Author: Klaas Plas

In the last months lots of growers have struggled with the quality of plant material. Not mainly about the variety, but just the quality of the plants. There are huge differences in the quality and this where quality is one of the main factors determining the profit of strawberries. Just some points:

• Generative plant: lots of flowers, not enough leafs to support the plant. It influences the whole year of strawberry growing: small berries, no taste, lots of work, yield relative poor. As the low LAI cannot support the growth of the berries. Value of such plants: negative.
• Vegetative plants: lots of leafs. If there are no flowers, harvest may be delayed with about 1 month or more. Normally i see way more generative plants, but a vegetative plant can also be an issue.
• Disease like Neopestalotiopsis, or Phytophtora or Crown rot. Some growers suffered with more the 50% of the plants starting to wilt. So they had to take out the plants from complete sections or greenhouses. Value of such plants: negative.
• Pests like Cyclamen mites, spider mites, aphids. A hard start to get those under controll
• Clean plants, but full with all kinds of insecticides, so predator programms just don’t work.
• Nice balanced plants, first harvest about 6-8 weeks after planting. Nice big leafs, good strong flower trusses. Value: can be easily twice the normal price. Such plants can grow big tasty fruits for a whole season.

During my last visit to Canada i have seen several growers with plants from different propagators. And really with the values of plants varieing from far negative (so a negative value) till positive even more then 2 times its current price.

One of the issues on the background is irrigation and substrate. As we need very frequent irrigation or better misting right after sticking, the substrate easily gets way to wet, without oxigen. For rooting tips that is a disaster, causing plants dying, black roots etc. Below you see some pictures i took last week in Hungary, from tips stuck in coir. Just normal nice coarse coir (pith, no chips).

hair roots and air

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What makes the difference. Or how to do biological control.
One of the items that works good is, to focus on the whole ecosystem in and around the strawberries:
– in the greenhouse – for example on the soil
– around the greenhouse – close by
– in a wider area around the greenhouse

Below you see some pictures of the production sight of a German growers. For about 5 years she decided to spray at all on the strawberries. So no chemical treatment, neither a biological or organic spraying. Not against pests not agains diseases.
She had the guts to start that way. I respect this dicission of her. And it works.
Spidermites: no problem at all – lots of natural predators (like Andersoni) in the grass / cloaver below the table tops and quite a lot of Feltiella.
Aphids: In the spring allready aphidius kinds in the grass and a lot of hoverflies later in the spring.
Thrips: comercial Cucumeris and Orius
White fly: normally from a predator that looks like Encarsia

Grass / Cloaver – next to a good banker and source for predators, they influence the climate quite strong. Especially in hot summers the temperature drops and the humidity is a bit higher. This influences the growth and the mildew pressure.

At the end of the pictures two pictures that look like thrips, but it is not thrips damage. You can see very good that if you zoom in, the brown spots are one spot, and not the small lines caused by thrips.

greenhouse-

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This time a few nice pictures of cyclamen mites: eggs and larvea. But also some Aphidoletes, Hoverfly and Ladybug.

Cyclamen mite, can be really a big issue in strawberries. I see that in case of chemical pest controll, there are always some issues. In case of biological control (cucumeris or andersoni) cyclamen mite are no big problem.
The biggest problem of cyclamen mite is, that they are so small. If they where as big as an elephant, they could never develop. But if we see a problem, there are allready lots of them and mostly hard to treat.

Below 2 video’s: one of cyclament mites and one of a spidermite predator. To be honest i don’t even know its name…

This week again several new pictures of bugs.

Especially the lady bug eggs look great. We saw them in the Northern part of Germany (Area Langförden).

The other predators for aphids where also quite nice available this week: Aphidius, Praon, Aphidoletes. Just nic to see so many predators. They are needed, because the numbers of Aphids are increasing. But with some good natural sircumstances around the crops, they are not a big issue (although they may become).

Against spidermites there where some nice feltiella and andersoni active.

Most important way of getting these is:
-don’t use insecticides,
-don’t use too much oil or wetting agent if you have to spray
-take care of natural circumstances aournd the strawberries: for example bushes, flower zones etc will help a lot.
-don’t be too clean and accept some weeds and flowers around the strawberries (seems contraproductive, but isn’t always).

This week a lot of spidermites and predators crossed my road. A beauty to see the interaction between the spider mites – predators – climate. With a good climate and with good ecology in and around the production site.

Below you see a (quite – sand road is a pity) good example of a nice climate for predators and strawberries: grass (or better a grass – cloaver – flower mix) around and below the tabletops. Advantages:
– development of a natural predator population right around the strawberries
– buffer for predators
– attraction of predators like hover flies, lacewings, feltiella etc
– an excellent climate for strawberries: a humidity buffer in dry periods – causing less problems with milldew, cooler climate and a better production.

Spint-feltiella-2a

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Yes, irrigation is hot. In the last 6 weeks, i have seen quite a lot of issues with irrigation. At first sight it should be good: drainpercentages and sum EC totall fine. But:
– Roots quite bad
– Plants just not growing right

The color of these roots are really fine. But the location isn’t. I would like to see the roots from top (2-3 cm below top) till bottom, and eavenly spread.

Then just sit down and check everytyhing. For a good check we have a few tools:
– first irrigation standard 2 hours after sunrise, or better: 60-90 joules after sunrise.
or even better, just 1-2% drydown after sunrise
– last irrigation standard 2-3 hours before sunset, or better: about 125-100 joules before sunset
– the irrigation over the day should be stable. Stable means not in time, but in radiation. The correlation between radiation and evaporation is quite good. Thus stable in ml/joule (officially: ml/lm / joule/cm2). So the amount of ml/joule should be stable between the irrigations within a day, but also between the days.
Normally this is about 1,5 ml/joule. But the number is not very important, it is much more important that it is stable with normal drain percentages (5-35% – depending on plantsize and climate).

With this check (ml/joule) we could find out on several companies, that is was not stable: in most cases in the darker parts of the day too high (for example going in the direction of 3-4 ml/joule), in the sunnier parts of the day too low (going down to 0,7-1,0). That means within one day, plants are drowning or are thirsty.

This caused bad rooting, and bad plant development.
Main reason was in the most cases:
– irrigation on time
– irrigation on radsum, but with a min time interval and a max time interval.

My experience is, that from a certain plant size, irrigation on radsum is way the best system. But it is important to check if the joule and amount settings are correct by:
– drain% measurement and calculation
– drain timing (when do you get the first drain)
– measurement of dry down (between last irrigation yesterday and the first irrigation in the morning); between irrigations; between sunrise and first irrigation and between last irrigation and sunset.

Above a graph with the drydown numbers: 4,09% – quite a lot for strawberries. As you can see in the graph, irrigation started too late. With such a drydown strawberries get easy to generative.

If i would ask all my clients what they see as the hardest issue in growing strawberry, i think about 95% of them would mention irrigation.

It is spring, and in this time of the year i see the struggles again. lots of growers with to wet soil or substrate, and in the meantime enough growers with too dry substrate.
The weather is changing all the time. In the morning it seems to be autumn, and a bit later, summer comes closer and in the afternoon it turns out to be spring.

How to irrigate under such circumstances?
Recently a grower mentioned: “We invest quite a bit of money in a climate controll system, a lot of money in plants, predators, gutters etc. But nothing in the controll of irrigation. It is time to change it…”.

Important to consider:
– The correlation between radiation and evaporation is very high
– Normal evaporation (good developed plants) is about 1,5 ml/joule (or better (ml/m2)/(joule/m2).
– lower LAI (Leaf Aria Index) means also lower evaporation (leaf pruning –> less evaporation, thus changes in the irrigation).

Withgoing a presentation about irrigation for strawberries. It was originally developed for tomatoes, but i was allowed to change the numbers, so it is suitable for strawberries.

A new beginning, a new start. Everything ready for the new spring. Days are getting longer, flowerbuds in the hart of the plant promise a new future.

In the same way is Christmas the sign of a new future. God born in a stable, sleeping in a manger. Proof of a future life without war and pain, without tears.
But with fruit, and i hope we will enjoy strawberries as well.

I wish you all Blessed Christmas – a blessed future – a blessed 2024

Irrigation in strawberries seems to be one of the hardest issues. If i ask growers i work with 90% of them will mention this as so.

In my last post on LinkedIn, i had a poll about the dry down for strawberries overnight. Interesting to see 640 impressions, but just 16 votes. An indication for the fact that good irrigation is hard working?

But first, what is dry down? Dry down is the difference in moisture content between the frist irrigation in the morning and the last one of the previous day. In the schedule aboveyou can see the level at the irrigation of the previous day and the level at irrigation of the current day (between the red lines in the graph above).

Interesting to see the answers also: no one voted for 4-6%. Although i didn’t mention the substrate in this poll. I ment to ask for organic substrates like coir or peat.

Most of the answers where on the 9-11%. For Rockwool where dry down is a known concept, i do think 9-11% makes sense. For coir i see 4-6% as the optimum. Reasons:
– Rockwool 9-11%:
* Strawberry is a plant that really likes air / oxygen in the rooting zone. The best soils are still the coarse sandy soils. The best substrates those with a lot of oxygen/air in the rooting zone. The oxygen content in Rockwool is essential lower as in most coir i see. A period with more oxygen in the rooting zone is essential for good root growth. A higher dry down can help therefore.
– Coir / Organic substrates 4-6%:
* Several items are directly related to this percentage:
** Tip burn (or calcium deficiency in the young leafs / flowers)
about more then 90% of the tip-burn i see is not related to fertilizer recipe but to climate. Calcium is passiv taken up by the plant with the sap flow (xylem). This means, Calcium is transported to those places where evaporation is taken place. Only in case of rootpressure it gets everywhere.
Low moisturecontent in the evening means low root pressure and thus higher risk on tip-burn.

** Root health and fluctuation in moisture content. Strawberry generally grow better if the fluctuation in moisture content is not too big. Periods with relative wett substrate seems to influence both rooting as well as browning of the roots, probably because of oxygen deficiency.
** EC / drainage. Strawberry have an optimum EC range from about 1,3-2,0. In case of low drain percentages the EC increases causing mainly yield and quality issues. In case of high dry-down more irrigation water is needed for remoisturing and less time on the day remains for drainage. This can be seen in quite strong increase of drain EC in case of high dry down levels.

Those experiences bring me to the following numbers:
– optimum drip EC: 1,3-2,0
– optimum drain EC: 1,5-2,0
– optimum dry down:
– coir: 4-6%
– rockwool: 9-11%
-optimum drain percentages:

Important to know, that these numbes are quite general, but differ for individual situations. Irrigation is not easy, it is subject for at least a days discussion if not for a week.

One of the most important basics is, that strawberries don’t handle big fluctuations very well. Both in EC as in Moisture content. They almost always lead to quality issues and sometimes to growth issues.

This means very practicle, that if i have a too high EC, i don’t advice to flush it suddenly, but decrease it steadily, slowely. The same for moisture content, if it is too low, don’t suddenly increase the moisture content.

Again several beauties together.

White fly predators: interesting to see the black larvea in stead of greenish colored larvea. 2 growers stopped using insecticides and those predators turned up naturaly.

Interesting: outdoor screening in order to keep the heat out. Works fine so far.

Lacewing

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