Powdery mildew is often misdiagnosed

We generally associate fungal diseases with moist conditions, but powdery mildew is an exception. Hot, dry conditions promote the development of this pathogen.
Issue date: 16 May 2008

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Although it’s not as quick to spread as many other fungal diseases, and although it’s not that difficult to control if correctly diagnosed, the problem is that it’s often misdiagnosed as early blight (Alternaria) as it can also on occasion form concentric rings. Consequently the incorrect products are used to try and bring it under control.

The most common form of powdery mildew is Leveillula taurica, which attacks the underside of the leaf, leaving irregular yellow blotches. When the leaf is turned over, there can be a slight, greyish fuzziness on the areas where the yellow blotches formed.

It may take a while to learn to recognise the symptoms, but once you know how, it’s easy.Most people associate powdery mildew with a white film on the leaves, often found on pumpkins, but this is not the case with L. taurica on tomatoes and peppers.

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once visited tomato farmers in a certain region who all complained they were unable to get Alternaria under control that year. Eventually asked to be taken to a tomato field where identified the Alternaria as powdery mildew.
he local pesticide representative who was not accustomed to identifying powdery mildew in that particular region was at fault. He had given all the farmers products to apply which would not control the powdery mildew.
his pathogen usually starts on the lower leaves and works its way up the plant.

his gives you a bit of time, because in the early stages the damage is at a less important part of the plant.
he infection may be insufficient to justify control and it may spread or stop according to the weather. The trick is to recognise it for what it is and then monitor the development.

There is another form of powdery mildew which is a much more recent problem.This is Oidium lycopersicum which looks like the pumpkin’s powdery mildew and starts as blotches on the leaf’s surface and then spreads all over the leaf.
t doesn’t start at the base of the plant and it can spread very rapidly and cause much damage as the leaves become scorched.

his form of powdery mildew is more prevalent on tomatoes grown under protection and more so when there is a lower light intensity due to the weather or dirty plastic coverings.Both forms of the disease can occur at the same time.

At least the second-mentioned form is usually easily and correctly diagnosed. It seems to be more prevalent later in the season and on older plants, just as is the case with pumpkins.

Both forms of the disease may be controlled with the same product. – Bill Kerr ((016) 366 0616 or e-mail [email protected]) |fw

Farmers have options

I was interested to see an insert recently on SABC 2’s farming programme Agriculture Today – the combined format of AgriTV and Ulimo – in which the CEO of the Milk Producers’ Organisation explained how they are launching a trading desk for milk producers. He said, most other agricultural commodities had trading desks, such as Safex for the grain industry, which gave farmers that all-important option of knowing what prices to expect for produce – and thus the option to accept or not.

Milk farmers are largely at the mercy of buyers – mostly large distribution and marketing organisations that pretty much “call the shots” when it comes to the price paid to farmers. The new trading desk will give farmers the option of deciding if the price on offer is acceptable or not.

What does the price of milk have to do with fresh produce marketing?
n South Africa we have a system of commission markets, scattered around the country, which is unique in the world. Our fruit and vegetable farmers have options because they are not bound to one buyer.

Despite what some critics say, the single most important benefit of a fresh produce market is the establishment of prices. If that didn’t happen, how would farmers know the value of their produce on a given day? Market prices are a farmer’s benchmark.
here was a time in our recent history (50 years or more) when fruit and vegetable farmers were price makers. In those days the marketing boards were powerful entities and could also “call the shots”. But times have changed. The consumer has risen to the fore and eagerly catering to his every whim are the supermarkets. Massive buying power and global reach gives them almost total dominance of the fresh produce business in many parts of the world. The farmer has become a price taker.

Retail groups battle for market share and use fresh fruit and vegetables as a drawcard. The only reason they don’t totally dominate our local fresh produce industry is because of the markets.

Don’t get me wrong, for a farmer to supply a supermarket can be a good option, but it shouldn’t be his only option. fresh produce farmers want to be price makers, they can do it, but they need to produce quality produce.

No matter to whom the products are sold, top quality will ensure the farmer is the price maker. Quality remains the best option. – Mike Cordes ([email protected]) |fw