Ammunition for mildew

It hasn’t been difficult to find mildew on many cereal crops this autumn.

DuPont will be hoping it is much more difficult to find if crops are treated with its new mildewicide this spring, registration permitting.

The product, already sold in Poland as Talius, is a completely new active ingredient, proquinazid, from a new chemical group, and offers long-lasting protection against mildew, according to DuPont fungicide product support scientist Isabelle Gasnier, although it doesn’t have any curative activity.

“In the field growers can expect to see four to six weeks of protection from a single application depending on rate.”

Typically that is two weeks longer than current mildew fungicides, she says.

Proquinazid works at every stage, hence its protective properties, by either preventing mildew spores germinating or by stopping the initial infection process, Dr Gasnier explains.

“Lab tests have indicated around half the spores fail to germinate.

If it does germinate, in the presence of proquinazid, the spore will produce a germ tube which will elongate without forming an appressorium [infection peg] from which infection of cells proceed.”

Eventually the spore will run out of energy and die, UK product manager Mike Ashworth says.

“Spores generally expect to have tapped into the plant within 24 hours.”

The product also affects the viability of any treated spores, so any spores produced by mildew already established should inhibit the spread of the disease, Dr Gasnier suggests.

That property together with some local systemic movement in the leaf should mean treated leaves are effectively protected from further infection after treatment, Mr Ashworth says.

“A lot of farmers will look at a low level of mildew as a trigger for spraying.

[The properties of] proquinazid will make sure the rest of the plant is protected.”

Vitally proquinazid will also protect any new growth coming through after treatment through what DuPont describes as a “super halo” effect. Micro-emissions, or minute vapours, act as a shield to protect the new growth, rather than any direct systemic movement of the chemical into those tissues, says Mr Ashworth.

The effect has been tested in the laboratory experiments, Dr Gasnier says.

A row of pots containing plants sprayed with proquinazid were placed in a sealed container next to three rows of untreated plants.

All the plants were inoculated with powdery mildew 24 hours later, and subsequently examined for mildew.

The test was repeated with quinoxyfen, kresoxim-methyl and fenpropimorph.

“The result was proquinazid protecting untreated tissues on adjacent plants as well as new tissues forming after application.”

Proquinazid also appears to switch on, or induce the crop’s defence mechanisms to mildew.

“Researchers have found the key drivers for the plant’s own resistance to mildew, and we’ve shown that proquinazid switches on many of those genes.”

That could help delay resistance developing, European fungicide manager Robert Bird says.

“The product itself is inherently toxic to mildew, but it looks like it has two ways of affecting the disease, which is good news for preventing resistance.”

Yield responses in trials have averaged around 6% over a standard triazole programme, he adds.

“Typically growers are getting a three-to-one return on their investment.”

If approved, proquinazid will be available in the UK next spring in enough volume to satisfy the market, Mr Ashworth confirms.

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