PROJECT RESULTS

Quantifying Herbicide Drift Damage

Table of Contents:

• Background and Objectives
• Procedure and Project Activities
• Results and Discussion
• Conclusions

ARDI Project:

Total Approved:

Date Approved:

Project Status:

#98-115

$3,500

May 27, 1998

Completed June, 1999

Background and Objectives:

The use of glyphosate has increased dramatically in recent years. The registration of glyphosate tolerant canola varieties has meant that glyphosate based products are now being used in-crop at a time when other crops are present. This coupled with the non-selective nature of glyphosate means that risk of drift injury from glyphosate onto non-target crops should be a concern to producers and custom applicators. This concern will be heightened when Roundup Ready Hard Red Spring Wheat varieties are registered. Almost no data exists for the quantification of the potential impact of glyphosate drift onto important crops.

The objectives of the project were:

1. To determine the impact of varying levels of glyphosate drift (in the form of Roundup or Roundup Transorb) on the yield of Canola, Peas, Flax and Wheat.
2. To present this data to producers and custom applicators and help them to form better drift prevention strategies and for use in accurately settling drift claims.

Procedure and Project Activities:

The project was conducted at the Faculty of Agriculture and Food Science Research Farm in Carman and coordinated with Dr. Tom Wolf of AAFC, Saskatoon. Matching funding was provided by Monsanto, Canada. A dose response of peas, canola, wheat and flax to two glyphosate products (Roundup and Roundup Transorb) was examined at two leaf and six leaf stages of canola and at various application rates ranging from 0.75-25% of the recommended in-crop rates. The two spray timings (two and six leaf of canola) represent common in-crop timings for these products in Roundup Ready canola. In order to catalogue typical drift symptoms for these crops according to rate, visual damage assessments were performed at 21 days after treatment. Relative maturity of the crops was assessed by monitoring days to 50% flowering. At the end of the season, each plot was harvested to determine grain yield.

Results and Discussion:

Effect on Crop Yield

It appears that there is an effect of both Roundup and Roundup Transorb on the yield of all four crops. The sensitivity of the four crops tested could be ranked as follows

(Least sensitive) Peas --> canola --> wheat and flax (Most sensitive)

There was a consistent downward trend of yield as related to dose of Roundup or Transorb for all crops except peas. Pea yield seemed relatively unaffected by either of these products applied at these low doses. The relative sensitivity of the crop species to these products was quantified in the rate required to achieve 50% yield loss, compared to the untreated plots. There did not appear to be any consistent difference between Roundup and Roundup Transorb with regard to their effect on crop yield.

There did not appear to be any consistent significant difference in effect on crop yield when the products were applied either at 2 leaf stage or 4 leaf stage of the canola. This was true, as well, for injury symptoms and for effects on days to 50% flowering.

Visual Injury Symptoms

The ability to visually detect crop injury due to the application of low doses of Roundup or Roundup Transorb varied with crop species.

(Least injury) Peas --> canola --> wheat --> flax (Most injury)

There was no consistent difference in detection of visual injury systems between treatments of either Roundup or Roundup Transorb. The visual injury symptoms were not an entirely accurate means of assessing potential yield loss due to applications of Roundup or Roundup Transorb. Although flax displayed injury symptoms more readily than wheat, the declining yield response of wheat and flax to applications of Roundup and Roundup Transorb, were similar. It is true, however, that canola and peas, which showed significantly less injury than either wheat or flax, were also less sensitive to applications of Roundup or Roundup Transorb with respect to yield loss.

For canola, it would be very difficult to predict yield loss from visual injury symptoms. For wheat and flax the relationship between visual injury symptoms and yield loss were strong and could be used to predict yield loss on the basis of visual injury symptoms.

Effect on Flowering Date

Time to 50% flowering was measured as an indication of the effect of Roundup or Roundup Transorb on maturity rate of the crop and potential effects on crop quality. Time to 50% flowering for all four crops was influenced by the application of Roundup or Roundup Transorb.

Conclusions:

Both Roundup and Roundup Transorb applied at very low rates (25% of the 0.5 l/acre rate or less) have an impact on the yield and flowering date of peas, canola, flax and spring wheat. Of these four crops, peas were least sensitive to these products at these rates, and flax and wheat were most sensitive. Canola had moderate sensitivity. Relative injury levels were indicative of the level of yield loss and of the relative yield sensitivity of the crops to Roundup and Roundup Transorb. The exception to this was flax, which gave grave injury symptoms but suffered yield losses no greater than those of wheat. There was an effect on flowering date which was most pronounced in wheat followed by flax. This effect was minor in peas and canola.

Both Roundup and Roundup Transorb are increasingly popular in-crop products. This work has shown the absolute and relative extent to which four of the common field crops grown in Manitoba are affected by very low rates of either of these products. These results suggest that drift prevention is critical with these products, especially around crops of flax and wheat.

Monsanto Canada Inc. is a project partner providing in-kind support for this proposal.

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