ONIONS IN THE CONNECTICUT VALLEY 29 



Spray Schedule for Thrips Control 



At the height of the growing season, the rate of reproduction of thrips is high 

 so that reinfestation of the onion plants is very rapid. Consequently a follow-up 

 spray is practically essential. This should be applied as close as possible to the 

 time when all the eggs have hatched and before the first larvae to appear have 

 reached maturity and left the plants for the nymph stage. Life history studies 

 have shown that in the Connecticut Valley region the duration of the egg stage 

 averaged 5 to 6 days, while the larvae required about 7 days for full development. 

 It would appear, therefore, that the second spray should follow 5 to 6 days after 

 the first. In view of the residual effect of many of the above sprays the period 

 between applications, therefore, could be safely extended to 7 or 8 days. 



If the attack is very severe, reinfestation either by young newly-hatched larvae 

 or by thrips migrating from neighboring fields (particularly sets) may make one 

 or more later sprays necessary. After the first week of August, the plants have 

 usually reached a size and stage of development where they can successfully 

 withstand an ordinary attack, as do set onions earlier in the season, so that further 

 spraying is unnecessary. 



SUMMARY 



Experiments were conducted on alluvial soil typical of most of the soils on 

 which onions are grown in the Connecticut Valley. In the experiments with 

 fertilizers, five crops were grown from seed and three from sets. The principal 

 results and conclusions were: 



1. Starting with a soil having an initial pH value of 5.3, marked increases in 

 yields of onions were obtained by liming. Two tons of ground limestone, given in 

 two applications of 1 ton each, caused an average increase in three years of 35 

 per cent. In the year immediately following the application of the second ton, 

 increases in yield varied from 70 to over 100 per cent. On this soil 3 tons of ground 

 limestone gave almost as large yields as higher quantities in initial application. 

 Onions grew well in a slightly acid soil, and the optimum reaction appears to be 

 between pH 6.0 and 6.5. A desirable practice seems to be to bring the soil to the 

 optimum range of reaction by one or two applications of lime, and then maintain 

 it there by frequent small applications, say 1 or lJ/£ tons every 2 or 3 years. 



2. In a test of several grades of fertilizer in which the ratio of nitrogen, phos- 

 phorus, and potassium varied, greatest response was obtained from an increase 

 of phosphorus, but significant increases were obtained only when potassium was 

 increased also. No significant increases were obtained by raising the percentage 

 of nitrogen from 4 to 6 when all was applied before seeding; but when the extra 

 nitrogen was applied later in the growing season as a side dressing, increases 

 resulted with onions grown from seed, but not with those grown from sets. In 

 this experiment onions did best with a 4-12-8 mixture applied at the rate of 2500 

 pounds per acre. For the Connecticut Valley a mixture of approximately this 

 ratio is recommended, although a little higher percentage of nitrogen may be 

 better for the average Valley soil. 



3. It was found that a 4-12-8 mixture carrying one-half its nitrogen in organic 

 form gave better results with onions grown from seed than did another of the 



