Graduate Thesis Or Dissertation

Improving Best Management Practices for Potato Production in the Columbia Basin : An Evaluation of Essential Oils for Control of Verticillium Wilt and the Fate of Chloride in the System

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  • Although the potato (Solanum tuberosum L.) is a global crop, few growing regions rival the high yields of the Columbia Basin of Eastern Oregon and Washington. Two research projects were conducted in Hermiston, OR to contribute to best management practices for the region. The first project evaluated the efficacy of essential oils to manage Verticillium dahliae Kleb., a persistent soilborne pathogen of potato that when untreated leads to significant yield loss. The objectives of this research were to: 1) evaluate if essential oils inhibit V. dahliae growth in vitro; 2) evaluate whether essential oils adversely impacted plant growth; and 3) determine whether an integrated management approach using essential oils and selective fertilizer application could be an effective approach in mitigating crop loss from V. dahliae in vivo. Twelve treatments including carvacrol (an extract of Origanum vulgare), clove (Eugenia spp.), lemongrass (Cymbopogon spp.), and garlic (Allium sativum) were evaluated by transferring from an actively growing V. dahliae VCG 4A colony on Sorensen's NP-10 media to similar media amended with varying concentrations of essential oils. Hyphal growth was measured after two time periods. Carvacrol, clove, garlic, cinnamon, thymol, and lemongrass were most effective in the laboratory assay. V. dahliae growth was reduced by 100% with at least one dilution of these treatments when compared to the untreated controls. These six treatments, as well as salicylic acid, were then used as potato seed treatments in replicated greenhouse trials to determine efficacy in reducing V. dahliae infection. Calcium chloride and ammonium phosphate, which reduced V. dahliae infection of potato in previous unpublished work, as well as four combination treatments of both fertilizer and essential oil applications, were also evaluated in greenhouse trials. No differences were observed among treatments in emergence, plant height, or number of nodes in the greenhouse trials. Treatment impact on V. dahliae infection in vivo was limited but in vitro results suggest that it may be possible to reduce V. dahliae infection with an integrated management plan using essential oils. Further research is required to evaluate best application methods and rates to achieve consistent disease reduction. The second project evaluated the effects of different potassium (K) fertilizer applications on nutrient levels in the potato production system. Petiole sampling is used to make decisions about in-season nitrogen (N) application. Past research has documented an antagonism in uptake between nitrate-N and chloride (Cl), which suggests that N recommendations should be adjusted to take Cl application into account. The objectives of this research were to evaluate: 1) where Cl moves in the system from time of soil application to uptake in plant; and 2) the effects of different K fertilizer applications on nutrient concentrations in plant matter, including potato petioles, with particular emphasis on the effect of the accompanying anions (Cl vs. sulfate). In this experiment, two years of field trials were conducted in a field with high soil test K (0.79 cmol kg⁻¹ exchangeable K; 0-20.3 cm depth) so that differences in yield were minimized across treatments. The source of K (KCl, K₂SO₄ (SOP), or K₂SO₄*2MgSO₄ (Kmag)), rate (0, 112, 224, 448 kg K₂O/ha), and time of application (seven months pre-plant, two weeks pre-plant, or in-season) were evaluated. Plant Cl levels were elevated when K source was KCl, with increased KCl application rate, and as applications were made closer to the time of plant uptake. Plant Cl concentrations for KCl treatments applied in September were 1.1 g kg⁻¹ in tubers and 15 g kg⁻¹ in tops; for treatments applied preplant were 2.2 g kg⁻¹ in tubers and 22 g kg⁻¹ in tops; and for treatments applied in-season were 1.9 g kg⁻¹ in tubers and 24 g kg⁻¹ in tops. Petiole Cl levels were highest with KCl treatments as compared to SOP and Kmag. This data supports the conclusion that Cl can be taken up unhindered by potato plants in large quantities when available, and that Cl availability is increased when KCl is applied at higher rates or later in the growing season.
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