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M A R C H 2 0 1 6 POTATO GROWER 25 were best for pink rot control. Timing is important because it was found that an application after July 9th gave the best pink rot control. Surfactant and sili- cone adjuvants can help reduce injury when phosphoric acid rates were low 5 pta. This means that multiple applications of low amounts 5-7 pta of phospho- rous acid at the right time with a surfac- tantsilicone will provide the least injury and best protection from pink rot. Aphid Alert II Trapping Network Mr. Nathan Russart UMN said the results of Aphid Alert can be found at www.aphidalert.blogspot.com and at www.aphidalert.umn.edu. They created a risk index which reflects the relative efficiency of PVY transmis- sion of aphids compared to that of the green peach aphid Myzus persicae. Using five traps in the post-harvest test in Hawaii the risk index helped indicate that because of the very low number of aphids the probability of current season infection in Hawaii was negligible. Optimizing Metam Sodium Fumig- ation in Fine-Textured Soils Dr. Neil Gudmestad NDSU said that the primary cause of early dying is Verticillium dahlia. It is primarily soil- borne and the fungus survives as microsclerotia in the soil and on crop debris. Microsclerotia are released into the soil from potato debris breakdown after 1.5 to 2 years. He stated that Verticillium dahlia is probably the most important cause of economic losses in potato industry in the U.S. today when calculating the cost of control with the direct losses. Crop rotation is necessary to allow plant tissue to release the sclerotia Dr. Gudmestad said. The challenge is to kill the pathogen in the top layer of the soil. Eight Verticilium propagules per gram soil is the number at which fumigation becomes necessary. The highest propor- tion of Verticillium dahliae inoculum is in the top 4 of soil. However the Verticillium inoculum in 4-8 depth may be more efficient and has a greater influence on wilt development and totalmarketable yield. Trials showed that temperature had less impact of fumigant efficacy in a fine-textured soil high in organic matter than in a loamy sand low in organic matter. Dr. Gudmestad stated they have not observed a metam sodium rate response. He also said that correct tillage is needed before fumigation. One should till deeper than the applica- tion depth when there is between 80- 85 available soil moisture. That may be less on difficult soils. He emphasized that we need a grant to study soil health. One comment was that if you can bury debris with for example a