Top wilting in asparagus

Wilting and dying off of young shoots of the second flush of asparagus are typical symptoms of one of the soil-borne diseases of this crop. Fungi could not be isolated from these shoots. A positive correlation was found between an increase of the pF-value of the soil and the occurrence of topwilting.Samenvatting Een van de ziekten van asperge is topverwelking, waarbij de stengeltoppen van jonge scheuten vrij plotseling verwelken, en vervolgens de gehele stengel afsterft. Dit komt vooral voor in jonge stengels van het zogenoemde tweede schot in juli en augustus. Er werd een positieve correlatie gevonden tussen het optreden van dit verschijnsel en het oplopen van de pF curve (Fig. 3). Schimmels konden uit juist verwelkte stengels niet geïsoleerd worden.     

Footrot in asparagus caused byFusarium oxysporum f. sp.asparagi

In the asparagus crop at least four soil-borne diseases can be distinguished. Footrot is one which appears to be caused byFusarium oxysporum f. sp.asparagi and is characterized by brown oval lesions on the lower parts of stems. A method is described for testing for pathogenicity the species ofFusarium and other fungi isolated from diseased plants. A negative correlation was found between the number ofF. oxysporum f. sp.asparagi isolates and the ‘G-value’ which provides an indication of the development of an asparagus crop.     

Treatment of Domestic Wastewater by Enhanced Primary Decantation and Subsequent Naturally Ventilated Trickling Filtration

To treat household wastewater, a sequence of ‘primary decantation–trickling filter percolation’ was applied in a lab-scale designed treatment system. Poly-electrolyte was used as coagulant to enhance the primary treatment and charcoal was used as carrier material in the trickling filters. Oxygen was supplied to the trickling filters by means of natural ventilation. In the lab-scale system, the enhanced primary stage removed more than 91% of the suspended solids (SS), and 79% of the total chemical oxygen demand (CODt). The subsequent trickling filtration brought a complete nitrification to the wastewaters at a volumetric loading rate (Bv) of 0.7–1.0 g CODt L^-1 d^-1. On average, the concentrations of the CODt and SS in the final effluents were about 55 and 15 mg L^-1 respectively. With respect to phosphate, physico-chemical removal was the dominant process. About 46–62% of total P was removed from the tested wastewaters. The integrated treatment system also achieved a fair degree of hygienisation. The numbers of total coliforms, fecal coliforms and fecal streptococci were decreased by 2–4 log units. The sludge production of the entire treatment system was about 1.7% (v/v) of the treated wastewater. Only primary sludge was produced; secondary sludge produced in the trickling filters was negligible. The cost savings in terms of minimization of sludge production and aeration energy are estimated to be substantial (i.e. some 50%) relative to a conventional activated sludge system.