Visiting Paul Thorne's Custard Apple and Lychee farm

The Club was invited to visit Paul and Glenda’s property, and invited to bring along secateurs and pruning saws to gain practical experience in the correct method of pruning custard apple trees.

Background
Arrived 25 years ago, when the property held 100 Pinks Mammoth and 100 African Pride, a large dam but no reticulation system, surrounded by bush.  Then he started growing small crops down in what is now the ‘lychee patch’, and bananas.  Five years (2005) ago all bananas went, and Paul concentrated on replacing the bananas with lychees, and custard apples.  The latest ‘patch’ is KJ Pinks Custard Apple variety, about 5 years old, and there was also a smaller patch about 8 years old.

Pollination, and tree spacing
If Paul had his time over, he would probably go with the V trellis systems (see note, below).  When Paul took on the property, the early plantings had been done (in the 1970’s), they were big trees and needed heavy pruning over a number of years.  The trees are at 10m by 8m, the original plantings were on a 7.3m by 7.3m (25 foot square) which was too close together.  For better access, Paul is picker, packer and all the rest, he would now consider even planting one in between those trees.  There are 10m in between rows, which he likes, but he would prefer more of a hedgerow system.  However, he is not planning to develop more, there are 360 custard apple trees now on the farm, which are more than enough for him to hand pollinate and keep up with (prune, fertilize etc.) plus the lychees.  He would like to try the new (trellising) system, but it would probably require more staff and he would prefer to keep his simple one-man operation.
He does not like the KJ even though they are great for fruit set, because he believes that the time and labour required to thin fruit repeatedly is more than to hand pollinate his other varieties to produce a large marketable fruit (KJ don’t require hand pollination).  He grows primarily for export market which returns higher prices for larger fruit.  However he considers that the (genetic/rootstock) material of the trees, his old stock, Pinks Mammoth, may be a factor in the better size of his fruit, and he has another block of 60 Hillary White which he feels are great fruit.  As he hand pollinates his old plantings selectively, he prunes a block, waits for them to come on and then prunes again, so he can systematically go through pruning.  But since he planted the KJ, about 139 of them, he worries that he will not be able to keep up with picking the KJ over an extended time compared to pollinating systematically one block at a time, which then can be picked out and move onto another block.  The KJ are the only variety he has to de-fruit to obtain marketable size fruit.  KJ flower from each leaf axial, they normally get 3 flowers out, they also get doubles, and he has seen numerous triple fruit at each leaf axial.  Sheryl asked Paul about the new ‘Tropic Sun’ variety and he replied “there’s one just up there, it’s prolific enough for a home garden, DPI are just grafting up now and it should be released this season … through Fitzroy Nurseries (Rockhampton)”, Sheryl “Yarrahapinni was also doing it.”  Only about 4,000 – 5,000 plants will be released in 2011.
Paul hand pollinates his Hillary White but says that with age, after about ten years, they do start self-setting.  However, he prunes quite vigorously which doesn’t leave a lot of the tree for self-setting to occur, so he hand pollinates so he can put it on and count so many months later, and pick the whole orchard at once on a schedule.  He has 22 trees of African Pride, which he uses as pollinators because of their prolific flowering, and because he gets a lot of flowers from them at once.  At 2.30 pm he picks the male flowers, after picking he removes the petals which are then placed into a sieve waiting for the stamens and pollen to fall, at 4.00pm he goes out with the collected pollen and starts pollinating.  He has used KJ at different times, but prefers African Pride because they start flowering earlier in the day than all the other varieties and the pollen separates earlier than that from Pinks Mammoth flowers.

Fertiliser
Paul fertigates from a dam over a kilometre away and pumps water to a holding tank.  He fertigates every 2nd week using potassium nitrate, urea, calcium nitrate and magnesium sulphate.  He recommended chook manure and ECO 88(s) (http://www.qldorganics.com.au), for home gardens, and prefers to fertigate small amounts and often.  The only other fertiliser he uses is Nitrophoska®, which he uses before he prunes a block then leaves the prunings to lie on top of the fertiliser, and as long as the soil temperature is sufficient this practice helps to “kick” the growth along.  He likes Nitrophoska® because it has lots of trace elements, but the main reason he uses it is to kick the trees along so he can get on to (pruning) the next block.  When he does use it, Paul applies chook manure gradually so as to control the trees’ vigour, however his trees are vigorous regardless and he hasn’t seen that much difference with chook manure and hasn’t used it for a while.  According to Paul, not many growers (including himself) use the chicken manure clumping methods any more.

Soils
Paul has red Chromosol* soils, a clay/loam soil, and his water profile is sideways across the orchard (see http://www.derm.qld.gov.au/science/slr/queensland_soils.html, 14/1/2011).  He has soil moisture metered across his orchard (tensiometers http://www.dpiw.tas.gov.au/inter,nsf/WebPages/RPIO-4ZK6CS?open, 14/1/2011) and a small data logger which measures the vacuum in the tubes, one 30cm and one 60cm, and can download the data onto a computer which charts a dry and wet point for him, so he knows when and how often to water.  His soil pH doesn’t seem to change very much, occasionally he will have a soil pH test done.  If there is a need for change, he amends the soil through his water supply.
He hasn’t had a custard apple leaf analysis for years, the soil is currently about pH 6.5.  Sugarcane mulch and fertilizers have been applied over the years, but finances and physical demands of mulching have reduced those activities.  He now just leaves (custard apple) leaf clippings as it’s too much effort to remove them, they are on ground which is “bare ground is dead” ground, they help retain soil moisture, provide organic carbon.
* Chromosol - soil has an abrupt clay layer down the soil profile.  They occur in most districts and may have impeded internal drainage.  The geological setting is in the Neranleigh Fernvale beds that are predominantly infertile old sediments but there as some volcanic beds. – Bruce Ham
Elephant Weevil (Orthorhinus cylindrirostris)
The problem he had with the prunings when he first started was that the bigger wood favoured the elephant weevil.  He has counted up to 20 in a tree at times, they sit in the leaf axial, and if there is a fruit there they ring bark the fruit stem and the fruit drops off.  The beetle has to be picked off because “nothing kills the damned things, except two fingers and a brick”, and the beetles can be seen at any time of day.
Fruit Spotting Bug (Amblypelta lutescens or A. nitida)
Fruit spotting bug has been a problem, but because over the years he has kept on top of it, it’s not a big problem.  Paul sprays Endosulfan (this is currently a highly controversial agrochemical http://en.wikipedia.org/wiki/Endosulfan, 16/1/2011) about three times, the first around late November early December when he sees them moving in.  A strawberry mango tree and other trees, which may host the bug, are sprayed along with his custard apples.  He does not have “trap” trees, although he did mention that there is a certain variety of Murraya that attracts the bug, but then added “why introduce something” that will attract them when they are going to come in any way, and that there are already many native species in the bush that the fruit spotting bug come out for anyway.

Fruit Piercing Moth (Eudocima phalonia)
They don’t appear to be a problem with his custard apples, however he says mangos may get more affected than he realizes.  He has only seen them once, on the lychee netting two years ago.  Paul does a lot of controlled burning (in the bush areas) and thinks this may help keep them down, by controlling the vine they are attracted to, and has mainly a Sclerophyllic woodland (hard leaved open woodland) around rather than a wetter rain forest.

Scale and Wooly Aphid (Coccoidea)
He sprays Bio-pest®, he only sprays hard chemicals because he wants to make a living.

Mealybug (Pseudococcidae)
This is Paul’s biggest pest problem.  When he first started hand pollinating, the fruit produced were “immaculate”, but over the years mealy bug became more entrenched, as the trees got bigger and denser.  He has been advocating on the committee of Australian Custard Apple Growers Association (ACAGA) for a suitable chemical for mealy bug, because even though Bio-pest® and Supracide® are good chemicals, although he doesn’t like spraying Supracide®, as it’s a contact chemical, and because of the nature of (the shape of) the custard apple and the density of the tree, complete cover is needed to get good control.  He has been buying in Cryptolaemus montrouzeri (Mealybug and Scale predator), and hopes to have Leptomastix dactylopii (a very effective parasitoid for Citrus Mealybug).
ACAGA currently has a project developing use of a Confidor®-type chemical, which he does not want to use topically, but as a drench under the tree.  Using a chemical in this way he hopes to not hurt existing beneficial insects, get a good kill rate, and not worrying whether to spray or not if he buys Cryptolaemus in.  ACAGA is also hoping to do some research on a similar (not a perfect match) product to Confidor® called Samurai® (Sumimoto Chemical), an insecticide currently used to control mealybug in apple and pear orchards.
Paul sees mealybug as custard apple growers’ worst enemy, even now in NSW getting into KJ.  African Pride don’t seem as susceptible as Pinks Mammoth because of the Pinks Mammoth heavy carpel; he thinks mealy bug likes Pinks Mammoth more.  NSW industry is growing more into Pinks Mammoth, so as the change is made over from African Pride to Pinks Mammoth, it is important to get good quality fruit.  It is more the sooty mould, which affects the appearance of the fruit, and is associated with the mealy bug, which causes a problem.  AzaMax™, which is a registered pesticide, was also mentioned as producing good results, as was Azadiractin (a chemical compound belonging to the limonoids, and present in Neem seed) the active ingredient found in some commercial insect growth regulators.

Water
Paul has 200 litre/hr sprinklers, and waters according to his water gauges.  He pumps from a diesel pump at the dam to a 30,000 litre tank at the top of the orchard, because if he is watering one custard apple block it drains the tank in a short amount of time.  He tries to stress the custard apples a little and dry them out over winter, however if it is a dry year there is still a need for a certain level of moisture required in the soil.
After pruning he gives a bit of fertiliser to try to get the carbohydrates back into them if there’s been a heavy crop load, then eases off watering over winter, but continues to monitor the soil moisture gauges.  In August if it is dry he will start pumping the water in, his two thresholds on his gauge are 10 and 25, so he allows them to dry out to 25, but the ones he is pruning he loads up to 10.  He doesn’t usually suffer a lot of fruit splitting, as long as he gradually builds the watering up (as long as he is able to allow for natural rainfall).

Defoliation
Paul would prefer natural defoliation to happen before he prunes, but he has tried defoliating a few times.  He believes natural defoliation allows the tree to pull (nutrients) back in from the leaf.  He does a ‘tip and strip’ with the KJ in January if enough fruit is not set.  He will reduce the stem lateral down, and take off just the last two leaves because energy is required in the last two to get a good flower.  He does not take all the leaves off in the middle of August as growers used to do (which he used to do with 25% urea), as he had trouble with limb dieback.
Paul believes if you defoliate too early and push the tree too early, it can cause a “sour sap” which in turn leads to limb dieback.  “Sour sap” can also come from pruning the tree too early.  Custard apples develop slowly, they don’t come until October, a bit later on they start swinging in, unlike nectarines (for example), which are a “Spring tradition, bang we’re away”.  “If you push them too early and it’s still cold, and you get cold snaps, you get that (limb dieback from defoliation) problem”.
Because many of his trees were very large when he started out, their limbs were too high and required heavy pruning to allow ease of hand pollination.  He pulls down big long laterals and ties them to a certain point to try and start new frameworks coming out.  Ideally he would like to stump them all at one time then prune for good structure afresh, but instead will he have to do this gradually to avoid loss of production.

Fruit fly (Bactrocera tryoni)
Richard Bull (Research Entomologist) did a lot of work with Dick Drew (Centre Director for The International Centre for the Management of Pest Fruit Flies) and Paul uses Amulet Cue-Lure® (Cue-Lure, foam blocks) which he places every 25 metres according to directions on the packet, now (August-September).  Fipronil (a slow acting broad spectrum insecticide) is the active ingredient, and Paul says the research suggests that the lures seem to improve after a little ageing.  They come in a pack of 16, however because he picks fruit mature green, fruit fly is not a big problem as long as baiting and lures are maintained; he does not cover spray (fruit fly stings in the stem end of mature fruit).   When there are a lot of fruit on his old mango trees he targets those trees.  As well as Amulet Cue-Lure® he baits, every tree gets 10ml of bait (Bugs for Bugs, fruit fly lure yeast autolysate).  If he is worried about fruit fly, he will let the ‘seconds’ ripen, then cut them open and check for maggots.
He removes larger off-cuts from the orchard in order to discourage the Longicorn beetle (Family Cerambycidae), which used to occur in his African Pride, causing gnarling of the limbs.  He loses young trees to wind, and wallabies, which will rip young trees down from below the graft.  He believes that until custard apple trees reach about 8 years old and in his type of soil, they are not rooted well and he stakes out his new plantings.  Over 25 years with old Pinks Mammoth, he has lost probably 2 trees, however since he started planting KJ he has lost numerous trees, apparently due to poor rootstock, some larger growers have lost hundreds.  The grafts are low on the KJ trees.

Pruning and Thinning
Paul explained that compared to his old Pinks Mammoth trees, what he intended with the KJ because they are close spaced and he didn’t want to be high up picking, was to have a small widespread tree.  However with the KJ he lost 3 years of growth when he tried to encourage a lot of lower branches, and because of KJ prolific fruiting those branches finally touched the ground and had to be removed.  Now with KJ he lets them grow up, and then lets them cascade over.  He does not have much trouble with sunburnt tree limbs after pruning, and even when he has pruned some of the older trees hard, and they are half sunburnt on the top, they still appear to thrive.

Paul does not paint tree wounds after removing a limb, although he used to.  When he prunes long laterals he breaks them up small so that they rot down faster.  To kill grass around the trees he uses Gramoxone® (herbicide registered for commercial use only Ed.) at the label dose, using it often and keeping the perennial weeds down, Paul still uses Roundup® occasionally in the orchard but mostly in non-commercial areas.  He related that Glyphosate is deactivated by clay, and because avocados have the feeder roots up in the mulch, they can uptake it, he had related problems with lychees, and a backyard stonefruit.

He also had read a report of growers with very sandy soil having similar problems due to low soil clay content.  However he likes to use Roundup® to kill ‘blue weed’ or ‘Billy goat weed’ (Ageratum spp.) which grows up and smothers any other grass he has.  Bob Cosgrove relates that Gramoxone® at half strength with urea proved efficacious and saved money, as long as the urea was dissolved before adding to the spray equipment, Sheryl Backhouse added a reminder that when using powdered urea with a stainless steel tank that the urea must be completely dissolved.  Paul uses carpet grass (Axonopus) wherever possible, it mows easily and produces good mulch that is thrown under trees.  When harvesting fruit that is no good he drops it on the ground and the wallabies soon take care of the rejected fruit…
Transcribed and edited by Russell Reinhardt.
[Note:  The KJ Pinks Custard Apple variety (PBR# 2002/049) has been awarded Plant Breeders Rights in Australia and is protected against illegal propagation.  This exciting new custard apple variety sets heavy fruit crops without the need for hand pollination (41% set vs. 3% of standard varieties).  It is a self-pollinating sport from Hillary White Pinks Mammoth.  This variety is well suited to high-density, mechanically pruned orchard systems for viable production systems.
Timely pruning to encourage out of season flowering will make reliable Spring/early-Summer fruit possible in suitable climates. http://www.anfic.com.au/kjpinks.htm, 29/12/2010.  See also Custard Apple Industry Report 06/07.  Maroochy V trellis is planted at between 750–1,300 trees per hectare compared with about 300 trees per hectare for the standard open vase system.
Consequently, early yields on this system are significantly higher than for vase-trained trees.  On a commercial farm, six-year-old trees on Maroochy V trellis produced six trays per tree, or about 5,000 trays per hectare, and at full maturity, it is predicted that this system will produce in excess of 6,500 trays per hectare (http://cms2live.horticulture.com.au/industries/Custard_Apple, 7/1/201010 for new ways of managing custard apples.] Ref: Russell Reinhardt

Birdwood Nursery has now released to the public the self-pollinating Custard Apple ‘Paxton’s Prolific’.  The other name for the same plant which they have been selling to commercial growers under Plant Breeder’s Rights is ‘KJ Pink’, named after Keith & Judy Paxton from Woombye who noticed a branch on their Pink Mammoth which always produced fruit which they didn’t have to hand pollinate.  There will also be another new custard apple variety for retail sale, ‘Tropic Sun’ from Fitzroy Nursery in Rockhampton.
Sheryl   I was told that when you prune a custard apple to always take off the nearest leaf as it will sit there otherwise for 12 months.