A M E R I C A N P O T A T O J O U R N A L ~ 7

Even in such cases the grower must be prepared to resume sp ray ing at the first suggestion of late bl ight weather condi- tions. I t is doubtful , therefore, whether the saving of one or more addit ional spray applicat ions is just if iable under even the most favorable conditions.

Weed Control and the Potato Virus Problem

~V D VALLEAI" ',Hd E M. JOHNSON, Univerql ty of Kentu( 'ky. Lex]lLgton

In raising certified seed potatoes the most impor tan t con- s iderat ion in Kentucky, and perhaps likewise in the more nor the rn potato sections, is obtaining a stock of seed potatoes relat ively free f rom virus or degenerat ion diseases. The grow- er is not so much concerned with dis t inguishing the types of virus disease as he is with methods of the i r el imination. The s t anda rd method of e l iminat ing virus diseases is tha t of pull- ing out, as soon as recognized, all diseased p lan ts and removing them f rom the field. This method, while proving highly suc- cessful f rom a commercial s tandpoint , has not been as success- ful as might be expected f rom the s tandpoin t of complete e l iminat ion of the disease.

I t appears probable, under Kentucky conditions, tha t a fea- ture of importance in lowering the effectiveness of roguing may be the presence of certain weeds commonly present in potato fields, which may act as reservoirs of infect ion f rom year to year.

While the evidence for infection of potatoes f rom weeds is not conclusive, it appears to be sufficient to raise the question as to whether the potato grower would care to take the risk of leaving the weeds in the vicinity of his high-grade potato stock when a l i t t le ext ra work will e l iminate them and the con- sequent danger to potatoes.

In working with the virus diseases of tobacco, the wri ters have found tha t cer ta in of them are a lways more abundan t in or near fields where potatoes have previously been grown for several years. In one field, for example, where Cobblers have been grown f rom t ime to t ime for the past 14 years and ca re fu l ly rogued dur ing tha t time, five virus diseases developed in abundance in tobacco, of which three, a t least, go readi ly to potatoes and may be t r ans fe r red f rom them again to tobac- co. A field on the Exper imen t Stat ion f a r m at Lexington has been under observation fo r several years, in which at least nine virus diseases, other t han the t rue tobacco mosaic, develop each yea r in tobacco. A port ion of this field was planted to a po-

258 A M E R I C A N P O T A T O J O U R N A L

t a to var ie ty tes t for at least two years, about 20 years ago. The p a s t u r e connect ing the two pa r t s of the field has been in blue- g rass cont inuously since tha t t ime and is near ly a ma t of horse- ne t t les (Solanum carolinense) and contains numerous ground- cherr ies (Physalis sp.). Many individuals of both species are infec ted wi th a virus. The supposi t ion is tha t the weeds be- came infected f rom the po ta toes at tha t t ime and, as they are perennials , have carr ied the diseases since tha t time. That the vi rus diseases of tobacco, g rown in the vicinity of this field, or iginate la rge ly f rom the weeds has been c lear ly demons t ra t - ed, both by t rans fe r r ing the viruses f rom the weeds to tobacco and back to weeds again and also by el iminat ing the weeds in and abou t one tobacco field, the reby near ly comple te ly control- l ing these virus diseases, and al lowing them to remain in and abou t ano ther tobacco plot with the resul t that , by the middle of summer , the tobacco in the la te r was fu l l y 85 per cent in- fected.

The f ac t tha t several of these virus diseases may be t rans- f e r red to virus free seedling pota toes and then r e t r ans fe r r ed to hea l thy tobacco and t~hat the viruses may likewise be obtained f rom n a t u r a l l y infected weeds or t r ans fe r red to hea l thy weeds, where symptoms are produced, seems to be sufficient evidence to w a r r a n t the recommendat ion tha t as much a t tent ion be given to the elimination of these two genera of perennial weeds as is usua l ly given to the el imination of po ta to p lan t s known to be infected with one or ano the r of the virus diseases.

The problem of el imination of these weeds is not so simple as would at first appear . They sometimes root as deeply as 30 inches, and in some cases when cut off 16 inches below the sur- face have been found capable of pushing up th rough this a m o u n t of packed soil. In sod, however, they a p p e a r to send roots tocks for a considerable distance paral le l to the sur face and not to root so deeply. In cul t ivated fields, where clean cul- tu re is used continuously, the roots tocks are p lowed up and cut into small pieces in work ing the sod, and each of these is then capable of growing and making a vigorous plant . The method which we have employed in cul t ivated fields, in r idding them of the weeds, is to dig each individual p lan t wi th a spade, p r e f e r a b l y a ' t i l i n g spade, pu t it into a sack hung over the shoulder and, when the sack is full , ca r ry it to the road where it is emptied. Here, in the sun, the roots r ap id ly die. As the chief method of propagat ion , in cul t ivated fields, seems to be by these cut t ings of roots tocks r a the r than by seed, the method, a l though tedious the first t ime over the field, becomes simple f rom tha t t ime on. Removal in pas tures is not so simple, bu t the weeds have been m a r k e d l y reduced by pul l ing the p lan ts up, thus breaking the individuals off at the underg round root- stock. In this way they become weakened and have less chance

A M E R I C A N P O T A T O J O U R N A L 259

of survival in compet i t ion with grass than when le f t un- molested.

In Kentucky, where only second-crop po ta toes are used fo r seed, if the weeds are removed f rom cul t iva ted fields by hand, they may very p robab ly be handled in nea rby pas tu res by al- lowing them to g row to the flowering stage, when they may be moved close to the g round j u s t before second-crop seed pota- toes are planted. Then, pul l ing by hand in pas tu re land in the vicinity of pota to fields or one or two more mowings dur ing the fal l should be effective in el iminating them as sources of in- fect ion to nearby potatoes .

While "it has not been c lear ly demons t ra ted tha t the weeds" do act as a source of the virus diseases of potatoes , the evidence seems sufficiently conclusive to w a r r a n t thei r complete destruc- tion on f a rms where certified seed po ta to stock is being grown yea r a f t e r year.

The New Jersey Potato Industry

~V. C. LYNN, New Jersey Depar tment of Agriculture, Trenton

I f product ion figures alone were taken into consideration, the f ac t t ha t New Je r sey annua l ly accounts fo r two per cent of the nat ional product ion of pota toes wou ld indicate tha t this s ta te is re lat ively un impor t an t in this line of agr icul ture . Actua l ly , however, a l imited seasonal product ion creates an impor tance wor thy of consideration. New J e r s e y pota toes are avai lable in a f ew marke t s for ten or eleven months in the year, bu t app rox ima te ly 80 per cent of the annual crop is class- ed as "second ear ly ," and for the most pa r t is marke ted be- tween the last few days of J u l y and the middle of September . Dur ing the pas t five years one-fourth of the count ry ' s Augus t sh ipments have or iginated in this state.

The commercial p roduc ing area of the s ta te is in two dis- tr icts. The more impor t an t of these, known as "Central Jer - sey," is comprised of Mercer, Middlesex and Monmouth counties, and extends east f rom Trenton to within a few miles of the coast. The o ther district, known as "Sou th Je rsey ," in- c luding Cumber land and Salem counties, is about th i r ty miles south of Phi ladelphia j u s t east of the De laware River. There are two other counties ly ing between these two distr icts which are p roducers of a second ear ly crop, bu t which t ruck to nea rby markets , pr incipal ly Phi ladelphia , and do not ship in carlots .