Sunraysia grower Matthew Cottrell shares practical insights from his experience with high-density plantings. Matthew Cottrell is a citrus, wine and table grape grower in Nangiloc, Victoria. His family-owned business, Cottrell Farms, has 230 hectares of citrus orchards, including a range of early, mid, and late navels, as well as seeded Daisy and Tangold mandarins.
A visit to California in the early 2000s inspired Cottrell Farms to explore the concept of high-density plantings, based on their potential for early yield gains and robust cash flow.
During the mid-2000s, Cottrell Farms embarked on a significant new citrus development on a green fields site, planting many blocks in a high-density pattern. This followed a plant spacing seen in California – 5m × 2.5m, equating to approximately 800 trees per hectare.
"The high early yields and subsequent financial returns made high-density orchards an attractive prospect," Cottrell said.
Canopy management
Initially, the results were promising, with yields exceeding expectations over the first nine years. However, a decline in yield after the tenth year was encountered for certain variety/rootstock combinations, a problem Cottrell attributed to canopy congestion and shading.
"We knew tree congestion would be a challenge, but we believed careful pruning could effectively manage this issue as the trees matured," Cottrell explained.
Numerous challenges arose around pruning during the initial seasons. Hand pruning offered a potential solution but was expensive and time-consuming.
"Contractors charged a per-tree rate, regardless of the number of trees per hectare, leading to higher pruning costs per hectare," said Cottrell.
To mitigate these challenges, Cottrell used mechanical hedging supplemented with hand pruning only. However, mechanical hedging threw-up a new management issue, being less selective and removing all types of shoots, including the next season's bearing wood. Additionally, the trees had to be mechanically topped to maintain a safe height for picking, sometimes requiring topping in both spring and autumn to keep the trees under control.
Rind colour development is often delayed in high-density blocks because the canopy shades the fruit.
"Further to all this, tighter rows increased the risk of mechanical damage and achieving optimal fruit colour became more challenging due to the increased shading caused by the denser canopy. Although there was a reduction in blemishes, which I believe can be attributed to the windbreak effect created by closer row and tree spacing," Cottrell explained.
Cottrell Farms also has a high density planting of Afourer mandarins, protected by a permanent netting structure. "While the nets help to reduce wind blemishes on the fruit, they also lead to increased vegetative growth, requiring additional pruning to manage excessive water shoots," Cottrell said.
The trees under the nets are also more susceptible to certain pests, particularly Light Brown Apple Moth and Red Scale. "Weekly monitoring during spring is necessary to detect and mitigate pest issues before they escalate and cause significant blemishes on the fruit," Cottrell said.
Source: citrusaustralia.com.au