GN120206

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Volume 38, Number 3 | February 6, 2012

$4.25

PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER

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Plan Rotations to Avoid Fungicide and Herbicide Resistance As fungicide use becomes more common, pathogens are likely to develop resistance. Find out how to avoid this problem on your farm BY ANGELA LOVELL

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athogens, organisms and plants will eventually find ways to adapt and develop immunity to the various methods used to control them. This has been shown clearly with the announcement of glyphosateresistant kochia in Alberta. Other recent challenges for farmers include increasing amounts of Group 2 herbicide-resistant cleavers and wild mustard in pulse crops. Group 1- and 2-resistant wild oats in cereal crops continue to have significant economic impacts for some growers.

FUNGICIDE RESISTANCE As fungicide costs have come down it’s more economical to use them. Fungicide use in wheat has been fairly high for a number of years, as farmers spray to control diseases like fusarium head blight and rust. As the use of chemical controls increases, is resistance in crop varieties under greater pressure? “There are some concerns in using fungicides but variety resistance should not be overcome any quicker with fungicide use,” says Brent McCallum, a plant pathologist at Agriculture and Agri-Food Canada in Winnipeg. “The concerns with continual fungicide use are that the pathogens will develop resistance or tolerance to the fungicide and the environmental effects of fungicides, since they are broad spectrum and control all fungi (beneficial and harmful) in the crop, and to some extent the soil.” Application of fungicides can, in some cases, hamper research work. As most wheat fields in Manitoba are sprayed with fungicides, there are limited samples that researchers can collect to test for virulence. Samples are more easily available in Saskatchewan, where fungicide

PHOTO: KUTCHER, CDC, UNIVERSITY OF SASKATCHEWAN PHOTO: BRENT MCCALLUM, AAFC WINNIPEG

Resistance can develop to the fungicides that prevent diseases like this stem rust on wheat. Combining management techniques can help. use is lower and from other sources like nurseries and experimental trials. “Monitoring is very important,” says McCallum. “This year we found virulence to Lr21 for the first time in Canada. Lr21 is in many of our wheat cultivars and many lines in development, so knowing that it is less effective is important information for the future.”

PRE-MIXED FUNGICIDES New products are coming to the marketplace all the time, including pre-mixes, which promise better efficacy by combining different modes of action in one, ready-to-use product. But the theory behind pre-mixes, especially fungicides, is somewhat confused, says Bruce Gossen, a plant pathologist with AAFC at Saskatoon. “The accepted best practice for managing fungicide risk includes use of pre-mixes,

which are expected to substantially reduce the risk of fungicide insensitivity,” he says. “But some of the modelling that is being done doesn’t actually substantiate that approach. How effective it’s going to be in the long term is still being assessed.” In the field, pre-mixed fungicides offer advantages to growers in Western Canada, where farmers have not used a large amount of fungicides over many acres for a long time. These fungicides often mix one product, which may be at a high risk for insensitivity but that has a lot of activity against a particular pathogen, with another product that may not be as effective against that pathogen, but which has a much lower risk of insensitivity. This makes the odds of getting resistance to both products very low. “From a grower’s standpoint, these fungicide mixes are a smart

Pathogens that cause blackleg cankers on canola can become resistant. Experts don’t recommend applying the same pre-mixed fungicide year after year. way to deal with the issue,” says Gossen. “We don’t recommend that growers apply the same mix year after year on a field. But if they are rotating fungicides and crops and including mixes as part of the approach, the odds of having trouble with fungicide sensitivity are much reduced.” Farmers should, however, be cautious about seeing any one product as a solution in and of itself. “The lessons learned with herbicide-resistant weeds should be applicable to the evolution of fungicide-resistant pathogens,” says McCallum. “In some places, such as Europe, where fungicide use is high, they have seen the appearance of fungicide-resistant, or tolerant, or less-sensitive pathogens, so we should watch for that here as well.” Farmers should not rely on just fungicides, but also make use of the genetic resistance in the host

In This Issue

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plant and McCallum advises farmers to regularly consult their provincial seed guides, which list the levels of resistance of each cultivar to various diseases. These can change over time if a pathogen population evolves increased virulence on a particular cultivar. “The combination of improved genetic resistance and fungicide application has proven effective in controlling diseases such as fusarium head blight,” says McCallum. “We don’t want to get into a situation in which we rely on fungicides and neglect genetic resistance. In some cases in Europe the reliance on fungicides has lead to a decline in genetic resistance to diseases such as rust. Recent legislation in Europe has mandated a reduction in fungicide use and now they are trying to develop genetic resistance, which can be a hard task.”

» CONTINUED ON PAGE 4

Wheat & Chaff ..................

2

Features ............................

5

Crop Adviser’s Casebook

14

Columns ........................... 20 Machinery & Shop ............ 27 Cattleman’s Corner .......... 33

On-farm experience with grazing corn KEVIN ELMY

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Deere offers tracks on European combines SCOTT GARVEY PAGE 27

FarmLife ............................ 37


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