Advice on climate and crop management? (temperatures, window positions, moisture, etc.)
Increasing humidity in late summer
In the event of expected high 24-hour temperatures, strive to reduce the greenhouse temperatures as much as possible. However, we are seeing an increase in moisture in the greenhouse; In the morning the greenhouse roof is wet again from condensation and the moisture deficit is sometimes lower than 1gr per m3! Even with the current warm and sunny weather, the crop must first be warmed up in the late night and early morning before aeration can take place (smoothly). Activate the crop sufficiently in the morning so that it evaporates quickly when the sun comes through. You can then ventilate easily in the morning with an air line close to the heating curve.
Climate and settlement
In a (possibly) inactive outdoor climate, always aim for a significant DIF by means of an afternoon peak (with possibly an increase in light) to properly activate the crop and therefore steer it generatively. This is certainly also important in late summer! This promotes flower quality and flowering. A good guideline is to have a maximum of 3 flowers open per bunch. More than 3 open flowers per bunch indicates that flowering is too slow. Too high a daytime temperature must be compensated for at night to prevent too high a 24-hour temperature.
During the afternoon and evening hours, the air vents may be closed, mainly on the windward side. In this way the greenhouse temperature can be kept below the outside temperature.
CO2
Provide - if available - sufficient CO2 when the weather permits, to guide the plant generatively and optimize assimilation. In warmer weather with greenhouse temperatures above 30°C and weaker crops, the CO2 dosage can be greatly reduced, especially if the moisture deficit is very high.
Always be careful when using climate screens to screen out light, incorrect use can easily weaken the crops.
Further cultivation technical points for the next 6 to 8 weeks
Maintain plant vigor by controlling the plant load
It is important to maintain sufficient strength in the crop towards the autumn. The fruit development time for snack tomatoes will increase by approximately 1.5 days every week from mid-August, which may increase the plant load slightly. The irradiation and light sum will decrease further around this time, while the moisture and outside temperatures are relatively high. Pruning, especially at this time of year, will not cost production and will increase the harvest standard. A rule of thumb for snack tomatoes is to aim for fruit production of approximately 85-90 fruits per m2 per week until the end of August, 70-75 until the 3rd week of September and 65 until the end of cultivation. A guideline from now on is to remove the after-flowering from the 4th truss from above and, with higher production as indicated above, to remove the after-flowering from the 3rd truss from above. With weaker plants, (part of a) bunch can occasionally be removed to even out the crops.
Provide adequate nutrition
It is important to provide sufficient nutrition when evaporation is low! Otherwise we quickly see pale heads and faded flowers. When watering less than approximately 25 liters per m2 per week, it is better not to drip below 3 mS. Naturally, the EC rises easily during a period of possibly warmer weather. However, do not reduce the drop of EC too much, the plant needs sufficient nutrition. Preferably do not let the EC drop below 2.5 mS.
Watering strategy
Be careful with watering in the afternoon with increasing moisture and shorter days. One rule remains: when in doubt, don't pour. It is better to top up in the evening to achieve the desired moisture level. Apply at least 12% of tar overnight to keep the roots strong.
What is the current situation with diseases and pests?
Insects
Tuta absoluta is a huge problem in some companies. We see (very) good results with the use of pheromones, but it is very important to scout well and use the pheromones in a timely manner.
Mold
We are seeing quite a few problems with cladosporium (also called leaf spot) in varieties that are not resistant. This fungal disease develops easily, especially with varying moisture conditions in the greenhouse. It is best to choose resistant varieties.
Phytophthora has been observed remarkably often this year, well into the summer. Pay close attention to preventing this fungal disease when moisture increases from the end of summer. Be sure to pay attention to the use of screens in crops that produce a lot of moisture; this is where we often see the most problems.
General tips for the coming period
Bees
Keep a close eye - if the flower quality is less good (due to whatever circumstance), the flower is less attractive to the bumblebees. When conditions are better for the bumblebees, they often have to fly over many flowers; having sufficient (new) bumblebees available is then important.
Coatings
Any used coatings on the deck can be removed after the beginning of September. Crops become unnecessarily weak if they are left on the deck for too long.
This was the last crop information for this cultivation, the next one will appear at the start of the new cultivation in January.
We wish everyone a successful last part of the cultivation!