Dirk wk20/21 / 2010

The weather conditions in March and April were very good to grow tomatoes. Sufficient light intensity and no high temperatures yet, so the plants could be cultivated as we want to. The first week with less light intensity than the weeks before was week 18.

It is possible that the fruitload is increasing next week. Because of this it is necessary to keep enough speed at the plant development to stimulate the maturing of the fruits. For Dirk a fruit weight of 125-130 grams (6 fruits/truss) is the maximum. Otherwise we are cultivating too slow and this results in a too slow maturing of the fruits. The productions of Dirk are approximately 11-12.5 kg/m2 until week 20.

Temperatures

At powerful crops it is necessary to steer to a more generative plant (CO2, D/N-difference). This can be achieved to set a pre-night of 15 degrees, starting 1 hour after sunset at nice days. At balanced crops this is achieved at sunset. A sufficient generative position of the plant results in an extra size of the fruits and extra production. A well set average-24-hour-day-temperature for Dirk is 21 degrees at nice weather conditions and 19.5 degrees at dark weather conditions. All this is depending on the position of the crop; a powerful crop can handle a higher 24hours-temperature with more difference between day and night temperature. At a powerful crop the temperature always must be 23 degrees ore more for a period during the afternoon. At a cold night temperature heating up is an important issue to achieve an active crop at sunrise. If there is a low humidity the windows can be closed a little bit at the side the wind comes from during the afternoon.

Try to decrease the average-24-hour-day-temperature at hot summer days, this can be achieved to extend the pre-night. With a pre-night of 14-15 degrees, at 2.30 a.m. at the latest the temperature is increased in 2 to 2.5 hours to the later part of the night with a temperature of 17.5 to 18°C. To achieve the morning temperature it is advisable to use a minimum pipe temperature of at least 45 degrees.
It is advised to ventilate sufficient (humidity not to high) this helps to strengthen the truss stems. Also a morning dip of 1 degree in temperature from sunrise improves stronger trusses.
 

Irrigation

With sunny weather we give at least 3-3,5cc/joule (at the lightest part of the day 4cc/joule).
Achieve drain in time at the morning. After 3 to 4 times irrigation it is advised to create the drain, but not later than 10.15 a.m. The quantity of irrigation after 14.30-15.00 p.m. is depending on the light intensity. If the EC is increasing, most of the times too less water is used. Try to achieve that the Ph at the slab and the drain water is lower than 6. This improves the picking up of Fe and Mn.
Take care of sufficient Potassium (K) at the slab; this must be 7 to maintain a good colouring of the fruits.

Pruning and crop-protection

From end of June/beginning July it is advisable to prune at 5 fruits again.
Dirk is intermediate resistant against mildew, however be aware to do not too less against fungus diseases (like Botrytis). At varieties which are susceptible to mildew we always used remedies against mildew which also had an effect on other fungus diseases.
It is advised to take out a leaf at the top of the plant; certainly at strong crops.