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Fungicides and plant health

Farmers are well aware of the value of fungicides in protecting crops from plant diseases. But some fungicides promise even more. Crop protection companies now promote the plant health benefits of certain fungicides. They claim that using these fungicides can result in higher yields, even in the absence of disease.

Group 11 fungicides

The fungicides being promoted for having plant health benefits are the Group 11 Qol strobilurin fungicides. The active ingredients of this fungicide group were first derived from wood rotting mushrooms in 1992 and the first fungicides of this group launched in the U.S. in 1996. Today there are about two dozen Group 11 fungicide products sold in North America (eight with registration for use in Canada) for use in a wide range of crops.

Headline, a BASF product registered for the use in Canada in cereals, peas, chickpeas, beans, lentils, flax, soybeans, sugar beets, potatoes, oilseeds, and grasses and legumes grown for seed, is the fungicide most often associated by Canadian farmers with plant health benefits.

BASF has coined the term AgCelence to promote these benefits to growers. Jason Leitch, BASF fungicide brand manager, says, “Research has shown the use of AgCelence fungicides results in greener leaves, stronger stems, increased root development, reduced plant stress and better utilization of nitrogen. The plant is more efficient in converting nutrients into yield.” According to Leitch, farmers are getting an average of three more bushels of canola per acre because of the AgCelence benefits of a Headline application in canola.

Leitch says that all BASF fungicides which have the active ingredient pyraclostrobin provide farmers with AgCelence benefits. Besides Headline, this includes Headline Duo for use in peas and lentils and Twinline in cereals. As well, BASF will be offering two new fungicide products that promise plant health benefits in 2013.

Priaxor DS is a premix of the Group 11 fungicide pyraclostrobin (the active in Headline) and a brand new Group 7 active, Xemium, for use in peas, chickpeas and lentils. Leitch says: “Priaxor is able to move around in the leaf so it provides more consistent, continuous control of disease. Growers will also see larger pods, more consistent seed size, improved harvest-ability and up to three bushels per acre more yield.”

The other new fungicide BASF will be marketing is a seed treatment product: Insure Cereal. This is the first Group 11 seed treatment registered for use in cereals in Canada and the only strobiliurin seed treatment marketed with the claim that it provides plant health benefits. Insure Cereal is a cereal seed treatment with three actives. Group 11 pyraclostrobin is combined with a Group 3 active, triticonazole, and a Group 4 active, metalaxyl — both of which are already components of a number of popular seed treatment products. Leitch says the addition of pyraclostrobin in the Insure Cereal premix results in better emergence and increased seedling vigour. “It provides a jump start to the crop.”

Not rocket science

Dr. Paul Vincelli, plant path-ologist at the University of Kentucky, has studied Qol fungicides and says: “Strobiliurin fungicides have a number of physiological effects on plants and most are positive. Most researchers have no doubts this group of fungicides offers plant health benefits. However, this is not rocket science and the outcome is not guaranteed. The hardest question to answer is how often these benefits occur.”

In 2011, Vincelli compared the plant health benefits of Headline with another popular fungicide in field scale, repeated, randomized trials. In fact, the trials were so big that the fungicides were flown in by aircraft. According to Vincelli, there were real, substantial differences noted in two of the three trials.

In Trial 1, there was no difference in the yield of the white corn but there was a slightly better straw strength in the Headline-treated areas.

Yellow corn treated with Headline yielded 20 bushels more than the control and had better straw strength in Trial 2.

There was a 27-bushel improvement in the Headline-treated yellow corn in the third trial.

All of the trials were disease free so Vincelli attributes the improved straw strength and yield to the plant health benefits of the strobiliurin fungicide.

Still, Vincelli is of the opinion that the likelihood of disease should be the criterion farmers use in deciding whether or not to use a fungicide rather than potential plant health benefits. “University plant pathologists will say disease risk is the best indicator of economic benefit from fungicides.”

Vincelli also says farmers should time their application of fungicides for disease control. “The best time to put on a fungicide is the early reproductive stage. I can’t convince myself to go earlier. We see no measureable long-term disease control from earlier applications.”

Finally, Vincelli warns farmers of the high risk of resistance development to Group 11 fungicides. “Strobiliurin fungicides are very susceptible to resistance development. However, in just the last few months we have identified a genetic quirk in some fungi that development of high resistance to strobiliurin fungicides is lethal in itself to those diseases. However, fungi can certainly develop moderate levels of resistance to strobiliurin fungicides.”

Syngenta’s Group 11 fungicides

BASF is not the only pesticide manufacturer marketing Group 11 strobiliurin fungicides. However, most of the other companies in the market have made a decision to promote their products only on the basis of their products’ performance in combating disease. Part of the reason for this is Canada’s Pest Management Regulatory Agency’s (PMRA’s) stringent documentation requirements and proof of performance before any claims can be made. Given the inconsistency in plant health responses, most companies have decided not to make these claims of improved plant health or yields for their Group 11 fungicides.

Syngenta was one of the first companies to isolate the strobiliurin active back in 1992 and its research has shown there are four physiological effects within plants that has been sprayed with a Group 11 product.

First, and the only performance claim Syngenta makes when marketing Quilt (which has the Group 11 active azoxystrobin), is very good broad-spectrum disease control.

Syngenta researchers have also noted three other changes within the plant itself which can result in plant growth and yield benefits. Rob Klewchuk, Syngenta’s technical lead for Western Canada identifies these factors.

“There can be improved C02 assimilation which enhances photosynthesis. Group 11 fungicides seem to help a plant manage C02 and fix the C02 carbon for higher yields.”

“Second, these strobiliurin fungicides preserve green leaf area. Plants sprayed with Quilt stay green longer, which allows the plant to realize its full genetic potential. These plants follow their natural path to maturity more closely — even when stressed by environmental conditions like drought.”

“Third, there is improved water- use efficiency. These fungicides act as a respiratory inhibitor by reducing loss of water from the leaf.”

Klewchuk says growers who use Quilt have noted a difference in straw colour and straw strength between treated and untreated areas of fields. They have reported treated fields stay greener longer, have better standability, and even higher yields. However, Klewchuk insists excellent disease control is a strong reason for using Quilt and that is one factor, along with yield and quality, promoted in its marketing.

Still, it is interesting to note that in the U.S. where regulations governing the marketing of pesticides are less stringent, Quilt is also promoted for its plant health benefits. Syngenta has even coined a term for marketing such plant health benefits: Plant Performance.

Arysta LifeScience products

Arysta LifeScience is another company actively marketing a Group 11 fungicide for plant health benefits in the U.S.

Disarm, with the active fluoxastrobin, is a Group 11 fungicide registered for use in turfgrasses and ornamentals in the U.S. Online advertisements for this product state: “Disarm is now proven to increase plant health.” Ads also state: “in a new study conducted by a major university, Disarm was also proven to show superior plant health benefits.”

Arysta also markets a concentrated strobiliurin fungicide, Evito, for use in corn and soybeans in the U.S. An Evito online marketing page states: “Evito provides the plant health effect that you have grown to expect; those include increased efficiency of carbon assimilation, nitrogen fixation, and water utilization, among others. Plants you treat with Evito will have greater tolerances to adverse conditions and recover more quickly, giving you maximum yield potential.”

It is important to note that Disarm is not registered for use in Canada. In mid-December 2012 Arysta LifeScience received conditional registration from PMRA for Evito 480 for use in cereals, turf- grasses, soybeans, and a number of horticultural crops in Canada. Evito 480 has the same active as Disarm and Evito. I was unable to confirm with a representative of Arysta LifeScience if and when this product will be available to western Canadian growers or how it will be marketed here.

Use fungicides wisely

Research is showing there are definitely plant health benefits that result from using Group 11 fungicides. However those benefits do not always result in higher yields. Disease control should be the No. 1 reason to use any Group 11 fungicide.

Equally important is preventing the development of disease resistance to Group 11 fungicides by following good agronomic practices. These include refraining from using the same fungicide product or group more than once per season. Rotate to a different fungicide group each year. Use fungicides that have multiple modes of action or tank mix fungicides with different modes of action if such use is allowed. Follow label directions. Scout fields before and after applications to make sure the use of the fungicide is required and that it worked. If control of disease has not been achieved, consult a plant pathologist.

Editor’s note: as this article was going to press, a spokesperson for Arysta LifeScience confirmed that conditional Canadian registration of Evito 480 has been received, but Evito 480 will not be commercially available for use in Canada in 2013. †

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