The effect of foliar application of phosphonate formulations on the susceptibility of potato tubers to late blight

Abstract

Foliar sprays of potato plants with phosphonic acid (partially neutralised with potassium hydroxide to pH 6.4) substantially reduced infection of the tubers by Phytophthora infestans, the cause of late blight, in glasshouse and field experiments over a 4-year period. Healthy tubers of blight-susceptible cultivars removed from treated plants and artificially inoculated by spraying with sporangial/zoospore suspensions of P infestans did not develop disease symptoms, demonstrating that the phosphonate applications had directly reduced the susceptibility of tubers to infection, probably as a result of translocation into tuber tissue. In contrast, foliar application of fosetyl-aluminium did not significantly reduce tuber blight development following inoculation. Five to six sprays of partially neutralised phosphonic acid (2 kg ha-1) applied at 10-14 day intervals resulted in the least tuber infection, but such a treatment regime may not be economic. In trials where the effect of timing and rate of application of 2-4 kg phosphonic acid ha-1 was examined, a single treatment of 4 kg ha-1 applied mid- or late-season proved the most effective. A spray programme in which one or two applications of phosphonic acid are combined with use of a non-systemic or systemic fungicide to enhance foliar protection offers the possibility of controlling both foliage and tuber blight and could have a major impact in reducing overwinter survival of P infestans in tubers.

Efficacy of fungicide combinations, phosphoric acid and plant extract from stinging nettle on potato late blight management and tuber yield

“…This study revealed that there was very little variance in the incidence of tuber blight recorded among treatments of fungicides, phosphite, and plant extract combinations at both locations and seasons. In previous research, it was observed that phosphoric acid and other protectant fungicides applied in the field prior to harvest and on harvested tubers can protect potato tubers from P. infestans upon subsequent inoculation (Cooke and Little 2001;Johnson et al 2004). The same studies also demonstrated that foliar applications of phosphoric acid can reduce late blight infections occurring during the growing season (Cooke and Little 2001).…”

“…The mode of action of phosphonate has been reported to be direct antifungal activity affecting mycelia growth (Fenn and Coffey 1989) and indirect stimulation of host defenses (Guest and Grant 1991). These compounds are also thought to have some systemic characteristics with basipetal and acropetal activity for control of foliar and tuber blight (Cooke and Little 2001). This chemical characteristic allows the compounds to be stable in plants for several weeks and offer long-term protection in potato leaves and tubers (Ouimette and Coffey 1989a;Smillie et al 1989).…”

Effects of Mulch and Potato Hilling on Development of Foliar Blight (Phytophthora infestans) and the Control of Tuber Blight Infection

“…The management of tuber blight has often been accomplished by control of foliage blight involving the use of host plant resistance or fungicide applications (Cooke and Little 2002). Fungicide applications to control foliar late blight and vine kill using desiccants prior to harvest are the most common methods for reducing tuber infection (Stevenson 1993).…”

Effect of foliar applications of phosphite on post-harvest potato tubers

“…Potassium phosphite (KPhi) utilized in the present work is commercialized as a "nutritional compound with antifungal action" (Agro-EMCODI). Several plant species have been treated with phosphites to protect them against pathogens (Cooke and Little 2002;Guest and Grant 1991;Johnson et al 2004;Lobato et al 2008;Ouimette and Coffey 1989;Panicker and Gangadharan 1999;Reuveni et al 2003); however, their mode of action is not completely understood yet. As alkali metal salts of phosphorous acid (H 3 PO 3 ), phosphites can not be directly used by crops as a sole source of nutritional phosphorus (McDonald et al 2001).…”