Gerbera & Roses growing article August 2008

With the increasing cost of replacing plastic covers on greenhouses, growers should be more aware of the quality of the plastic and the use of sulphur pots.

1.    Make sure that you buy good quality anti condensing plastic, if condensation happens the crop will get wet and you need to activate the heating pipes which will increase your heating bill.

2.    Some growers have stopped using sulphur pots in their plastic greenhouses because the sulphur could reduce the live span of the plastic by up to 50%.

If you would like to keep using sulphur pots for the control of powdery mildew you need to keep a few things in mind;

1.    Use the sulphur pot only when the circulation fans are on, the airflow of the circulation fan will avoid that the sulphur stay concentrated on one area of the greenhouses.

2.    Only use the sulphur pots for 1 or 2 hours a night when the greenhouse is close, it doesn’t make sense to use sulphur pots when you can’t build up a concentration of sulphur in the greenhouse because of opened windows / vents.

If you can’t control the powdery mildew by running the sulphur pots for a few hours a night you need to spray for the powdery mildew!  

How to control Powdery mildew other than using sulphur pots;

1.    Spray with double amount of water on a dark day, the most important thing is that the leaves stay wet for a few hours. Don’t spray on a sunny hot day, but if you do close the screens until the leaves have dried up. If you don’t have screens spray very early in the morning or late afternoon / evening.

2.  A backpack powder blower (see picture) is often used in Holland to dust sulphur, this work very well because the sulphur powder will cover all the leaves and will work for a few days.

Note, don’t use Flint and Prosper for powdery control in gerberas, I have seen quite a lot of damage of these chemicals.

Preparing for the new planting season;

1. After removing the old crop you need to sterilize the greenhouse, bench system, pots, etc.  A clean start avoids a lot of problems with diseases.
2. Drippers need to be cleaned with Acid for fertilizer residue and chloride for algae or organic residue, once the new plants are planted and you find out some drippers are blocked you are too late to clean them proper because the cleaning chemicals could harm the plant.
3. Before you start to plant the first new plants it will be a good idea to spray the remaining weeds in the greenhouse. Be careful with the use of herbicide in the greenhouse, ask you supplier which herbicide you could use in the greenhouse without damaging you plants.
4. Every weed you remove in the first 3-6 months after planting saves a lot of time later in the growing period.

Drip EC & PH;

Make sure that you check the EC & PH by the irrigation unit and by the drippers, sometimes the settings at the irrigation unit are at a PH of 5.4 but at the dripper it could be as high as PH 6.

A few things you could do to get a more stable PH;

1. Don’t  use a to strong concentration of acid at the irrigation unit, if you need to add a lot of acid to bring down the PH, it could be a better idea to use a PH controller in the storage tank and dose the acid in the tank.
2. Put 80 % of the acid in the A & B tank and do the fine tuning of the PH with the separate ph dosing pump.
3. Keep the dripper lines clean, dirt in the dripper line could lower the PH when the drip water stands in the dripper line overnight. The least thing you could do is to take off the end cap and flush the dripper lines every month.
    

**Although we trust that this information could be of considerable help to the success of the crop, we cannot accept any liability for the results of your crop. All the information in this growing newsletter is without committing ourselves.

This article is written by Job Roskam of Roskam Young Plants Pty Ltd. and also published in the Australian flower industry magazine.