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During summer, growers experience a lot of problems with tomatoes. This article deals with the effects of temperature on tomatoes – on pollination and fruit set and also on ripening.  I will deal with diseases in another post.

Tomatoes are affected by high temperatures in a number of ways. Some sensitive varieties are affected when average daily temperatures exceed 25°C, whereas more heat tolerant cultivars are not impacted until daytime (maximum) temperatures exceed 32°C. There are even some cultivars are able to set fruit at temperatures above 35°C.

Under marginal conditions fruit may set without adequate pollination but the internal fruit segments will contain few seeds and the tomato will be flat sided and puffy. Irregular pollination can also cause ‘cat facing’ (http://vric.ucdavis.edu/veg_info/catface.htm).

In general fruit set is adversely affected when temperatures fall below 10°C or rise above 27°C. Optimum temperature for fruit set is 18° to 24°C. Even moderate increases in mean daily temperature (from 28/22°C to 32/26°C day/night) result in a significant decrease in fruit set.

As a general rule, the 8 to 13 day period prior to flowering is the most critical phase. If the average maximum temperature in that time exceeds 29°C, pollination and fruit set are impacted. However as pointed out earlier, this does vary according to cultivar.

Why aren’t my tomatoes ripening?

In hot weather people expect fruit to ripen faster. But with tomatoes the optimum temperature for ripening is 21 to 24ºC. When temperatures exceed 29 to 32ºC, the ripening process slows significantly or even stops. At these temperatures, lycopene and carotene, the pigments giving the fruit their typical orange to red appearance cannot be produced and so the fruit stays green.

For tomatoes light has very little to do with ripening. Light is not needed for ripening and fruit exposed to direct sunlight can heat to levels that inhibit pigment synthesis (As explained above). Direct sun can also lead to sunburn. Do not remove leaves in an effort to ripen fruit. Also, soil fertility doesn’t play much of a role. High magnesium and low potassium can cause blotchy or uneven ripening or yellow shoulders. But slowness to ripen is generally not due to poor nutrition and adding more fertilizer won’t help.

You can remove fruit which are just showing the first colour changes (mature green), and store them at 21-24ºC in the dark, preferably in an enclosed space or in the presence of fruit that give off ethylene gas such as bananas. This may speed up the process by up to five days.

References and further reading

http://www.managingclimate.gov.au/wp-content/uploads/2012/04/Critical-temperature-thresholds_Tomato_V2.pdf

http://cvp.cce.cornell.edu/submission.php?id=91

 

 

It has been a long held belief that Rosa x fortuniana Lindley is the only rootstock suitable for local conditions in Western Australia. Rosa x fortuniana Lindley has produced outstanding yields under conditions in Florida (McFadden 1962). The reasons for its superior performance include better adaptation to warm weather and sandy soils. Resistance to soil borne pathogens such as Pythium, Phytophthora,  Rhizoctonia and crown gall has been found in Florida trials. Hybrid vigour is also a possibility – Rosa x fortuniana Lindley is believed to be a hybrid of R. banksiae x R. laevigata. Superior uptake of iron during hot weather could also be a factor.

Rootstocks found in Western Australia include R. multiflora, R. x fortuniana, R. indica major, R. ‘Dr Huey’, R. manetti and R. canina inermis. Some of these are being used for inground cutflower production whereas others are used in the home garden as well.

Characteristics of a rootstock which are important include:
1) Ease of propagation
2) Lack of suckering
3) Disease resistance and/or tolerance to nematodes
4) Vigour
5) Tolerance of local conditions eg salinity, heat and drought.

Multiflora is noted as being more salt sensitive and more cold tolerant. It is less tolerant of alkaline conditions. It also picks up virus infections from the scion material very easily (however in Australia there is no virus free material, I can write separately on this topic). There are numerous lines of multiflora used internationally and at least two lines have been found Western Australia. One line is greatly lacking in vigor and displays a multitude of trace element deficiencies. Even the other line of multiflora seems susceptible to trace element deficiencies, especially copper and iron. Studies, both at the Department of Agriculture and overseas have shown it to be an ideal host to both root knot nematode and to lesion nematode, but particularly, root knot.

‘Dr Huey’ appears to perform quite well especially on heavier soils. In both McFadden’s study and in that of the Department of Agriculture, it came second to fortuniana. I have not seen any obvious problems with ‘Dr Huey’. It is reported to be susceptible to black spot which may be a problem in more humid climates.

R. manetti, used commercially, appears to have some degree of resistance to nematodes and has solved grower issues with trace element deficiencies. The growth is far superior to R. multiflora and on a par with ‘Dr Huey’.

R. canina, also used commercially, also appears to have some degree of resistance to nematodes. Studies overseas have supported this. R. canina is extremely tolerant of root knot nematode and reasonably tolerant of root lesion nematode (Coolen and Hendrickx, 1972). Growth is superior to multiflora and trace element deficiency symptoms not evident.

R. x fortuniana is planted extensively in home gardens and to a lesser degree in commercial inground production. It is definitely superior to multiflora. It does seem to have some issues with trace element deficiencies. One disadvantage is that it is more difficult to propagate. It also suckers more freely.

Trials in Florida (Gammon and McFadden, 1979) compared flower production between bushes on fortuneana, odorata, multiflora and manetti. Odorata produced the highest yields, followed by fortuneana, manetti and multiflora. They also found large differences in the accumulation of trace elements. Fortuniana accumulated five times more manganese than odorata but this was not related to flower yield. Odorata was a superior accumulator of potassium and under low nutrient conditions both fortuniana and odorata were good accumulators of nitrogen and potassium and this was related to flower yield.

The results of the trial at Medina Research Station (1980 to 1982) did seem to support the superiority of fortuniana, especially for bloom counts. However the following factors should be borne in mind:

• High pH water and soil (both around pH 8),
• Medina soil is a Spearwood sand unlike most of the soil in the metropolitan area with is much poorer in nutrient status, and
• Climate – Medina is recognised as being a particularly cold spot in winter.

All these factors could have a significant bearing on the performance of any rootstock. Finally the experiment at Medina lasted for only three years when the normal lifespan of a bush in the average home garden is many times that.

Summary
In Western Australia which has a hot climate and nutrient poor sandy soils prone to nematodes and with poor water holding ability, R. x fortuniana is the logical choice. However home gardeners often modify their soils to varying degrees which may decrease this advantage. In areas with colder night temperatures multiflora may perform better than on the Swan Coastal Plain. In the clayier soils of the scarp, ‘Dr Huey’ also does well.

Solid fertilisers should be easier to measure out but often aren’t. Some manufacturers put a handy measuring container in the packet but most don’t. Statements such as a handful to the square metre aren’t that useful when you consider the variation in the size of hands! Filling an everyday container, such as a cup, with your fertiliser and weighing it can be a useful guide.

• A teaspoon holds about 4g of fertiliser;
• A tablespoon holds about 16g;
• A match box holds about 25g;
• A cup holds about 250g.

It can be useful to have a rough guide to what your crop needs (see my post on “Crop removal or how do you know how much fertiliser to apply?”. Commercial lettuce crops generally get 2-300 kg/ha nitrogen. Things like cabbages which are much slower but also much bulkier get 5-700 kg/ha. Tomatoes are also in that ballpark. Then you have native plants which only use a fraction of that – say 80 kg/ha nitrogen for an adult Geraldton wax bush which is being picked heavily for its flowers and foliage.

Evaluating the nutrient value of a solid fertiliser is done in the same way as for liquid fertilisers. For example, something like CSPB’s garden fertiliser is 13.5% nitrogen (N), 1.9% phosphorus (P) and 8.0% potassium (K) with a range of other nutrients including trace elements. That means in every kilogram of the product there is 135g (13.5/100) x 1000 (g) = 135g of N. Using the same system we come up with 19g P and 8g K.

It does pay to check the bag to compare fertiliser products. If you are paying twice as much for a product with 5% N then its not as good value for money.

Products from many other countries are sold here. You may find American products that have analyses like 10-10-10 – that is because they express formulae as the oxide form . The N is OK, it’s the same but the P need to be multiplied by 0.44 and the K by 0.83 to be equivalent to the base element.

Always be wary of any product that has a really high figure in the middle (ie for P) check the label and the origin and its probably American.

These days fertilisers aren’t registered. That means almost anything can be packaged up and sold as fertiliser. Ideally it shouldn’t because there is an industry code of practice (which isn’t law yet) but I do see a constant flow of new products coming onto the market (coming and going). And the buzz these days is microbes and humates (humic acid). So companies will try and sell you something with almost no nutritional value but lots of other buzz words for a hugely inflated price!

Just bear in mind that for microbes to prevail in soil they need a food source which is carbon (organic matter). Put them in your sand and they won’t last 5 minutes! And if you put them into and environment that is already highly organic and has its own microbe population they may well get out-competed by those already in residence!

So is a high nutritional analysis everything? Not necessarily. If the fertiliser is a quick release one the higher the analysis the more likely you are to come to grief if you overdo it. Quick release fertilisers are designed to be applied every couple of weeks or monthly.

You can of course use slow release fertiliser like Osmocote™, Nutracote™, Macracote™ and so on. They are expensive, you pay for convenience but you only need to apply them every few months. And you may waste a lot less – the danger with quick release fertilisers is that you irrigate them away in the next few days. We monitor growers who fertigate (fertilise through the irrigation) and we see soil nitrate levels (nitrogen is highly mobile) plummet between fertiliser applications – going from 80 mg to 20 within, say 3-4 days.

Some cheap fertilisers may also contain things like muriate of potash – potassium chloride. Chloride is salty and you probably don’t want it. Better to go for potassium nitrate or even potassium sulphate for your potassium. Potassium sulphate will make your soil more acidic but the sulphur can be useful.

Fertilisers imported from overseas can also contain nasties like heavy metals (cadmium, lead, nickel). These are particular risks from China or India. There is random sampling of fertilisers on entry for these sorts of things so it shouldn’t be an issue but things can slip through occasionally. You also need to be aware that manures and composts can also contain toxic levels of heavy metals, microbes like E coli or even amoeba and they are largely unregulated unless you buy bagged product made to the Australian Standard. There are plenty of places where you can back up a trailer and buy – who knows what! Not exactly what you want if you are trying to produce healthy food on your block.

When to apply fertilisers?

Most people assume you should fertilise when you see activity but we only see what’s happening above ground. It’s the roots that take up fertiliser and its root activity you need. Its widely said that you shouldn’t fertilise in winter. But many natives have their active root growth in winter and are largely dormant in summer. Other deciduous species also take up nutrients during that time and store them in the plant frame for later redistribution and use in the plant. But when its really cold, nutrients ARE taken up more slowly and of course rain leaches fertiliser away from the root zone and it is wasted. So for this reason fertilising in autumn can be a good thing. Just remember that however you fertilise, plants need it to be dissolved in water to take up. No point in spreading fertiliser around the canopy of a plant that is watered from one dripper in one spot! If its watered using overhead retic or mini-sprinklers and the soil is uniformly wet all around – then fine.

Foliar fertilisers

Foliar feeding is largely a very expensive way of doing things. More often than not what you apply to the leaves gets washed off into the soil and feeds through the roots anyway. Only in very special cases is it worthwhile and that is mostly for commercial growers who can’t afford crop failures. Calcium is often fed in this way because its immobile in the plant and bouts of high humidity can prevent its uptake by halting the transpiration stream that carries it around. Immobile trace elements such as iron can also be foliar fed.

So you’re standing in the aisle at Bunnings and you are being confronted with about 50 different fertilisers.
There are fertilisers for azaleas, citrus, veges, fruit trees…………
Then there are fertilisers you dispense through the garden hose, those you put a spoonful in a bucket of water, the controlled release, the powdered, the liquid, granular…………….
Oh and don’t forget the organic, the natural, the hydroponic………………….

Are you worn out yet? How do you make sense of all this?

First stop – the label. It should have something like a list of ingredients on it. It may go something like:
Nitrogen (as urea) 12%
Phosphorus (water soluble) 2%
Potassium (as sulphate) 8%

If it’s a liquid there should be something to indicate that those % are w/v (weight by volume), if its solid/dry/granular it will be w/w (weight for weight).

Next thing to look for is a rate – how do you dispense this product? One handful per square metre? One capful per bucket, one spoonful per 20 cm pot?

Lets look at the liquid feeds first – they are the most complicated. They will usually give you a measuring cap or a teaspoon and say use one of these in a 8L bucket of water (for example).

If they are really good they will tell you the volume (if it’s a liquid) or weight (if its powder) of the measuring cap or the teaspoon! If not you might have to weigh it yourself. To get an accurate result on your kitchen scales you might need to do say, 10 spoons and divide the answer by 10.

So lets suppose your powdered fertiliser comes with a spoon that hold 4 g product (when level) and you put that in 8L water. The analysis of your product is 22:4:15 (N:P:K) % w/w.

That means there is 22 g nitrogen in 100g of the powder. So one measuring spoon of the powder contains 22 x 4/100 g nitrogen = 0.88 g nitrogen or multiply by 1000 to get milligrams or mg: 880 mg N.

Put that spoon in 8L water and you get a solution that is 880/8 = 110 mg/L nitrogen.

You can repeat that for the P and K.

Take another liquid fertiliser and read the label. This time it says 10:3:6. And it says take the same sort of measuring spoon full of powder and put it in 5L water. The final solution will be 10 x 4/100 = 0.4 g N or 400 mg N/5L water = 80 mg/L N. So a bit weaker that the other one. Which is fine if its cheaper to buy but if its more expensive think again!

For liquids the sums are much the same except the analysis will be w/v so your 10 unit of N as in the last example will be 10g/100mL or 1g/L of product. If your measuring cap holds 20mL and you’re putting that into 5L water the sums are:
10 g/100mL means 10 x 20/100 = 2 g N or (2000 mg). In 5L water that’s 400 mg/L – quite a strong solution!

I recently went through this exercise from a supposed wonder product from the US – a liquid one at that and came out with something like 0.8 mg/L nitrogen as applied! It would have had to have been wonder product to do anything! Not only that liquids are often not very cost effective because you are shipping water around the countryside – very inefficient. Bear that in mind when you buy any ready-to-use product, typically those ones you attach to a garden hose and water on – they are terribly expensive for what you are getting in terms of chemical. They are convenient but you are paying for it big time!

It’s worth doing the sums. Kevin Handreck in his book Gardening Down Under did this exercise with about 20 products and the final nitrogen concentration went from 45 mg/L right up to 900mg/L! And I’m sure there wasn’t much correlation with price!

We’ll have a look at solid fertilisers next time.

Experimentally we can measure the amount of nutrient a crop removes from the soil or from a nutrient solutions when it grows. That means we can calculate how much nutrient is used to produce a crop. Crop removal can be measured in a few different ways. Sometimes its done in hydroponics. Then its easy to calculate what nutrients are put into the system and what is taken out. You can harvest the crop, dry it and analyse it to see exactly what’s in the root system, the leaves, the actual crop and so on. Of course it will never balance exactly because there are inefficiencies in the system. Plants require energy to grow and some nutrients will be lost to the environment.

Another way of doing it is to grow a crop in its usual situation such as soil, and then go through the same process of measuring what is in the plant at the point of harvesting the crop. Either way you end up with a set of figures such as those in the table below.

Crop removal table

As with hydroponics there is a fudge factor. If you were to apply just those amounts of nutrients you’d not achieve similar yields. Nutrients are always lost the environment because plant roots don’t explore 100% of the soil, so many nutrients may be lost through leaching. Where you have clay soil, if the clay is highly adsorbent (ie you haven’t been applying phosphorus fertilisers or manure for several years), then much of the phosphorus you apply may be adsorbed by the clay and not readily available to the plant (not in the time frame of that crop anyway). Perth’s sands are generally below 1.5% clay so this is not an issue.
Crops vary in their ability to take up nutrients. Some are very efficient, others not so. Much of that is to do with the architecture of their root systems.

The figures above are per hectare so have to be related back to a per plant basis but you can see that there is great variation between the relative amounts of nitrogen, phosphorus and potassium that each crop uses. The figures can vary a lot depending on things like:
• climate – in countries with low light levels generally have lower yields and therefore lower crop removal figures
• crop variety, and
• time of year.

In our work, we find we may have to apply 30-50% more nutrients to a crop over winter than summer. Why? Rain and slower growth are the reasons. No matter how well you apply fertiliser one decent shower of rain will leach most of it away. And because winter is cooler, invariably the time the crop takes to grow is longer and those inefficiencies multiply.

So what is the fudge factor you have to apply to actually grow a crop? About double is not a bad average. Some crops you might get away with 40% more.

The other consideration is the amount of each nutrient that a plant can access. Each nutrient comes with its own set of problems. Nitrogen is highly leachable. In sand so is phosphorus and potassium. In clay soils things may slow down a bit for the latter two but nitrogen is still converted to nitrate within about 24 hours of application in Perth so the advantages of applying ammonium are not great.

Lets now they can relate some of this to the manures and composts you may use. I’ve used this table before.

Manure composition table

Using tomatoes as an example. If you need 297 kg N per hectare – lets say 30 g N per square metre, then that amounts to 3.3 kg of sheep manure (at about 40-50% moisture content) per square metre per crop. And if we double that for our inefficiency factor then we’re up to over 6 kg manure per square metre of ground.

But that amount of sheep manure contains almost the same amount of phosphorus and our tomato crop only needs just under 20% of that! What happens to the rest?

And what about potassium? Our crop needs more potassium than nitrogen so we will be short changed on that score.

You can see how easy it is to waste heaps of phosphorus and probably how much better your yields may be if you added a lot more nitrogen. And why you might run into disease problems and fruit quality issues due to lack of potassium.

We haven’t even considered yet is at what stage in its life cycle our tomato crops needs each of these nutrients. The figure below shows the pattern of nutrient uptake over the life of a tomato crop.

Crop removal Yara

OK, so sheep poo is not a good idea. What about using chook instead? Well, you will be slightly better off for the relative amount of nitrogen to phosphorus but you are even more short changed on potassium!

If you use half sheep and half chook , the ratio of N:P:K changes to 13.5:10.5:6.5. Not a lot of help – well over on P again and well under on K.

What is my message? Well if you’re growing veges organically using animal manures and compost, unless you are operating in a closed system, don’t kid yourself you are being environmentally friendly. You might be saving on food miles and pesticides but the Swan river isn’t going to thank you for all that phosphorus you are dumping in to the groundwater. And if you are using some sort of closed system, at some stage you are going to have to dump nutrient as the levels of phosphorus (and other plant exudates) become toxic – and where will you put it?

Nematodes

OK, I know I have done much for a while but this came up on a forum today so it seemed like a good opportunity.

Nematodes are tiny worm like creatures. They are a particular problem around Perth because we have sandy soils. If you live in one of the older suburbs you probably have them for sure!

How can you tell if you have them?

Plants will be unthrifty, they may simply appear unwell, nutrient deficient or they may be getting a lot of other problems. For example roses or eucalypts with nematodes often have stem cankers as a secondary problem. If you dig the plant up and examine the roots they may have knots on them – or they may not. Most people aautomatically think of root knot nematode when they think of nematodes however many other species of nematodes don’t produce galls or knots. You may just see roots that seem more branched and profuse then normal (not to be confused with proteoid roots on banksias, hakeas etc. Or on leaves, you may see angular blackened sections.

Types of nematodes

Most nematodes can’t really be seen by the naked eye – the commonest species may be up to 1mm long. Some nematodes feed from the outside of the root (dagger, needle or stubby-root nematodes), or they may go inside the plant and either stay in one place (eg root knot nematode) or move around inside the plant and feed along the way (lesion or burrowing nematodes. Some other types of nematodes move around inside the plant but feed on above ground parts such as leaves or stems (such as Aphelenchoides that infect leaves of eg Chrysanthemum or some ferns)

How do you get nematodes?

They can come in on plant material which is already infected or in soil/soils mixes.

What conditions do they like?

Ideal soil conditions vary with species. Moist soil is required by all to reproduce and move. The optimum temperature varies with species. The pore size of the soil affects nematode movement. The small pores of clay soils make movement difficult so the nematodes have to move in the spaces between aggregates. The larger pores in coarse sands may be too big to allow nematodes to gain leverage between particles.

Control

The home gardener has a different range of options to a commercial grower. Nematicides used to be available to the home gardener (Nemacur® granules) but aren’t any more. They are all S7 pesticides so pretty nasty! Over time the microbes in the soil that break the chemical down build up numbers so over a period of a few years the pesticides become less and less effective. There are natural predators of nematodes – such as fungi or other nematodes but these aren’t really commercially available. Method more suited to the home gardener include:

Rotation – the use of a rotation crop that is resistant to the particular nematode. So for root knot, that may be something from the grass family eg a grass or sweetcorn or sorghum. This will not eliminate them entirely but reduces numbers to levels that don’t cause problems.

Fallow – leaving an area fallow has a similar effect to rotating with a resistant crop – numbers fall because they can’t reproduce.

Solarisation is another option. The use of clear plastic laid over tilled moist soil for several weeks during the hottest part of the year.

Bio-fumigation – there are some crops that can be grown and hoed back in that contain chemicals that will help control pests and diseases including nematodes – such as some of the mustards. These crop residues are planted densely and hoed in while in full flower. Castor oil plants and marigolds have root exudates that may kill nematodes – they can be grown as rotation crops and hoed in. The type of marigold matters, not all are useful. Tagetes patula has traditionally been the one to use but some other species also work.

Sugar and molasses – In some Brazilian work, 300g granulated sugar per litre of soil at 7 days intervals controlled root knot.

Work in Australia on field grown tomatoes found 150 m³/ha of sawdust plus urea (600 kg/ha) to be quite effective. Molasses at 375 litres/ha per week for 14 weeks helped reduce numbers but was inferior to the sawdust.

In some other trials, urea concentrations of 4% totally eliminated nematodes but adversely affected plants. A combination of urea and molasses reduced the phytotoxic effects. Some papers mention molasses in water with a final sugar concentration of about 2% reduces nematodes numbers by about half in just over a week.

Other plant extracts – many have been trialled. Things like calendula, rosemary, lantana, onion, fennel, datura and liquorice which are ground up and put in water. What works probably depends on the type of nematode and the crop. Many of these trials have been in vitro and not in field situations.

The APPS website has some good info if you’d like to do any further reading.

Just a quick one – firstly, observations in my own garden last weekend.  Wherever there was a layer of organic matter over the ground there was bone dry soil underneath nice wet organic matter.  Not much point in that being wet though when the  soil which is where the roots are! Now, I don’t mulch as a general rule, so I’m talking whatever lands there from trees around the place, and breaks down over time.  Fine textured organic matter.   Conversely, wherever there was soil only and no layer on top, the rain of the past week or so had wetted the soil up to a depth of a few inches. 

I also received some progress reports on the mulch work done at Murdoch TAFE over the last summer.  They quite definitely show that coarse mulch is the way to go and no more than 50 mm thick if you still want soil to be wetted in the root zone (bear in mind that work was in summer with supplemental irrigation).

We are doing some work outside of Perth (north by a few hours actually) in some quite clayey soils with a range of soil moisture monitoring gear.  We’re getting quite high moisture levels in the soil but the shape of the graphs and the way the probes react to irrigations are telling us that much of that water is not plant available, the bulk of it simply sits  there making the soil feel moist but not helping the plant much at all!

And in case you haven’t been tracking rainfall and you have just been blindly following the watering days regime, perhaps you wouldn’t like to know that in May I had 210 mm rain at home compared to 21 mm in June.  So if you didn’t water in June  as per instructions, you may be in some degree of trouble especially if you’re growing things with shallower root systems eg veges or if you have new plantings in the garden.

 

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