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US: Battling tomato blight should start early

About this time of year, you might hear complaints about the sorry state of tomato plants.

Yes, many do look unhappy, and it all began early this summer. Surprisingly, such tomato plants might still be loaded down with a reasonably large crop of fruit _ surprising considering the leaf loss on each plant. Then again, the crop might seem abundant only because there are fewer leaves now hiding the tomatoes.

AND THE CULPRIT IS...

Look more closely at tomato leaves to pinpoint the cause of the problem. Find a leaf that still has some green on it and you may see spots, each consisting of concentric light and dark rings. That's a symptom of early blight, a disease especially troublesome in wet summers.

Early blight also attacks tomato fruits, causing small ones to drop off and leaving dark leathery spots near the stem ends of older ones. In a bad year, early blight kills entire plants.

There's not much you can do now. Earlier in the season, picking off infected leaves may have helped, but this kind of treatment often results in a race to see which kills a plant first, premature leaf loss or diseased leaves infecting healthy ones. Fungicide sprays, such as Bordeaux mixture, are effective, but also would have to be applied earlier in the season. And who wants to eat vegetables that have pesticides on them? Especially when pesticides can be avoided.

KEEP BLIGHT AT BAY

First let's deal with this year's fruit. Whole tomatoes, or sound parts of any ripe ones, are perfectly good to eat from a human health standpoint. Taste them before plopping them into the saucepan, though, because they might taste sharper than usual.

As for averting blight next year, the disease spends the winter in infected plant debris, so thoroughly cleaning up and composting every bit of your old tomato plants at the end of this season lessens the sources of infection for next year. Clean up potato plants, too, because they also harbor early blight.

To put distance between any overlooked debris and young plants, next spring set your tomato transplants as far as possible from where this years tomatoes or potatoes grew. The ideal is to let three years elapse before returning them to where they grew previously.

Also, attack early blight by creating inhospitable conditions for the fungus. It festers on moist leaves, so always grow your plants where sunlight and gentle breezes dry the foliage quickly. And when you water, avoid wetting the leaves.

CHOOSE RESISTANT VARIETIES

How badly your tomatoes are battered by early blight also depends on what varieties you grow. So-called determinate tomatoes, which have a bushy growth habit, are more susceptible to early blight than are indeterminate tomatoes.

Early blight is also most severe when tomato plants are heavily laden with fruits, and this puts determinate tomatoes, which ripen their whole crop over a short period of time, most at risk. Seed catalogs, seed packets and plant labels usually specify whether a tomato variety is determinate or indeterminate.

It turns out that most paste tomatoes are determinate _ good if you want to cook up a batch of tomatoes all at once, but bad when early blight threatens. One way to decrease early blight on your paste tomatoes is to grow one of the few indeterminate varieties. Try, for instance, San Marzano, an indeterminate paste variety that is awful-tasting when fresh, but which cooks up into a most delectable and tangy sauce.


Source: wtop.com

Publication date: 8/26/2008


 


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