What to do about aphids attacking my weeds?

- I have a small urban garden intensely planted with green leafy vegetables and young fruit trees.
- I allowed dandelion weeds to grow among them to improve the soil. Spring's now here and aphids are generally only attacking the dandelions- they absolutely love it!

If I do nothing, will their numbers grow and end up infesting the whole yard? Should I chop down the dandelion and squash it with the aphids on to keep their numbers under control?

Insects like ladybirds like them but when ants protect the aphids they're invincible.

Leave the weeds as a "trap crop" for the aphids, since they love them.  If you remove the "weeds" the aphids will find your favored plants to eat.

BTW, the aphids know what they're doing - Dandelions are some of the most nutritious vegetables you can grow!

I agree with Tyler.  If the aphids are not attacking your choice plants, then they serve the purpose of giving the aphids a place to be.  If you were to remove the plants that are being infested by aphids, then the aphids will find another place to be-namely on your choice plants.  Also, the more aphids you have that are not harming your choice plants, then the more likely your garden will be accumulating some of the creatures who prey upon aphids, like ladybugs.  

The more you keep old stalks (like from last years brassicas, for instance, in your garden (rather than removing them at the end of the season), the more habitat for ladybug eggs to be laid and hatched out in the spring.  That is assuming that you have ladybugs in your area. I'm not sure what the natural predator of aphids is in your climate/country.  

Either way, great to observe your aphids and see what, if anything, is preying on them.  If you don't see the population being preyed upon at all, but it is stable, then it is likely that you are just not noticing the predator.  

If the population expands and begin to affect your choice plants too much, then you might need to take action.  Diluted garlic spray is supposed to be effective.  Some people spray with a diluted (organic) soapy water solution as well, with good effect.  

It could be a sign that your garden has too many ants, since some species of ants farm aphids, but ants are almost always beneficial to your garden as they do much the same job as earthworms in many regards.  It could also mean that you are nearing the end of that particular weed's cycle in your garden, and this is nature's way of beginning to take it out.

You may have too much nitrogen in your soil. I watched a video from Stefan Sobkowiak about aphids, he says they attack to plants with high nitrogen.

Gurkan Yeniceri wrote:You may have too much nitrogen in your soil. I watched a video from Stefan Sobkowiak about aphids, he says they attack to plants with high nitrogen.

My experience is that "pests" indicate when plants are stressed - and even too much nitrogen can be a stressor.

Here I see "pests" mostly when plants are under drought stress or planted in the wrong season.

Aphids are a constant here. I plant 'trap' plants, like nasturtium, and then just pull them when they become completely inundated, but nasturtiums are easier to pull than dandelions. I would just leave those and be grateful the aphids seem happy with just that. Some aphids, like black aphids seem to have boom years where they take out lots of new plants and other years they are almost non-existent. Unless you are completely isolated, I doubt removing the dandelions will reduce their overall numbers. They will just move elsewhere.

You may have too much nitrogen in your soil

I forgot to mention that.  I meant to.  

Considering your use of seaweed as mulch, this might be the case, Tim.  Also, this (too much nitrogen and aphids) and the alkalizing element of the seaweed might be contributing to the possible phase-out of dandelion, which is said to be an alkalizing plant from what I remember.  I think dandelions are generally calcium-rich, if I'm thinking right.

I know I have aphids when I see ants walking along a plant. Over here the ants herd them and protect them from predators. I've seen a ladybug just sitting on a neighbouring leaf watching them but unable to attack them because of the ants.

I'll leave the plant but wipe off the aphids. If I let them kill it they'll look for a new one. How wonderful that a weed like dandelion acts as a pest magnet.