64 MASS. EXPERIMENT STATION BULLETIN 449 



of tobacco mosaic also take their toll. Several strains of Worldbeater have 

 shown themselves to be resistant to this disease but they are variable within these 

 strains as to productiveness. A number of single plant selections appear to have 

 considerable merit. Seed is now being increased so that they may be sent out 

 for trial. 



Toviatoes. — A number of Fi hybrids introduced by seedsmen and experiment 

 station workers indicate that this type variety m^ay have considerable merit. 

 One of the hybrids developed and tested here, Pennheart by Firesteel, performed 

 exceptionally well in the trials last year. Several selections now in the Fe genera- 

 tion from a cross of Bounty by Stokesdale also look very promising. One of the 

 lesser known varieties, Firesteel, and selections from this variety were among the 

 best of the early varieties. These plants were especially prolific and the fruits 

 were large, solid, and smooth. 



Weed Control in Vegetable Crops. (William H. Lachman.) The use of 

 Stoddard Solvent as a weed control agent in fields of carrots and parsnips is now 

 considered standard practice by commercial vegetable growers. There is a 

 tendency to apply this material rather late in development of these crops with 

 the result that a rather severe necrosis develops in the crown of the roots. This 

 is particularly disturbing since these roots do not keep well in storage. 



The results from studies designed to find selective weed killers for set onions 

 have been most promising. Recently some investigators have recommended the 

 use of a .5 percent solution of sodium pentachlorophenate for this purpose. 

 This material was not effective in killing annual grasses, however, and the yields 

 from these plots were the lowest among the treatments. Dinitro compounds 

 such as Sinox and Dow Selective Herbicide were also ineffective in controlling 

 annual grasses but did not damage the onion tops as much as the previous treat- 

 ment. The yields from these plots were also significantly lower than those from 

 the cultivated plots. Plots in which the weeds were controlled with a hand weed 

 turner also yielded less than the checks, although not significantly so. Good 

 weed control but with rather severe damage to onion foliage resulted from several 

 applications of Aero Defoliant Chemical Dust (Cyanamid) at the rate of 60 pounds 

 per acre. The average yields from these plots were also lower than from the 

 checks although the difference was not significant. Some preliminary work 

 with Aero Cyanate Weed Killer (potassium iso cyanate) indicates that this materi- 

 al is well adapted as a weed killer in the culture of onions. It is relatively harm- 

 less to onion foliage in low concentrations (1 to 2%) and is toxic to most small 

 weeds until they have developed to about ^ inch high. Lamb's quarters is 

 especially resistant to this m-aterial after it has passed the cotyledon stage. 



Isopropyl n-phenyl carbamate at the rate of 5 pounds per acre was particularly 

 effective in controlling annual grasses in a late summer planting of spinach and 

 beets. Overwintered spinach on these plots was completely free from chickweed 

 whereas the check plots were badly infested with this weed. In a cooperative 

 experiment with one vegetable grower isopropyl n-phenyl carbamate at the 

 rate of 5 pounds to the acre was very effective in controlling chickweed in a 

 planting of early spring lettuce. 



Pre-emergence application of No. 2 fuel oil prevented the growth of weeds in 

 sweet corn for a period of 5 weeks. 2, 4-D, in pre-emergence applications to 

 fields of sweet corn at rates of 1 J^ to 2 pounds per acre, was particularly effective 

 in preventing growth of weeds except for smartweed which is apparently very 

 resistant to this treatment. Post-emergence applications of 2, 4-D were ineffec- 

 tive in controlling grasses. Pre-emergence applications of Dow Contact Weed 



