Dirk wk07 / 2007
The grower information on this website is to keep you informed about the latest developments concerning Dirk, our new tomato variety for the medium fruit size segment. The advice in this grower information will focus on both the early sowing dates (20 Oct-10 Nov) and the later sowing dates (after 10 Nov).
Current situation
There is great diversity as far as the sowing dates and growing methods of Dirk are concerned. The quality of the plant is generally good and uniform. The fruit setting proves to be good at all companies and the fruits develop relatively fast. Lately, the Pepino Mosaic Virus has been found at a number of grower sites. As the amount of light is still low, this virus results in the plant to become weak and to recover a bit slowly. However, maintain a similar cultivation strategy as when the virus would not be present.
The plants of several growers are fairly vegetative the moment (especially those with a later sowing date). It is important that these crops are grown in a generative way: a considerable day/night temperature difference, twenty-four hours' temperatures that are sufficiently high and a drip EC of between 3.5-4.
Temperatures
Most growers need to maintain a generative growing regime with Dirk. The twenty-four hours' temperatures have to be between 17-18.5 degrees for early sowing dates and between 18.5-20 for later sowing dates. The pre-night temperature is to be set at 14-15 degrees (for 6-7 hours a temperature of 14-15 degrees when early sowing dates are concerned and a temperature of 15 degrees for 2 hours in case of later sowing dates). The night temperature should be set at 17.5 degrees when sowing at early dates and 18-19 when sowing at later dates. In the afternoon, the highest 'peak temperature' have to be 21 degrees or higher for at least a few hours. On days when light conditions are low (less than 200 Joules) and when the plant shows little vigour in the head, a maximum temperature of 19 degrees during the day is sufficient when early sowing dates are concerned. On days with high light intensity (500 Joules), it is important that the twenty-four hours' temperatures are high enough and that the day temperature is maintained a bit longer to avoid the plants from getting too vigorous.
Water
For now, water the plant with an EC of 3.5-4 depending on the growth stage: young plants need an EC of 3.7-4 and companies where the tomatoes are already well developed should use an EC of 3.5. The last mentioned companies have to make sure to water sufficiently: good weather conditions require 2.5 to 3 times the light energy (this means 1750cc/m2 on a day with a light energy of 700 Joules). On days with less favourable conditions, 1000cc/m2 would be enough. The slab volume also plays an important part in this. It is important to keep an eye on the colour of the plant. Stop watering the plants after 2 PM and, if necessary, water the plants once more in the evening to make sure the plants colour perfectly in the afternoon.
Thermal screens
Most fixed films are already taken out or will be shortly. Some growers retain the temperature a bit longer by closing the moveable screens in the late afternoon (especially done when vegetative plants are concerned). They have to make sure they reach the pre-night temperature fast (in a short time go down with the temp.) to avoid the plant from becoming weak. The screen has to be opened around 10.00 AM and to be closed around 04.00 PM.
Extra stem
For an extra stem to develop nicely, you have to make sure the day temperatures will not be too high, especially when light conditions are low. Otherwise, the side shoots will be too weak. For Dirk, an end distance of 3.3 stems/m2 is sufficient. The last side-shoot is maintained in week 10-11. In case of later sowing dates and a fairly great planting distance, extra stems can be maintained sooner.
Bracing/Truss treatment
For now, it is important to continue bracing the trusses. Only stop doing so when the trusses are strong enough that they will not bend. Until March-half March, you are advised to prune the trusses to five fruits a truss. Then, until July, prune the trusses to six fruits a truss. Subsequently, revert to pruning to five fruits. The last three trusses can be pruned to six fruits again.
Enza Zaden
All descriptions and general recommendations are based on general conditions and should be used as a guide only. The user should apply it in accordance with his own knowledge and experience of local conditions. No liability will be accepted by Enza Zaden for the final performance as based on this information.