Anna Pavord's A to Z of pests and problems: F is for frost, fasciation and the flea beetle

The next instalment of Anna's essential A-Z of horticultural pests and problems.

Falling down

Improvident gardeners such as myself are used to things falling down around them: pergolas (twice), trees (every winter), plants (every week). Frequently I join them, slipping on the stone paving slabs which never get scrubbed with the chemicals that are supposed to drive away algae. So I accept falling down as a fact of life.

Some variations on the falling down theme are more unsettling than others. Trees are the worst, and they are the things you can do least about. Apple trees fall when they suffer from honey fungus at the roots. Gales push over trees that are already past their prime. All you can do is clear up the mess and plan a replacement.

Pergolas are another matter. Our solution (I wish we'd thought of it sooner) was to rebuild after the second disaster using green oak rather than the larch poles with which we had made the first two. So far, so good. The weakest link seems to be the point at which the pole meets the ground. Some people swear by Metposts, to strengthen the foundation.

In the best gardens, falling plants do not happen, because all the potential suspects have been beautifully and invisibly staked with lobster pots of woven hazel twigs. Every year I mean to do something similar. Every year, time runs out and I persuade myself I can get away with not staking anything but the most obvious specimens. Every year I am proved wrong. Staking is desirable, yes. Achievable? Not always. But where you do it, make sure the stakes don't show.

Fasciation

You see this sometimes on the stems of lilies, where the normally rounded stem flattens out like a strap, often ridged along its length. Flowers appear as normal, but sometimes there are more than usual on the one stemf Fasciation happens when several stems fuse together in one, or one stem develops broad, winged flanges. Sometimes it is caused by slugs or snails damaging the emerging shoots. A sudden late frost can also trigger fasciation in plants such as lilies or delphiniums. Forsythias and daphnes are prone to it, too. Although some scientists suspect that a virus or genetic malfunction might be the cause, fasciation is not generally thought of as harmful.

Fertiliser

If you are looking after your soil properly (plenty of bulky mulches), the only fertilisers you are likely to need will be for plants in tubs and other containers such as hanging baskets. The compost you plant in initially will provide enough nutrients for about six weeks. After that, you need to feed as well as water. Miracle-Gro, a powder which you add to the water in the watering can, gave good results in a Gardening Which? trial but I use Miracle-Gro sparingly on plants in pots. You don't want to stimulate too much fleshy growth. It encourages greenfly and other pests and diseases. Indoor plants, especially the flowering kind, seem to do well on a dilute mixture of tomato feed.

I also use slow release fertiliser (Osmocote) in containers. It lasts for six months, releasing more nutrients as the soil or compost warms up in summer. The NPK ratio is 14:13:13, an equation you see on most inorganic fertilisers. It's telling you the relative proportions in the mix of nitrogen (N), phosphorus (P) and potassium (K). Nitrogen helps leaf growth, phosphorus is good for roots and potassium (potash) is essential for fruit and flowers. That's why tomato feed shows a higher rate of potash than other fertilisers.

Organic gardeners like to make their own fertilisers, such as sheep manure steeped in water and comfrey liquid. Grow a non-invasive comfrey such as 'Bocking'. You can cut the leaves several times a year, though they are at their most nutritious in late spring. Pack the leaves into a container, preferably one fitted with a tap. Do not add water, but collect the dark liquid that is produced as the leaves decompose. It keeps for up to a year. Dilute the concentrate with 10-20 times the amount of water. Comfrey liquid is high in potash so makes a good feed for tomatoes.

Flea beetle

Flea beetles (there are 130 species in Britain alone) feed on plants of the brassica family, which unfortunately includes rocket. You know they have been visiting when you find young leaves peppered with tiny holes. Young wallflower plants, radish and turnipf are attacked too. April and May is when they are busiest, feasting on the young foliage of plants that may be so discouraged by their attentions that they keel over and die. Once plants are past the juicy stage, they become less attractive to flea beetles, which have increased hugely in numbers since oil seed rape became a widespread agricultural crop.

The beetles can be black and yellow, or bluish-black all over and are about a quarter of an inch long. You'll know them by the way they jump. Because they jump so far and fast, they are difficult to hit with a spray. Concentrate on keeping seedling crops growing fast, so you can outpace them. You can also protect seedlings with fleece covers. If you are really cunning you can catch flea beetles on a sticky trap, by tickling the foliage of your seedlings while the beetles jump onto the trap you are holding over the top. But this method is very hit and miss. Mostly miss.

Frost

This is an ancient enemy, whose sudden attacks still take us by surprise. They shouldn't because we half expect it to strike. The dodgy months are April and May, especially May when gardeners are longing for summer to start and for all the plants sitting around on windowsills and in greenhouses to go outside and get their feet into some real soil. But many annual flowers that we use for summer decoration (especially those best suited for tubs and hanging baskets) are only half hardy and will be killed by temperatures that suddenly plunge in the night.

Fungicide

This can be used to fight against a wide range of common diseases. It can combat powdery mildew, particularly prevalent in hot, dry summers. It will also work against grey mould (botrytis) which attacks strawberries and other plants. Leaf spots, such as black spot on roses, may also be controlled with a systemic fungicide such as Bayer Advanced Disease Control, which can also be used against powdery mildew.

Fungicides work in different ways. The systemic types are absorbed through the leaves into the sap of the plant, there killing any resident fungus spores. Contact fungicides work by making a barrier between the leaf surface and any hopeful external spores. They will only be efficient if they are applied regularly, usually at 10- to 14-day intervals.

All fungicides are better at prevention than cure. Unfortunately, most gardeners are better at reacting than foretelling. If plants are growing strongly in well nurtured soil and in the sort of position that nature intended for them, they will be less prone to any kind of disease. This is your best defence.