The article about pencycuron (part 3)

The attacks are normally more severe in southern and western Sweden than in northern Sweden. The economical importance is less than that of late blight. Different symptoms on sprouts, stems, stolons and tubers, which are caused by R solani, are described. The possibilities for reducing the attack by the fungus are discussed. This can be done by using seed free from black scurf, by planting in thoroughly cultivated soil and by chemically the seed borne infestation are presented. Tolclofos-methyl and Pencycuron have had the best effect against Rhizoctonia canker and have considerably decreased the occurrence of black scurf in the yield. Attempts to control both the seed and soil borne infestations by using spray equipment mounted on the potato planter are being made in field trials. Both this method and the use of a powder applicator on the planter are favourable for hygienic working conditions, but so far these methods have not given a satisfactory control of the fungus. To achieve such a control the fungicide probably must have a fumigating effect. An effective spray method demands a larger dosage. Control was maintained for 50 d after application. Mixing pencycuron at a rate of 2 g/litre soil and irrigation with 100-fold dilute solution at a rate of 9 litres/msuperscript 2 after full germination were not inhibitory to seedling growth. Sprouts of seed tubers, sprouted in daylight, were inoculated with Verticillium biguttatum, an ecologically obligate mycoparasite of R solani. Fungicides were mixed with the top soil. Biological control by Dbiguttatum increased the percentage of harvests with <5% loss due to grading from 24% to 56%. Fungicides at the recommended rates usually gave good results but lower doses were less effective in sand than in loam soils. When fungicides were combined with biological control, the results were often better: harvests with <5% sorting loss increased from 56 to 81%. Integrated control with pencycuron at 25% of the recommended rate was about equal to chemical control with pencycuron at full rate. Single green ring applications of propiconazole at 0.18, 0.32, or 0.48 kg a.i./ha and sequential green ring and boot sprays effectively reduced disease incidence over time. Severity of sheath blight over time, expressed as percent lesion height to total sheath height, was increased by green ring applications. With the loss of fungicidal activity over time, lesions on treated tillers progressed upward at a faster rate and reached higher levels than on nonsprayed tillers. Single boot applications at 0.18, 0.32, and 0.48 kg a.i/ha; both application of propiconazole at 0.32 kg a.i/ha followed by heading applications of either benomyl, iprodione, or pencycuron; or boot and heading sprays of benomyl had little effect on disease incidence. In contrast, disease severity was significantly reduced by all boot and heading treatment combinations. Diasese progress measured as incidence or severity was reduced most effectively by the application of pencycuron at boot and heading. Consistent positive yield responses compared with the nonsprayed control resulted from all boot and heading applications, whereas green ring applications generally resulted in a negative yield response. Yields were significantly negatively correlated with areas under the disease progress curves based on weekly severity measurements.
Sixteen of these fungicides were evaluated as seed treatments against pre-emergence damping-off and 8 against post-emergence seedling root rot of canola cv Westar and cv Tobin. Seed was planted in soilless mix infested with an isolate of AG-2-1 or AG-4, or their mixture. Benodanil, benomyl, carbathiin, cyproconazole, flutolanil, furmecyclox, iprodione, thiabendazole and tolclofos-methyl showed strong in vitro activity against both isolates. Fenpropimorph, flusilazole, propiconazole, triadimenol and vinclozolin had moderate activity and tebuconazole, triadimefon and chlorothalonil poor activity; while fenarimol, imazalil and nuarimol were ineffective against both isolates. Pencycuron gave very strong inhibition of the AG-2-1 isolate but was ineffective against the AG-4 isolate. Fenpropimorph, furmecyclox, iprodione and tolclofos-methyl, applied to Westar and Tobin seed at 1 g a.i./kg, provided about 90% control of pre-emergence damping-off in pots infested with either isolate AG-2-1, AG-4 or both. Furmecyclox and iprodione at 2-4 g a.i./kg were the most effective fungicides against post-emergence seedling root rot caused by the AG-2-1 isolate. Cyproconazole provided 90% control against damping-off at the lowest rates of 0.03 and 0.12 g a.i./kg seed of Westar and Tobin, respectively, but gave poor control of seedling root rot. Generally a higher quantity of fungicide was required in cv Tobin than in cv Westar for an equivalent level of disease control. Crops are predisposed to high disease incidence by high seed rate and high N fertilization with low K input. Spraying with pencycuron and triphenyltin hydroxide reduced infection in the field. No resistant lines were found in screening trials. Pencycuron or tolclofos-methyl applied as soil drenches or soil fumigation with chloropicrin, chloropicrin + methyl bromide, methyl isothiocyanate or dazomet reduced damage caused by the disease. In the laboratory, all treatments reduced the incidence of Colletotrichum gossypii, Rhizoctonia solani, Botryodiplodia theobromae and Fusarium spp Tolylfluanid, pencycuron + tolylfluanid and benomyl were the most effective against G gossypii, pencycuron was most effective against R solani, while pencycuron + tolylfluanid was the most effective against B theobromae and pencycuron + tolylfluanid and benomyl were best against F spp All fungicides improved the crop stand, and pencycuron + tolylfluanid gave the best control of damping-off. Five cultivars of B rapa, four cultivars of B juncea, four cultivars of B napus and one cultivar/strain from each of B carinata, B nigra and B oleracea were grown in soilless mix infested with an isolate of Rhizoctonia solani AG-2-1. B nigra and B juncea were considerably less susceptible to R solani than the four other species. Cyproconazole at 0.05-0.1 g a.i./kg seed and the other fungicides at 2-4 g a.i./kg seed provided almost complete control of pre-emergence damping-off in most Brassica species and their cultivars Their efficacy varied against the post-emergence seedling root rot. Furmecyclox, iprodione, tolclofos-methyl and pencycuron consistently gave good control of seedling root rot in all Brassica species and their cultivars Benodanil and fenpropimorph provided moderate control, and carboxin and cyproconazole gave poor control against root rot.
Also, the efficacy of three experimental combinations of fungicides and two fungicide combinations sold commercially was reduced. All herbicides caused visible damage to cotton plants in Tifton loamy sand soil in Georgia but not in the silty loam soil in Egypt. The most rapid recovery from herbicide damage and the least reduction in efficacy of fungicides were observed with herbicide norflurazon. In Georgia, the efficacy of fungicides was evaluated with no herbicides for four planting dates between 29 March and 2 May. Planting on 12 and 19 April did not affect the efficacy of the fungicides chloroneb, flutolanil, pencycuron, tolclofos-methyl, metalaxyl, or pentachloronitrobenzene, but it significantly reduced the percentage of stand with carboxin. Of the four strains two were sensitive, and the other two tolerant to pencycuron. Strain S1 metabolized 85% of the pencycuron in a 0.5 ppm liquid medium, while strains S2, T1 and T2 slowly metabolized only 10-20% of the pencycuron 24 hr after incubation. Main metabolites were cis and trans-3-hydroxycyclopentyl pencycuron, whose fungicidal activity was weaker than pencycuron.

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