Effect of photoperiod and host distribution on the horizontal transmission of Isaria fumosorosea (Hypocreales: Cordycipitaceae) in greenhouse whitefly assessed using a novel model bioassay

A model bioassay was used to evaluate the epizootic potential and determine the horizontal transmission efficiency of Isaria fumosorosea Trinidadian strains against Trialeurodes vaporariorum pharate adults under optimum conditions (25±0.5°C, ~100% RH) at two different photoperiods. Untreated pharate adults were arranged on laminated graph paper at different distributions to simulate varying infestation levels on a leaf surface. Four potential hosts were located 7, 14 and 21 mm away from a central sporulating cadaver simulating high, medium and low infestation levels, respectively. Percent hosts colonized were recorded 7, 12, 14 and 21 days post-treatment during a 16- and 24-h photophase. After 21 days, mean percent hosts colonized at the highest, middle and lowest infestation levels were 93 and 100%, 22 and 58%, 25 and 39% under a 16- and 24-h photophase, respectively. From the results, it was concluded that the longer the photophase, the greater the percentage of hosts colonized, and as host distance increased from the central sporulating cadaver, colonization decreased. The use of this novel model bioassay technique is the first attempt to evaluate the epizootic potential and determine the horizontal transmission efficiency of I. fumosorosea Trinidadian strains under optimal environmental conditions at different photoperiods. This bioassay can be used to assess horizontal transmission efficiency for the selection of fungi being considered for commercial biopesticide development

Effects of subsurface drip irrigation rates and furrow irrigation for cotton grown on a vertisol on off-site movement of sediments, nutrients and pesticides

Abstract – Subsurface drip irrigation can reduce off-farm movements of fertilizers and pollutants and improve the water use efficiency of irrigated agriculture. Here we compared the effects of furrow and subsurface drip at different irrigation rates, based on a percentage of daily crop-evapotranspiration rates (ETc), on run-off and off-site movement of suspended sediment, nutrients and pesticides from cotton crops grownon a vertisol. Our results show that furrow irrigation significantly increased suspended soil loss, of 5.26 t ha−1, compared to that of subsurface drip irrigation at 120% of ETc, of 2.53 t ha−1, whereas no erosion was recorded with deficit subsurface drip irrigation. Off-site movement of nitrogen in furrow, of 18.63 kg ha−1, was five times greater than subsurface drip irrigation at 120% ETc. It was much less with 105% ETc(0.37 kg ha−1) and 90% ETc (0.15 kg ha−1), and absent for 75% and 50% of ETc. Phosphorus loss from furrow, of 778 g ha−1, was greater than for the wetter subsurface drip treatments that gave 23 g ha−1 for 90% ETc and 19 g ha−1 for 120% ETc. No P loss was recorded from drier subsurface drip irrigation rates. Herbicides such as atrazine and diuron were applied in the year prior to the experiment, but considerable amounts were recorded in furrow run-off in both years, but only at 90 and 120% ETc subsurface drip irrigation in the first year. Concentrations of applied herbicide residues in the runoff exceeded the minimum threshold level for 99% species protection and, although the total amount of herbicide movement was higher in furrow, at times the concentration was greater for wetter subsurface drip irrigation run-off. Residues of insecticides, such as endosulphan applied in a previous year and dimethoate applied in the current years, were recorded in runoff from subsurface drip at 120% and furrow irrigation. Their concentrations in each year exceeded minimum threshold level. Subsurface drip irrigation at 75% ETc offered the best trade-off between off-site run-off, erosion and pesticide movement and yield and water use efficiency