Background and Objectives

1. Determine the interval between the application of selected herbicides and the re-cropping to commercial potatoes.
2. Determine the interval between the application of selected herbicides and the re-cropping to commercial and seed potatoes.
3. Multiply seed from the same location or source for the variety comparison trial the following year.
4. Compare the efficacy of four fungicide application schedules in the control of early blight and late blight.

Procedure and Project Activities

Procedure:

Plot size: 4 rows by 40 feet (assessments conducted on 2 centre rows)
Trial design:  RCBD, 4 replicates
Plot location:  Edwin, MB
Soil Type: Almassippi Loamy Sand
Crop/Variety: Potatoes/Russet Burbank
Row Spacing: 1 metre
Seed Spacing: 15 inches
Planting Date: May 3, 2000
Harvest Date: September 9, 2000
Time Line: 1999 - Herbicides applied at the rates listed under "Treatments".
2000 - Evaluate commercial potato production 1 year after herbicide application.

Treatments:

Herbicide Family:

The herbicide was applied at a late spray date of June 25, 1999, using a tractor mounted CO₂ sprayer with Teejet 8002 flat fan nozzles (30 psi, 10 gpa).

Monthly Precipitation (mm):

Fungicide applications were made weekly starting in late June to control early and late blight. As well, insecticide applications were applied to control Colorado potato beetles throughout the growing season as required.

Assessments were made as to crop tolerance, tuber yield and grade. Phytotoxic assessments were conducted two times throughout the growing season. Crop tolerance was rated according to the Expert Committee on Weeds rating scale listed below:

9 complete tolerance * 8 possible effect *
7 slight effect * 6 definite effect
5 severe effect 4 severe effect
3 severe effect 2 severe effect
1 severe effect 0 complete kill

* commercially acceptable

Potato tuber samples were collected at harvest and assessed for tuber number, percentage of rough tubers, percentage of hollowheart and specific gravity. Total (cwt/ac), maingrade (cwt/ac of tubers greater than 2.0" diameter) and undersize (cwt/ac of tubers <2.0" diameter) potato yields were measured at harvest. Due to excess rainfall in 2000, plants were severely stressed and tuber number and size were affected. As a result, grade data (tuber #, roughness, specific gravity and percent bonus tubers) were not collected.

Procedure:

Plot size: 4 rows by 40 feet (12 m)
Trial design: RCBD, 4 replicates
Plot location: La Salle, Loam to Clay Loam, dry land, Gaia Research Station
Crop: Potatoes
Variety: Russet Burbank
Planting Date: May 2, 2000
Row Spacing: 1 meter
Seed Spacing: 15 inches
Harvest Date: September 12, 2000
Time Line: 1998 - Herbicides applied at rates listed under "Treatments".
2000 - Evaluate commercial potato production 2 years after herbicide application.

Treatments:

Note: In 1999, Odyssey herbicide at the 1X rate showed very little phytotoxic symptoms and had no deleterious affects on yield and grade. As a result, assessments of Odyssey residues were dropped from this trial in the 2000 season. As well, treatment #1, an untreated check was also not assessed.

Herbicide Family:

Herbicides were applied on June 15, 1998, using a CO₂ hand sprayer with 8002 nozzles (30 psi, 110L/ha).

Monthly Precipitation (mm):

Fungicide applications were made weekly starting in late June to control early and late blight. As well, insecticide applications were applied to control Colorado potato beetles throughout the growing season as required.

Assessments were made on crop tolerance, tuber yield and grade. Phytotoxic assessments were conducted two times throughout the growing season. Crop tolerance was rated according to the Expert Committee on Weeds rating scale listed below:

9 complete tolerance * 8 possible effect *
7 slight effect * 6 definite effect
5 severe effect 4 severe effect
3 severe effect 2 severe effect
1 severe effect 0 complete kill

* commercially acceptable

Potato tuber samples were collected at harvest and assessed for tuber number, percentage of rough tubers, percentage of hollowheart and specific gravity. Total (cwt/ac), maingrade (cwt/ac of tubers greater than 2.0" diameter) and undersize (cwt/ac of tubers <2.0" diameter) potato yields were measured at harvest.

Procedure:

Plot size: 4 rows by 40 feet
Trial design: RCBD, 4 replicates
Plot location: Loamy sand
Crops: Canola and wheat
Time Line: 2000 - Initiate trial
2001 - Commercial production evaluation
2002 - Seed production evaluation

Treatments:

Procedure:

Plot size: 2 rows by 150 feet
Plot location: MCDC Portage
Crop: Potatoes
Number of seed pieces: 380
Seed spacing: 10 inches
Soil type: Neuhorst, Clay Loam, medium textured, irrigated

Treatments:

Midwest variety 5, ACLR Russet, Russet Burbank, Shepody, Ranger Russet, # 350 NewLeaf Plus Russet

Utilizing seed in research trials from more than one seed source may introduce the added variable of variety to the trial. By obtaining seed from one seed source, the seed can be standardized thereby eliminating any affects due to environmental, storage and handling differences. This project involved growing seed at one site to standardize the seed for future research trials.

Procedure:

Plot size: 4 rows by 12 m (Assessments conducted on 2 centre rows)
Trial design: RCBD, four replicates
Plot locations: MCDC Portage la Prairie
Crop: Potato
Variety: Russet Burbank
Planting Date: May 5
Row Spacing: 1 metre
Seed Spacing: 12"
Soil type: Neuhorst, Clay Loam
Harvest Date: September 19, 2000

Treatments:

Procedure:

Plot size: 4 rows by 12 m (Assessments conducted on 2 centre rows)
Trial design: RCBD, four replicates
Plot locations: MCDC Winkler, MB
Crop: Potato
Variety: Russet Burbank
Planting Date: May 15
Row Spacing: 1 metre
Seed Spacing: 15"
Soil type: Reinland Fine Sandy Loam
Harvest Date: September 28, 2000

Treatments:

Results and Discussion

Herbicide re-cropping trials were conducted in 1997-98, 1998-99 and 1999-2000. The herbicides listed in the Procedure section of this report with the exception of Rival, Edge DC, and Curtail M were applied in 1997 and again in a separate plot in 1998. In 1999, Rival, Edge and Curtail M were added to the protocol. Potatoes were then planed in 1998, 1999 and 2000, one year after the herbicides were applied.

1998 Summary Results
In 1998, producing potatoes one year after the application of the herbicides did not result in a reduction of the yield or grade.

1999 Summary Results
In 1999, producing potatoes one year after the application of the same herbicides produced deleterious effects on yield and quality. The difference in response between 1998 and 1999 trials can be attributed to the amount of rainfall in the year of herbicide application (see Procedure – Mean Precipitation of the KMM 1999 Potato Research Report). In the months from July to October, there were 299 and 127 mm of precipitation in the years of herbicide application – 1997 and 1998 respectively. The above average precipitation in 1997 increased the micro flora activity in the soil that accelerated the breakdown of herbicide residues, thus minimizing the carry over effect in the potatoes planted in 1998. The below average precipitation in 1998 reduced the micro flora activity in the soil which in turn reduces the rate that herbicides breakdown, thus increasing the carry over effect in the potatoes planted in 1999. In spite of the severe crop damage observed in the 1999 trial, only Pursuit and Muster affected yield or grade at the 1X rate.

2000 Summary Results
In 2000, producing potatoes one year after herbicide application yielded similar results to those found in 1999. In both 1999 and 2000, Odyssey, Lontrel and Assert caused some crop injury, but no reduction in total yields. Muster, Pursuit and Accord caused severe crop injury and reduction in total yields in both years. Of the three new herbicides added to the protocol in 1999, only Rival at the 2X rate showed severe crop injury but no significantly yield reductions.

Although rainfall amounts in 1999 were above average compared to 1998, the similarity of response to herbicide residues in 2000 can be attributed to soil organic matter and higher percentage of sand. Sandy soils tend to have fewer micro flora for breakdown of herbicide residues.

The herbicides listed in the Procedure section of this report were applied in 1998. Potatoes were planted in 1999, one year after the herbicides were applied. In 1999, producing potatoes 1 year after the application of the herbicides produced deleterious effects on yield and quality (see - the Keystone-Midwest-McCain 1999 Annual Potato Research Report). The below average precipitation in 1998 reduced the micro flora activity in the soil which in turn reduced the rate that herbicides breakdown, thus increasing the carry over effect in the potatoes planted in 1999.

This trial was initiated in the 2000 field season. A trial site was located and sprayed with the appropriate herbicides as listed in the Treatments section above. In 2001, the site will be re-cropped to potatoes and phytotoxicity (crop injury ratings), yield (undersize, maingrade and total yields) and grade (tuber number, percent hollowheart and percent tuber roughness) assessments will be made to observe the effects of herbicide residues on commercial potato production one year after application. Tubers will also be collected from the plots and retained for seed for the following field season.

In 2002, the potato seed collected from the herbicide re-cropping site will be planted into a residue free site and the effects of herbicide residues on seed potatoes will be assessed (including phytotoxicity, yield and grade).

Two, 75 lb. samples were collected for each potato variety to be retained for seed for variety testing in 2001.

2000 Data
Disease assessments were conducted on a weekly basis starting in mid July. All fungicide application schedules reduced the incidences of early blight and late blight when compared to the untreated check. There was no difference in the disease levels between the application schedules (treatment #’s 1-5).

All fungicide application schedules produced a higher total and main grade yield compared to the untreated check. There was no difference in the main grade and total yields between the application schedules (treatment #’s 1-5). The untreated check also had a significantly higher percent rot at harvest level compared to the fungicide application schedules. There were no significant differences in percent rot at harvest between the fungicide treatments.

1998-2000 Data
The data from three years of research at two trial sites (Winkler and Portage la Prairie) (six station years) were combined and a unit cost per hundred weight (cwt) was calculated for two differently priced, commonly used fungicides. The results for those three years of data is as follows:

• All of the fungicide programs provided better control of late blight compared to the untreated check. All of the treatments had a significantly higher main grade yield and had significantly lower unit costs/cwt compared to the untreated check (table 1).
• The 7-day fungicide application schedule and the Ulrich Schroeder model provided the best control of late blight.
• In terms of risk factor, although the 7 day schedule requires more fungicide applications, it offers increased assurance of late blight control for a similar cost to those schedules with fewer applications.

2000 Data
Disease assessments were conducted on a weekly basis starting in mid July. No late blight occurred at the Winkler site. All fungicide application schedules reduced the incidences of early blight when compared to the untreated check. There was no difference in early blight levels between the application schedules (treatment #’s 1-4).

All fungicide application schedules produced a higher total and main grade yield compared to the untreated check. There was no difference in the main grade and total yields between the application schedules (treatment #’s 1-4).

There were no significant differences in percent rot at harvest between the untreated check and the fungicide application schedules.

1998-2000 Data
The data from three years of research at two trial sites (Winkler and Portage la Prairie) (six station years) were combined and a unit cost per hundred weight (cwt) was calculated for two differently priced, commonly used fungicides. The results for those three years of data is as follows:

• All of the fungicide programs provided better control of late blight compared to the untreated check. All of the treatments had a significantly higher main grade yield and had significantly lower unit costs/cwt compared to the untreated check (Table 1).
• The 7-day fungicide application schedule and the Ulrich Schroeder model provided the best control of late blight.
• In terms of risk factor, although the 7 day schedule requires more fungicide applications, it offers increased assurance of late blight control for a similar cost to those schedules with fewer applications.

Conclusions

Overall, caution should be used in planting potatoes into sites one year after application of Muster, Pursuit and Accord especially on soils with low organic matter and high sand content or at sites where the preceding growing season received below average rainfall amounts.

The presence of significant detrimental affects on potato production one year after the application of certain herbicides, especially on sandier soils, may restrict the amount of land area available for rent by potato producers, restrict the use of certain herbicides in weed management strategies, and influence crop rotations.

In 2000, two years after herbicide application, only Muster at the 1X and 2X rates was observed to influence potato grade by increasing the percentage of rough tubers. All of the other herbicides tested in this study had no adverse affect on potato yield or grade. The absence of significant detrimental affects on potato production two years after herbicide application despite significant adverse affects one year after application greatly shortens the re-cropping interval for potatoes. This in turn increases the land available for potato production and allows producers greatly flexibility in planning crop rotations and weed maintenance.

No conclusions yet.

No conclusions yet.

In the potato industry, fungicide applications are time consuming and expensive, but as the results of the past three trial years have shown, are extremely beneficial to the producer in terms of decreasing early and late blight infections and increasing marketable yields.

This research provides the potato grower with a tool to select fungicide application schedules that provide the best results in terms of reducing the unit cost/cwt as well as maintaining/increasing overall yields and quality.

Collecting multiple years of data greatly increases the ability of researchers to provide results with a greater statistical certainty. In terms of this trial, 3 years of data provides information not only on which fungicide programs provide the best control of early and late blight but has also provided enough information for assessments on unit costs to be made. This may be of the greatest importance to potato producers.

In the potato industry, fungicide applications are time consuming and expensive, but as the results of the past three trial years have shown, are extremely beneficial to the producer in terms of decreasing early and late blight infections and increasing marketable yields.

This research provides the potato grower with a tool to select fungicide application schedules that provide the best results in terms of reducing the unit cost/cwt as well as maintaining/increasing overall yields and quality.

Collecting multiple years of data greatly increases the ability of researchers to provide results with a greater statistical certainty. In terms of this trial, 3 years of data provides information not only on which fungicide programs provide the best control of early and late blight but has also provided enough information for assessments on unit costs to be made. This may be of the greatest importance to potato producers.