The causal agents of damping-off of quinoa seedlings were determined in greenhouse experiments. Ascochyta caulina, Fusarium avenaceum, Fusarium spp., Alternaria spp. and Pythium spp. were isolated from infected parts of quinoa seedlings. The most frequent Pythium sp. was P. aphanidermatum. Pathogenicity tests confirmed that P. aphanidermatum and F. avenaceum were the causal agents of damping-off of quinoa seedlings under greenhouse conditions. A comparison of the reaction of quinoa with that of other susceptible plants (spinach, cabbage, sugar beet) showed that quinoa is most susceptible to the pathogen before emergence, during germination till the end of the stage of the first pair of true leaves. Germinable quinoa seeds seemed to have a lower ability to emerge from the soil. This serious problem is caused not only by pre-emergence damping-off from pathogens but more so by a complex of several adverse factors during germination when quinoa is most sensitive.

Veverka K., Štolcová J., Růžek P. (2007): Sensitivity of fungi to urea, ammonium nitrate and their equimolar solution UAN. Plant Protect. Sci., 43: 157-164.The sensitivity of oomycota, saprophytic and pathogenic fungi to urea, ammonium nitrate and UAN (urea plus ammonium nitrate in equimolar solution) was studied in laboratory trials. The compounds were applied in agar in concentrations of 0.06, 0.19 and 0.6M. The most toxic was urea. Ammonium nitrate inhibited the growth of fungi only in higher concentrations. In contrast, the growth of Gaeumannomyces graminis was stimulated by even the highest concentration of 0.6M ammonium nitrate. The fungi most sensitive to urea and UAN were alternaria tenuissima, Botrytis cinerea, cladosporium cladosporioides and Pseudocercosporella herpotrichoides. No synergistic effect between the two compounds in UAN was found. Urea was toxic also to colletotrichum acutatum which does not produce urease. Likewise, the urease inhibitor NBPT did not decrease the toxicity of urea to fungi; the urea degradation product ammonia should, therefore, not be assumed to be the only toxic agent. Application of urea in agricultural practice can decrease the population of a pathogen not only by the stimulation of antagonists, but also by the direct toxic effect. The tested concentrations of 0.06-0.6M correspond to 0.36-3.6% (w/w) solution of urea and to 0.64-6.4% UAN used in agricultural practice as a 75% water solution. If the dilution and metabolisation under natural conditions is taken into account, the concentration of urea 0.06M (0.36%) was too low to have an effect of practical importance on fungi. While after application of urea on plants or on plant debris its concentration is increasing due to water evaporation, the concentration of the extremely hygroscopic UAN is decreasing. Therefore, the control effect will depend more on the applied rate than on the concentration.Keywords: urea; ammonium nitrate; UAN; fungi; urease inhibitor NBPT The nutrients in both inorganic and organic fertilisers are able to influence the incidence and severity of biotic plant diseases, pests and weeds populations and their impact on the crop. Most of the information on this aspect deals with the effect of nutrients via plant. Individual elements have different roles; in general it can be said that they change the losses caused by pests by influencing plant resistance, alter plant growth and in this way the microclimate in the stand. Increased nutrition used to be prescribed as the first measure to control plant diseases. The most important aspect of this is an increase in the ability of the crop to compensate the losses. The effect of indi-

Zelená V., Veverka K. (2007): Effect of surfactants and liquid fertilisers on transcuticular penetration of fungicides. Plant Protect. Sci., 43: 151-156.Penetration of active compounds into the leaves plays an important role in their systemic activity. The effect of surfactants and liquid fertilisers on the penetration of fungicides was studied in model trials with the cuticle from Bryophyllum calycinum. Solutions of the fungicides were pipetted on pieces of cuticle laid on agar covered by spores of Cladosporium cladosporioides. The diameters of the inhibitory zones were measured and served to gauge the level of penetration by the variants. The size of the inhibitory zone of the control variant of Alto Combi 420 SC pipetted on the cuticle was only reduced to 92.6% of the variant where the solution was pipetted directly onto the agar; thus, the cuticle's effect on penetration was minor. Penetration through the cuticle decreased the diameters of inhibitory zones also of other fungicides: Discus to 84.1%, Horizon 250 E to 83.0%, Baycor 25 WP to 77.7%, Topsin 500 SC to 60.0 and Amistar to 37.8% of their control variant. The high penetration by the original formulations Alto Combi and Discus left no or little room for any increase of their penetration when mixed with additives. A higher penetration by Discus would also be undesirable because of its contact activity. The additives increased penetration most when mixed with Topsin and Amistar. The effect of surfactants and liquid fertilisers on the penetration of fungicides cannot be generalised. It was unique to each fungicide/additive combination. While the conditions of the trials enabled high penetration of some original formulations, the question arises how the additives will perform under conditions that will allow only low penetration.

The effect of droplet spectra on efficiency of contact and systemic herbicides was evaluated. As a model components were used: mixture of clethodim 240 g/l + surfactant (90% raps fluid, 10% polyetoxyl esters); bentazon 600 g/l and bentazon 480 g/l + Wettol LF 150 g/l. The effect of droplet spectra on Elytrigia repens (L.) Desv. was evaluated using systemic herbicide (clethodim 240 g/l + surfactant). No significant differences of the efficiency were observed between different droplet sizes at the treatments of mixture of clethodim + adjuvant between very different droplet size ranging from VMD = 193 µm to VMD = 929 µm. The effect of droplet spectra on Chenopodium album L. and Galium aparine L. was evaluated using contact herbicides (bentazon 600 g/l and bentazon 480 g/l + Wettol LF 150 g/l). Six droplet spectra, ranging from VMD = 183 µm to VMD = 911 µm, were used. The efficiency significantly increased with smaller droplet sizes. The worst results were achieved by droplet spectra of 586 µm and 911 µm for both bentazon 600 g/l and bentazon 480 g/l + Wettol LF 150 g/l. Effect of droplet spectra is more pronounced in contact compounds. Translocation of systemic compounds may be the main mechanism that nullifies the effect of the droplets size and lower leaf coverage.

The effects of droplet spectra, spray volume, and the addition of an adjuvant to the spray solution against Phytophthora infestans were evaluated using contact fungicides, mixtures of contact and systemic fungicides, and a contact fungicide + an adjuvant. Six droplet spectra, ranging from VMD = 183 µm to VMD = 939 µm, were used. The spray volumes were 300, 450 and 600 l/ha for the contact fungicides, and 300 l/ha was used for the mix of contact with systemic fungicides. No significant differences in efficiency were observed between different droplet spectra when used for the mix of contact with systemic fungicide treatments. However, the efficiency of treatments with a contact fungicide significantly increased with smaller droplet spectra. The larger droplet spectra required larger spray volumes for greater efficiency. The addition of the adjuvant (pinolene, 96%) to the spray solution of the contact fungicide caused the efficiency to be similar for all droplet spectra. The effect of droplet spectra is more pronounced in contact compounds. The translocation of the systemic compounds and the ability of the surfactant to improve the coverage with contact compounds may be the main mechanisms that counteract the effects of larger droplet spectra and lower leaf coverage.