TABLE XVI. SPRAYING TESTS FOR POTATO LEAFHOPPER CONTROL.

12-gallon capacity hand spray pump was used and all plants were thoroly covered with these preparations. The tests were planned not only to determine which of the three insecticides was the most effective against the leafhopper, but also to ascertain the number of applications needed for control. Check plots were left for comparison. Frequent examinations were made to determine the comparative percentages of burning in the different plots as well as the number of nymphs present. Yields were taken later, but were not conclusive owing to the small size of the plots. During this year the leafhopper was not nearly so severe a pest as in 1919. The results are summarized in table XVI. It is seen that of the three insecticides used the bordeaux-nicotine sulfate combination was by far the best. Three applications of either the kerosene emulsion or the nicotine sulfate-whale-oil soap combination gave at best only temporary relief. In contrast two sprayings with bordeauxnicotine sulfate solution gave sufficient protection.

In Mitchell county, which is the center of the potato trucking district of Iowa, two fields were sprayed twice with 4-4-50-9 bordeaux-nicotine sulfate mixture, using a traction sprayer

capable of covering four rows at a time. Comparative nymph counts, hopperburn percentages and yields all demonstrated the effectiveness of this spray on a field basis.

SPRAYING TESTS FOR 1921

3

In 1921 further spraying experiments for the control of this potato pest were carried out at Ames, and at St. Ansgar, Iowa. At Ames small plots were used while at St. Ansgar the control measures were tried out on a 20-acre field basis. Green Mountain, Irish Cobbler and Early Ohio varieties were used in the tests. Bordeaux mixture (4-4-50) both with and without the addition of nicotine sulfate1, whale-oil soap-nicotine sulfate combination (1-2-6)2 and kerosene emulsion (1-15) were the insecticides tried out. The sprays were applied June 17, 28 and July 7 and 19. Yields were taken but were not considered conclusive. However, the comparative effectiveness of the different compounds was determined by leafhopper counts in the different plots as well as by comparative hopperburn percentages (table XVII, figs. 18 and 19). The various factors entering into the consideration of results are rather complicated owing to different varieties used, and therefore each type of treatment is discussed separately.

Bordeaux 4-4-50. Green Mountain was the variety used in this experiment and the bordeaux spray was applied once, twice and three times respectively to the different plots. The percentage of hopperburn on the sprayed plants was lower at all times than on those in the check rows, and each additional application decreased the relative amount of this. August 29 the check plot showed 50 percent injury in contrast to that one receiving three applications which was only 12 percent injured by this disease. There was no question that the three applications of bordeaux alone gave sufficient protection to this variety.

Bordeaux-nicotine sulfate 4-4-50-8. Irish Cobbler was used in this test. Rows of this variety received one, two, three or four applications of the bordeaux-nicotine sulfate spray respectively. Altho no counts were made on the check plants, these showed much more burning than those which had been sprayed and succumbed to the disease much sooner. Cobbler was more susceptible to hopperburn than Green Mountain, but in spite of this, three applications of the bordeaux-nicotine sulfate spray gave good protection. It is doubtful if the nicotine increased the effectiveness of this spray in this experiment.

Fig. 18. Diagram showing daily hatching record from plant syrayed with 4-4-50 bordeaux in comparison with count taken from unsprayed plant, Ames, Iowa, 1921.

Proprietary dry bordeaux powder1. One plot of Irish Cobbler, of a different strain than the above, was sprayed three times with a proprietary compound of bordeaux mixture. This gave sufficient protection at first while the applications were being regularly made. Later, the plants developed serious burning and went down sooner than those treated with the home-made mixture. The chief difficulty with the brand tried was its failure to stick to the foliage during a heavy rain. However, the plants stood up longer than the checks showing good control.

Whale-oil soap-nicotine sulfate solution. This mixture was tried out again on both the Irish Cobbler and Early Ohio potatoes. On the former variety one or two applications were made, on the latter four. The Ohio was the more susceptible of the two varieties, but even four ap plications failed to give relief as the table shows. Control was also ineffective on the Cobblers.

Kerosene Emulsion

Bordeaux

nicotine Sulfate

Bordeaux

Fig. 19. Diagram showing average daily hatching record of Empoasca mali from one unsprayed potato plant at Ames, Iowa, 1921, in comparison with similar counts made from plants sprayed with bordeaux, soap-nicotine sulfate, or kerosene emulsion preparations.

1Recommended to be mixed with water.

Kerosene emulsion. This mixture was tried out on Early Ohio pota

toes. An eight percent solution caused serious burning and did not give any control.

At St. Ansgar, Iowa, a 20-acre field of potatoes was selected for treatment. The varieties grown in this were Green Mountain and Rural New Yorker. The plants were sprayed three times with a traction sprayer June 27, July 12 and 25 respectively, both 4-4-50 self-prepared bordeaux and a proprietary preparation of this compound being used. Both of these spray materials gave increased yields there being little difference between the two in the amount of protection afforded. There was no rain for a ten weeks' period during the critical part of the experiment and as a result the proprietary brand adhered to the foliage as well as the self-prepared.

Average yield of field sprayed 3 times..
Average yield of unsprayed checks.
Average yield of Rurals sprayed..
Average yield of Rurals unsprayed.

Average yield of Green Mountain sprayed.
Average yield of Green Mountain unsprayed.

SPRAYING TESTS FOR 1922

.110.8 bu.

49.5 bu.

.122 bu.

35 bu.

89.5 bu.

56.9 bu.

The 1922 spray plots were arranged crosswise of the rows, and were larger than those used in previous years. Five varieties of potatoes were used in these experiments and three applications were made (table XVIII). Three brands of proprietary bordeaux powders were mixed with water at recommended strengths and tried out in comparison with the self-prepared 4-4-50 formula. of this mixture. In the first preparation of the home-made bordeaux, the lime used was of an inferior grade and this possibly decreased yields in plots treated with this insecticide. Check rows were located at various intervals across the field, and this fact, together with the care in application and the arrangement of the plots, reduced experimental error to a minimum. Comparative yields showed that one proprietary brand of bordeaux gave a 48.5 percent increase over the check; next

TABLE XVIII. SPRAYING TESTS FOR POTATO LEAFHOPPER CONTROL, AMES, IOWA, 1922