These strategies can be used in combination with other strategies, such as using clean seed, crop oils, and insecticides. The only way to effectively reduce levels of mosaic in the SLV is through the use of a combination of these strategies, not just relying on one strategy and hoping for the best.

— By Andrew Houser, Colorado State University Potato Certification Service

Source: Colorado Potato Commision