Horticulture Magazine

How To Deal With Blackfly On Broad Bean Plants

a gardener inspecting blackfly on a broadbean plant

Blackfly are sap-sucking insects which can sometimes become a problem on broad bean plants.

However, by using the right approaches in your organic garden, you can easily prevent blackfly infestations from occurring and easily deal with blackfly infestations if they do arise.

There is no need to resort to extreme and non-environmentally friendly solutions. A few simple steps should help you avoid any issues with your broad beans, and make sure you still get a good crop.

close up of blackfly infestation on broad beans
Blackfly on broad beans

Prevention is Better Than Cure

First things first, in an organic garden, it is always better to deal with potential problems not when, but before, they happen.

So the first phase in dealing with blackfly on broad bean plants is to make sure that the blackfly population in your garden is not out of control. It is also important to make sure that your broad bean plants are as healthy as they can be – since healthy plants are far less likely to succumb to any pest problems.

Keeping Blackfly Numbers Down

In an organic garden, pest management mostly involves making sure that no one species gets out of control, and that the whole ecosystem remains in balance.

Keeping blackfly numbers down means thinking about their natural predators. By attracting plenty of natural blackfly predators, such as ladybirds and lacewings to our gardens, we can keep their populations in check.

Companion planting to attract ladybirds and lacewings is the key strategy that can be adopted in an organic garden. Close to your broad beans, you should plant companion crops that draw in these predatory insects.

Some great examples of companion crops for broad beans which can achieve this are yarrow, tansy, dill, alyssum, oregano and thyme, though there are plenty of other companion plants to consider.

Generally speaking, the more biodiversity there is in your garden, the less likely it is that populations of pests like blackfly will get out of control.

a ladybird sat on white cow parsley
Ladybirds are natural predators of the blackfly

Making Sure Broad Beans are in Tip Top Condition

If your garden is diversely planted and you have already given some thought to pest control, another key thing to consider is the health of your broad beans.

The health of your plants, of course, begins with the health of your soil. But with broad beans (a nitrogen-fixing plant) adding too much fertility can be counterproductive and may actually decrease the health and vigour of your plants.

Over-fertilised broad beans may sometimes be more likely to encounter a pest problem.

Water is another key area to look into. Broad beans which are not provided with enough water (or which are given too much) will not be as healthy. 

Broad beans, even dwarf cultivars, also need support. Those without adequate support may not be as strong, and are more likely to be infested by blackfly or other pests.

Another final thing to remember is that the young tip growth of the broad beans is the most enticing to blackfly.

Once your broad beans have sufficient flowers, and the first pods begin to form, pinch off the growing tip. This will encourage the broad beans to put their energy into pod and bean formation – but will also reduce the chances of a blackfly infestation.

Incidentally, you should note that the tips from your broad beans can be cooked and eaten as a fresh spring green vegetable. So do not just discard them or add them to your compost heap.

Distracting Blackfly With Trap Crops

Blackfly on orange nasturtium flowers and foliage
Blackfly on nasturtiums

Of course, even with natural predation, there will often still be blackfly in your garden. It is important to remember that they are not the enemy.

Like all other garden pests, they are also part of the garden ecosystem. And like all other garden wildlife, they too have their roles to play.

It is important to remember that we do want some blackfly and other sap-suckers around. Aside from anything else, if we do not have them around, then we do not have the beneficial wildlife which preys on them.

When we eliminate pests entirely, therefore, we risk making a rod for our own backs. When blackfly inevitably return to a garden that has been cleansed of them, their populations can grow exponentially, when predatory species are absent.

Rather than getting rid of blackfly, therefore, our strategy should not be to keep them away altogether. Instead, it should be to keep them away as much as possible from our broad beans and other culinary crops.

In an organic garden, we can achieve this by planting trap crops. This is another type of companion planting that should be used as part of your companion planting strategy.

Trap crops are plants which are chosen because they attract blackfly more than broad beans. Placing these in another part of the garden can keep the pests distracted and make it less likely that your broad beans will have a serious infestation.

One common trap crop to use for blackfly to keep them off your broad beans is nasturtiums. Blackfly and other aphids seem (at least anecdotally) to be drawn to the nasturtiums more than to beans.

You may also see ants herding these insects onto such trap crops. The growth of the nasturtiums themselves may be affected – but your main crops will remain safe.

Getting Rid of Blackfly on Broad Bean Plants

If you take the steps mentioned above to make sure your garden ecosystem is in balance, your broad beans are healthy, and blackfly are distracted by other plants, then you should find that you encounter fewer serious infestations on your beans.

But if you do see blackfly on your broad beans, you should:

  • Try to remove them by hand, or with a jet of water from a hose.
  • Consider introducing predatory species (to make up for a lack of these in your garden). Introducing native ladybird larvae, for example, is one strategy to consider where companion planting has not successfully distracted the insects.

However, remember that introducing species is always a last resort, and you should make sure that those you choose were not wild harvested. It is always better to work on naturally attracting wildlife through diverse planting.

Pesticides, even organic ones, should be considered as the nuclear option. These will often target species which are not pests, as well as blackfly and other aphids which sometimes are.

Killing pest species in your garden is rarely the best option, since this will also have an impact on their predators, and have a knock-on impact on the garden ecosystem.

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