M A R C H 2 0 1 8 12 POTATO GROWER ing areas. Plant growth was ideal in Hawaii. Kent Sather of the North Dakota State Seed Department mentioned that the North Dakota post-harvest test was at Algers Farms in Florida, where the plant growth was as good as it gets. There were 364 lots, representing 8,000 acres. In both states there was an increase in PVY strains: PVYNTN and PVYwi. They show milder symptoms and may cause tuber necrosis. Dr. Gary Secor, NDSU, gave a presenta- tion aboout Soft Rot and Dry Rot Seed Decay. He mentioned that soft rot was the most common cause of poor stands and emergence. Most decay is caused by the soft rot bacterium Pectobacterium and dry rot fungi, Fusarium. Dr. Secor gave a list of fungicides against Fusarium. He reminded the audience that managing Fusarium indirectly manages bacterial decay. He mentioned the most SDHI’s don’t work and resist- ance of F. sambucinum to TBZ (Mertect) is still widespread. Fusarium resistance to fludioxonil has been reported in sev- eral Canadian provinces, Michigan, North Dakota, Minnesota, Colorado and Nebraska. There is a fitness penalty asso- ciated with fludioxanil resistance which may explain why fludioxanil resistance does not have a huge impact on disease control in the field. However, MZ has good field activity. Difenoconazole and prothioconazole are very effective. Consequently, in both Emesto Silver and Cruiser Maxx Extreme, it is the tria- zole fungicide, prothioconazole or difenoconazole, that is doing the work to suppress Fusarium. Dr. Secor concluded that bacterial soft rot caused by Pectobacterium is the main cause of potato seed decay, but that Dickeya can also cause seed decay and poor stands. Fusarium dry rot in storage infects seed during cutting and can pre- dispose seed to bacterial soft rot decay. Dr. Secor emphasized that Fusarium together with Pectobacterium causes more seed decay than Pectobacterium alone. It is, therefore, worthwhile to manage Fusarium because you indirectly reduce bacterial seed decay. Some seed treatment fungicides do not have good activity against Fusarium sambucinum, our main cause of dry rot. F. sam- bucinum has become resistant to some fungicides. There are, however, differ- ences in susceptibility among varieties to soft rot with Fusarium. Increasing seed cutting temperatures from 45oF to 50oF reduces seed decay, caused by Fusarium with Pectobacterium, because the increased temperature enhances wound healing. There are differences in wound healing among varieties, which could partly explain differences in seed decay. Bacterial decay stabilizes in 3-5 days depending on variety, but decay due to bacteria and Fusarium continues up to 21 days. Dr. Amanda Gevens of the University of Wisconsin was the guest speaker for the Crop Expo Potato Program. Understanding and Managing Silver Scurf of Potato was one of her topics. She gave a summary of three to five years research. She described potato sil- ver scurf symptoms and suggested not to confuse them with the symptoms of black dot. Black dot lesions are raised and darker than non-raised silver scurf lesions. They found identification test kits available. Among non-chemical Silver Scurf Management Options are cultural strategies: In field; there can be site and seed selection, crop rotation, lower planting density, smaller seed size, enhanced tillage. Moldboard plowing showed reduction in silver scurf. In storage, there can be ventilation systems installed in such a way that they mini- mize cross-contamination, decrease rela- tive humidity and temperature as much as possible. Dr. Gevens suggested to avoid partial unloading of bins and have smaller volumes in storage. As far as resistant varieties are concerned, there are no resistant commercial cultivars available, although tolerance has been observed in a few wild accessions. Later maturing cultivars generally perform better in field trials. The results of their management trials were that Elatus® (azoxystrobin + ben- zovindiflupyr) performed best in most years, while a consistent control was obtained with Quadris® (azoxystrobin), Maxim MZ®, and Cruiser Maxx Extreme® (fludioxonil). There had been no significant difference with foliar Phostrol applications, but Stadium® usually performed as best post-harvest treatment. They had found several promising options for at-plant and post- harvest silver scurf chemical control. There are more in the pipeline. They completed their third full year of chem- ical control programs, in conjunction with pathogen sampling to determine critical pathogen infection windows. Managing Colorado Potato Beetle was the topic of Dr. Ian MacRae from the Univeristy of Minnesota Crookston who mentioned the adults overwinter in the shelterbelts and can colonize fields at a speed of 140 meters per hour. These adults do not fly unless the temperature is over 70oF. When identifying adults one should find that the hind wings (membranous) of overwintering adults are orange and of the newly emerged adults (F1) are clear. The extended emergence of overwintered adults in the last few years has resulted in a different temporal distribution of larvae (feeding stages) throughout the summer, although cold springs may explain late emergence too. This means that both central Minnesota and the RRV are now