1988)

M E C H A N I C A L VINE KILLING OF POTATOES 1

James L. Halderson, Lloyd C. Haderlie, and Alojzy Skrobacki 2

415

Abstract

Six chemical and mechanical vine killing methods were compared for their effects during tuber maturation and subsequent harvesting of commercially-produced Russet Burbank potatoes. Pulling of vines resulted in tuber specific gravities which were equal to those of other vine killing treatments even though pulling terminated plant growth more abruptly. Dehydration tests show no significant difference among treatments and that the tuber maturation period could be less than the customary 21 days. Overall results suggest that pulling of vines might be done several days later than for other vine killing methods. An experimental vine puller placed pulled vines between adjacent rows to entirely eliminate subsequent harvester pickup. Pulling increased the amount of vine fragments in the harvested tubers compared to chemical vine killing methods. The number of tubers exposed to light was greatest for the vine pulling treatments.

In troduct ion

Potato vine killing, in preparation for harvest, is commonly practiced in some production areas of the United States. Vines are primarily killed in commercial production to aid tuber maturation (6, 9). Mature tubers maintain higher quality during subsequent handling and storage.

Specific gravity is considered to be very important by potato processing firms and some contracts contain an incentive for higher specific gravity. Halderson, etal. (4, 5) in a study during 1981 through 1983, reported that vine pulling by hand tended to produce higher specific gravity than other killing methods for commercially-grown potatoes and that pulled vines might be advantageously placed to avoid being taken into harvesters. Vine pulling has not been a major method for killing potato vines in North America but interest in pulling has increased in the past 10 years due to limitations with other methods, such as the restriction on dinoseb. Bouman and Weerd (2) compared several experimental pullers to burning, steaming

1Approved for publication as paper No. 8731 of the Idaho Agricultural Experiment Station. 2J.L. Halderson, Associate Research Professor of Agricultural Engineering ( 208 - 397-4181 ); L.C. Haderlie, Associate Research Professor of Weed Science, Research and Extension Center, University of Idaho, Aberdeen, ID 83210; and A. Skrobacki, visiting Professor from Agricultural University, Warsaw, Poland. Accepted for publication April 27, 1988 ADDITIONAL KEY WORDS: Vine pulling, desiccation, specific gravity, dehydration, tuber maturation.

416 AMERICAN POTATO JOURNAL (Vol. 65

and chemical vine killing on different cultivars in Europe. They determined that pulling permitted a longer growing period compared with chemical desiccation and therefore resulted in somewhat greater yields and less rhizoctonia on the tubers. Subsequently, these same investigators developed an improved model of a flat-belt puller, but it was sensitive to field conditions such as hilling uniformity (1, 3). This machine was compared in New Brunswick by Misner and Everett (8) with hand pulling, a chemical desiccant (diquat), and flailing on several cultivars of seed potatoes. Mechanical pulling achieved about 89 to 99% leaf desiccation and 79 to 98% stem desiccation, but some stems subsequently rerooted. Hunter (7) reported similar results in Maine.

Stem-end discoloration of tubers, thought to be primarily due to rapid desiccation of the vines, was not directly caused by the speed of vine kill (5). Additionally, yield increased approximately 450 to 550 kg ha -1 day -i at vine killing time (4). These studies were conducted on commercially-grown potatoes in southeastern Idaho where vines are normally killed about September 1. Vine pulling offers the possibility of killing vines several days later than other common methods. If vine pulling can be done while achieving adequate tuber maturity, yield and specific gravity would be increased. Dinoseb has shown a tendency to consistently depress specific gravity when compared to other commonly used vine killing methods (4).

Vine killing within this study was done solely to initiate tuber maturation for commercially-produced potatoes. The studies of 1981 through 1983 (4, 5) were continued with specific emphasis on tuber changes during maturation. The objectives of this study were 1) to compare vine killing by hand pulling, pulling with machines and killing with sulfuric acid, dinoseb and flails, and 2) to examine the feasibility of vine placement during pulling operations to avoid intake into harvesters.

Materials and Methods

Cut seed of Russet Burbank potatoes was planted in early May each year in rows 91 cm apart with a seed spacing within the row of approximately 28 cm. Cultural practices were as recommended for high yield and quality by the University of Idaho (10). Water was applied by solid-set sprinklers. Vine killing treatments were applied on the same day at approximately the first of September each year but prior to 10% senescence. Vine killing treatments were: 1 ) dinoseb (at 2.5 kg ha -1), 2) sulfuric acid (at 89 kg sulfur ha -1 from a 93% acid solution), 3) an Ace 3 flail, 4) a Nimos 4 puller, 5) an experimental puller (Figure 1), and 6) a control. Vines were left to die

3Mention of commercial names is for information only and does not imply endorsement over other unnamed products. Manufactured by Ace Supply, Inc., Caldwell, Idaho 83605. 4This machine is manufactured by Drost Mahines BV, Prostbus 96, Rhenen, Holland.

1988) HALDERSON, eta]." VINE KILLING 417

naturally in the control. After vine rolling, dinoseb and sulfuric acid were applied at 164 1 ha -1 (except in 1981 when all treatments were applied at 328 1 ha -1) with a 4-row, tractor-mounted boom sprayer with Tee Jet TJ8002 nozzles spaced 46 cm apart and operated at 152 kPa.

A Nimos (flat-belt) puller (Figure 2) was obtained for experiments during the 1984 and 1985 crop year, to more fully investigate the potential of vine pulling in a commercial application. Vine pulling had been done by hand during 1981 through 1983 to simulate the best achievable pulling performance. An experimental one-row puller was constructed for use in 1984 and 1985. It used a flat belt on one side and a rubber-faced wheel on the other to move the vines away from the row (11). This configuration was developed to place the pulled vines in the wheel-track in an attempt to avoid pickup by harvesters. The machine was hydraulically powered to permit variation in belt speed relative to ground speed.

A randomized block design was used for specific gravity and tuber dehydration tests. Earlier study (4) had established the relationship between specific gravity and yield. The plots in the current study were four rows in width by 18.2 m in length and replicated four times. The two center rows of each plot were harvested. Tuber samples were hand-dug three times each

FIG. 2. Nimos two-row puller with flat belts. The PTO driven gear box has several gear ratios for varying belt speed.

418 AMERICAN POTATO JOURNAL (Vol. 65

FIG. 1. Experimental pulling machine with hydraulic drive for control of pulling speed.

week for three weeks following the treatment date and specific gravity measurements were made by the water immersion technique. Tuber dehydration tests were done by periodically reweighing bagged samples of 3 to 4 kg which were maintained at 10 C and 60% R H for three weeks.

A two-row commercial harvester equipped with a deviner chain was used for harvesting the vine separation plots. Plots were replicated four times for this completely randomized experiment, were four rows wide by 91 m long and included all vine killing treatments except dinoseb. All vines and vine pieces, which arrived at the picking table on the harvester, were collected, bagged and dried at 103 C before weighing. This procedure was designed to permit comparison of the harvester's vine separation effectiveness for the various vine killing treatments.

Results and Discuss ion

A. Specific Gravity There were no significant differences in specific gravity among the six

vine killing treatments during 1984-85 (Table 1). Vines had apparently

1988) HALDERSON, et al." VINE KILLING 419

reached full ma tu r i ty by the t ime of v ine killing. L o n g - t e r m tests, however, show tha t specific gravi ty is general ly highest for the control , somet imes significantly so (Table 2). Changes in specific gravi ty corre la ted closely wi th changes in t ube r yield for the t ube r ma tu ra t ion period. Specific gravity increased two points (0.002) every three days and total yield increased 450 kg ha -1 day -1 for the control . T h e earlier s tudy no ted that yield f rom the control was 14% greater than f rom the pul led t reatments . Th i s informat ion indicates tha t substantial benefits could be ob ta ined if vine kil l ing could be delayed if only for two or three days. De layed harvest is not feasible due to the increased risk of f reezing wea ther du r ing the last par t of harvest.

Pu l l ing of vines d id not reduce specific gravi ty values as m u c h as ant ic ipated w h e n c o m p a r i n g yields f rom the six t reatments . I n fact, specific

TABLE 1. - - Specific gravity o f Russet Burbank tubers at several times following vine killing in 1 q84 and I q85. No significant differences

occurred over time or between treatments at P--O. 05.

Killing days after vine kill treatment 1 11 14 19

Control 1.0812 1.081 1.079 1.078 Dinoseb 1 1.079 1.081 1.079 1.079 Sulfuric acid 1.081 1.082 1.081 1.081 Flail 1.081 1.082 i .082 1.077 Nimos puller 1.081 1.081 1.081 1.078 Exp. puller 1.080 1.082 1.080 1.077

1For 1985 only. 2Replicate means of data combined over years.

TABLE 2. - - Specific gravity o f Russet Burbank tubers after vine killing durfng several years of tn'als in southeastern Idaho.

Killing YearD treatment 1981 1982 1984 1985

Control 1.086 a 1.085 a 1.082 a 1.078 a Dinoseb 1.082 bc 1.082 b # 1.079 a Sulfuric acid 1.081 c 1.082 b 1.076 ab 1.081 a Pulling* 1.084 ab 1.082 b 1.073 b 1.078 a Flail 1.081Tc # 1.073 b 1.077 a

# No reading. T Vines hand cut. *Vines hand pulled in 1981-82 and mechanically pulled in 1984-85. D Specific gravity data flawed in 1983; means within a column followed by the same letter are not significantly different (P=0.05) by Duncan's multiple range test.

420 AMERICAN POTATO JOURNAL (Vol. 65

gravities from the pulled treatments were equal to those of the other treatments (excluding the control). It is anticipated, based on tuber growth cessation, that vine pulling initiates tuber maturation earlier than for other vine killing methods. Other studies (2) support this observation but additional maturation data is needed. Specific gravities of tubers from machine-pulled vines compared favorably with those from hand-pulled vines (Table 2).

B. Dehydration Dehydration tests show that initial high rates of weight loss were

reduced to a plateau level by approximately 10 days after vine killing (Figure 3). These tests were conducted under accelerated conditions in 1984-85 and do not necessarily indicate tuber weight loss during several months of normal storage. There were no apparent differences between vine killing treatments. Dehydration tests indicate that the tuber maturation period could be reduced from 21 days.

C. Intact Stems and Exposed Tubers Of the mechanical vine killing treatments, the flail caused fewer tubers

to be exposed to the greening effects of light (Table 3). More uniform hilling in 1985 reduced tuber exposure in pulling treatments compared to the previous year. The uniformity of hilling and the relative location of vine stems to the crown of the hill greatly improved the performance of both of the mechanical vine killing methods in 1985 versus 1984 (Table 3). Vine breakage increases when the puller grasps the vine farther away from the soil surface. During the study of 1984-85, the Nimos puller was not modified but the experimental puller was extensively changed, particularly with regard to the skid plates which hold tubers in place while the vines are being pulled. It is estimated that the experimental puller has the potential to be further modified to give pulling performance and tuber exposure results equal to those of the Nimos machine.

Regrowth appeared to be a problem during the first few days after vine killing, but the newly emerged leaves soon died. Earlier study indicated no evident effects of regrowth on tuber stem-end discoloration (5). These studies indicate that regrowth does not result in tuber quality degradation for commercially-grown Russet Burbank potatoes in southeastern Idaho. Regrowth was also evident for chemically-killed vines but to a lesser extent than for mechanical killing. Regrowth occurred in most New Brunswick trials with several cultivars but tuber quality apparently was not affected (8).

D. Vines in the Harvester Vines that were killed with sulfuric acid were most readily removed by

the deviner chain because they were intact and moved over the deviner chain in a continuous stream (Table 4). The flail treatment caused the greatest amount of vine pieces to appear at the picking table. A harvester

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TABLE 3. - - Intact stems and exposed tubers from several mecham'cal vine ktTh'ng methods in lO0 m @single row @Russet Burbank potatoes.

Killing Intact stems v Exposed tubers v treatment 1984 1985 1984 1985

% No./100 m of row

Flail 0 a 1 (1)* a 1.6 a 1.0 a Nimos puller 15 a 10 (0.5) a 27.8 b 1.0 a Exp. puller 49 b 29 (2} b 39.0 b 19.0 b

* Percent regrowth at 11 days after vine killing. v Means within a column followed by the same letter are not significantly different (P--0.05) by Duncan's mulitple range test.

TABLE 4. - - Weight @vines and vine pieces on the harvester picking table as a result of vatT"ous vine kil[ing methods

in 1984 and 1985/br Russet Burbank potatoes.

Killing treatment kg/ha

Wet Dry weight weight

Control 39.9 a 21.8 a Nimos puller 56.9 a 29.1 a Exp. puller 56.9 a 31.5 a Flail 365.4 b 215.5 b Sulfuric acid 15.7 a 12.1 a

*Means within a column followed by the same letter are not significantly different (P=0.05) by Duncan's multiple range test.

tha t was e q u i p p e d w i th a b l o w e r w o u l d r e m o v e most of these v ine pieces. I n d i v i d u a l v ines tha t were b r o k e n in t he p u l l i n g t r e a t m e n t s d i d no t feed s m o o t h l y over the d e v i n e r cha in and , consequen t ly , these shor t v ine s tubs t e n d e d to r e m a i n w i t h t he tubers . If t he da t a for t he flail is r e m o v e d in ca l cu l a t i ng new LSR ' s in T a b l e 4, the pu l le r s resu l ted in s ign i f ican t ly m o r e v ines on the ha rves t e r p i c k i n g t ab l e t h a n w h a t o c c u r r e d after sul fur ic ac id t r e a t m e n t . O t h e r chemica l s were no t used in th is pa r t of t he e x p e r i m e n t b u t are e x p e c t e d to pe r fo rm s imi la r ly to sulfur ic ac id in this respect . P l a c e m e n t of the p u l l e d v ines b e t w e e n pairs of ad j acen t rows, by the e x p e r i m e n t a l pul ler , c o m p l e t e l y e l i m i n a t e d ha rves t e r p i c k u p of p u l l e d v ines in these trials. T h i s resul t c o u l d be of c o n s i d e r a b l e i m p o r t a n c e d u r i n g we t w e a t h e r ha rves t ing w h e n v ines b e c o m e ve ry t o u g h and in ter fere w i th harves t ing .

1988) HALDERSON, eta/." VINE KILLING 423

A c k n o w l e d g m e n t s

T h i s w o r k was p a r t i a l l y s u p p o r t e d by a g r a n t f r o m the I d a h o P o t a t o C o m m i s s i o n . A p p r e c i a t i o n is expressed to F r e d B e r m e n s o l o for his h e l p in c o n d u c t i n g t h e e x p e r i m e n t s .

Literature Cited

1. Bouman, A. 1975. Development of a pulling-machine for potato haulms. Eur Assoc Pot Res Cong at Wageningen, Netherlands, p. 212-213.

2. Bouman, A. and B.v.d. Weerd. 1976. Destruction of potato haulms. Publication 48, Institut Voor Mechanisatie, Wageningen, Netherlands.

3. Bouman, A. and J. Bouma. 1978. Potato hanlm pulling. Landbouwmechanisatie 29: 291-293.

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. 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.

6. Halderson, J.L. and L.C. Haderlie. 1986. Mechanical killing of potato vines. 11l." Engi- neering for Potatoes. (B.F. Cargill, Ed.). Amer Soc Agric Engr, St. Joseph, MI 49085.

7. Hunter, J.A. 1957. The design and development of a mechanical vine puller for potatoes. M.S. thesis, Univ of Maine, Orono.

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

9. Murphy, H.J. 1968. Potato vine killing. Am Potato J 45:472-478.

10. Potato Handbook. 1986. Agric Publications Bldg, Univ of Idaho, Moscow 83843. 11. Power Farming. 1982. Pre-harvest haulm puller, Sep, p. 15.