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Title: POST HARVEST APPLICATIONS OF ZOXAMIDE AND PHOSPHITE FOR CONTROL OF POTATO TUBER ROTS CAUSED BY OOMYCETES

Author
item MILLER, JEFFREY - UNIV OF IDAHO
item OLSEN, NORA - UNIV OF IDAHO
item WOODELL, LYNN - UNIV OF IDAHO
item Porter, Lyndon
item CLAYSON, SHANE - UNIV OF IDAHO

Submitted to: American Journal of Potato Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/9/2006
Publication Date: 7/1/2006
Citation: Miller, J.S., Olsen, N., Woodell, L., Porter, L., Clayson, S. 2006. Post harvest applications of zoxamide and phosphite for control of potato tuber rots caused by oomycetes. American Journal of Potato Research 83:269-278.

Interpretive Summary: Pink rot and late blight can cause severe rot problems in potato fields during the growing season and in storage facilities after potatoes are harvested. Entire potato storages have been lost in eastern Idaho due to pink rot and in the Columbia Basin of Washington and Oregon due to late blight, resulting in millions of dollars of lost revenue for potato growers. The efficacy of current products on reducing or preventing potato tuber infections in storage facilities by these two pathogens has not been highly effective. Additionally, the pink rot pathogen has developed resistance to mefenoxam which has been used since 1987 to manage the disease in the field, which has increased the risk of potato tuber rot. The purpose of this study was to evaluate the efficacy of post-harvest applications of zoxamide, hydrogen peroxide, and phosphites on reducing potato tuber infections caused by the pink rot and late blight pathogens when applied at various rates and time intervals after potatoes were artificially exposed to these pathogens and then placed in storage. Products were applied to the potato tubers at 0, 1, 2, 4 and 6 hours after the tubers were exposed to the pink rot and late blight pathogens, respectively. Phosphite was effective at reducing late blight development at all time intervals. Zoxamide appeared to have good disease control if applied soon after tubers were exposed. Significant reductions in disease were observed at 0 hours for HPPA (28%), 2 hours for zoxamide (55%; 64 g a.i./MT) and 6 hours for phosphite (13%) when compared to potatoes that were exposed to the pathogens but not treated with any products. Phosphite provided consistent disease control even when applied several hours after inoculation and has potential to be a reliable post-harvest fungicide for the potato industry.

Technical Abstract: Potato storage tuber rots caused by the late blight and pink rot pathogens can cause severe economic losses warranting the need for effective post-harvest fungicide applications. The purpose of this study was to evaluate the efficacy of selective post-harvest fungicides in reducing tuber infections by the late blight and pink rot pathogens when applied at various post-inoculation time intervals.. ‘Russet Burbank’ potatoes were inoculated by submersion in a suspension of Phytophthora infestans or P. erythroseptica zoospores at 0, 1, 2, 4 and 6 hours prior to receiving a post-harvest treatment. Products evaluated were zoxamide (various rates and formulation), phosphite (335 g a.i./MT), and hydrogen peroxide/peroxyacetic acid mixture (HPPA, 9 g a.i./MT), all applied at 2.08 L/MT of tubers as a low pressure spray prior to storage. Zoxamide and phosphite significantly reduced late blight and pink rot incidence and severity when applied immediately after inoculation. HPPA was less effective at controlling disease development. Phosphite was effective at reducing late blight development at all time intervals up to 6 hours post-inoculation (7% vs. 80% in untreated). Zoxamide appeared to have good post-harvest disease control if applied soon after inoculation. The maximum time intervals between inoculation and treatment where significant reductions in pink rot incidence were observed was 0 hours for HPPA (28%), 2 hours for zoxamide (55%; 64 g a.i./MT) and 6 hours for phosphite (13%) compared to the untreated (73%). Phosphite provided consistent disease control even when applied several hours after inoculation and has potential to be a reliable post-harvest fungicide for the potato industry.