Dry season management — pears

As the dry weather conditions are continuing in Victoria, fruit growers need to consider all available options to get through the dry summer conditions and minimise losses.

Managing young pear trees during the dry season

• Delay planting as long as possible to assess the season and water allocations. If water is in short supply, it might be easier to hold new trees in a nursery site for the season or in a cool room for 12 months and plant next year.
• Make sure the irrigation system is in place and fully operational by the time trees are planted.
• Water new trees in thoroughly at planting time — especially smaller trees with finer, more easily dried out root systems.
• Mulch newly planted trees after the frost period if straw or other material is available. This reduces water losses from soil evaporation.
• Irrigate close to the tree, not the whole paddock (for example, invert micro-jets so the surface wetting pattern is reduced or replace existing micro-sprinklers with smaller wetting pattern micro-jets).
• Eliminate weed competition early and widen the herbicide strip.
• Remove any fruit on trees planted this season or last year.
• Summer prune and train trees more frequently.

Strategies for management of mature pear trees during the dry season

In the growth cycle of pear trees, there are critical stages that require adequate soil moisture to produce a commercially viable crop:

1. pre-flowering
2. flowering and fruit set
3. fruit growth
4. post-harvest

Pre-flowering

Root growth commences from late August onwards, so the soil must be moist and soft to establish an early root system before flowering.

Apply an irrigation if the soil is dry in August. Evaporation is very low in winter so the soil will not dry out once it is moist.

Flowering and fruit set

Bare or closely slashed tree rows with moist soil are needed to absorb heat during the day to minimise the impact of frosts. Irrigation can be used to keep the surface soil moist but avoid over-irrigating and wasting water.

Adequate soil moisture until approximately 4 weeks after full bloom is critical for root growth, fruit set and to maximise cell division during the early stages of fruitlet growth.

Don't discount thinning as an option for pears. Aggressive flower thinning or secateur thinning early after flowering may be warranted to maximise fruit size for the more valuable pear cultivars, especially if water availability for irrigation is low and flowering and fruit set have been strong.

Fruit growth

Pear fruit growth is slow during November to mid-December. Moisture stress during this time reduces the growth of leaves and shoots but not the fruit. This presents an opportunity to use regulated deficit irrigation (RDI).

Fruit growth by cell expansion, and the accumulation of sugars by the fruit depends heavily on optimum soil moisture and good irrigation during the final rapid fruit growth stage in the last 6 to 8 weeks before harvest.

Post-harvest

Irrigations after harvest can be reduced but not to the level that causes significant leaf loss. Post-harvest irrigation is needed to water in nitrogen fertilisers and maintain leaf activity (photosynthesis) for some of the day.

Minor wilting in the hottest part of the afternoon won't be too detrimental. A water saving of 1 to 1.5 megalitres per hectare is possible during this 6-week period.

Avoiding excessive water stress after harvest ensures nutrients are accumulating in the tree for budburst, fruit set and early shoot development in the following spring.

Dry season issues

Other issues you're likely to face because of dry seasons include:

• insect and mite pests — pests can flare up quickly in a dry season when trees are water stressed. Introducing predators earlier in the season and monitoring or scouting pear orchards will need to be thorough and regular.
• severe frosts — frosts are likely to be more severe and occur later into the season during dry seasons. Install a frost alarm system. Use the irrigation system, soil management and other frost reduction methods in the orchard. If there is no frost damage, heavy fruit set is possible because of fine weather at flowering that is likely to occur during dry seasons.
• fruit shedding — there could be excessive fruit shedding in November if the soil was dry during flowering and fruit set.

Irrigation strategies in a dry season

The following strategy is suggested if irrigation water entitlements are low:

• Consider installing a drip irrigation system to save water.
• Before the season starts, set out a water budget for each irrigation block on a monthly basis that uses long-term irrigation requirements, incorporates RDI strategies, assumes no effective summer rainfall.
• On a regular basis review water allocation, long-term rain forecasts and market potential for each cultivar.

If there's not enough irrigation water available, decide on one of the following strategies:

• Purchase water.
• Irrigate at a deficit for the entire season and suffer a fruit size loss. Heavier thinning will offset some of the loss in fruit size.
• Do not irrigate lower productivity blocks and de-blossom or even pollard (main limbs cut in half or pruned even lower) to reduce water needs. Wound dressing must be applied to these larger pruning cuts. Alternatively, some older trees may be close to being non-viable. This might be a good time to pull them out earlier than planned and transfer the water to productive blocks of trees to ensure some commercially viable fruit can be harvested.

Saving water in orchards

Incorporate the following orchard management to save water:

• Prune the most valuable and productive blocks first. Leave the lower value blocks to be pruned until last. This gives more time to evaluate the seasonal rainfall and means decisions about abandoning poorer blocks to save water can be left until later.
• Strip all fruit off trees 1 and 2 years old and those just planted. Trees that are 3 or 4 years old should be thinned heavily or the fruit stripped off if water is short, and a deficit will be applied for the entire season.
• Measure soil moisture to schedule irrigations.
• Eliminate all weed competition. If micro-irrigated, spray weeds emerging in the irrigated zone during spring and summer.
• Slash the orchard more often and as close to the ground as possible. Under drastic water shortages you might need to spray out all the understorey pasture and weeds.
• If possible, mulch and irrigate the tree-line and not out in the traffic row area.

Irrigation requirements for pears

The following tips can help you manage water in pears:

• Irrigate at budswell to enable root growth to commence ahead of flowering.
• Irrigate to maintain good soil moisture from budswell to 4 weeks after flowering. Make sure the water penetrates to the full depth of the root zone — but not past the root zone. Moist soil is needed at this stage for early fruitlet growth, root growth and to reduce frost risks.
• Soil moisture measuring instruments will indicate when and how much irrigation is needed. This will be of great benefit to guide irrigation needs while trees are leafing up and if there has been any effective rainfall which can save on irrigation water.

Requirements for specific cultivars:

• Use RDI for Williams' Bon Chretien (WBC) from November to the first week of December, and for Packham in November to mid-December.
• Using drip irrigation, assume 4 to 5 megalitres of water per hectare are needed to grow WBC.
• Using drip irrigation, assume 5 to 6 megalitres per hectare for Packham's Triumph and later cultivars.