| 5 The most likely Tomato diseases and
disorders Just a word of caution. Currently there
is no Australia-wide registration of chemicals for home garden use. Each state and
territory has its own registration system, so you are advised to check with your local
Department of Primary Industry or Agriculture to get the recommended and registered
products for your region. I have mentioned some of the products that are registered for
home garden use in my home state, South Australia. This is not a recommendation, merely a
fact.
Fungal diseases
Damping-off diseases Caused by various Pythium &
Rhizoctonia spp . on a wide range of plants, not just the fruits of love. Can be a
problem with raising seedlings under glass in winter. Symptoms are that the geminated
seedlings collapse due to what appears to be a restriction in the stem, so they fall over
and die. Remedy is to improve drainage in the seed raising mixture, reduce watering and
improve air flow around the sown seed flats. There are systemic fungicides such as
Fongarid® by Ciba-Geigy and Previcur® by Schering that reduce incidence, but
re-infestation can be rapid unless seed raising hygiene is improved.
Fusarium Wilt Caused by three races of the fungi Fusarium
oxysporum f.sp. lycopersici . which is a soil borne organism that penetrates the roots
of plants. Symptoms begin with the older leaves turning yellow and often only yellow on
one half of the leaf. The effected leaves eventually wither and die. When the stems are
cut, the outer most tissue will be a red-brown colour instead of the normal healthy green.
There are resistant cultivars to all three races of this Wilt, but for the home gardener
without the capacity to have the particular race of the Fusarium fungi analysed, it is
best to grow the most resistant cultivars. 'Mighty Red', 'Duke', Floradade', 'Walter' and
many others are resistant cultivars for growing in high risk areas. Light infestations can
be controlled by dusting with Mancozeb. If Fusarium is a common problem in your region,
consult your local Primary Industries office for advice.
Grey Leaf Spot Caused by the fungi Stephylium
solani . The spores are spread by the wind and symptoms are tiny brown specks on the
underside of the leaves. The specks are often surrounded by yellowing of the leaves. The
condition is spread quickly in humid conditions or where watering is by overhead sprinkler
onto the foliage, as opposed to drippers or flood irrigation, which is preferred. Zero
Multi-purpose Fungicide® by Taylor-Samuel and Bravo® or Garden Fungicide Spray® both by
Incitec can control but better watering practices are generally enough. Caused by the fungi Stephylium
solani .
Grey Mould Caused by the fungi Botrytis cinerea
, which is the "Noble Rot" of wine makers, but the ignoble rot of Tomato
growers. Easily diagnosed by the tell tale grey woolly growth on fruit or stems where
morning fog or humidity is present. Treated with fungicides such as the three sprays used
to control Grey Leaf Spot.
Powdery Mildew Caused by the fungi Leveillula
tauica . Spread on the wind, the symptoms are yellow blotches that turn brown with age
and the silver velvety spores that are barely detectable on the underside of the leaves.
Control is by puffing a dusting sulphur or spraying a water soluble sulphur powder such as
Sulfine®.
Sclerotinia or Timber Rot Caused by the fungi Sclerotinia
sclerotiorum. Detected as a white mouldy growth on brown stems. The bush wilts and
collapses. Most common in cool moist conditions. Control with fungicides such as Bordeaux
Powder, Copper Oxychloride or Lime Sulphur.
Target Spot Caused by the fungi Alternaria solani
. Symptoms are a black to dark brown spot with concentric circles on leaves, stems or
fruits. Control with fungicides such as Bordeaux Powder or Kocide® by Multicrop, use
disease free seed and do not plant back onto areas where Tomatoes, Capsicum or Eggplants
have grown the previous year.
Verticillium Wilt Caused by the fungi Verticillium
dahliae , which is a fairly common soil organism. There are two races of the fungi and
fortunately we have many cultivars resistant to the ubiquitous race 1, while race 2 is
less widely spread, which is just as well because we currently have no cultivars resistant
to race 2. The fungi is easily spread by any soil transfer, even from your gum boots being
washed at the back tap! Detected when the lower leaves on your Tomato and Capsicum bushes
turn pale yellow and the leaf margins die. The bushes wilt during the heat of the summer
but seem to recover at night. When you cut a stem at the base of a bush a distinctive
cream-brown discoloration can be seen. Control can be gained by solar sterilisation. That
requires a sheet of black poly film to be draped over the soil and anchored down so that
the solar heat virtually 'cooks' the fungi in situ. There are of course fumigants
and fungicides for commercial growers, but these are not registered for use by home
gardeners in most states.
Bacterial diseases
Bacterial Wilt The organism that spreads it is Pseudomonas
solanacearum. Detected by a wilted Tomato bush that has retained its healthy green
appearance and when the stem is cut a slimy grey material oozes out. Quite common in hot,
wet weather in the tropics and sub tropics. Best remedy is to spell the site and use
resistant cultivars for future planting such as, 'Summertaste', 'Tropic' and 'Scorpio'.
Bacterial Spot The organism that spreads it is Xanthomonas
campestris pv. vesicatoria. This is spread from infected seed, caused by leaving
infected fruit lying around. The symptoms are interveinal water soaked spots on the leaf
that eventually fall out leaving irregular holes. The fruit can be effected in the green
stage, when crater-like scabs appear on the fruit. Can be controlled by spraying Kocide®
by Multicrop.
Viral diseases
Tomato Mosaic Virus Transmitted by sowing contaminated
seed and handling any diseased plants. Since certified seed in Australia is generally free
from TMV, it would probably have to have come from seed illegally imported into Australia.
The symptoms are that the Tomato bush looks paler than a healthy plant and inside the
fruit turns brown. Best remedy is to soak all pruning tools in a solution of White King®
and destroy all off the infected crop, then spell the plot for year.
Tomato Spotted Wilt Virus Transmitted by sap-sucking
Thrips who over winter on Thistles and a wide variety of other hosts. Symptoms are that
the young leafs become covered with fine purplish-brown spots and droop downwards. Best
remedy is to control the weeds, both in winter and spring near your Tomato crop or where
you aim to grow it.
Tomato Yellow Top Virus Transmitted by Potato Aphids
and the Green Peach Aphids. Symptoms are chlorotic leaf margins that turn yellow and
leaves reduced in size. Main remedy is to try and control the Aphid vectors by spraying
the systemic insecticide Rogor.
Tobacco Leaf Mosaic Virus Not usually a problem in
Australia, but if you try sneaking foreign Tomato, Capsicum, Chilli or Eggplant seed back
into Australia and New Zealand it soon will be!
Mycoplasma-induced diseases
Big Bud The Big Bud you see on top of some Tomato and
Eggplant bushes, is reminiscent of aborted stems and weird rosette flowering spikes. It is
caused by the Common Brown Leaf Hopper spreading Mycoplasma-like substances. Best remedy
is to remove the infected shoots and control the Leaf Hopper vector, by spraying a contact
insecticide such as Carbaryl or Malathion, or by spraying a Dimethoate compound such as
Rogor, which is a systemic spray or possibly an Omethoate spray such as Bayer's Folimat®,
which is systemic as well as contact in its action. Alternatively you could use a NIMBY*
repellent that drives them over the neighbour's fence, such as a Pyrethrum or Garlic based
spray. (Not-in-my-back-yard)*
Nematode-induced infection
Root-Knot Nematode The nematode is a tiny soil
roundworm that lances roots of many horticultural crops and in doing so causes galls to
form on their roots. There are also many species of indigenous Nematodes Meloidogyne
spp. that don't lance Tomato roots too! The first above ground symptoms are that your
infected Tomatoes start to wilt or look stunted. When you pull a bush up you will be left
in no doubt, because the root swellings are very distinctive. The Nematode vector can be
repelled by planting perennial Marigolds near your vegetable garden. The soil borne
repellent takes 3-5 months before it is an effective deterrent, so the miniature annual
marigolds aren't much use. Best remedy is to spell the site. There are organophosphate
controls such as Bayer's Nemacur® but they are pretty expensive to treat large areas.
Solar sterilisation would be worth trying.
Disorders
Blossom End Rot With the increase in organic gardening
we are seeing more Blossom End Rot than previously. It is caused by a calcium deficiency
and organic gardening with the reliance on acidic humus products, makes the uptake of
calcium more difficult from acid soils. The symptoms are an ugly brown patch at the base
of ripe and ripening fruit, that turns into a black leathery patch. There are some
resistant cultivars, such as 'Moneymaker', 'Striped Cavern' and 'Summit'.
Catface Is an irregular cracking or scaring of the
fruit at the base or blossom end and can be caused by abnormally cold or hot weather.
'Grosse Lisse' and 'Tropic' were particularly susceptible, but most modern cultivars have
had this disorder selected out in the breeding.
Concentric Ring The symptoms are concentric circular
rings at the stem end of the fruit, caused by periods of very fast fruit growth during
humid conditions or rapid growth following dry conditions. Some cultivars more susceptible
than others. 'Duke', 'Floridada' and 'Walter' are resistant.
Sunburn or Sunscald Usually caused by removing too
much foliage when pruning, then hot weather on the fruit causes a shiny white blister. The
remedy is not 15+ sun screen, but simply leave the leaves to cover the fruit.
Insect vectors
Aphids, Whitefly & Thrips These Tomato predators or
vectors that often carry viral diseases, can be controlled by the simple use of sticky
yellow boards in the vegetable garden. The yellow boards attract and impale the
soft-bodied insects onto their sticky coating, which fortunately doesn't seem to attract
many non-target insects, such as the friendly Lacewings or Ladybirds, which both graze on
Aphids as their natural predators. For further information on the use of insects to fight
insect infestations consult manuals on Integrated Pest Management. There are of course
many more insects that graze your vegetable garden, but it's amazing what you can capture
with a torch at night, without having to resort to insecticides. If however the sap
suckers and chewing insects get out of control, there are systemic insecticides, such as
Rogor, Disyston® and Folimat® both by Bayer that when applied move through the plant and
anything that chews the plant for 2-3 weeks, gets a fatal dose of an organophosphate or
Dimethoate in the case of Rogor. The precaution is that you cannot pick and consume the
fruit from your plants during that withholding period of 14-21 days or whatever period is
on the label. The positive aspect of using systemic sprays is that they do not leave long
term toxic residues in your garden soil. You will need to weigh up whether sprays fit your
management plan or if you are prepared to eat your fruit with a few blemishes. |
