Lars Wiik

Induced resistance in potato to Phytphthora infestans —effects of BABA in greenhouse and field tests with different potato varieties

We have investigated to what degree induced resistance with β-aminobutyric acid (BABA) can protect potato from late blight infection under Swedish field conditions and if synergistic interactions occur if BABA is applied in combination with a commonly used fungicide, Shirlan. In greenhouse experiments we also investigated the durability of BABA induced resistance, the dose-response relationships in susceptible (Bintje) and partially resistant (Ovatio, Suberb) cultivars and effects of combined applications of BABA and fungicides. We found a clear effect of BABA on P. infestans infection of greenhouse grown potato plants. The lesion sizes were reduced by on average 40–50% compared to untreated control. However, this effect lasted for only 4–5 days after BABA treatment and then the efficacy was lower. When BABA was given in combination with the fungicides it appeared to have an additive effect both in greenhouse and field experiments. Higher concentrations of BABA gave a stronger protective effect. The partially resistant cultivars Ovatio and Superb reacted to lower concentrations of BABA where no effect was found in susceptible Bintje. According to our field data, 20–25% reduction of the fungicide dose in combination with BABA gave on average the same result on late blight development as full dose Shirlan alone; while reduced dose of Shirlan alone sometimes resulted in less effective protection. Our results indicate that induced resistance could be used in practice in combinations with fungicides in order to reduce the amount of toxic compounds under north European conditions.

Fusarium seedling blight of wheat and oats: effects of infection level and fungicide seed treatments on agronomic characters

The effects of seed-borne Fusarium spp. and Microdochium nivale infection in spring wheat, winter wheat, and oats in Sweden was investigated in field trials for the agronomic characters yield, thousand kernel weight, grain volume weight, gluten, protein, starch, straw strength, and plant density. Seed with high and low levels of infection was mixed to obtain six infection levels in the proportions of 100/0, 80/20, 60/40, 40/60, 20/80, and 0/100 percent. The seed was untreated or treated with Celest Extra Formula M (CEFM, difenoconazole + fludioxonil) or Celest Formula M (CFM, fludioxonil). In the field trials using untreated seed, there were significant differences between infection levels only for some agronomic characters and levels. Fungicide seed treatment with CEFM in spring wheat had no significant effect on most agronomic characters including yield. In winter wheat and oats, seed treatment with CFM increased yield by 7–11% and plant density by up to 33% while having no effect on other characters. The percentage discoloration of crown roots and stem bases due to Fusarium/Microdochium spp. was also investigated visually in winter wheat and oats and found to increase with higher infection level. Fungicide seed treatment thus mainly increased plant emergence in seed lots with low-to-moderate Fusarium/Microdochium spp. infection and had little or no effects on other agronomic characters.

Study on Biological and Economic Considerations in the Control of Potato Late Blight and Potato Tuber Blight

An economic analysis was made of old results from 1993-1996 (22 field trials) and new results from 2010-2013 (12 field trials) obtained in field trials with different doses of fungicides to control potato late blight (PLB) and potato tuber blight (PTB) caused by Phytophthora infestans. The objective was to determine the economically optimal dose for effective control. In 1993-1996, the economic net return was highest for long intervals of about two weeks between treatments and a dose of 60% of the recommended level. The difference between the experimental treatment with the highest net return and the untreated control was 1587 € per hectare (ha-1) in susceptible cultivars, but only 531 € ha-1 in moderately resistant cultivars. In addition, the mean difference in net return between all treated susceptible and all treated moderately resistant cultivars was 874 € ha-1. In the half of the field trials with the lowest maximum attack of PLB, the difference between the experimental treatment with the highest economic income and untreated control was 547 € ha-1, while it was 1571 € ha-1 in the half of the trials with the highest maximum attack. The results for 2010-2013, which were all based on a short treatment interval of about one week between treatments, showed that in table potato the economic net return was highest at 100% and 75% of the recommended dose, whereas in starch potato cultivars it was highest at 50% and 25% of the recommended dose. The net financial result was calculated for 13 different scenarios. As expected, potato price and potato crop yield and quality were of the greatest importance. The price of fungicides affected net profits by between 167 and 656 € ha-1 depending on treatment intervals and dose. These results challenge the way in which late blight is controlled in conventional potato farming today, especially in starch potatoes. We therefore propose investment in future years be based on the dose-range response in cultivars with differing host resistance to both PLB and PTB, and on forecasting and warning with respect to PLB- and PTB-control in different potato cultivars. We believe that such investment could be very valuable in optimizing the use of fungicides in potato cultivation.