Advice
Further cultivation technical points for the next 6 to 8 weeks
For most varieties it is important to aim for a growing and vigorous crop, so that we maintain sufficient Leaf Area Index (LAI) and speed in development. Growing crops can cope better with moments of stress. The following applies to most varieties: always grow some 'surplus' so that sufficient strength is available to cope with a dark period and to maintain sufficient leaf elongation.
Warm up to daytime temperature
Energy prices are back to a “reasonable” level. However, we still see that sometimes too little energy is used to heat the crops to the daytime temperature, resulting in risks of, for example, crops getting wet. Sufficiently warming up to the daytime temperature is the best spent energy at this time of year! The minimum tube may be recalculated as irradiation increases with a sufficiently active climate, but above 350 W it may disappear.
Depending on the achieved daytime temperature, we must enter the nighttime temperature to send to the desired 24-hour period. When the light level is low, try to keep the 24-hour temperature as low as possible.
Airing
At lower outside temperatures, it is better to have the ventilation temperature close to the heating curve with a fairly high P-band, so that ventilation occurs quickly but not too much. At (expected) higher outside temperatures, the P-band can be set slightly lower so that ventilation can flow more smoothly.
In sunny weather we like to see a RH of between 70-80% to maintain growth. If the RH falls below 70%, the windward side can be reduced to a maximum of 10-20%. From 3 to 4 hours before sunrise, you can consider limiting the window positions further to create a more growing climate. Please note that the previous control is only recommended if the greenhouse temperature and crop condition allow it.
CO2
We have seen CO2 emissions decline somewhat in recent years due to less CHP use. This will generally result in more vegetative crops. In any case, try to introduce a minimum amount of CO2 into the greenhouse, for example by controlling at least the outside value in the greenhouse.
Points of attention
Watering strategy
The root quality is good so far. Possibly more changeable weather makes it more difficult to keep the roots in good condition. Aim for a volume percentage of digestion of 8-12% to maintain growth and root quality. In darker weather it will be possible to aim for 12% or more digestion.
Try to drip between 2 hours after sunrise and 3-4 hours before sunset to achieve the desired digestion. Additional night service(s) may be necessary if evaporation is unexpectedly high. The first drain can be realized approximately 4-4.5 hours after sunrise, depending on the weather.
Fertilization schedule
The nitrogen (nitrate) supply should no longer be limited at this time of the year so that the plant can maintain sufficient growth. Keep in mind that at a high pH the availability of calcium and phosphate for the plant decreases considerably, which increases its susceptibility to blossom end rot.
Aim for an EC of 4 - 4.5 mS in the slab to maintain sufficient growth. Drips can be applied with an EC of 3.0 – 3.5 mS, with high irradiation it can be reduced to 2.7-2.8 mS. Too low a drop of EC will negatively affect the taste. Please note that in weather conditions with little evaporation and watering, sufficient nutrition is provided to prevent pale heads and “weak” crops.
Diseases and plagues
Sulfur use and biological control.
Sulfur vapors during the build-up of the Macrolophus population have a very negative effect on the development of the population. Only use them during the night hours and build up gradually so that the Macrolophus population can grow. We clearly see less gall mites than in other years. Good scouting and preventive sulfur spraying has clearly helped many growers. Spraying sulfur (at the top meter) against gall mites is less harmful to the young Macrolophus population.
General tips for the coming period
The maximum irradiation will increase considerably in the near future. Consider a coating in areas with higher irradiation and/or poor climate.