Learning to Grow Tomatoes

What else could possibly go wrong?

Having dispatched with the pests (…in words) we’re now left with pathological disorders and diseases – fungal, bacterial and virus.

The fungal list seems dauntingly long. They clearly love to go sporth and multiply.

So we’ll leave them for another day and start with the less daunting list of Bacterial (1) and Virus (1).

Tomato Pith Necrosis

Bacterial disease. Spread by rain water, water splash or transferred by hand.

With no treatment avaliable affected plants have to be removed and burnt.

Symptoms are upper leaves wilting and turning yellow and stems developing dark brown/black patches which continue into the inner stem tissue.

TMV

Virus. Short for Tobacco Mosaic Virus. With lots of hosts, it’s easily spread by hand, tools and on clothes so disinfecting and sterilising are important as is aphid control. Those sap sucking pests are trouble.

Again no treatment which means removing and burning affected plants and then doing that with all plants and soil at the end of the season.

Symptoms are a plant reduced in vigour and stunted in its growth.
Leaves have mottled/mosaic patterning in yellow or light/dark green and are often small and deformed. When fruit ripen they have bronze blotches or yellow streaks.

Varieties are available bred for resistance against TMV.

Photo by wili hybrid

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Still in Pestville today. Just hanging out, getting to know which evil characters to look out for.

Glasshouse Red Spider Mite

Niche opportunities exist within the Red Spider Mite franchise. Other operators specialise in Box, Conifers and Fruit trees. But it’s the glasshouse variety, the one with sap sucking designs on greenhouse tomato plants which concerns us.

Another sap sucker. More mite than a spider, though it does weave miniature webs, which with a bad infestation, stretch across between leaves and stems.
Miniature, because it’s tiny. Less than 1mm long. What it lacks in size, it makes up in numbers, both of its kind and in eggs. Its invasion can last from mid spring to late summer.

All that collective sap sucking results in the life being sucked dry out of the leaves which end up with white/yellow mottling, losing their green colour, curling up at the edges, drying up, giving up and falling off.

• Chemical control
  Too long being blasted has rendered them blasé and resistant
• Biological control
  However they need to beware the Predatory mite; Phytoseiulus Persimilis which eats Red Spider Mites for breakfast, lunch and tea and hopefully disregards rules about not eating between meals
• Cultural control
  They like their greenhouse nice and warm and dry so a blast of sprayed water or damping down, to up the humidity should fix that.
  If the plants are in pots they could be moved out of doors and if at the early stages of infestation affected foliage removed

However if it’s bad, the plant won’t recover in which case its best to watch the whole lot, plant and mite, go up in flames.

Other sap suckers which are not so likely but useful to know about are:

• Glasshouse Leafhopper whose sap sucking antics create coarse, pale spots on the leaves
• Southern Green Shield Bug. Invades from southern Europe and hasn’t made many inroads into the UK yet. Plus it doesn’t arrive until late summer/early autumn so toward s the end of the main tomato season

And then a couple of other creepy crawlies with nothing but eating on their tiny minds:

Tomato Moth – or more specifically its caterpillar.
The moth is small, brown and goes by the less drab name of Lacanobia Oleracea. Its larvae start by nibbling away at the underside of the leaf and then the caterpillar gets into full swing eating clean through the leaf and making holey inroads into the tomato fruit

• Chemical Control
  Pyrethrum or Bifenthrin (synthetic pyrethrin compound) on the larvae
• Cultural Control
  Finding all those caterpillars and dispatching by hand. And swatting and squashing the moth if spotted.

Vine Weevils

Again, the offspring are the biggest problem. The adults eat leaves, working their way round the edge of the leaf like a misshapen hole puncher but the larvae which are hidden in the soil munch their way through a plants roots.  The plant wilts and when the roots are eventually severed, dies. Plants in containers are especially vulnerable However I think the timing all of this underground destruction means main crop tomatoes may escape, as although the Vine Weevil lays it eggs earlier, the larvae don’t get going till earlyautumn.

• Chemical control
  Pah !
• Biological control
  The pathogenic nematode, Heterorhabditis ssp. and parasitic eelwormSteinernema kraussei nematode
  Frogs, toads and hedgehogs are also partial to a Vine Weevil
• Cultural control
  To get rid of the eggs and break the cycle, remove all the affected soil and burn

So when it comes to small, insect like pests, likely to upset the UK tomato cart, all the above with yesterdays’ Aphids and Greenhouse Whitefly complete the cast.

Lets hope this summer they remain in the Green Room rather than making it out to the Green House.

Vine Weevil Photo by Chris@184

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When I was growing tomatoes last year I felt researching and writing up all that could go wrong was to court certain disaster.

I don’t know if a term exists for a by-proxy plant hypochondriac but when it rained hard overnight I lay awake imagining Billy Blight making his way from plant to plant and a scene of MGM biblical destruction awaiting me come morning.

However as we’re still in wannabe season as far as tomato plants are concerned, now seems like a good time to be brave and look at the horrors which can strike.

Disease and destruction arrive in different ways so before holding the identity parade I thought I’d get straight in my head, the nature of what we’re up against.

Disease

Plant disease results from a band of baddies collectively known as Pathogens: Fungi, Bacteria and Viruses. They spread in different ways often involving pests.

Destruction

Pests also cause damage in their own right. Slugs and snails come into this group.

Disorder

Physiological Disorders are not caused by pests or diseases. They are caused by a problem originating in the environment in which the plant is growing e.g. frost/wind/drought/water logging. They may also be caused by nutritional deficiencies. Or a gardeners neglect.

Depending on what needs addressing there are also different ways of fighting the problem

Cultural control: A traditional, no chemical approach using barriers, traps and intervention by hand to prevent the problem. Crops are protected from pests by appropriate physical barriers and pests are removed from site. (E.g. beer traps for slugs, picking caterpillars off by hand)

Biological control: This refers to the practice of using one organism to limit the population of another. It’s the creation of a hit squad, the drafting in of a pest’s natural enemy to come in and clean up.

Something which occurs all the time in nature but in this instance a gardener introduces a predator/parasite to target a particular problem. For example in a greenhouse, Glasshouse Whitefly can be controlled by the introduction of Encarsia Formosa.

Chemical control: This covers the use of Insecticides/Pesticides and Fungicides.
If used in spray form there are two different ways in which these work, Contact or Systemic.

Contact insecticides are applied so that the chemical either sprays the pest directly or sprays and covers the leaf surface and the pest picks it up from there.
Contact fungicides will kill fungal spores which are present on the surface of the plant.

Systemic insecticides and fungicides move beyond the surface of the plant and are absorbed by it. This means systemic insecticides can kill pests which feeding off the sap of the plant and systemic fungicides can kill fungal spores which are present in the tissue of the plant.

Tomorrow we take our first peek into knowing your enemy ( or your tomatoes enemy).

Photo by freeparking

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