Dirk wk35 / 2007

Friday, 31 Augustus 2007, Dirk was presented for the second time this year to those interested in the variety. The company Seasun (Gresnigt), where this open afternoon was organised, cultivates 9.5 hectares of Dirk, grafted 1 on 1 onto Maxifort.

Started with a planting distance of 75 cm, the stem distance is now 35 cm. Dirk was sown 1 November and brought to the company in Kapelle on 11 and 12 December.

Dirk, increasingly more vigorous and fuller

Looking back on the cultivation at Jan Gresnigt's so far, Dirk has given us a good idea of its characteristics. Jan's choice for Dirk was based upon a variety trial at his company last year. Back then, Dirk started to produce more fruits than the standard variety around week 31. At the end of the season, Dirk even gave 2 kg/m² more.

 This year, Dirk started as a small, somewhat slender plant. Therefore, it was brought to the company a bit later than originally planned. However, Dirk has become increasingly more vigorous and fuller along the season. Jan continued bracing the plant until a radiation of 6000 Joules/week was reached. This year, this equalled 10 trusses.

A remarkably strong plant

Growing side shoots turned out harder than expected. Jan decided to adjust the climate and to steady the cultivation. In hindsight, it would have been better to have the plant grown a bit stronger 2 weeks before the side shoot was wished for. Later in the cultivation, this characteristic of side shoots not growing too easily has been very beneficial.

Jan repeated once more that Dirk is a remarkably strong plant. “Dirk should be grown generatively. This variety is ideal for better summer conditions than those of this year. And Dirk cannot be burnt off.” Therefore, a stem density of 3.3 per m² would have been enough. Dirk should not become too vegetative, because then the flowers will become too strong and Dirk may produce outsized tomatoes. We therefore advise a generative growing regime with a good dose of CO2. In the 2 months that Dirk was administered half of the set CO2 dose, as a result of a mechanical defect, the fruit size and production had periodically been reduced.

As far as energy costs go, Dirk is not more expensive than the standard variety in the medium sized truss tomato segment, because the higher temperature at the end of the day is to be realised by slightly closing the windows. Despite the climate that was created this way, Dirk was not affected by Botrytis. Mildew has, thanks to its intermediate resistance, neither been a problem with Dirk.

Just as in June, during our first visit to Seasun, Dirk showed a strong and healthy plant. The affects of the aggressive Pepino virus, present in the Dirk section of the greenhouse earlier this year, did not show at all on the fruits. The consequences of this virus, that was present in the greenhouse in the beginning of April, were clear on other varieties in this greenhouse, all of them trial varieties. This summer, Jan had decided to prune the trusses to 5 fruits again from week 23 to maintain the plant's strength against the Pepino virus.

This year, Dirk's production is again higher than that of the standard variety in the medium sized truss tomato segment, which Jan still cultivates in one of his greenhouses. And Dirk has been planted even a week later than this standard variety. This lead is also the result of the slightly higher fruit weight. At this moment, Dirk's trusses are about 650 grams. A fruit weight of 125 to 130 grams is considered optimal. The risk of trusses with fruits much heavier than that is that they may tear off. Of course, nutrition also plays a part in this. Dirk's Boron target value in the slab can be easily 250. The production is now (wk 35) about 42 kg/m², but a production of at least 60 kg/m² is expected.

 

Performing well in the Netherlands and abroad

During the discussion afterwards, Dirk proved to also perform very well at other companies, both in the Netherlands as abroad. In Belgium, about 7 ha of Dirk is cultivated by 5 different growers. Despite the fact that Dirk has been a bit too vegetative in this country, and therefore produced some outsized tomatoes, the variety's performance is well appreciated. In Germany/Austria (30 ha of Dirk), growers have been changing from one variety to another for already 3 years now trying to find a variety that is able to deal with the Pepino virus. After evaluating Dirk in trials, they have switched over to this variety. The grower that started his cultivation early in the season did have some Pepino marks on the fruits, but thanks to the firmness and the perfect colouration of the tomato, no complaints from the market were expressed. Moreover, the green parts remained of an attractive fresh green colour. The last few weeks, the growers realised a twenty-four hours' temperature of sometimes 27 °C thanks to the summery conditions. Dirk continues to perform well and it is still very well appreciated.

At the end of this second open afternoon at Seasun, Dirk was concluded to be a very reliable choice.

• Dirk produces a good amount of fruits, even in a summer in which the conditions were pretty poor for this variety.

• Dirk recovered well after the infection of an aggressive Pepino virus.

• Dirk is intermediate resistant to mildew and relatively strong against Botrytis.