Of the Caufe and Cure of the Difeafe in the Potatoe Plant called the Curl. From Tranfactions of the Society of Arts, c. vol. viii.

THE

HE curl in potatoes, is a difcafe which admits of three different stages or degrees. ift. The half-curl. 2d. The curl.

3d. The corrupted. ift. The half-curled plants have leaves fomewhat long, and curled only in a moderate degree: they produce a tolerable crop, if the fummer be not very dry; but if otherwife, the potatoes will be fmall and watery.

2d. The completely-curled plants are feldom more than fix or feven inches high: they foon ripen and die. The potatoes are generally fmaller than a nutmeg, of a rufty red colour, and unwholesome as food.

3d. The corrupted potatoes, or those in which the vegetative power is nearly deftroyed, never appear above ground. The feed may be found, at Michaelmas, as fresh, to appear ance, as when it was fet, with a few fmall potatoes close to it.

The first cause of the curl in potatoes must be traced to the manner in which the feed was railed the preceding year.

If the potatoes be fet late in the

feafon, that is, from the middle of May to the middle of June, in a rich foil, well manured, having a fouthern afpect; and if the summer fhould be hot and dry till (we will fuppofe) the beginning of Auguft, when the blow of the plants has fallen off, then the feed will be exhaufted in feeding the plant only; and very few potatoes will appear. Should the weather now become moift and genial, the plants, efpecially if they fhould be earthed, will blow afresh, and a plentiful crop of very large potatoes may yet be produced.

Thefe potatoes are perfectly fit for ufe as food; but as they were produced from the ftalk of the plant, after the feed itself was exhaufted, they will be defective in moisture and vegetative power: and the plants which proceed from them the following year, will be found to be curled.

Second caufe. The curl may be produced without manure or earthing, provided the potatoes be fown (at the end of May) thick together, in a rich foil, and covered with green fern, or other litter, before the plants appear. The rain rots the fern or litter, and enables it to penetrate as a manure to the roots; and the plants are forced, as in the preceding experiment, to a fecond growth and blow. The feed

G 2

thus

thus raised produced plants that were curled.

The forcing potatoes by cultivation, as above defcribed, I find to be the cause of the curl, both from my own experiments, repeated for feveral years fucceffively, and also from the obfervations I have made upon the practice and ill fuccefs of my neighbours.

It is well known that the flowers of many plants, fuch as the poppy, the rofe, and many others, are much altered by cultivation; they become double, the ftamina are converted into petals, the generic character is loft, they become what botanists call Monsters; the parts of generation being changed, no feed is produced. If I may be allowed to confider any part of a plant in which the vegetative power refides as a feed, it will be found that rich cultivation produces, if not abfolutely the fame, at least a fimilar imperfection in the potatoe; for the flower and the bulbous root are both enlarged by cultivation. In the flower, little or no feed is produced: in the potatoe, the vegetative power is impaired or deftroyed, according to the degree of the disease.

It is obfervable that, wherever the vegetative power is impaired, there is always a deficiency of moisture; which is proved by the following experiment, from which it appears, that both healthy and curled plants may be raised from the fame potatoe.

Dig up, in the beginning of October, fome potatoes raifed as is defcribed in the preceding pages. Amongst the largest will be found fome that have, in different parts, different degrees of moisture, the leaft at the butt, and the most at the crown end, the quantity of

years.

The best time of fetting, is from the beginning of April to the middle of May. Make ridges a yard afunder: put your manure first into the trench, and with moderation: fet the potatoes in a triangular form, five or fix inches afunder; cover them with the foil to the thickness of five or fix inches. There is but little danger of laying on too much of the foil: the deeper are the fets, the better will they be protected from the fcorching heat of the fun, if the feafon fhould be dry. This distance of five or fix inches is fo fmall as to prevent the plants growing too rank, and yet fufficient for each of them to be exposed to the fun and the air.

zdly. When they have grown to the height of fix or seven inches above the ground, you must not earth them, as is the ufual practice. You must take away the weeds, and may draw a little mould to them; but you must be careful to do it before the bloffom-buds appear,

which time is generally about the end of June.

They will now require no further care, excepting that of weeding.

I am of opinion that early fetting is advantageous, on account of the greater chance of early rain, which will be very beneficial to the plants if the fummer fhould be dry. By this process, the plants will be healthy; the young potatoes will be formed in due feafon; they will grow gradually; the plant will ripen and die in due time, and will not be forced into a fecond growth by the rain which may fall in September. The fap being thus left in the potatoe, it becomes a feed endued with an unimpaired perfect vegetative power; and the plants which are raised from them will be found to be entirely free from the curl.

N. B. The potatoes may be dug as foon as they can be handled without crufhing the peel, that is, about the end of September.

Sound potatoes are procured with the greateft certainty from earth that has been peeled and burnt: the foil thus prepared is well fuited to the growth of potatoes. In this they grow gradually, and are not forced beyond their natural fize: in doubtful feed, it is fafeft to plant the Smalleft potatoes whole.

The foil the most likely to produce the curl, is that which is rich in itself, much manured, and has a fouthern afpect. In other fituations, where the foil is not rich, and the garden is cold, either from its being upon the fide of a hill, or expofed to the north, the curl has not yet appeared; which is known to be the cafe in the mountainous parts of Radnorfhire and Montgomeryshire. This is perfectly confonant with my theory; for where the foil is poor,

and the fituation cold, the plants cannot be forced into a fecond growth by earthing and manure.

I do not mean to diffuade thofe who are anxious to raise large crops for immediate ufe, from earthing and manuring to the utmoft extent; I only caution them against using potatoes fo raised, for feed. By earthing and manuring, you will doubtlefs raife large crops of large potatoes perfectly good, as food, but imperfect as feed; for the vegetative power will be impaired by this forcing cultivation. Hence it will be the intereft of every prudent cultivator, to allot a portion of his potatoe-garden to the raifing of feedpotatoes. If the directions which I have given be followed, I have not the leaft doubt of fuccefs; at least I am certain that the curl will not make its appearance.

The potatoe is also liable to other diforders: in very dry seasons, excrefcences will arife, vulgarly called the fcab; in moift feafons, little holes or cavities appear, called the canker; and both thefe diforders increafe according to the length of time they remain in the earth, after having acquired maturity. It is more than probable, that these disorders may haften the decay, and cause the curl.

One method of preventing the difeaie, namely, by changing the feed, has been already mentioned: another fource of prevention offers, from raifing new kinds from the feed or apple of the plant, or the fame kinds renewed again from the feed. Raifing new kinds from feed, however, requires no fmall portion of difcernment; for the feed from the fame plant will produce fo many varieties, that it requires nice judgment of the cultivator properly

to felect. Great numbers, from infpection only, will be weeded out and rejected; and of thofe retained, more will be again rejected, the fucceeding and following years of the remaining few, there may different characters ftill exift; fuch as ill or well flavoured, clofe or coarse grained, productive, non-productive, &c. &c. Each may have their refpective value: but I think it may be generally afferted, that the finer kinds fooner degenerate; the coarfe kinds, which are almoft, if not always, more productive, retain their vigour the longeft. The following example confirms this opinion.

Spring, 1785.-I procured a new kind of potatoe, called a DABB, lately raised from feed; where, I know not: the character of which was, large, coarse-grained, ftrongflavoured, and of courfe rejected from the table; but being very productive, was useful for cattle. The laft year, it was fo much improved, as to be no longer rejected; it ftill retains the quality of being productive, even so much as yielding, this present year, fix bufhels from every ftatute perch. It should be obferved, that the prefent very luxuriant crop may be in great measure owing to having been planted on a virgin foil, which was never before improved, or broken up; very little dung was ufed. Here is an evident change for the better; the plants are vigorous, and there is at prefent no appearance of decay this new foil may be a means of preferving the plant a few years longer; but a total change of feed will, in time, become abfolutely neceffary.

Hence it fhould appear, that although the disease, after the present ftock has been, to a certain degree,

infected, can never be cured, yet means may be taken for prevention: and that this is the cafe in this diftrict, is evident; few crops, of late years, having failed, by being much infected with this diforder: for, wherever the curl has appeared, in ever fo fmall a degree, that ftock has been rejected by the attentive cultivator, and new feed obtained.

I am the more encouraged to offer you these hints, for that, after having drawn them up, in the manner here fent, I read them over to a very intelligent farmer in this neighbourhood, who faid that these thoughts totally correfponded with 1 have fhewn them alfo

his own.

to a refpectable clergyman, who, to his other many excellent qualities, is always ready to communicate information, and has favoured me with the following extract from a private letter.

"A labouring man in my neighbourhood has got a very good potatoe: the only fault is, that out of four plants, three of them are abominably curled; on which account, I defired he would give me four potatoes. From each potatoe I took a boot, not a fet, in order to fee if the fhoots 'would be curled; they were not: fo, poffibly, their not being curled may be accidental, or poffibly the curl may arife from the fet planted. Another year, I will plant a dozen, or more, of thefe potatoe fhoots: then, if there should be no curl, I fhall be clearly of opinion, that the curl arifes from fome difeafe in the fet. What I mean by a fhoot, is-I put three or four fets into a flower-pot; when they have fhot to be about two inches high, and have fibres, I take the fets up, and, with a knife, cut

the

rifing of earth-worms, which, in a moist feason, will frequently deftroy

the

young crop.

If the feed is good, the plants often rife too thick; if fo, when they have attained fix leaves, they fhould be taken carefully up (where too clofe) leaving the ftanding crop eight or ten inches apart: thofe taken up may be planted at the fame diftance, in a fresh fpot of ground, in order to furnish other plantations. When the plants in general are grown to the fize that cabbage-plants are ufually fet out for a standing crop, they are best planted where they are to remain, in beds four feet wide, one row along the middle of the bed, leaving two yards diftance betwixt the plants, allowing an alley between the beds about a foot wide, for conveniency of weeding the plants.

In the autumn, when the decayed leaves are removed, if the fhoveling of the alleys are thrown over the crowns of the plants, it will be found of fervice.

Cultivation of Turkey Rhubarb by off-fets.

On taking up fome plants the laft fpring, I flipped off feveral offfets from the heads of large plants: these I fet with a dibble, about a foot apart, in order, if I found them thrive, to remove them into other beds. On examining them in the autumn, I was furprifed to fee the progrefs they had made, and pleased to be able to furnish my beds with forty plants in the most thriving state.

Though this was my first experiment of its kind, I do not mean to arrogate the difcovery to myself, G 4 having