Sorting through the weed-control maze

By PAT LYNCH

The first issue in the new millennium of Publication 75, Guide To Weed Control, will have some dramatic changes.

The weed rating system has changed from Excellent, Good, Fair and Poor to a number system of 0-9, the higher numbers indicating better weed control. There were long and heated discussions over these changes. Some members of the Ontario Weed Committee, the body responsible for this publication, felt growers would use the number too literally, taking a 9 to mean 90 percent control and thus 10 percent better than a rating of 8. This is not the case. All of these ratings are subjective. At any one location, conditions change. It is possible that with a certain set of circumstances a herbicide rated 8 might give better weed control than a 9.

The number system is felt to be easier to understand. Growers are used to a number system in the hybrid and variety selection, and numbers allow more graduations than an excellent-to-poor system. They are also computer-friendly, so programs can be developed that match herbicides to weeds. With a growing number of weeds and products, this capability can help sort through the weed-control maze.

Most products will have a single rating for weeds, but there are places where a product could have two ratings - an 8/9, for example. This signifies a difference in the ratings of this product. You will have to read the label to find out how to get the higher rating. This may be a product used to incorporate nutsedge and you must use the higher herbicide rate or incorporate the product to get better control.

Another change will be the addition of ratings on non-labeled weeds. This has always been a contentious area. On one hand, there is a reluctance to rate weeds in Pub 75 if they are not on the label. On the other hand, many weeds are already rated in Pub 75 even though they are not on the label. If control of a weed is rated as fair, it is probably not on the label, but by default, that product and weed have received a rating.

Part of the issue revolves around registration. Ottawa will not allow a weed on a label unless there is data from ten test locations to indicate the herbicide is efficacious on that weed. You could have a product that gives excellent control at eight locations on a certain weed, but the weed would not appear on that label. This system allows for the information to go to the producers without getting the chemical companies in trouble with Ottawa. In the 2000 issue, weeds that are on the label will be in bold face type. Weeds not on the label will appear in normal print.

For the 2000 edition, some tables will be combined. At present, some products are registered "early pre-plant", "pre-plant incorporated", and "pre-emerge." This means that three tables are needed to accommodate these various registrations. In the new issues, all soil-applied herbicides will be on one table. There will also be a table for post-emergent weeds. The tables will be grouped by herbicides that control mostly grasses, mostly broadleaf weeds, or grasses and broadleaf weeds.

In the past, there was some confusion over tank-mix partners. Now it will be up to you to find out what products are labeled as tank-mix partners. They will only appear in a table if the answer to either preceding question is " yes." A more detailed herbicide table is also provided. This table outlines what is generally the safe time delay for planting specific crops after a certain herbicide has been applied.

You can expect to see more changes in future issues - for example, a much larger weed list and a different listing of herbicides by crops. At the moment, if a herbicide is registered for multiple crops, there are separate tables for the weed control on all crops. And maybe in the future there will be a table, by crop, of all the registered treatments on that crop.

As you use the new issue of Guide to Weed Control, be aware that much thought and discussion have gone into making this document more farmer-friendly. When there so many changes made to a document such as Pub 75, there are bound to be some errors. Remember this as you read, and always go back to the label. This publication is not designed to replace the labels, but to help you sort through which labels you should be reading -- thoroughly.
Patrick Lynch is Head Agronomist for Cargill in Ontario.

© copyright 1999 AgMedia Co-operative Inc..

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Corn borer chewing up fields again this year

by CATHY SOANES

Growers continue to ask me what we saw when we scouted corn fields this summer to determine the level of damage inflicted by European corn borer (ECB). Growers want to know the scope of the problem and whether their fields could be on the corn borer hit list.

Well, the scouting results indicate that corn borer pressure can vary tremendously from year-to-year, county-to-county and even field-to-field, confirming that regardless of past pressure, corn borer is an ever-present concern to all corn growers.

Over the past two years the Novartis Seeds corn borer scouting project has been monitoring corn borer tunneling and feeding in cornfields and measuring the yield impact of this destructive corn pest. With a second year of scouting wrapped up, the consistent observation that we've noticed is the variability of corn borer pressure. In September, our scouts took to the fields and randomly selected 10 plants from each of the 332 fields that were scouted to assess tunneling damage. What they found was an average 6.2 cm of corn borer tunneling. This correlates to a moderate level of infestation using the definitions developed by Purdue University. (See Table 1)

Across Ontario, 26 of the 30 counties scouted had moderate levels of corn borer infestation based on the tunneling measurements. However, central Ontario counties, particularly Waterloo, Peel and Halton, showed the most severe levels of corn borer infestation. For example, an 82 percent level of ear feeding was found in fields scouted in Peel region this past September.

Tunneling length, however, varied widely within county samples. On the corn stalks cut open for the crop destruct, tunnel lengths ranged from none to over 35 cm. This kind of variability is what makes predicting levels of corn borer pressure so difficult.

Stalk rot and ear rot were also variable, although always present at some level. In general, corn borer feeding increases ear rot levels and also provides potential entry points for mycotoxin producing moulds.

During the past season, in fields under moderate to severe corn borer pressure, we found that non-Bt hybrids can have as much as seven times the amount of vomitoxin when compared to Bt hybrids. However, it was also clear that a Bt hybrid is not a good enough defense against mycotoxins. Hybrids that also have good baseline natural tolerance to ear mould pathogens are your best protection against mycotoxins.

What does a moderate level of infestation mean to corn yields? Yield observations from our 1999 scout indicate the yield advantage of Bt hybrids over their respective isolines varied across heat unit ranges.

After three years of collecting field data, we now have enough information to assess whether there is a difference in corn borer pressure depending on rotation and tillage practices. The data shows little or no difference in the level of corn borer pressure on continuous corn fields compared to first year corn, and also on no-till fields compared to those where conventional tillage was practiced.

Of course, yield is affected by a number of agronomic and environmental factors, but choosing Bt hybrids is the best way of realizing yield protection.

Aside from hybrid selection, there are environmental and agronomic "risk" factors that contribute to increased corn borer pressure. Risk factors include: significant corn borer pressure in the past, weediness, early or late planting, a productive growth environment, late-pollinating full season hybrids, hybrids with low corn borer tolerance, and fields surrounded by obstructions like woodlots or grass borders.

Conversely, normal planting dates, good weed control, a low yield environment, hybrids rated for your heat units and a hybrid that has good corn borer tolerance are factors that seem to decrease the likelihood of severe corn borer pressure.
Cathy Soanes is an agronomist with Novartis Seeds Agronomic Services and heads the Novartis Seeds' corn borer scouting project.

© copyright 1999 AgMedia Co-operative Inc..

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Yield monitors help reveal the secrets of your fields

By DON STONEMAN

Farmers shouldn't get hung up on the terms "precision farming' and "farming by the foot." They are most likely misnomers for the use of Global Positioning Systems (GPS) to aid in crop management, says crop consultant and farmer Brent Vankoughnet of Carmen, Man. Yet even the vague trends that farmers discover in their fields are an improvement on no information at all, he says. And even the imprecise use of yield monitors can make their use a worthwhile venture.

Vankoughnet is most excited about yield monitors as a way of determining what is going on in fields. He cites testing he has done on his own farm as evidence it can help producers get "a more precise average yield." And while Vankoughnet's techniques apply to Western Canadian canola, Ontario growers will likely find their own way to adapt them to soybeans and corn.

On a field of canola, he applied 30 pounds of nitrogen, leaving some untreated strips going north and south. He also sprayed the field in an east west direction with the fungicide Rovral, also leaving some gaps. On his field map, where measurements were taken every 56 feet, Vankoughnet got a cross hatch effect, with some areas getting both fertilizer and fungicide, some just one treatment and not the other, and some neither.

Just as important as the actual applications was their timing. Vankoughnet applied the fungicide during a dry season, after the bloom had peaked, when most crop advisors would have said that the application was useless.

The yield monitor told Vankoughnet otherwise. The $20 spray, under questionable conditions, netted him between 12 and 15 bushels on the field where the fungicide was applied. Yields were eight bushels less on fertilized areas where there was no fungicide. The lesson learned, Vankoughnet says, is that a farmer with a fixed crop input budget should back off a little on the fertilizer application, and put the money that was saved into fungicide.

Vankoughnet cited another instance where he planted into part of a field where there was a perfect seedbed, stopped for a brief rain, then finished planting on what appeared to be dry soil. The yield monitor recorded a yield loss worth $60 per acre when seed was planted into the imperfect seedbed.

In still another place in the canola field, a sparse stand of five plants per square metre seemed unlikely in early season to be productive. The thin plant stand area didn't register a loss on the yield monitor map. The lesson learned? Don't bother to replant; the surviving crop will fill the gaps.

Vankoughnet does throw in some caveats about monitors. He advises that the data should be used and that care be taken that there are enough replications for farmers to have confidence in the management decisions they are making, and "not create bad advice."

Vankoughnet also notes that yield monitors also let a crop manager determine if there are losses because a particular spray took too long to remove weeds, or if the delay of a custom application was costly in terms of yield loss. He has observed scenarios where a check strip was sprayed when a custom operator was scheduled to make a spray application, and compared to parts of the field sprayed later. A three to four day delay costs between three and four bushels of a $5 per bushel crop. A clean crop several weeks after spraying isn't good enough; a more expensive chemical that knocks weeds down faster than a cheaper competitor may be more profitable for the farmer over the season, Vankoughnet says.

© copyright 1999 AgMedia Co-operative Inc..

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