Allotment Gardening Advice Help Chat

Growing => Growing in Greenhouses & Polytunnels => Topic started by: maddave on September 06, 2021, 17:18

Title: Little black flies all over greenhouse
Post by: maddave on September 06, 2021, 17:18

First year with a green house and for most of the summer, my plants have been covered in little black flies. These aren't aphids or "black fly" like you get on beans etc., these are more like fruit flies that fly around you when in the greenhouse.  They are all over the soil on my sweet peppers which seem to be suffering the most with lots of little holes in them which then eventually make the fruit rot.  Also have some bigger holes on my aubergines, but think this may be a slug that's hiding somewhere!!  All other fruits - chilies, cucumbers and tomatoes - seem unaffected, despite the flies being all over the plants.

Does anyone know why I'm getting these flies?

Title: Re: Little black flies all over greenhouse
Post by: Mr Dog on September 06, 2021, 19:32

I'd guess 'fungus gnats'

https://www.rhs.org.uk/advice/profile?pid=804 (https://www.rhs.org.uk/advice/profile?pid=804)

Title: Re: Little black flies all over greenhouse
Post by: maddave on September 07, 2021, 10:23

Interesting. That does sound like them. Especially the running over seed trays part!!

Thanks.

Title: Re: Little black flies all over greenhouse
Post by: Hortic on December 06, 2021, 20:11

Yes, fungus gnats. These can be present in compost bags unfortunately. They thrive in overly wet pots so make sure the plants need water before watering and pots have good drainage off the ground. A thick layer of cinnamon on the compost surface helps but this has become expensive so I spray the surface with a pyrethrum spray when I first see the adult flies.

The holes might be a caterpillar. They hide among the foliage and come out at night. Look for slime trails if you suspect slugs/snails. Hunt at night.