Impact of Exclusion Netting Row Covers on ‘Honeycrisp’ Apple Trees Grown under Northeastern North American Conditions: Effects on Photosynthesis and Fruit Quality

Abstract

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.

Net Enclosure of ‘Honeycrisp’ and ‘Gala’ Apple Trees at Different Bloom Stages Affects Fruit Set and Alters Seed Production

“…The percentage of red color under black hail net was significantly reduced compared to a control [53]. Chouinard et al, showed reduced fruit color of 'Honeycrisp' in netted trees compared to non-netted trees in several years of a six-year netting study, though annual variation in fruit quality attributes was considerably high [38]. For 'Honeycrisp', trees netted at 'pink' had~15-30% fewer fruit than their later-netted counterparts in both years, albeit non-significantly.…”

“…In other cases, tree response to exclusion netting varied considerably based on biological (e.g., genotype) and environmental factors. For example, alteration of fruit quality under exclusion netting differed among seasons as a function of the environmental conditions [38,39]. Further, nets vary considerably in material construction (type of polymer, density, color, weave, etc.…”

“…Treatment trees receiving complete exclusion netting (Alt-carpo, 10% shading, 2.8 mm × 4 mm weave, Helios ® antihail systems, Bergamo, Italy) were monitored by calculating the percentage of open king bloom. Netting was installed over portions of tree rows as Alt' Carpo, enclosing whole trees, recently termed complete exclusion [38], ensuring that the bottom of the netting was tightly secured around each tree trunk to prevent bee entry ( Figure 1). When a predefined target bloom was attained and/or deemed adequate based on the progression of flowering (in combination with forecasted weather at each site), entire canopies of multiple tree replicates within a row were fully enclosed by nets.…”

Evaluation of Exclusion Netting for Coffee Berry Borer (Hypothenemus Hampei) Management

“…Additionally, exclusion nets modify the plant’s growing environment and can have a number of positive effects on the physiology of the plant (e.g., reducing water stress by lowering evaporative demand, reducing heat stress by shading, and reducing light stress by improving the penetration of spectrally modified light into the canopy) [ 49 , 50 , 51 , 52 ]. This reduction in environmental stressors often translates to improved photosynthesis and vegetative development, increased fruit set, larger fruit size, changes in time to maturation (either advancing or delaying harvest), and improved fruit quality [ 53 , 54 ]. Crops for which exclusion systems are best suited are those that are high value, perennial, and grown over a logistically manageable space for net installation.…”

Commercial bumble bee (Bombus impatiens) hives under exclusion netting systems for apple pollination in orchards

“…Exclusion netting systems appear to represent a good alternative to insecticides and may become the norm for organic orchard management in the future (Chouinard et al, 2017(Chouinard et al, , 2019. Currently, nets must be opened for a few hours on 2-3 suitable days during bloom to ensure successful pollination by honey bees and adequate fruit set.…”