Chemical vine desiccation of two potato cultivars

1991) 479

CHEMICAL VINE DESICCATION OF TWO POTATO CULTIVARS 1

Karen A. Renner 2

Abstract

Russet Burbank and Onaway potato (Solarium tuberosum L.) vines were desiccated with diquat (6,7-dihydrodipyrido (1,2-a:2T-c) pyrazinediium ion), ametryn (N-ethyl-N-methylethyl)-6-(methylthio)-l,3,5-triazine-2,4-diamine), paraquat (1,r-dimethyl-4,4'-bipyridinium ion), and endothall (7-oxabicyclo (2.2.1) heptane-2,3-dicarboxylic acid) applied at various rates alone or combined with surfactants, drift retardant, copper, or ammonium sulfate. Di- quat and paraquat at 0.28 and 0.56 kg ha -1 plus nonionic surfactant thoroughly desiccated Onaway and Russet Burbank potato vines. Only Onaway vines were thoroughly desiccated by ametryn at 1.3 and 2.3 kg ha -1. Endothall at 0.87 kg ha -1 provided thorough desiccation of Russet Burbank vines. The addition of a drift retardant did not reduce the effectiveness of diquat, while combining either ammonium or copper sulfate with diquat slowed the dieback of potato vines in 1987. Combining copper sulfate with diquat also slowed the dieback of Onaway vines in 1988. Both copper and ammonium sulfate, combined with diquat and nonionic surfactant, slowed the dieback of Russet Burbank vines when evaluated two days after application, but seven days later, no difference in vine dieback was evident. Crushing plants by rolling the field prior to desiccant application quick- ened vinekill by 18%. Applications of diquat using flat fan nozzles at 333 kPa provided vinekill equivalent to applications using hollow cone nozzles on a 25 cm spacing at 833 kPa, when spray volume for both applications was 467 L ha -1. Potato yield, percentage of U.S. No. 1 potatoes, and stem- end discoloration were unaffected by chemical desiccation.

Introduction

The desiccation of plants prior to potato harvest improves the potato fresh market appearance, enhances periderm development, and improves storability. Plant desiccation may also retard the spread of viruses in seed potatoes, reduce late blight tuber rot, regulate tuber size, and allow for flex- ibility in harvesting operations (7). Potato vines may be desiccated "natu- rally" by frost, mechanically, or chemically.

1Approved for publication by the Michigan Agr. Exp. Stn. J. Art. No. 13182. 2Assistant Professor, Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824. Accepted for publication December 5, 1990. ADDITIONAL KEY WORDS: Desiccants, drift retardants, regrowth, stem-end discoloration.

480 AMERICAN POTATO JOURNAL (Vol. 68

Seventy percent of Michigan's potato crop is chemically desiccated. 3 The effectiveness of chemical desiccants is dependent on the cultivar (8), maturity of the potato plant at the time of desiccation (2, 3), and the chemical desiccant and rate applied (4, 9). Research by Mutch et al. (8), found that Russet Burbank desiccated the slowest of seven cultivars including Monona, Onaway, Superior, Katahdin, Norchip, and Sebago. Research by Hader- lie et al. (2), found immature potato plants desiccated more slowly than par- tially senesced vines. High soil fertility caused potato plants to grow vigorously and stay lush and green at the time of chemical desiccant application. This resulted in reduced chemical effectiveness (2, 3).

Factors enhancing the degree of potato vine kill include weather at the time of desiccation, roiling the vines prior to desiccation (4), and the addition of surfactants, oils, and other additives to the spray solution (7, 8, 10). Complete stem desiccation is critical, and rolling the plants to ex- pose the stems prior to chemical application increased the effectiveness of desiccants to vine kill Russet Burbank (4). Surfactants increase desiccant activity by increasing leaf penetration, while drift retardants improve spray deposition, decrease spray evaporation, and reduce drift by increasing par- t ide size (10).

Chemical desiccation may alter potato yield or quality. Potato yield can be adversely affected when chemicals are applied too early during potato bulking. Sanderson et al. (9), found that the yield of potatoes increased following diquat applications, whereas other investigators did not (2, 3, 4, 6). Potato yield would not be expected to increase once plant stems and leaves are no longer producing photoassimilates or translocating carbohydrates for potato bulking.

Potato quality may be improved by an increase in periderm forma- tion with the use desiccants. However, dessicant application may be detrimental to the internal quality of the potato by increasing the incidence of stem-end discoloration (SED). Research in the 1940s and 50s concluded that rapid vine kill, with the exception of rotobeating and handpulling, resulted in an increase in stem-end discoloration (1, 5). However, recent research by Halderson et a/. (3), and others (2, 4, 6) concluded that the ra- pidity of vine kill alone did not affect the incidence of SED. Misener and Everett noted increased SED in potatoes from diquat applications in one experiment (6), whereas the results of other investigators found an increase in SED when potato plants had not begun to senesce at the time of desiccant application (3).

Studies were conducted in Michigan in 1987 and 1988 to evaluate the degree of potato vine desiccation over time and the effect of chemical desiccants on potato yield and quality for both Russet Burbank and Onaway

~Personal communication, Dr. Richard Chase, Extension Agronomist, Michigan State University, East Lansing, MI 48824.

1991 ) RENNE R: VINE DESICCATION 481

cultivars. Four chemical vine desiccants were applied at varying rates, alone or with the addition of spray adjuvants and/or drift retardants. In addition, crushing plants by field rolling prior to desiccation and diquat applications at differing spray pressures and volumes through varying nozzle types and spacing were evaluated to determine their effect on vine desiccation.

Materials and Methods

Onaway VinekillStudy-- Onaway potatoes were planted on April 10, 1987, and April 20, 1988, and vinekilled on July 9, 1987, and July 31, 1988. Each plot was 2.6 m (three rows) wide and 12.1 m in length. A randomized complete block design was used with four replications per treatment. Fourteen desiccation treatments were applied with a tractor-mounted compressed air boom sprayer, delivering 272 Lha -1 at 200 kPa using flat fan nozzles. Desiccant applications were made in 1987 at 1 p.m. under partly cloudy skies with air temperature about 28 C and a high relative humidity. In 1988, applications were made at 10 a.m. under partly cloudy skies with air temperature about 26 C and a moderate relative humidity (~50%). Adjuvants and additives applied are listed in Table 1. Adjuvants were added at 0.5% (v/v), and drift retardants were added at 0.125% (v/v).

Visual observations of plant responses were made 2, 7, and 14 days after application of desiccant treatments. Ratings ranged from 0 to 100; 0, green stems and leaves; 80, senesced leaves with green stems remain- ing; and 100, both stems and leaves completely desiccated. Each year the percent moisture of the vines was determined seven days after application by clipping at soil level three vines from the outside rows of each treatment replication and calculating the moisture percentage by drying in an oven at 21 C for six days.

The center row of each potato treatment was harvested fourteen days after chemical application, and potatoes from 6.1 m of row were graded for size distribution and yield. Specific gravities of a random sample of U.S. No. 1 potatoes from each treatment replication were determined by the weight in air weight in water method. The degree ofperiderm maturation was rated by applying a catachol solution on twenty, U.S. No. 1 potatoes from each treatment replication. 4 Potato yields were converted to a per hec- tare basis prior to data analysis. Data were combined over years unless other- wise noted, and significant treatment effects were separated using Fisher's least significant test at the 5 % level of probability.

Russet Burbank vinekill study-- Russet Burbank potatoes were planted on May 10 in 1987 and 1988 and were vinekilled on September 9, 1987, and

4R. W. Chase and G. H. Silva. "Potato Bruising" Michigan State University Coopera- tive Extension Bulletin E-2074.


August 31, 1988. Plot size for each t reatment replication was 3.5 m (four rows) wide and 9.1 m in length. A randomized complete block design was used with four replications per treatment. Seventeen vinekill t reatments were applied each year with spray equipment, pressure, and volume previ- ously described in the Onaway study. In addition, diquat plus nonionic surfactant was applied using six application methods to determine which method maximized vinekill. Each treatment replication in this experiment was 5.2 m (six rows) wide and 9.1 m in length arranged in a randomized complete block design with four replications per treatment. Applications were made with a pull-type sprayer with varying booms equipped with hollow cone or flat fan nozzles at 50 or 25 cm spacings. For one treatment, each replication was rolled with a field roller immediately prior to desiccant application. The roller was a 36 cm well casing with 36 cm non-inflated tires mounted on the casing. One desiccant application was made with an air curtain sprayer, with a spray volume of 47 L ha -1. Desiccant applications were made both years between 4 and 6 p.m. when skies were partly cloudy with moderate relative humidi ty (40-55%), and air temperatures about 28 C in 1987 and 22 C in 1988. Adjuvants and additives are listed in Table 1. Adjuvants were added at 0.5 % (v/v), and drift retardants were added at 0.125% (v/v).

Visual observations of vine desiccation were made and moisture con- tent determined as described in the Onaway study. Potatoes were harvested from the center two rows of the four or six row plots of each treatment replication. Six m of the two center rows of potatoes were graded and specific gravity of U.S. No. 1 potatoes was determined. Stern-end discoloration was

TABLE 1.--SuoCactants, crop oil concentrate, and drift retardant used with the desiccants.

Trade Name Composition Manufacturer (additive class)

Triton Ag-98 nonionic; alkylaryl polyoxyethylene, Rohm and Haas Co., (surfactant) gylcols Springfield, PA

X-77 nonionic; alkylaryl polyoxyethylene, Chevron Chemical Co., (surfactant) glycols, free fatty acids, and isopropanol San Francisco, CA

Herbimax Petroleum hydrocarbons (83%) - light Loveland Industries, (crop oil con- paraffinic distillate, odorless aliphatic Loveland, CO centrate) petroleum solvent, surfactant (17%) -

mono and diesters of omega hydroxypoly oxyethylene

polyvinyl polymer; polyacrylamide (1%) Chemtrol Loveland Industries (drift Loveland, CO retardant)

1991) RENNER: VINE DESICCATION 483

measured in twenty tubers from selected treatments after five months of storage at 5 C.

Results and Discussion

Onaway Vinekill Study--The speed of potato vine desiccation varied by treatment in 1987 and 1988 (Table 2). Two days after treatment (DAT) diquat at 0.28 and 0.56 kg ha -1 plus nonionic surfactant (NIS) and diquat combined with copper sulfate or drift retardant plus NIS provided the quickest plant desiccation in 1987. However in 1988, paraquat at 0.56 kg ha -1 plus NIS provided the quickest plant desiccation. By seven DAT in 1987, plant desiccation by ametryn at 1.3 and 2.3 kg ha -1 and paraquat at 0.56 kg ha -1 plus NIS was equal to that provided by diquat at 0.28 and 0.56 kg ha -1 plus NIS. In 1988, all ametryn treatments had visual dieback equal to the 0.56 kg ha -1 paraquat and diquat treatments plus NIS when evaluated seven DAT.

The addition of ammonium or copper sulfate to the diquat plus NIS application, with or without drift retardant, reduced the visual dieback of the potato vines when evaluated two and seven DAT in 1987. A reduction in the degree of visual plant dieback remained fourteen DAT only where ammonium sulfate and drift retardant were added. In 1988, the addition of copper sulfate without drift retardant reduced the degree of visual plant dieback compared to diquat alone when evaluated seven and fourteen DAT.

By fourteen DAT (at harvest) in 1987, all desiccants caused complete plant dieback except for the treatment control, diquat plus NIS combined with ammonium sulfate and a drift retardant, and the 0.28 kg ha -1 ofpara- quat plus NIS treatment. In 1988, all desiccant treatments provided a high degree of visual plant dieback except where diquat at 0.28 kg ha -1 plus NIS was combined with copper sulfate. Both ammonium and copper sulfate appeared to have the potential to slow or reduce vine desiccation.

No significant differences in total potato yield nor in the percentage of U.S. No. 1 potatoes were found among desiccant treatments. The potato yield in the handclipped treatment was similar to that of the treatment control, suggesting that potato bulking was not affected in the fourteen days following desiccant application. Lower specific gravity was noted for the potatoes in the handclipped treatment when compared to those from the treatment control and treatments of diquat at 0.28 or 0.56 kg ha -a plus NIS, diquat at 0.28 kg ha -~ plus NIS and copper sulfate, ametryn at 1.3 kg ha -1 plus NIS, ametryn at 2.3 kg ha -1, or the paraquat plus NIS applications. Chemicals that desiccate vines rapidly can reduce specific gravity (7). Hal- derson et al. (4), found that potato specific gravity was lowered by 0.002 points by all vinekill treatments compared to the treatment control.

A reduction in periderm maturation was noted on potatoes in the treatment control in 1987. However, there was no difference among treatments


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in 1988. Each year the potatoes were harvested with a windrower and hand picked. Greater loss ofperiderm may have occurred if potatoes were harvested commercially.

Russet Burbank Vine.kill Study-- Chemical desiccant treatments in the Rus- set Burbank study were similar to those applied in the Onaway study with the addition of the desiccant endothaU (Table 3). Potatoes were under drought stress in 1988, and by 14 days after desiccant application, plant dieback in the treatment control had reached 91%. Therefore, desiccant evaluations in 1988 were most informative two and seven DAT.

No difference in the dieback of potato vines treated with 0.28 and 0.56 kg ha -1 of diquat plus NIS was observed. The addition of a drift retardant did not alter plant dieback from 0.28 kg ha -1 of diquat plus NIS. The addition of ammonium sulfate to the diquat plus NIS treatment slowed the degree of visual vine dieback two DAT in 1987 only. By seven DAT however, vine dieback was equal to that of diquat plus NIS. Copper sulfate plus a drift retardant slowed the degree of plant dieback from diquat two DAT. However by seven DAT, vine dieback equalled that ofdiquat plus NIS. In 1988, the addition of ammonium or copper sulfate had no effect on plant dieback when combined with diquat plus NIS.

Potato vines treated with ametryn had the slowest vine dieback of any chemical desiccant treatment. No visual dieback had occurred two DAT in 1987, and dieback in 1988 was only 22 to 29% greater than visual dieback in the treatment control. By seven DAT, potato plants treated with ametryn had 43 to 45% visual dieback in 1987 and 72 to 77% dieback in 1988. This was only 20% greater than the untreated plot in 1987 and equal to that of the treatment control in 1988. There was no difference in the visual vinekill between the 1.3 and 2.3 kg ha -1 application of ametryn, which is similar to the results of the Onaway study. If potato plants had not natu- rally senesced, it is unclear from this research if ametryn would provide effective potato vine desiccation.

The 0.56 kg ha -1 paraquat plus NIS application increased the degree of vine dieback compared to 0.28 kg ha -1 when evaluated two DAT in 1987. No increase in the degree of vine dieback occurred from the 0.56 kg ha -1 paraquat treatment in 1988. By seven DAT in both years, plots treated with paraquat plus NIS had 93 to 97% visual plant dieback, regardless of application rate.

Potato vines treated with endothaU had a slower rate of visual dieback in 1987 compared to 1988. Endothall applications of 1.2 kg ha -1 gave a more rapid vine kill than the 0.87 kg ha -~ application rate in 1987, while no rate response occurred in 1988. By seven DAT in both years, potato vine dieback was 83 % or greater from all endothall applications. Plant dieback did not increase where crop oil concentrate was added or the application rate increased.


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There was no difference in the yield or percentage of U.S. No. 1 potatoes between chemical desiccant treatments and the treatment control and handclipped treatment. Potato specific gravity was lowest in the handclipped treatment and treatments of ametryn at 1.2 kg ha -1 plus NIS, diquat at 0.28 kg ha -1 plus NIS and either a drift retardant or ammonium sulfate, and paraquat at 0.56 kg ha -1 plus NIS.

Stern-end discoloration was evaluated in March of each year after potatoes had been in storage. Stem-end discoloration equalled 20% in potatoes from the treatment control in 1987 and 18% from the handclipped treatment. Potatoes from treatments of 0.28 kg ha -1 of paraquat plus NIS had 40% SED. However, potatoes from treatments with 0.56 kg ha -1 of paraquat plus NIS had only 27% SED. Less than 15% SED occurred in the potatoes in 1988, a year of drought stress, and chemical desiccants did not increase SED.

Desiccant Application Method Study- Potato vines rapidly senesced when the potato plants were rolled prior to a desiccant application made with flat fan nozzles at 333 kPa in 467 L ha -1 of water (Table 4). Application of diquat plus NIS with hollow cone nozzles on a 25 cm spacing produced rapid and thorough vine dieback in both years when observed 2 DAT. How- ever by 7 DAT, no difference was observed between diquat treatments applied through the 25 and 50 cm hollow cone spacings. The air curtain sprayer was improperly adjusted in 1987 resulting in banded and nonuni- form applications in the field. Vine desiccation by the air curtain sprayer was comparable to other treatments in 1988.

No difference occurred in potato yield or in the percentage of U.S. No. 1 potatoes. Potato specific gravity was lowest in the handclipped treatment in 1987 and 1988, concurring with results from the Onaway and other Russet Burbank study. SED was less than 15% in all treatments in 1987 and 1988, and no difference in SED occurred among treatments.

Summary Diquat, or paraquat plus NIS effectively desiccated Onaway and Rus-

set Burbank potato vines in 1987 and 1988. An application of 0.56 kg ha -1 of diquat or paraquat was more consistent over years than when either desiccant was applied at 0.28 kg ha -1. The surfactant rate used of 0.5% (v/v) was higher than the 0.25% and 0.125% (v/v) on the paraquat and diquat labels, respectively. Additional surfactant was not detrimental to vine kill, but it cannot be determined from this research whether it enhanced desiccation of potato vines. Ametryn would also be recommended for desiccation of Onaway plants, but not for Russet Burbank plants. Endothall would be an alternative to a diquat or paraquat application for desiccation of Russet Burbank vines. Lower application rates may slow vine kill but not reduce effectiveness if harvested fourteen days after application. Slight differences

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1991) RENNER- VINE DESICCATION 491

were noted among treatments when visually evaluated each year but vine moisture and potato yield did not differ between years or among treatments. All desiccant applications were made in 272 to 467 Lha -1 of water, which were adequate for vinekill. Desired spray pressures are not provided on any desiccant label, and 333 kPa in this research provided thorough vine desiccation. The addition of drift retardant had no effect on diquat, while the addition of ammonium and copper sulfate slowed the dieback of potato vines in one of two years of research. Chemical desiccation of vines resulted in lower potato specific gravity; however, SED did not increase in chemically desiccated plots.

Acknowledgments

I wish to thank the Michigan Potato Industry Commission for finan- cial support of this research.

I also appreciate the assistance of Gary Powe11, Dr. R. W. Chase, Dr. George Silva, and Richard Kitchen in this research and tuber quality evaluations.

Literature Cited

1. Cunningham, C.E., PJ. Eastman and M. Goven. 1952. Potato vine killing methods as related to rate of kill, vascular discoloration, and virus disease spread. Am Potato J 29:8-16.

2. Haderlie, L.C.,J.L. Halderson, P.W. Leino, P.J. Peterson and R.H. Callihan. 1989. Chemical desiccation of potato vines. Am Potato J 66:53-62.

3. Halderson, J.L., D.L. Corsini and L.C. Haderlie. 1985. Potato vine kill: stem-end discoloration effects on Russet Burbank. Am Potato J 62:273-279.

4. Halderson, J.L., L.C. Haderlie and D.L. Corsini. 1985. Potato vine kill: pulling, chemical killing and rolling effects on yield and quality of Russet Burbank. Am Potato J 62:281-288.

5. Hoyman, W.G. 1947 Observations on the use of potato vine killers in the Red River Valley of North Dakota. Am Potato J 24:110-111.

6. Misener, G.C. and C.E Everett. 1981. Vine pulling as a means of top killing potatoes. Am Potato J 58:103-109.

7. Murphy, H.J. 1968. Potato vine killing. Am PotatoJ 45:472-478. 8. Mutch, D.R., D. Penner, E Roggenbuck and R.W. Chase. 1984. The use of addi-

tives, temperature, and plant position to increase efficacy ofdinoseb for potato (Sola- num tuberosum) vine desiccation. Am Potato J 61:577-586.

9. Sanderson, J.B., J.A. Ivany and R.E White. 1984. Effect of time of desiccation on seed potato yield and size distribution. Am Potato J 61:691-696.

10. Van Valkenberg and J. Wade. 1982. Terminology, classification and chemistry, pp. 1-9 in Adjuvants for Herbicides. Weed Science Society of America, Champaign, IL.

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Chemical vine desiccation of two potato cultivars