Visiting Gavin Scurr's Mango Farm

Sheryl   This is part of a talk given by Gavin to our group earlier in the year.
Pruning
Gavin  We prune on a 15° angle in from the outside to the top – Christmas tree shape. Up north we do them vertical. Reason we do angle pruning here is because of the sun because we are further away from the equator and it lets in more light if we open them up. If you look inside the trees, you’ll see that we have stripped the leaves off on the old branches – we’ve just left the leaves on the outside. Just take off the ones in the shade on the inside of the tree. You need 80 leaves per piece of fruit as a rule of thumb. Any more than 80 just creates issues. You leave them on the outside to photosynthesis. They don’t do it in the north plus they would get sunburn up north if we did that. Down here ie our Rockhampton and Wamuran farms we strip the leaves by hand. We tried to do it with chemicals but it’s hit and miss but it would take off leaves you don’t want off so we do that when we prune in June and July. It lets more light and air in and is less place for disease to harbour.
Sheryl  Which way do you strip?
Gavin  From the outside in. Just wear cotton gloves.
Sheryl  Do you take the leaves away?
Gavin  No, we just leave them where they fall. They throw their leaves off by the tonne! They’re not a very good tree backyard tree from an aesthetic point of view – lots of leaves! You’ll notice we have a pretty clean environment under the trees. We use to throw all the grass clippings and mulch – nice organic matter which is good for the trees’ health however it breeds disease and because of our sprayers and we’re blowing air, it bounces off and throws all that disease back up into our tree so we now have a sterile environment. When we prune, we pull all the branches out but we don’t go through all the loose leaves. There are people who go through and rake and burn them and always have bare dirt but we don’t go to that extent. It’s pruned with secateurs and gets thrown into the centre of the rows then we run the slasher over it and it all stays out there because that’s where the roots are anyway. Five years ago we would have gone through and tip pruned and thinned them out whereas now we wait until winter to do that because we get a better crop from it. If you want to really prune a large tree right down, you can cut off half the tree one year and do the other half the year after. We prune June/July in winter. You can overprune mangoes – pruning knocks production around for that year so the less you do the better down here in SE Qld. Up in Nth Qld is different. We found that after harvest we’d go through and tip prune all the old flower panicles, stems etc. and tidy it all up and if that’s early enough and you get a reasonable run into winter, you’re probably OK but if your tree doesn’t flush back again and it only flushes again say end of March, you end up with a really weak flush.
Sheryl  I notice you don’t cut out the centre.
Gavin  No. We use to do that but what we found was that it can get sunburn and it encourages regrowth all on the inside so you’re forever in there pulling that out as well. The concept is that at flowering the tree will look like a fishbowl – there will be leaves all around the outside and inside will be totally open other than branches. You don’t get a heck of a lot of mangoes on the top of a tree – most are on the side so as you can see the tops have flushed again.

To rejuvenate big trees From a structure perspective you can prune as hard as you like with a chainsaw and you won’t kill them and they’ll just flush out. Late summer (is good but it’s important when you cut them down that you paint the whole tree that is left with a water based white paint otherwise they’ll burn badly and they won’t recover. Also cut on an angle so water will run off. We keep all our trees down to a height that is manageable from the ground – usually a max of 4 mtrs so when there is fruit on it, the weight of the mangoes will put it down to 3 mtrs. We then use a 1½ mtr picking pole so all the fruit are picked from the ground.
Member:  We were in Taiwan and their trees are only 2½ mtrs.
Gavin  They grow differently to us. They bag all their fruit, thin it out so they get perfect fruit.
Member:  Custard Apples are grown the same – about 2½ mtrs.

Anthracnose: If you get this, we take the whole branch right back. Some growers in NSW go through once the crop sets and when it is duck egg or bigger, they’ll go through and take all the dead panicles off because they will mark your fruit but if you are paying someone, it’s an added expense.   That wood is as thick as your finger so if you take it back to 500mm from where it last branched, it will push the flower out of that hardwood.

Spacing  6 metre x 3 metres. In the tropics 8 x 4 metres and most growers go with 10 x 5 metres but they only get around 10-12 tonne per hectare.  We’ve gone high density and keep the tree shape down. We can get 20-24 tonne to the hectare.

Foliar Fertiliser  We do this when the tree is flowering.
Vic  The Brisbane Organic Growers were asking a question in their newsletter about putting foliar sprays on trees. Is it absorbed more by the top of the leaf or the underside?
Gavin  It depends on what you are trying to do. If you are trying to get something into the leaf like nutrients it takes in very little on older leaves so it doesn’t matter. You need younger leaves that are soft which allows it to go in. As to the top or the bottom, we try and get coverage on both because I think it does go through both however you’ll get 10 times as much in a younger lime colour leaf than you will on the dark green leaf. Our mister goes right through the tree as well as the top. It will depend on what sort of coverage we’re looking for. If we’re applying a foliar nutrient and we just want it on the outside, we’ll travel along at 6-7 km whereas if we want good penetration with a fungicide or insecticide, we’ll slow down to 3-4km an hour.

Soil
Member  I notice you have sandy soil so obviously that controls your nutrient to your trees so you can control what goes into your trees a lot better than a backyarder on heavy soil.
Gavin  Mangoes don’t need a specific soil to be good but the type of soil influences how you feed it. They will grow anywhere. The heavier soil takes longer to respond but doesn’t leach so if you put nutrients in there, it stays in there whereas in sandy loam that we have, we have to keep putting it in as it leaches so we put little bits in regularly. They are a relative of mangroves and in the Northern Territory and the Top End, trees will grow in water up to a foot deep for 3 months so they are tough.
George?  On a heavy soil you would get more vegetative growth because it holds nitrogen better.
Gavin  Yes that is right. Ideally for mangoes, the harder country you put them on, the more fruit you will get off them. They are a very lazy tree commercially – they just want to keep growing vegetatively and there’s no money in mango leaves!  They don’t yield a lot compared to the amount of potential they’ve got with a big tree. The same size citrus will pull 40-50 tonne a hectare where the mango will have 8 tonne a hectare.

Gavin   In winter when you get a vegetative flush, we will use Mancozeb every two weeks in normal weather however if you get rain, you have to go back and put it on again. We also use it with a surfactant and it depends on whether we want to get coverage or penetration so if we are using a systemic fungicide eg Amastar that you wouldn’t be allowed to use. We use a systemic and with the Mancozeb we will use it with a bit of oil. We also use Copper and we’ll mix the two together. We don’t use Copper around flowering. It’s been proven safe but it can burn. Sometimes we use them separately but it depends on the season. When it’s been really dry, we’ll use Mancozeb then use Copper the next time but when it’s wet, we’ll mix the two together.
Sheryl  When do you stop your spray program?
Gavin   We don’t. We do it all year round. Whenever there is new growth, we’ll do it so while it’s flushing, you need to protect it about a month apart and then when it hardens off and if it hasn’t rained but if it rains we’ll still do it every two weeks and when it gets to flowering, that’s when it really cranks up and we’ll spray every 7 days regardless due to the dew factor. Dew is a big issue for us. You can use any type of copper depending on how much you want to spend. Cupric hydroxide is one of the better ones as it has a finer particle – the finer the particle, the better it will work but it’s more expensive so commercially we top end of the range so even in your backyard, I would use the top one as well. In this environment you need the best.
Two things will kill the flower - Anthracose if it rains before it got to a stage before it could pollinate or it’s been too cold so there is nothing to pollinate or the stomata is not open because it’s too cold.
George  You’ve probably heard about Peter Young’s boron recipe on the flowers. If your tree doesn’t have enough boron or not enough calcium, you’ll probably find you won’t get as good a fruit set as you should.
Gavin   We spray the flowers with fungicide obviously but nutritionally we put boron, zinc and iron twice during panicle extension. When they are about 6ins out, we’ll put a foliar boron, zinc and iron on. It will cost a bit more but we use a chelated form because we can mix them all together and we don’t need to go through as often. Boron is critical for opening the flower seed. With mangoes it’s easy to get boron toxicity so don’t go overboard on it. If we get a lot of rain, we won’t go through and refertilise. The rule of thumb is that canopy size is a similar size to the roots. If you have a 3 mtr tall tree, the roots will be 3 mtrs down. We’ll put a kilo of fertiliser on after rain. Compaction is an issue for us here as well because we’re playing in the wet ie every time it rains, we need to go down and spray so the mangoes are growing on raised beds. We’ve done that deliberately to shed the water away from the roots.

Rootstocks
The mango industry has very little data on rootstocks. There hasn’t been a lot of work done on this. The industry was based around Kensington Pride or KP as we call it and up until 15 years ago, that was the only mango. There is some rootstock work being done in the industry now however KP is still the most common rootstock only because we know what it is. There are probably better ones out there but they are unproven. It costs us $80,000 a hectare to put mangoes in the ground so you want to know what you are going to get. 

Sheryl  How do they take off the husk commercially?
Gavin   They put them in a tumbler to get the flesh off them then spread them out on a black piece of plastic to dry them out for a couple of weeks then do it by hand. A pair of secateurs to take the end off then an oyster knife! Very time consuming.

Pollination
We use European bee hives from a commercial apiarist. We also grow strawberries so the hives get shifted over to the strawberries so we get free pollination and he gets the honey! In the Northern Territory where we have 400 hectares of mangoes, you need a lot of hives and we need to bring bees in so it’s a commercial operation and we pay $28.00 a week per hive and we’ll have 2000 out during flowering and we do this for a month. When the bees are there, we can’t do any spraying until they are in bed and in the NT, that’s dusk and as soon as it’s light they are out so all our spraying is done in the dark. One of the issues with one of the properties in Katherine NT is that we are right up against 2000 hectares of watermelon and they need to be pollinated from April through October so they’re continually rotating the bees around. Bees will travel 8kms so we need to be mindful of them around vegetatively as we’ve taken out some of the hives with Fipronel which is lethal on ants and a bit spilt into a puddle and the bees came and drank from the puddle and took it back to the hive and nailed the hive.
Sheryl  The native bee people say they pollinate mangoes. Do you use them?
Gavin   There’s not many around and they are hard to manage. Any insect will pollinate mangoes as they are easy to pollinate particularly when it’s warm. The issue down here is the stomatas don’t open when it’s cold and mid July we will take off every flower because it’s too cool to pollinate properly. It takes about a month to prune then we’ll go back again middle of July and take off everything again.
George  They use to say that nubbins were caused by low 6° C temperature killing off the embryo but what you are saying is that the bees aren’t pollinating below a certain temperature so what causes the nubbins? Is it the lack of pollination or the cold or both? I think they’ve said that the embryo dies but you could see that by cutting the flowers when they are very little and looking at it under a microscope and you should see whether the embryo has gone or not. It’s the 1st time I’ve heard that lack of pollination causes nubbins.
Gavin  It’s the lack of pollination but it can be caused by both but we think it’s 10°C. Stomatas won’t open so they can’t pollinate even if something was there to pollinate them so if there are no insects and insects aren’t out at that temperature so basically it’s a lack of pollination that are causing the nubbins. 
Barbara:  We had a talk by Don Batten and he spoke about flower initiation in the drop of temperature and he says he prunes in May and that flower initiation happens when it’s cold.
Gavin:  I agree with the concept but there are many ways of doing something. We use to do a lot of things that we no longer do. If we had done it in May, what can happen is that it can have another flush after that – not a flower. It will either be vegetative or floral so if they go vegetative at the end of May you can be in trouble. You’re going to have to take it all off and start again. If it goes floral at the end of May, you’re still in trouble because it’s too early and they won’t set. There are a lot of insects around but they don’t get out of bed til its 18°C so both ways you lose out. We do it end of June or even July depending on the winter. If you get a warm
winter, you can do it earlier. The concept is sound – just the timing and we’re getting better results if we push it back to July.

Pests There’s Mango Leaf Scale that probably does the most damage. They’re little white specks and they will kill the leaves and the leaves go yellow where they are and in a month, the leaf will go dead. There are chemicals you can use but a vegetable oil is an appropriate way of handling Mango Scale. You need a fine mist and ideally some air as that is how commercial people spray mango. We throw the spray in front of the sprayer and use the air to spread it. It’s the uniformity of the coverage that is important – not the volume.

Flying Foxes:  They don’t like green mangoes so we don’t see them til we get some ripe fruit in the orchard ie just getting a bit of yellow tinge. In commercial orchards, we harvest just prior to that stage – what we call mature green. Control rats with bait. Lorikeets are also an issue with mangoes. In the NT we have a lot of problem with white cockatoos. They are very destructive. They don’t eat the fruit. What they do is land on a branch, and the fruit is on a panicle and they watch it drop on the ground then go to the next!!  When we are picking, we’ll continually cut a heap of fruit throughout the day to make sure that we are harvesting at correct maturity as we pick before they are ripe. It is difficult to tell what is mature and what is not because colour is not a good indicator. The best way to tell with most mango varieties is the smoothness of the skin. When you run your hand over immature fruit, it has little bumps like fine sandpaper but once that smooths out, it will be ready to pick. Also the shoulders at the top of the fruit will tend to puff up and the stem will be lower than the shoulders. The nose (bottom end of the fruit) as well will fill out but sometimes depending on the year. Usually you will only get one mango per panicle.

Fruit Spotting Bug:  It can attack green fruit and we monitor for that. We get it quite bad here around Nov-Dec – two months before harvest.
George  Do you get any damage from the fruit spotting bug on the young growth of the vegetative growth?
Gavin  We don’t have a major issue but as soon as there is a hot spot, we will spray and one of them is a natural pyrethrum but if they’re hiding behind a leaf, you won’t kill them. We also get a little caterpillar on the young growth that grows to 2cm long, brown and white and we get hot spots of them as well.
George  I know they get phytophthora in mangoes in the north – do you get any here?
Gavin   No, it’s not a big issue. Mangoes are not resistant to phytophthora but they have a massive tolerance to phytophthora.

Mango Picker  We built the machine ourselves. We have two people walking along cutting the mangoes from the stem and it needs to go into the water within 3 secs of picking otherwise the sap could burn the skin of the mango. There is also another person on a platform on the machine. Mango sap is toxic and burns the skin so the water circulates around the machine and we have another person takes the stems off. We put a detergent in the water to stop the smearing. The tank on the machine holds 1500 litres of water. We made another machine out of a Nissan Patrol 4x4 ute because when it’s wet, we kept bogging the other one and this machine can run down the centre and have two people either side. After we bring them back to the shed, we wash them again and put a fungicide in the water.
George  Does time of the day make much difference to the pressure of the sap?
Gavin   It does. The turga pressure in the fruit is higher in the morning than the afternoon. The pickers just have to be more careful in the morning.

Ripening Mangoes after picking  Try and find the coolest well ventilated place in the house until they colour up to what you would call ripe then put it in the fridge and if you’ve grown it correctly, they should keep for around 2 weeks. KPs will go mushy in the freezer but Honey Gold don’t – well – not as much! They’re not as good as fresh but they’re still a solid piece of fruit. Different people like them greener and others prefer them riper. Store at about 12°C for as long as you can but it will continue to ripen. When you ripen at this temp, it’s too cool for the sugars to come up. We don’t use the Brix meter on our mangoes but we do on Strawberries and Pineapples because they don’t ripen after harvest. Watermelon is another that doesn’t ripen after harvest. Brix is not an accurate measurement of eating flavour. If you get a mango perfectly ripe and measured the brix then, then it’s consistent and it should be 14 brix but by then it’s too late to do anything about it.

Water   On a drip feed.

Pineapples  They put Nemacur over them for nematodes and Phos Acid to control the phytophthora. There are certain types of nematodes that will get into mangoes. We can’t grow Pineapples without using Phos Acid for phytophthora whereas we don’t treat Mangoes for phytophthora or nematodes. We also get a big Tea Mosquito the size of a fruit spotting bug and they’ll mark the fruit. They leave a black mark on the fruit. We also have a problem with wood ducks in our strawberries. They just demolish them!

Pineapple  If you want to keep them longer, don’t snap the top off – cut it off and that way it acts as a plug and the shelf life won’t change. If you break it off, it will only last a few days. The pineapple top will store for 6-8 weeks before planting. 

Weeds  We mainly use glyphosate (roundup). We use a bit of Baster on woody weeds like vines. It’s important not to let your weeds go to seed. You can maintain it with very light doses of glyphosate but if you let it get knee high in seed, it’s hard work.

Mango Checklist

Fertilise after harvest We do a soil and leaf analysis immediately after harvest but for a backyard grower if you have a tree around 3 metres, spread approx. 800gms around the tree after harvest. Something like CK55. It is very important to fertilise at this time of year so you get them to flush before winter. We have all our fruit off by the end of February.

Prune in winter June/July.  Strip off all the old leaves in the centre leaving all the new ones on the outside. If you decide to do a hard prune, use a water based paint on all the branches and trunk.

Foliar Fertiliser when the flowers get to 100mm long with Boron and Zinc and about a month later when the flowers are fully opened and just prior to fruit set. We buy it in chelated (liquid) form which is more expensive but easier to spray.

Pests  We spray the fruit with Bugmaster (Carbaryl) to control the Fruit Spotting Bug. Check around November/December.

Diseases  We use Mancozeb every 2 weeks once flowering commences and we continue this until harvest. 

Propagation  Take your scionwood from the current year’s flush that has hardened off – best time is December and January. (SE Qld) There is a disease called Mango Malformation which is a type of Fusarium disease so if you were propagating, it is important to get the tree tested against this as it can lay dormant for many years.

There are around 800 commercial mango growers around Australia. They are even grown in Victoria along the Murray River and Renmark in South Australia.

Sheryl  Gavin was telling me that the Honey Gold variety they grow freezes quite well and doesn’t go mushy when dethawed. I tested it out recently as I still had some frozen and found that they were very acceptable so can recommend this method. Nice recipes here:  www.mangoes.net.au