Potato Grower

WWW.POTATOGROWER.COM 41 Author Brice Dupuis defended his doctoral dissertation about developments of crop management methods to control the spread of PVY in December 2017. The full dissertation is available at http://hdl.handle.net/2078.1/192701. the associated crops were in competition with potato plants for nutrients and water, which led to significant harvest losses (11 and 13 percent). Despite this, neither of the two associated ground covers caused any significant problems during harvest. Intercropping is probably the least expensive technique for controlling PVY. Estimates put the cost of sowing hairy vetch as scarcely higher than that of a one-off mineral oil treatment. straw mulChing Although rarely used in practice, mulching with grain straw is recognized as an effective measure against the spread of PVY. According to field studies, the efficacy of this approach ranges from 25 to 50 percent, lower than most mineral oils but higher than insecticides. The mode of action of straw is still poorly understood. It has been observed that fewer winged aphids land on fields mulched with straw. Over time, however, the straw becomes less effective. This is easily explained by the fact that the straw must be visible to the aphids in order to be effective. Since potato foliage develops and increasingly covers the straw, its efficacy diminishes over time. It appears that more straw ground cover produces greater PVY resistance in a field, though growers would need to consider how straw mulch would affect their individual harvest operations. straw with mineral oils Mineral oil is less effective when applied at the beginning of the season, but straw mulching is less effective toward the end of the season. Theoretically, a combination of these two control methods ought to offset their individual shortcomings when applied separately. After four years of Agroscope trials, the combination of the two methods was on average 16 percent more effective in controlling PVY than the use of mineral oil alone. The cost of distributing the straw with a straw spreader is about 50 percent of the cost of the mineral oil treatments for one season. These costs could be reduced by the producer using his own straw. FrequenCy oF mineral oil treatments It is recommended that the frequency of mineral oil treatments be increased during the first two to three weeks after emergence before continuing with weekly treatments. This method has demonstrated its effectiveness during heavy vector pressure at the beginning of the potato season. However, no study has yet investigated how long it is helpful to increase the frequency of these treatments. Once-weekly treatments can be resumed as soon as plants naturally become less susceptible to infection. Intercropping is probably the least expensive technique for fighting PVY. Here, potatoes are shown intercropped with oats (right) and hairy vetch. Many field studies indicate that straw mulching is a more effective measure against the spread of PVY than the use of insecticides.

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