Category Archives: pests and diseases

Pests and Diseases in the Vegetable Garden

Wednesday Wiggler ~~ Green Dock (or Sorrel) Beetles (Gastrophysa viridula)

Posted on by
2



http://www.flickr.com/photos/rachel_s/

 I’ve chosen this little green beetle as a Wednesday Wiggler because our garden is currently full of them.

I’ve been trying to identify and hunt out information on them over the past couple of days so that I can determine if I need to worry about these little bugs eating our veggies.

They’re a metallic green in colour, about 4mm long with the females slightly longer at about 7mm. The female also has a swollen black abdomen prior to egg laying during the mating season which lasts from March to October.

She lays clusters of tiny yellow eggs on the underside of dock leaves, laying up to 1,200 eggs in two to four broods a year.

The adult’s life span is only a couple of months but they can hibernate over winter.

As their name suggests Green Dock Beetles feed almost exclusively on dock and sorrel but if these are not available to them or are in short supply they will eat from the cabbage family (brassicaceae) as well as the borage, violet and buckwheat families. These choices would not be high on their menu though as their larvae will not fully develop if they feed on these plants.


So it would seem that we have a perfectly good reason for NOT ridding ourselves of all the docks in our garden and may have to forget about growing sorrel.
There does seem to be an alarming amount of eggs but as long as the beetles have a good supply of their favourite leaves (and I can attest that there are plenty spreading their seeds in the fields around us too) in theory we needn’t be overly bothered by green dock beetles.

This is a great example of why we should encourage all types of wildlife into our gardens to prevent a build up of any one type of insect. The green dock beetle’s natural predators are insectivores (such as birds and frogs) and parasites.

By regularly feeding birds, planting hedges, building ponds and not keeping our gardens overly tidy we can encourage a diverse range of wildlife and create a natural balance.

If you have a smaller suburban garden you may be thinking that’s all so very well but not feasible. I suspect however, that the little green beetle may be more rampant in a rural garden due to the abundance of food sources in the countryside.

Source: http://www.insectoid.info/beetles/

Wednesday Wigglers ~~~ Aphids

Posted on by
2
The aphid group includes all aphids, blackfly and greenfly and are definitely FOE.
They vary in colour from green, pink, and yellow, black, greyish-white to brown and are about 2mm long.  Most of us would be familiar with greenfly on our roses or blackfly on our broadbeans.
Aphids are sap sucking insects and produce honeydew that sooty mould can form on.  They attack exposed parts of plants and roots.
They can spread virus and ants farm them.
Shocking fact about aphids: 
A newborn becomes a reproducing adult at 1 week old, can then produce five offspring per day for up to 30 days.  Aphids can reproduce asexually.  As it’s babies all have babies after just one week, by the time the first newborn reaches the end of it’s reproductive life there could be 1,590,155 of the little devils!
They can also lay eggs and live young.
Control
Companion planting can encourage beneficial insects and predators such as hoverfly and lacewing larvae into gardens. 
Insecticidal soap is very effective but kills beneficial insects too.
Protective cloches can be places over crops to prevent aphids infesting them but as they’re so tiny they would be very difficult to stop.  Squashing them between your fingers or spraying them off of plants with a blast of water from the hose works well too but you have to check the plants daily.

Wednesday Wigglers ~ Leatherjackets

Posted on by
1

How well do you know your veg gardening friends from foes? On Wednesday’s I’ll be trying to highlight our gardening friends and enemies, from now on known as Wednesday Wigglers.  First off:

Leatherjacket

Leatherjacket – root eating cranefly larvae

Leatherjackets

Not the ones you wear and definitely pests!
What are they?
Leatherjackets are little grey-brown grubs that are fleshy with no legs that can grow as big as 50mm (the ones in our garden are more usually a couple of centimetres).

They’re the larvae of the Crane fly, also known as daddy long legs.  Adult females can usually be seen from late July to September flying around with their lollopy gait. (I can attest to this as I’m often camping when they’re about and I’m phobic, despite them being harmless!)

Each female can lay around 300 eggs in the soil surface that hatch about 3 weeks later. As soon as the eggs hatch the larvae start to feed on vegetables, root crops and grassland.  If it’s mild they can feed throughout the winter, but especially as temperatures warm up in the early spring.

In late May the larvae pupate in the soil, with the adults emerging during the summer months.

How do you spot them?
They’re often first noticed when turfed areas are turned into vegetable (or flower) gardens, or if you allow your patch to be overcome with grassy weeds.  You might notice that plants don’t look as well as you’d expect them to, wilting as their roots are attacked.
How can you get rid of them?
When you’re weeding or harvesting keep an eye out for them and remove them immediately (hens and pigs love them).
They like to live in dark, damp places so you could try covering the soil with cardboard or old carpet, pulling it back in the morning and leaving the birds to come in and feed on them.
For an organic solution, Supernemos can be watered onto wet soil once the soil temperature is over 10°C.
You could also try leaving bait around under pieces of bark with bran hidden underneath (also works for slugs), picking them off once you find them.
So good luck in your bug hunt!
Just for balance, next week we’ll look at a Friend.

Beet Leaf Miner

Posted on by
2
Another pesky pest, this beet leaf miner was found on the beetroot at the Community Garden a couple of weeks ago.




This is one occasion where vigilance really is the only cure as there are no home made remedies (or no approved insecticides) that will work on these little maggots.

Yes …. maggots. These little white grubs will turn into the pupae of flies. They wriggle about (or mine, as their name suggests) between the internal tissues of the leaves and if left unchecked may have two life cycles in one summer.

They are attracted to beetroot, spinach and Swiss chard so crops will be ruined once infected (yuk, who wants to eat maggots with their dinner?).

So what can you do?


If you spot the Beet Leaf Miner early on you can remove the leaves of the infected plants and destroy them. If not I’m afraid your crop will be ruined.

Mealy Cabbage Aphids on my Brussels Sprouts!

Posted on by
2

Last year it was caterpillars, this year it’s aphids. Something always seems to want to eat my brassicas!

These were found on the tips of the sprouts last week and weren’t immediately obvious.  We first noticed yellow patches on the young leaves that were starting to wrinkle.  On closer examination (hidden inside the new leaf) we found this colony of Mealy Cabbage Aphid.
A heavy attack can kill the tips of the shoots which may encourage new side shoots.  The aphids also like the taste of radish and swede so keep an eye on those veggies too.

As they are a sap eating insect (and can therefore spread virus’) control is encouraged.  An insecticidal soap spray can be used (see blog on home made recipes).

We suffered a similar problem last October on the kale.
This year I’ve removed the infected leaves as I’m attempting to garden without the use of any sprays, including home made soap or garlic.
Although the broad beans were heavily infected with black bean aphid, it was interesting to observe how many predatory insects were on the plants too – particularly ladybirds and what I’m fairly certain were soldier beetles, offering some form of control.