21.7.18 Winners and losers

We’ve had the hottest June since 1976 and the driest on record. Despite our best efforts, many of our plants have died, they’ve flowered and faded too quickly and our crops are much smaller than usual. But sadly, some diseases and disorders have taken full advantage of the situation, even if others have thankfully been challenged.

I’ll start by explaining the difference between diseases and disorders because you can always sort out a disorder, but a disease could be fatal, whatever you do. Plants are diseased when attacked by the likes of fungi, mildews and viruses. Some diseases like club root, onion white rot or pea foot and root rot even contaminate the soil for many years. But a disorder occurs when a plant lacks an element such as potassium or nitrogen, is stressed by lack of water or is exposed to too little or too much sun.

Most tomato problems are disorders. Tomatoes grown in pots or growbags often suffer from blossom end rot, especially during this year’s hot, dry summer. The nasty black blotch at the base of the fruit is caused by calcium deficiency. A good, steady flow of moisture should travel throughout the plant. This ensures calcium gets everywhere, including the tip of fruits, areas that are furthest away from roots. So, compost must be kept thoroughly moist to ensure this happens. Small dry corners in a growbag won’t do, so if you cut down on watering, tomatoes may suffer from blossom end rot.

Too much sun is as bad for tomatoes as too little water. Greenback, hard green blotches on the skin, can appear in very high temperatures, possibly the result of not having shading in a poorly ventilated greenhouse. The disorder may also be caused by lack of potassium, so you could be paying the price for not using tomato feed or liquid comfrey.

Luckily, as well as producing sweeter, tastier tomatoes, the dry weather keeps blight largely at bay. This disease is the scourge of tomatoes and potatoes. The fungus-like organism, phytophthora infestans, thrives in damp, humid conditions, killing leaves within days, before turning tatties and tomatoes to mush.

You can help prevent blight on tomatoes by keeping leaves dry in a greenhouse, polytunnel or temporary tomato shelter. But only a dry summer works for potatoes. So, depending on how the next couple of months pan out, a blight-free summer could be a gold-plated winner.

But we could get spraing instead. Although spraing, the tell-tale brown circles in tubers, in potatoes is usually caused by a virus, the culprit could be the prolonged dry weather.

It’s swings and roundabouts: there’s a disease for all weathers. The fungus, Powdery mildew thrives in dry summers, while fungus-like Downy mildew needs it wet. So, as I write, it’s Powdery 1, Downy 0. Fortunately, powdery mildew is much less damaging as, unlike downy mildew, the white coating doesn’t penetrate and seriously damage leaf tissues. If the leaf remains green beneath what looks like white paint, it’s powdery, while you’ll find a yellow damaged leaf with downy mildew.

The end of the dry spell also has winners and losers. Undoubtedly, the rain revives our plants and rescues many from certain death. But this sudden burst of life has its problems. Fruits swell rapidly, leading to split skins in the likes of tomatoes, and plums. Potato tubers can also swell quickly, leading to hollow heart. You don’t realise that the centre of the tuber is hollow, with rot round it till you start eating. Predictably, large, delicious-looking bakers are the main victims.

Plant of the week

Echinops ‘Veitch’s Blue’. Loving the sun and dry weather. ‘Veitch’s Blue’ will flower more than once in the season so you can enjoy the intense blue spherical flower heads over a long period. Its spiny leaves are very handsome.