Pest prevention in an organic garden

Pest prevention in an organic garden

It might seem a bit premature talking about pest control in mid March as we have very little in the ground but I think it is worth learning how to avoid some common issues before they arise. As you probably know, I run an organic garden so don't use chemical pest control products as they have a negative impact on the environment.

Pest control management in organic growing focuses on maintaining optimum growing conditions for your plants which, in turn, grow strong and healthy and are better able to cope with attack from pests or disease. Organic growers also focus on avoiding problems rather than dealing with an attack as avoidance strategies tend to be more benign while dealing with an issue is more likely to require a chemical product. In this article we will be looking at some of these avoidance strategies as well as looking at some of the kinder products you might need if you encounter a problem.

Soil profile

Rule No.1 - A healthy soil

I know we looked at this last week when talking about plant feed but, if there is any secret to green fingers, it is the quality and health of your garden soil. The nutrients released by the life in your soil provide the healthy diet for your plants to thrive and overcome attack from pests and disease. A good soil contains a broad range of nutrients which feed your plants but also strengthen their immune systems.

Feeding a chemical based fertilizer is a bit like us surviving on junk food, it is possible but there will be long term impacts with a lot more chemicals required to cope with the inevitable problems it will cause. In short, get your soil right and everything else more or less falls into place.

A handful of soil

As we said last week, getting your soil right basically involves adding organic matter in the form of garden compost, bought in compost, good quality manure, homegrown green manure, fresh seaweed or seaweed meal. There are other amendments depending on soil type but bulky rotted organic material is the most important addition bar none.

Black spots on leaves

Sowing and planting times

Smart sowing or planting times can also make a big difference when dealing with pests or disease as problems will be more prevalent at certain times of the year. By sowing or planting at the right time we can avoid the worst and produce a healthy crop with far less work on our end. I include a few of the most common tactical growing times below:

The fungal disease Potato blight is pretty much inevitable in late Summer when your maincrop potatoes are maturing. The only way to control blight is to spray regularly with either copper sulphate or a fungicide but if, like me, you prefer your potatoes chemical free you probably won't want to do this. There are some excellent blight resistant potatoes on the market (Sarpo Mira, Sarpo Axona, Setanta, Orla) which will help slow the disease but you can also grow trouble free tubers by choosing your variety and planting time wisely.

Seed potatoes are split into four categories depending on how long they take to mature; they are first earlies (90 days), second earlies (110 days), maincrop (135 days) and late maincroop (160 days). Potato blight is at its worst in late Summer so if you sow a first or second early variety in mid March you will be ready to harvest by late June/early July and have your crop lifted by the time the disease hits.

Fine insect protection mesh over a bed of carrots

Carrots can be a little tricky to grow as they are so particular about soil but even if you have the perfect plot you are still likely to be troubled by the very common carrot root fly. The fly lays eggs around your young carrots which produce grubs that burrow into the roots and spoil the crop. The pest can be avoided by growing under a cover of fine insect mesh for the lifetime of the crop but you can also greatly reduce the problem by late sowing.

There are 2 generations of carrot root fly in a year, one in Spring and one in early Autumn. By holding off sowing until mid May/early June you will avoid the Spring generation of the root fly and by harvesting your crop before August you will avoid the Autumn generation and are far more likely to lift perfect smooth roots.

Powdery Mildew on pea plants

Peas are a great beginners crop with big easy to sow seeds and relatively trouble free growth. The two problems you may encounter are pea moths and powdery mildew, I have never had a problem with moths (but they are very common in Southern England) but powdery mildew is very likely in late Summer and early Autumn especially in dry years.

Fast maturing peas varieties sown in March will have a good chance of cropping before the pea moth lays her eggs (the resulting maggots burrow into the peas) but will also avoid powdery mildew as your peas will have finished before the drier days of late Summer and Autumn when the disease takes hold.

Cabbage collar

The two main issues with growing any member of the cabbage family are cabbage root fly and cabbage white butterfly. The root fly is controlled by covering the crop with mesh or using cabbage collars around the stem of the plant but is not something you can avoid by adjusting your planting times. Cabbage white butterflies are at their worst in late Summer and unless you cover your crop or are vigilant about removing the yellow eggs from the undersides of the leaves you can sustain heavy losses from the hungry caterpillars that emerge.

Pointed Spring cabbage is a delicious treat in Spring when the heads mature from an Autumn sowing the previous August. The plant spends most of its life in a relatively pest free environment as it puts the the initial growth down in Autumn, stands for the winter before maturing in April/May when pests are not around.

Early sowings (indoors, to be planted out later) of cabbage, calabrese, cauliflower, turnip and radish will also mature in late Spring before there are too many pests about.

Pest control moths and butterflies

The introduction of micromesh or enviromesh (they are both the same thing) in recent years has given us a very effective barrier material to keep pests off crops while allowing air, moisture and light to get through. Mesh is a relatively light material that can be simply draped over crops but is best when given some kind of support; this can be a hoop or a frame system that holds the mesh above the foliage of your plants.

Micromesh is effective against a range of pests but is particularly effective against some of those mentioned above, namely cabbage and carrot root fly and cabbage white butterflies. I use it for both and have found it very successful for cabbage root fly where I use our Quickcrop mini tunnels (pictured above) until the plants are properly established. The cabbage root fly maggots will almost certainly kill new seedlings but a more established plant can normally grow through an attack.

Due to the height of crops like flower sprouts, Brussels sprouts and sprouting broccoli mesh is not really suitable for the later stages of growth where protection against the cabbage white fly is required but it is ideal for lower growing brassicas like red and green cabbage. An organic solution here is to spray with the naturally occurring soil bacteria 'bacillus thuringiensis' which is toxic to caterpillars but not to us.

Mainframe micromesh cover protecting a bed of carrots

A micromesh cover works like a dream on carrots due to their relatively compact foliage which can be safely enclosed from seedling stage right through to harvest. Remember to do any weeding or thinning in one session and to get the cover back on quickly as the smell of the damaged foliage will attract the fly.

The Quickcrop mini tunnels are available on our website as component kits and can be arranged to fit a range of bed shapes and sizes. The system can also be used with a choice of coverings depending on you requirements and include mesh, fleece or polythene.

Flowers in the garden to balance your ecosystem

Balance your Ecosystem

Keeping your garden ecosystem well balanced will save you a lot of trouble with pests like aphids (greenfly etc...) and hoverfly larvae as other insects (encouraged by a diverse habitat) will eat them. You will notice, for example, that aphid attacks are more severe early in the season but tend to control themselves as the year progresses when predatory insects come on stream.

It is worth remembering that pests are always present in any garden but if your beneficial insect populations are healthy they will be keeping numbers down to barely noticeable levels. Predatory insects are encouraged by having a wide selection of plants including flowers and, god forbid, weeds like stinging nettles. If you have room in may be a good idea to 'cultivate' a wild margin to your garden to include nettles and flowering plants for the important habitat they provide.

Yellowing leaves on Brussels sprouts

Tidy Up

Finally, keep your vegetable garden tidy. Remove any dead or dying foliage like the yellowing leaves on these Brussels sprouts above as they will harbour fungal diseases and will be attractive to, and provide a hiding place for, slugs.

Slugs and snails will be the most common issue you are likely to have to deal with but by keeping slug habitats to a minimum you can usually control populations reasonably well. Anything that creates a dark, shady refuge will be a slug home like piles of rocks or timber, keeping the place neat and tidy will help a lot.

Organic Slug Pellets

Slugs can be controlled organically using various methods e.g. beer traps that attract and drown slugs but, especially when sowing seeds or planting out new seedlings, a slug pellet may be required. If you are using a slug pellet, use a pet and wildlife friendly (well, not all wildlife, they won't do the slugs much good) like 'Growing Success' above. Most organic certified pellets have the same active ingredient 'Ferremol' which is toxic to slugs and snails but won't poison birds or animals even of the slug is eaten.

OK, that's it for today, I hope some of the above was helpful and relevant in your garden. Next week we will be covering growing and caring for vegetable seedlings.

See you all next week!

Andrew