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Exclusion nets have been used successfully to protect fruit from insect pests of apples under various conditions, but the effect of each particular netting system on the plant itself has rarely been investigated. In this study, a complete exclusion system—in which the soil is also excluded—was used to grow ‘Honeycrisp’ apples for six years in southern Quebec, Canada. Abiotic conditions, as well as plant photosynthesis and fruit quality characteristics (colour, firmness, size, sugar content, number of seeds, ripeness and skin integrity) and yield were estimated yearly and compared in netted (either with or without a rainproof top) and unnetted row units. Although annual variations were high and results showed little or no difference between netted and unnetted rows for all measured variables, with the following exceptions; colour (increased red surface on fruits from unnetted rows some years), size (fruits from unnetted rows were smaller) and maturity (fruits from unnetted rows matured slightly faster). Fruits produced under nets had fewer microcracks at the surface than fruits produced without nets. Reduced cracking possibly helped decrease sooty blotch and flyspeck incidence and severity. Impacts for pest control and prospects for pesticide-free production are discussed.

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To improve exclusion systems for fruit trees, insect nets of various types were evaluated for their permeability to different beneficial and pest species, under laboratory and field conditions. Pests studied were the apple maggot, Rhagoletis pomonella (Diptera: Tephritidae) and the spotted wing drosophila, Drosophila suzukii (Diptera: Drosophilidae). Beneficials were Aphidoletes aphidimyza (Diptera: Cecidomyiidae), Aphidius matricariae (Hymenoptera: Braconidae) and Aphelinus abdominalis (Hymenoptera: Aphelinidae). Mesh nets with five different apertures (square, rectangle, triangle, rhombus and hexagon) and six different sizes (from 0.4 to 2.8 mm) were 3D-printed from strands of polylactic acid and tested in the laboratory along with two commercially available nets made of polyethylene. The physical and behavioral characteristics of the six studied species affected their ability to cross the nets. For an equal size (open area), the intrusion rate was generally greater through the square- and/or hexagonal-shaped meshes. Rectangular-shaped apertures totally excluded the apple maggot in both laboratory and field trials, provided their shortest side did not exceed 1.9 mm. For the spotted wing drosophila, a maximum of 1.0 mm was similarly required for exclusion in the laboratory. The shape factor (length/width ratio) of the apertures appeared to affect net selectivity. Field trials confirmed that more aphid predators and leafroller parasitoids colonized trees covered with larger mesh nets (2.3 × 3.4 mm), while still excluding the apple maggot. Thus, for a similar aperture size (area), an elongated rectangular-shaped mesh appears to facilitate access for beneficials, while continuing to provide effective protection against apple pests.