Abstract
The nematicidal efficacy of milbemectin and its commercial formulate Milbeknock® on (i) egg hatching, (ii) juvenile motility and (iii) infective capacity of root-knot nematodes was evaluated in vitro and in planta assays. Serial dilutions of pure milbemectin were tested against nematode eggs and juveniles and lethal concentrations LC50 and LC90 calculated. Exposure of egg masses to milbemectin at a concentration of 30 μg/mL for 72 h reduced egg hatching by 52%. The increase in exposure time to 240 h did not increase the egg hatching inhibition at the highest concentration 30 μg/mL (53%) but reduced egg hatching at 15 and 7 μg/mL by 35 and 24%, respectively, when compared to untreated controls. The inhibitory effect of milbemectin on juvenile motility ranged from 41 to 87% depending on its concentration, and this effect was persistent after rinsing the juveniles in water. The probabilistic dose–response model indicated that lethal concentrations of milbemectin for juvenile motility were LC50: 7.4 μg/mL and LC90: 29.9 μg/mL. The pre-plant application of Milbeknock® to soils infested with the nematode reduced its infective capacity by 98–99% compared to untreated soils in pot experiments. Milbeknock® reduced nematode soil population densities by 50–60% in natural infestations under field conditions. Milbemectin shows a high level of efficacy against root-knot nematodes as it reduces egg hatching, persistently immobilizes nematode juveniles, and reduces tomato root infection.
Highlights
IntroductionRKN control has been performed through soil chemical fumigation, but bans and restrictions on the use of most chemical fumigants, such as methyl bromide, 1.3-dichloropropene, chloropicrin or metam-sodium have brought serious concerns regarding control of plant parasitic nematodes in intensive horticulture
Plant parasitic nematodes of the genus Meloidogyne are important plant pathogens difficult to control due to their wide host range and huge reproductive potential.Conventionally, RKN control has been performed through soil chemical fumigation, but bans and restrictions on the use of most chemical fumigants, such as methyl bromide, 1.3-dichloropropene, chloropicrin or metam-sodium have brought serious concerns regarding control of plant parasitic nematodes in intensive horticulture
The probabilistic dose–response model indicated that lethal concentrations of milbemectin for juvenile motility were LC50: 7.4 μg/mL and LC90: 29.9 μg/mL
Summary
RKN control has been performed through soil chemical fumigation, but bans and restrictions on the use of most chemical fumigants, such as methyl bromide, 1.3-dichloropropene, chloropicrin or metam-sodium have brought serious concerns regarding control of plant parasitic nematodes in intensive horticulture. Five active ingredients are authorized as nematicides for use in vegetable crops in Spain: abamectin, fenamiphos, fosthiazate, fluopyram and oxamyl. The frequent use of these nematicides could exert high selective pressure on RKN and soil microbiota. For this reason, the search for new efficient nematicides with different modes of action to the long-time used organophosphate and carbamate nematicides is presently a priority in nematological research. The search and use of natural pesticides (biopesticides) are promoted by environmental and plant health authorities in Europe. Biopesticides are chemicals derived from natural materials as animals, Plants 2020, 9, 839; doi:10.3390/plants9070839 www.mdpi.com/journal/plants
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