Newsletter aubergines

Crop tips Jaylo RZ

September/October 2011 (final tips for this season)

The highest productions and often also the best quality can be found on nurseries where the crops are looking generative. Usually these are, of course, the glasshouses with the most light, combined with a high CO2 capacity. It is important to capitalise on the sunny days by allowing the temperature to rise at a faster rate. After all, the days are getting markedly shorter, so that you need not worry too much about a too high 24-hour temperature. After 3.30 pm radiation reduces fast now, so make sure you have reached the desired temperature by 3.00 pm at the latest. On one nursery that temperature may be 27°C while on another it needs to be 28 or even 30°C, depending on the generative or more vegetative condition of the crop. If necessary, have the pipe come on again at 40 - 45°C and try to prolong the day. Around sundown the glasshouse -  and, therefore, the plant -  needs to cool down. Whether the vents need to be opened to achieve this depends, of course, on outside conditions. On a clear evening/night this is definitely not necessary.

The advantage of letting the temperature increase gradually by means of keeping the vents almost closed is that CO2 levels also rise more readily. This will influence assimilation positively. By subsequent accelerated cooling down of the crop, you impart speed to the developing aubergines and you are assured of good fruit set. If the buds/flowers become too heavy/slow it will be necessary to increase the temperature towards morning by 0.5/1°C. You see this happening where the crop is relatively close to the (cold) glass. It is important, though, that the measuring unit hangs near the head of the plant.

Due to the mild weather at this time of the year it may be necessary to allow the glasshouse to 'leak' day and night. By having the vents just barely open (hardly discernible with the naked eye) you will still get some sort of air exchange. And by ventilating close to the temperature set point, combined with an adequate pipe temperature, you are creating an active climate. During the day we must aim to remain below 80% relative humidity (moisture deficit 3 - 4) and towards morning we would prefer not to see more than 90% relative humidity (moisture deficit 1.5/2). If the relative humidity is too high, there is less transpiration and, therefore, less feed is transported and you will end up with a weak crop/root mass and laborious fruit set and/or bad fruit quality.

In crops that are too vegetative, crop work is (more) important. More frequent topping of the sideshoots or even removing the head (near the wire) will do no harm in that case. Taking a leaf out in between, if necessary, depends very much on how much longer you intend to continue the crop. You can still get fruit set until mid-October but that does mean that you have to continue the crop until mid-November. As long as you want to get fruit set, pollination should be in order, so regularly check the bees and/or bumble bees on quality and numbers. If in doubt, release some more populations.

The first watering round is after 9.00 am. After 3.00 pm watering is done only at 90/100 joules and when 200 W is measured. Try nevertheless to realise 30 - 40% run-off between 11.00 am and 2.00 pm. That way you more or less equalise the water content and the EC of the substrate slabs again and you prevent a water shortage along the gables and/or in certain warm spots.
Once the weather turns more variable (i.e. autumnal) it's better to allow the EC in the slab to rise a little to somewhere near 4.0. It is important in this that the potash and calcium levels are the same and that the other (trace) elements also meet the target values. This is necessary to maintain Jaylo's good quality in October as well.

Remain alert to insects to the very end of the crop: a caterpillar outbreak can very quickly cause a lot of damage. This also applies, of course, to red spider mite, (black) aphids and whitefly. Whitefly in particular can cause a lot of mess and stickiness on the aubergines and lead to problems in the trade channels. Try to keep the thrips under control as well, although that is not so easy now that only a limited number of permitted chemical preparations against thrips are left.

Excessive root growth has given a number of nurseries quite a few problems.
During the crop change-over the following matters are important:
- remove all crop/root remains

- hose down the crop gutters and glasshouse structure with chlorine

- treat nozzles and hoses/conduits with chlorine, both inside and out

- use new plastic and clean substrate

- if possible, let all the irrigation water pass through the disinfector.
While the crop is growing, a number of preparations against excessive root growth are used in practice but these have only a limited, at most an inhibiting, effect. The perfect solution against excessive root growth has yet to be invented.
VAN DER KNAAP CONSULTANCY COM V
C. van der Knaap