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40 POTATO GROWER | JULY 2019 Utilizing mineral oils to reduce PVY transmission in seed potatoes Oil It Up Potatoes sold for seed must pass rigorous certification requirements that vary depending on the state or province in which they are grown. Acceptable end-of-season PVY levels can vary between 0.5 to 5.0 percent, so seed potato growers must do all they can to reduce the transmission of PVY in the field. It has been reported that over 50 different aphid species are able to transmit the PVY virus. Because of the non-persistent nature of the virus in aphids, acquiring and transmitting the virus often occurs in a matter of seconds. It is understandable how aphids moving from another host crop can wreak havoc on a seed potato field as they fly overhead, land, probe, fly to the next plant, probe some more, only to move off in a short period of time. Meanwhile, as they have probed several plants during their pit stop, they have not only picked up, but consequently transmitted PVY from an infected plant to a non-infected plant. There are a few known principles of limiting the spread of in-season PVY, some easier to implement than others. First, and probably most important, is to begin the season off with the cleanest seed possible. Other principles aim to avoid aphid movement and corresponding PVY spread in time and space. These items are more difficult to control, especially the closer a seed field is to a commercial grower. The last major strategy to manage PVY is to employ several in-season chemical and cultural control methods. These methods often include the use of insecticide applications, mineral oil applications, and border crops. Of these, mineral oil applications are the most effective at controlling the in-season transmission of PVY. A combination of in-season insecticide and mineral oil sprays has been shown to enhance PVY control measures, but mineral oil remains the most critical component. Mineral oils have long been used as insecticides and fungicides in agricultural crops. They primarily work by smothering insects and disease spores they come in contact with, disrupting the normal functions of the organisms. Mineral oils also remain at the application site and possibly provide a barrier to entry when applied to the leaf surface, as well as repel pests by interfering with their recognition of the plant environment. There are several theories as to why applications of mineral oil to potatoes are effective at decreasing the spread of seasonal PVY. It is likely that a combination of theories is correct. As noted, mineral oil works through asphyxia to control insects on contact. It is possible that if aphids are present at the time of application, this mode of action contributes to the control of in-season PVY transmission. Another contributing factor is the interaction with the oil and the stylet of the aphid. It has been shown that transmission of PVY is inhibited when the aphid stylet comes into contact with the oil. Mineral oil on the leaf surface may also influence aphid probing behavior. Some studies show a positive interaction between oil on the leaf and an increase in aphids' time to initiate probing. While still uncertain, mineral oil seems to disrupt the attachment and release process from receptors on aphid mouthparts. Another piece to the puzzle is the evidence that mineral oil actually penetrates the leaf, which may help prevent the further spread of PVY. Since mineral oil provides a barrier of protection on each potato leaf in the field, it is important to ensure good coverage to the potato canopy. Growers should choose the appropriate nozzle type and carrier volume for maximum canopy coverage Diggin' In Diggin' In DISEASE CONTROL | By Bradley S Sladek