Dear Trevelyans avocado grower,
The 2020/21 season will be remembered for the challenges that the small fruit profile presented. And the lack of experience with a small fruit size profile crop meant that some approaches used to try to manage the harvest did not work that well. In hindsight, the matrix of crop flow and size picking could have been done much better. As it turns out most of the avocado industry is now left picking a crop of smalls!
Small fruit Hass is not uncommon. The Hass “small fruit syndrome” is widely reported in the international avocado literature and appears to be a bigger problem in warmer production areas like Northern Queensland, North Eastern South Africa, warmer regions of Chile, Israel, Spain and Southern California to mention a few. These areas all have Mean Annual Temperatures (MAT) well above 20oC. Even the warmest areas of New Zealand would still be considered “cool” production areas with the Kaitaia MAT only 16oC. As a matter of interest the MAT in Katikati is 14.5oC. The big question is “is a smaller fruit profile here to stay?”
To begin to understand and manage fruit size we do need to understand avocado fruit growth. The avocado fruit growth pattern is a sigmoidal curve with three distinct phases:
- Cell division phase. This occurs shortly after pollination and continues for approximately 60 days, slightly longer in cooler climates. In New Zealand this is from mid-November to mid-January. Research work by Cowan and co-workers showed that larger fruited have the same number of cells as smaller fruit but that the cells were larger in larger fruit.
- Cell expansion phase. This exponential growth phase follows cell division and continues for approximately 75 days, slightly longer in cooler climates or in larger fruit. In New Zealand this is from mid-January to mid-April. There are normally several fruit drop episodes during this time with fruit drop typically being complete by late April. During the cell expansion phase fruit can gain up to 2g per day!
- Slow sizing phase. This is a period of slow and steady fruit sizing. This continues until the fruit is harvested, or the fruit becomes ring necked (no net gain of carbon into the fruit). Fruit typically gain 0.3-0.5 g per day. Larger fruit gain more per day that smaller fruit. Smaller fruit never truly catch up with larger fruit but do continue sizing until harvested. For example a 42 count sized fruit won’t become a count size 20 fruit but left long enough could become a count size 32!
Fruit sizing is obviously a complicated biological process, especially for a single seeded fruit that, under normal conditions, is very prone to fruit drop. A number of biochemical pathways are involved and fruits exert competitive processes against each other and vegetative fruit growth. Stressed heavily laden trees often struggle to put on sufficient vegetative growth which in turn has an impact on alternate bearing and fruit size.
So what do we need to do and can we manage our trees to deliver better fruit size?
We what do we know?
- Good healthy trees with plenty of leaf cover give crops of larger fruit.
- Very heavy flowering can result in a large crop of small fruit
- Fruit load can impact fruit size
- Excessive cropping can cause a wide distribution of fruit size
- Severity of Phytophthora infection is corelated to fruit size
- Leaf to fruit ratio is important for getting larger fruit
- Size picking larger fruit can improve the overall fruit size profile for smaller fruits provided there is enough time for the slow sizing phase to work
- Most environmental or pest stresses reduce fruit size.
Key inputs to improve/ manage fruit size
- Soil water availability – install irrigation and manage it well. Use some method of soil moisture management. A note to provide some context is that evapotranspiration can be anything from 3-7mm per day rainfall equivalent at this time of the year (mid to late summer). That means that the orchard of just 1 ha is using half a million litres of water each week, when water is not limiting, the days are sunny and warm and the wind is blowing. Even low wind speed has a major impact on water use. Put differently, this is equivalent to 45-50mm of rainfall every week ( and not counting rainfall of less than 5mm – this is largely ineffective due to evaporation from the canopy and mulch and would not wet the soil in any meaningful way). An important point is that higher density orchards are expected to use even more water!
- Flower load – undertake twice annual pruning to manage flower density and restore/ maintain a good balance between roots and leaves. Open canopies and the management rather than removal of water shoots is key.
- Six spotted mites – monitor and then deal with six spotted mites before they become a problem. Use an integrated approach to insect pest management in the orchard and pay careful attention to chemical choices. Remember predator insects are very important in six spotted mite management – learn to both identify them and love them!
- Leaf cover and tree health – implement a proactive fertilizer/ nutrient approach. Remember it is very hard to catch up on nutrition once you have fallen behind. Consider fertigation in summer.
- Phytophthora management – do an annual orchard health assessment, if in doubt and poor root health is suspected, do root analysis and deal with Phytophthora before it becomes a problem.
- Drainage issues – poor drainage and winter flooding does significant root damage – roots are unable to repair in time for summer and key root produced plant hormones are not produced impacting fruit size, leaf life and leaf health. This in turns affects tree health by reducing available and storage photosynthate.
- Use restorative or regenerative orchard floor management principles. Healthy orchard soils with good structure, plenty of bio-diversity and increasing amounts of carbon are essential to the efficient use of water.
One my travels I am concerned that I am seeing the start of another small fruit season. The good thing is that there is plenty of fruit drop but the weather is not helping. The factors affecting fruit size are all large and complicated topics and worthy of one on one discussion…..and the discussions could take some time!
If you require more information or would like to talk over any of the issues covered in this Tech Tip please contact Daniel (0274866969), Katherine (0272119181), Anne (0276126636) or Jonathan (0279733513).
It is now the end of November, fruit set, or lack thereof, is now becoming evident.
- Very little change in insect pest pressure during the past month.
- Insect pressure is in line with long term trends.
- Small spike in leaf roller and we would expect this trend to continue with the regular rains and time of the year.
- Six Spotted Mite risk is large with many orchards infected from Athenree to Opotiki (see chart). Levels in some orchards are now very high. The problem does appear to worse on young orchards (1-3 years olds).
Key AvoGreen and insect pressure points from the past two weeks:
- Leaf roller pressure is showing signs of starting to build.
- Thrips pressure is very low
- Six spotted mite pressure is present in many orchards and there is severe leaf defoliation in many young orchards.
According to the monitoring data leaf roller caterpillar levels are low but caterpillars were recorded on a small number of orchards.
- Growers are encouraged to start looking for leaf roller in the orchard
- Contact the office if you need any guidance.
- Some growers need to think about spraying for leaf roller as low levels are appears in the monitoring results
- If you do need to spray please review with holding periods if you still have fruit for export
- Methoxyfenozide (Prodigy) is a good spray to consider as a first spray on new season fruit if it is the only pest as it fits with most IPM programmes and is considered “soft” on predator insects
- Do not mix with oil
- Make sure flowering is over as Prodigy is “moderately” toxic to bees
Thrips pressure is low.
- Contact the office if you need any guidance but there should be no reason to spray based on monitoring data (with possibly four to five exceptions in the past fortnight).
Mite pressure is very high in some orchards. The avoGreen monitoring data suggests not all orchards are affected but most are and in some cases infestation is severe (average infestation is 10-11%). Young orchards are very high risk – go out and monitor and premature leaf drop is sign to probe harder.
- Please talk to us before spraying. If you do need to spray review with holding periods if you are still picking.
- The best option is to wait till bees out and flowering has over and apply Abamectin. Apply Abamectin plus a “super spreader” when there is sufficient new season leaf flush.
- Very toxic to bees. Accoring to the label Avid cannot be applied to avocado trees in flower if the flowers are likely to be visited by bees. Therefore night spraying is not legal.
- Best to use in spring on young full or partially expanded flush and before mite levels are very high. Go hard and go early!
- Remember there is a maximum use of three Abamectin sprays per year.
- Your pack out reports may show a record of scale on your fruit found in the pack house. You are notified of this as it’s a justification to spray. Please talk to us if you want to use this justification to spray for scale.
- This is an important time for fruit quality both blemish and rots. Leaf roller moves from flush to young fruitlets and from mid-summer fruitlets become infected with latent infections. Make sure you have a plan for fruit quality for the coming season.
There is a legal requirement not to apply class 9.4 (toxic to insects) if:
- bees are foraging on the crop
- non target plants (flowering shelter belts or orchard floor plants) that are likely to be visited by foraging bees are in flower or part-flower.
If you require more information or would like to talk over any of the issues covered in this AvoGreen Update please contact Daniel (0274866969), Katherine (0272119181), Anne (0276126636) or Jonathan (0279733513).