Aug. 21, 1916 



Control of Powdery Dryrot of Potatoes 



823 



was the known fact that seed infected with dryrot had been planted. 

 To determine the effect on the stand of planting seed infected with dry- 

 rot, several plots of potatoes were planted as follows: 



Plot 1. — Each seed piece showed at least one healthy eye, but was 

 almost wholly decayed. The variety planted was Idaho Rural. 



Plot 2. — Each seed piece showed a pocket of dryrot at least half an 

 inch in diameter and about as deep as wide. The variety planted was 

 Idaho Rural. 



Plot 3. — This plot was planted with seed of the same character as that 

 used in plot 1 , except that the variety was Netted Gem. 



Plot 4. — This plot was as nearly as possible a duplicate of plot 2, except 

 that the variety planted was Netted Gem. 



Two check plots were also planted, one of Netted Gem and one of Idaho 

 Rurals. In each of the check plots only seed entirely free from disease 

 was used. The plots were planted on the grounds of the experiment 

 station at Jerome, Idaho. Table I shows the stand which resulted. 



Table I. — Percentage of stand of potatoes in plots infected with powdery dryrot 



In plots 1 and 3, in which the seed planted was nearly totally decayed, 

 the stand never exceeded 82 per cent of the Idaho Rural nor 85 per 

 cent of the Netted Gem. The plants in these two plots were much 

 slower in coming up than those in the check plots or in plots 2 and 4. 

 One month after planting, all the seed in the check plots had produced 

 plants larger and stronger than those in plots 1 and 3, but no difference 

 was observed between the plants in the check plots and those in plots 

 2 and 4. Although the stand in plots 2 and 4 was not quite perfect at 

 the end of the first month, the stragglers soon appeared, and a perfect 

 stand resulted. The results of these experiments specifically agreed with 

 the observations in commercial fields. It is believed that had the wet 

 weather of the early spring continued throughout the month of June, a 

 much smaller percentage of the seed would have produced plants. The 

 plots were carefully watched throughout the growing season; but after 

 the plants had thoroughly established themselves, there was little or no 

 difference between the plants in the diseased plots and those in the 



