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XII. Relation of Yield and Tuber Composition to Plant and Soil Analyses

XII. Relation of Yield and Tuber Composition to Plant and Soil Analyses

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POTATO PRODUCTION



375



in the plants on plots without added phosphorus, soluble phosphorus was

less than 70 ppm. Soluble potassium was never less than 10,000 ppm.

The starch content decreased from 17 per cent in tubers produced without nitrogen to less than 13 per cent in tubers grown on plots receiving

210 lbs. nitrogen per acre. Throughout the season nitrogen was lower

in all parts of the plants grown on the plots lacking nitrogen than in

plants on plots receiving nitrogen, Phosphorus was low both in plants

grown without nitrogen fertilizer and in those without phosphorus. OmiPsion of nitrogen from the fertilizer greatly reduced the absorption of phosphorus and the amount in all parts of the plant analyzed. Potassium

was high in all samples and was unaffected by any of the fertilizer treatments. Calcium was highest in plants grown without nitrogen and lowest

in plants grown without phosphorus. Lorenz (1947) showed later that

the largest amount of growth and the greatest intensity of nutrient absorption occurred between about 75 and 110 days after planting or between 45 and 80 days after emergence. A yield of 658 bushels per acre

absorbed 139 Ibs. of nitrogen, 36 of phosphoric acid and 253 of potash.

The tubers alone removed 106 IbR. of nitrogen, 31 of phosphoric acid and

196 of potash.

Hawkins (1942) reporting from Maine, states that potato plants

capable of producing upwards of 400 bushels per acre, absorb about 120

to 160 lbs. of nitrogen, 25 to 30 lbs. of phosphoric acid, 200 to 250 lbs.

of potash, 60 llp. of calcium oxide, 30 Ibs. of magnesium oxide and about

10 to 12 Ibs. of sulfur per acre. The Green Mountain variety absorbed

about 70 per cent of its total consumption of plant nutrients between

50 and 80 days after planting. The earlier varieties, Cobbler and Chippewa, usually emerge and make more rapid growth early in tqheseason

than do the later-maturing varieties, and the period of more rapid absorption of nutrients occurred with these two varieties about one week

earlier than for the Green Mountain variety. The magnesium content

of the tops and roots of the Cobbler variety was considerably less than

that of the other varieties, but there was comparatively little difference

between varieties in the magnesium content of the tubers. During the

first 50 days after planting, the Green Mountain variety absorbed 9 per

cent of the total major nutrient elements while making 3 per cent of the

growth for the season. The later varieties, Green Mountain and Smooth

Rural, each absorbed about 100 lbs. more total major nutrient elements

during the season than did the earlier varibties, Cobbler and Chippewa.

The later varieties absorbed considerably more nitrogen, potassium and

calcium, and, as compared with the Cobbler variety, particularly more

magnesium. The Cobbler variety absorbed 22 per cent of its nitrogen requirements by the 50th day as compared with 8 per cent for the Rural



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variety. By t,he 70th day, Cobblerv had absorbed 86 per cent of the

nitrogen absorbed during the season BS compared to 52 per cent for the

Rural and 56 per cent for the Green Mountain varieties. Hawkins (1946)

later 'reported that the proportion of the nutrients absorbed that were

translocated into the tubers was approximately as follows: 80 per cent

of the Pz05,67 per cent of the N, 60 per cent of the S, 50 per cent of the

KzO,40 per cent of the MgO, and about 5 per cent of the CaO.

Regardless of rate of fertilizer application, 1200 and 2400 lbs. 5-10-10

to the acre, method of placement, source of nitrogen or source of potash,

Smith and Kelly (1946) found no significant difference in phosphorus

content of leaf petioles at any time during the growing season. Petioles

of plants of all treatments contained large quantities of potassium and

evidently sufficient potassium was taken up by all treatments to result

in high yields. Correlation of nitrogen and magnesium content of petioles

with yields of potatoes was highly significant at all treatments. Jones

and Plant (1942) found, however, that deficiency symptoms of potassium and magnesium agreed with chemical analysis of the leaves.

Soil analyses, especially variations of the so-called quick soil tests,

have been made in attempts to establish relationship between such analyses and subsequent potato yields. These have been reasonably successful and show considerable promise 8s a tool for detecting deficiencies of

soil nutrients. Sparks and McLean (1946), working with alkaline soils in

Colorado, found a close correlation between the results obtained by soil

analyses and yields following applications of nitrogen, phosphorus and

potassium. Peech (1945) reported a marked accumulation of readily

soluble phosphorus in all soils studied from the important potato-producing areas along the Atlantic Coast. This accumulation varied in

different soils. I n general, the amount of readily soluble phosphorus

increased with the increasing degree of saturation of the soil with

phosphate. I n the light-textured soils containing large amounts of

readily soluble phosphorus in the surface layer, there has been appreciable

downward movement of phosphorus into the subsoil. Despite the low

cation-exchange capacity and the low p H value, the exchangeable potassium content of many of these soils has been greatly increased by fertilization. This accumulation is relatively small as compared with the

total amount of potassium applied over a period of years. The majority

of the soils had p H values below 5. The amounts of exchangeable

calcium and magnesium were very low. I n some areas the soils were

extremely deficient in magnesium. The organic matter content was low

and was quite variable in many of the soils even within the same series,

I n some of the areas the organic matter content of the soils has been

increased, whereas in other areas it has been decreased by cultivation.



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Hawkins (1945) found that in Maine and North Carolina the increase in

yield of potatoes per pound of PzOa applied was usually lower a t locations where there were high amounts of residual phosphate in the soils.

In Maine no significant increases in yield were obtained from additional

potash above the 100 lb. base rate. Analyses of virgin and cultivated

Northern Wisconsin soils show that when potatoes are grown on these

soils from 10 to 30 years the available phosphorus and soluble manganese

content and acidity are increased, while the available potassium, caIcium

and magnesium contents are seriously depleted (Berger, 1948).

Nelson and Hawkins (1947) made a study to show the relationship

between the amounts of readily soluble phosphorus and exchangeable

potassium in the soil and the response of potatoes to applications of these

nutrients. Results from North Carolina shoved that applied phosphorus

gave significant increases in yield a t all six test locations. Significant

increases were obtained on 8 of the 9 experiments in Maine. The degree

of yield response to applications of P z O ~

was related to the amount of

readily soluble phosphorus in the soil. Yield increases from the first 80

lbs. of P205applied decreased as the amount of readily soluble phosphorus in the soil increased. The phosphorus content of the leaves in

the North Carolina experiments was related to the amount of readily

soluble phosphorus in the soil and to the amount of phosphorus applied.

Phosphorus was particularly important in influencing the number of

tubers per hill on soils low in readily soluble phosphorus. Significant

increases in yield from applied KzO were obtained in all experiments

in North Carolina and in 5 out of 8 experiments in Maine. The weight

of potatoes resulting from the first 60 lbs. of KzO tended to decrease as

the amount of exchangeable KzO in the soil increased. I n the North

Carolina experiments the KzO content of the leaves was related to the

amount of KzO in the soil, and to applied KzO up to 120 lbs. per acre.

The amount of potassium extracted from the rachises of the potato plants

in the Maine experiments was related to the exchangeable K20content

of the soil and to the amount of K20 applied.



XIII. KILLINGPOTATO

VINES

During the past few years potato growers have shown growing interest

in killing potato vines preparatory to harvest.. The use of chemicals as

killing agents has increased steadily each year since the practice was

started on an appreciable scale. This may be attributed in part to the

increasing importance of varieties which remain veget.ative and green

over a longer period of time and to the intensive spraying programs now

practiced by good commercial growers which reduce insect and disease

injury to a relative minimum. It usually is the desire of any grower



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to maintain strong, vigoroue top growth as long as feasible in order

to obtain greater total photosynthesis, translocation and increase in tuber

size. It may be desirable or necessary, however, to destroy the above

ground vegetation for one or more of the following reasons: (1) to avoid

the risk of having potatoes left in the ground after extreme weather

conditions arrive, (2) to avoid oversize tubers, (3) to prevent late virus

spread in fields certified for seed, (4) to prevent second growth of tubers,

(5) to prevent late blight infection of tubers, (6) to enable harvesting in

time to meet a favorable market, (7) to increase the proportion of tubers

within the size limits for good seed, (8) to enable completion of harvest

with the labor and equipment available, and (9) to destroy late weed

growth along with the vines. When it is desirable to begin harvesting before natural death of the yines occurs, some means of destroying top

growth is needed because: (1) commercial digging equipment will not

move heavy vines with green leaves and succulent stems over the conveyor belt in a satisfactory manner, (2) tubers will stick or hang onto

green vines thereby making picking extremely difficult, and (3) tubers

will not mature until after the vines have died and will skin or bruise

easily when in an immature state.

Wilson and Boyd (1947) and Wilson e t al. (1947) found that certain

tar-acid compounds provided the most efficient noncorrosive substitute

for sulfuric acid which is the killing agent of most widely accepted usage

in England. Sodium chlorate gave fair leaf kills, but poor stem kills.

Calcium cyanamid dust provided inefficient kills even when used a t very

heavy rates of application. Dinitrocresol derivatives were only moderately effective while copper sulfate and sodium chloride gave fairly

efficient kills on senescent haulms only. Young haulms kill readily but

become more resistant as the season advances and finally again susceptible during senescence. Varietal differences in susceptibility were attributed largely to differences in stage of maturity. Complete kill was

rarely accomplished in less than 10 days. Comprehensive tests indicated

no differences in flavor, texture, nr internal color of tuber attributable t n

vine killing treatments.

Bates and Martin (1935), MacDowell (1935), Main and Grainger

(1947),Small (1935), and some British workers (Anonymous, 1945), have

reported experimental results which indicate that destruction of vines by

chemical means is very important in the control of tuber infection by late

blight. Chemical destruction is preferable to cutting of the vines (Small,

1936). Bonde (1935) reported satisfactory kills with 6 to 7 per cent sulfuric acid, and later found Sinox with ammonium sulfate to be very effective as a vine killer in the control of late blight infection of tubers (Bonde

and Schultz, 1945). Schultz et al. (1944) found that 2 gallons of Sinox



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plus 10 lbs. of ammonium sulfate per 100 gallons of water a t 135 gallons

per acre could be used as a less tedious substitute for pulling the vines

in early harvested seed plots in Maine. Such early harvesting materially

reduced the spread of virus infection as compared to plants remaining

green to a later date. Findlay and Sykes (1936, 1937) reported no

significant effect of vine killing treatments on yield in 1935, but a

reduction of yield in 1936. Kraus (1944) reported little, if any,

reduction in yield from vine killing in 1943 and 1944, but stated that

this would depend primarily on relative maturity. Samuel (1944) found

that killing of the vines may reduce potato yields and states that even

in September, crops with green tops can put on as much as half a ton

of tubers per acre per week. He considered 10 days or more necessary

between killing date and harvest date for satisfactory setting of the skins.

Idaho Experiment Station workers (Anonymous, 1940) also concluded

after microscopic examination of tubers dug a t frequent intervals that

normal ripening changes occurred after killing of the vines and that

potatoes were sufficiently matured in 10 days to prevent abnormal surface

damage during harvesting.

Steinbauer (1945) reported that sprays were more effective as vine

killers than dusts under Maine conditions. Dilute sulfuric acid was the

most rapid killing agent studied, but Dowspray 66 Improved and Sinox

gave fairly satisfactory rates of kill. Varieties such as the Sebago were

more difficult to kill than others. Plants making rapid growth with

abundant soil moisture and moderately high temperatures were more

readily killed than when they were toughened by low soil moisture or

low temperature. A yellowish discoloration of the xylem vessels was

reported in tubers from Sinox-killed vines. Greenhouse tests indicated

that this did not impair planting behavior. Some tuber growth takes

place after vines are sprayed with a slow acting vine killer and the killing

date may be advanced a few days with such chemicals without large

yield reductions. I n lQter work, Steinbauer (1947) reported that oil

preparations were much more expensive than most other vine killers

with ordinary sprayers and using 125 t o 150 gallons per acre. Products

mch as Stoddard Solvent were fairly satisfactory as defoliants but not

for complete kill of vines. Of the compounds studied those with a high

content of aromatics were most effective. Otis (1946) stated that maturing yellow vines were more easily killed than green vigorously growing

ones. Low humidity or low temperature a t time of application was unfavorable to both dusts and sprays. Varietal differences did not govern

speed and completeness of kill as much as maturity and size of vine

growth. Kunkel e t al. (1948) state that killing the vines prematurely

resulted in lower specific gravity and increased stem end discoloration.



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Hoyman (1947) found in field experiments in North Dakota that

discoloration in and near the vascular tissue of tubers was positively

correlated with rapidity of kill and was less when applications were made

later in the season. Such discoloration may or may not be a direct effect

of vine killing chemicals. Tubers from vines cut a t ground level showed

the same type of discoloration as those from chemically killed vines.

The effectiveness of Dowspray 66 Improved was increased by the use

of aluminum sulfate as an activator, Brentzel (1944)obtained unsatisfactory kills with dusting treatments in North Dakota, but a 95 to 99

per cent kill resulted from 2 gallons of Sinox plus 10 lbs. of ammonium

sulfate in 100 gallons of water applied a t the rate of 173 gallons per acre.

Fernow and Smith (1944) stated that experience of New York growers

indicates that the vines die more rapidly when application is made during

comparatively warm weather or is followed by fairly high temperatures.

Ennis et al. (1946) found that 2,4,5-trichlorophenoxyaceticacid applied to the foliage of potato plants caused pronounced stunting and distortion of vegetative growth and scab-like injury on the tubers. Smith

et al. (1947) found potatoes resistant to spray applications of 10 ppm

of 2,4-D and 10,000ppm naphthaleneacetic acid methyl ester when applied during August. Injury similar to that reported by Ennis et al.

occurred on many tubers from plants which had been sprayed with the

latter material.

Callbeck (1948) found that tubers from untreated cut vines showed

a greater incidence of stem-end discolorat,ion than tubers from untreated

plants or from plants destroyed by slow acting herbicides. Tuber vascular discoloration appears to be correlated with rapidity of kill of the

tops. The amount and intensity of discoloration in tubers from plants

killed a t different stages of development with dinitro ortho secondary

butyl phenol increased quite regularly with the age of the plants; those

killed late in the season exhibited the greatest injury. This is in accordance with the work of McGoldrick and Smith (1948)and of McGoldrick

(1948). Hoyman (1947), in North Dakota, found less discoloration when

the applications were made later in the season. Callbeck (1948)detected

no differences in flavor or texture of the cooked tubers from the several

treatments, McGoldrick and Smith (1948) and McGddrick (1948),

however, found that those killing agents which destroyed top growth

most efficiently and rapidly reduced specific gravity of the tubers compared to poorer kills and controls. Discoloration of the vascular region

of tubers was decidedly increased by killing injury to top growth.

Further results of comprehensive field and greenhouse experiments by

McGoldrick (1948) showed that Penite 6 plus an activating compound

resulted in the most efficient kill of vines. Dowspray 66 Improved,



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Penite 6 without activator, Sinox General plus diesel oil, and sizz flame

treatment also gave satisfactory kills. 2,4-dichlorophenoxyacetic acid

a t the rate of 6% lbs. plus 118 gallons diesel oil to the acre or 125 lbs.

sodium nitrite to the acre resulted in satisfactory kills on relatively

senescent plants at the, last killing date only. Fairly satisfactory vine

destruction, especially of leaves, resulted from spray applications of

Cyanamid x-1 and x-5. The following materials at concentrations named

were worthless as vine killers: 2,4-D, 6% and 25 lbs. to the acre; methyl

ester naphthaleneacetic acid, 21/2 gallons per acre, and a petroleum

product a t 6% gallons to the acre. 2,4,5-trichlorophenoxyaceticacid as

a spray a t the rate of 25 lbs. to the acre caused some leaves to turn yellow

and die alt.hough there was no death of the plants. Increase in tuber size

during late stages of maturity warrants delaying the application of vine

killers as long as possible unless greater size is objectionable. Some discoloration of the vascular region was found in tubers from untreated

plants as well as in those from treated plants. This browning of the

vascular bundles, however, was decidedly increased by killing injury to

top growth. Sprouting and shrinkage loss other than sprouting in subsequent storage was not significantly affected by killing agents. Early kill

resulted in significantly greater loss than later kill. Neither killing agents

nor application dates appeared to have a significant effect on the value

of tubers as a source of seed the following season. More effective kills

were obtained a t 100 per cent relative humidity than a t approximately 75

per cent. Drying and shriveling of killed tissue, however, was faster a t

the lower humidity level. Artificial rainfall applied a t intervals up to 10

hours after killing treatment reduced the effectiveness of Sinox General

and Dowspray 66 Improved.

Recent experience with machines such as the “Roto-Beater,” which

chop the vines to small pieces, indicates that this method of vine destruction will gain wide acceptance by growers.



XIV. RECENT

DEVELOPMENTS

IN INSECT

CONTROL

The potato crop is infest,ed with many insects which result in tremendous losses in yield and quality. Programs for combating them cost

millions of dollars annually. The most important insects are aphids,

leafhoppers, flea beetles, Colorado potato beetles and wireworms. Several

of these insects were not satisfactorily controlled until after the general

adoption of DDT as an insecticide for potatoes. This occurred mainly

in 1945 and 1946. After an amazingly short period of testing, this one

material has largely repIaced the various insecticides formerly recommended for potato insect,s throughout North America. Several other in-



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ORA SMITH



secticides introduced even more recently than DDT are especially lethal

to aphids and appear very promising for their control in potato fields.

I n many areas the potato leafhopper, Ernpoasca fabae Harris, probably is the worst pest of potatoes. Leafhopper injury results in premature death of vines and a resultant decrease in starch content, mealiness and yield. Until the advent of DDT, control of this insect was

erratic and incomplete. Under such conditions it was extremely difficult

to evaluate potato varieties for anything other than leafhopper resistance.

It has been found repeatedly that almost perfect control can be obbained

with DDT without injury to the plants (Granovsky, 1944; Apple and

Arnold, 1945; Wilson and Sleesman, 1945; Heuberger and Stearns, 1946 ;

Wolfenbarger and Heuberger, 1946 ; Wilson and Sleesman, 1947).

Potato varieties vary widely in their susceptibility to hopper-burn

(Sleesman and Bushnell, 1937; Allen and Rieman, 1939; Allen et al.

1940; Sleesman and Stevenson, 1941 ; Sleesman and Bushnell, 1945;

Maughan, 1947) ranging from the very susceptible Bliss Triumph and

Pontiac to resistant Sequoia. There is no agreement, however, as to why

some varieties are more severely injured than others. It has been claimed

that early varieties are more susceptible than later varieties but Allen

et al. (1940) state that relative earliness or lateness is not the prime

factor; early varieties such as Bliss Triumph and Warba were more

attractive to the insects than the later varieties, Katahdin and Houma.

The correlation between earliness and susceptibility may not be a true

relationship as it is difficult to differentiate between natural maturity and

that caused by leafhoppers (Sleesman and Stevenson, 1941). Allen and

Rieman (1939) d a t e that leafhopper tolerance of Katahdin and Houma

might account in part for the heat, and drought resistance attributed to

these varieties. Varietal response to leafhopper control has been measured by adult and nymphal populations, severity of hopperburn and yield

increases with but little emphasis on increase in starch content of the

tubers. Sleesman and Wilson (1943) report a high negative correlation

between nymphal populations and yield, between dead foliage and yield,

and a high positive correlation between nymphs and dead foliage. Apple

and Arnold (1945) found a highly significant correlation coefficient. of

-0.87 between nymphal populations and specific gravity of the tubers.

Linn et al. (1948) measured the effects of leafhopper control with D D T

on length of season, quality and yield of seventeen new and old varieties.

Control of leafhoppers increased the length of season most in the case of

very early varieties. Yields of all varieties were increased except Erie

and Sequoia in one location. Control of leafhoppers also increased the

specific gravity of tubers of most varieties.

Post et al. (1948) obtained significant increases in yields from spray



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