Gummy Stem Blight (Didymella) is an issue currently affecting some growers.

Pre-morning warming and hygiene are very important to reduce the spread of Didymella

Gummy stem blight, caused by the fungus Didymella bryoniae (previously named Mycosphaerella melonis), is prevalent at the moment. The weather conditions in the past two months have caused some real headaches for growers.

In the photo it is hard to see the rot from the outside (internal fruit rot).  If the rot is on the inside of the fruit and it has been accidentally sent to the supermarket it becomes unsellable in about 5 days as it becomes visible from the outside. Growers definitely do not want their end customer, the consumer, cutting the fruit open to find half of it is not edible.  Preventing infected fruit, going to the supermarket, is probably nearly impossible, preventing and limiting fungus spores infecting fruit is possible.

Before I cut into the cucumber

After I cut into the cucumber!!

Paula O'Hanlon, from Nunhems seed, supplied me with a fantastic factsheet supplied via the Ministry of Agriculture, Food and Rural Affairs, from Ontario, Canada.  Please contact either Paula or myself if you would like to recieve the PDF.  Contact paula.ohanlon@bayer.com or stefan@grower2grower.co.nz

Below are some important points you could implement to prevent the incidence of the Gummy Stem Blight (Didymella):

1. Pre-morning temperatures; This means approximately three hours before sunrise lift your night temperatures to the morning level, it will help prevent a sudden change in humidity in the morning. 
2. Keep heating and venting temperatures closer together (use P-bands if you have the ability with your computer systems), along with 1, if you vent more actively in the morning you will drive the high humidity out of the greenhouse more effectively. 
3. Prevent Guttation, along with 1 and 2 you will prevent what generally occurs in the morning period when the rapid change happens in the greenhouse, if your moisture can not be forced out of the greenhouse then it will sit on the end of your leaf veins!!  This is a major cause of fungal issues. 
4. Irrigation, this is very tricky with cucumbers but stop earlier and go into the night dryer, don’t have as much available water in the morning unless you use steps 1 through 3.  I like to have the water available to the plant early as possible in the morning but not if it means you will increase the incidence of guttation.
5. Spraying; Chemical and biological options are available to help, since spores which cause Gummy Stem Blight form on the flowers you can target the spraying towards that area.  However, if you follow the first four steps your frequency for spraying will be reduced.  So, you either spend money on energy or chemicals and spraying.  It comes down to your most limiting factors.
6. Hygiene; This is something that cucumber growers especially are very relaxed with.  People and equipment will spread spores.  I definitely like the idea of cleaning the knifes and cutters regularly in disinfectants.  I also like the idea of using a lot of Sodium Hypo-chloride in between crops to supress spore numbers. 

One week after being picked the damage is clearly visible from the outside making the fruit un-sellable 

An end on cut showing the intitial spread on the inside of the cucumber.

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Article Written by Stefan Vogrincic, Consultant, Grower2Grower