20 BULLETI]Sr 807, IT. S. DEPARTMENT OF AGEICULTURE. 



It would seem, therefore, from consulting the tables giving the per- 

 centages of infestation for seed planted in different months, from 

 the insect's life history, and from the rate of growth and pod setting 

 by the plant, that whenever possible it will be advisable to delay the 

 planting until from the latter part of February or the first of March 

 to May. A glance at Tables XIV and XVII will show that plantings 

 prior to Februar^^ and March show much higher percentages of 

 infestation than those planted subsequently. 



This contention is further borne out in the experience of the 

 Oceano-Morro district in San Luis Obispo County. It was the cus- 

 tom there to begin planting about November, continuing all winter 

 and spring. For several years the horse beans had been seriously in- 

 fested with the bean aphis {Aphis ruirdcis L.) which also did severe 

 damage to the later planted crops of small wliite and pink beans. 

 Assuming that the early planted horse beans acted as a winter host 

 for the bean aphis, propagating it in great numbers before the more 

 extensive plantings of other beans were made, the horticultural com- 

 missioner persuaded all horse-bean growers to delay planting in the 

 1917-18 season until March 1. This agreement was adhered to with 

 a few minor exceptions, and the result is shown in Table III. The 

 maximum and average percentages of infestation for the Oceano- 

 Morro district for 1916 are 50 and 14.5 per cent and for 1917, 63 and 

 14.5 per cent. In both-these years a good share of the crop was from 

 seed planted early, that is, from November to March, but in 1918, 

 when practically no seed was planted until after March 1, the maxi- 

 mum and average per cent of weevil infestations are 17.2 and 2.92, 

 a reduction of over 75 per cent. The majority of the plantings were 

 not infested at all, particularly those which had been planted in 

 April and May. 



The planting season begins soon after the first rains, or ordinarily 

 in October and November, in some sections, while in others it is de- 

 layed until spring. The former are the drier inland sections where 

 the crop must be matured before the warm dry weather of the early 

 summer, and the latter are the low, cooler, coastal valleys where the 

 sunamer heat is not high enough to affect the crop. 



The earlier plantings, especiallj^ in the dryer sections, usually pro- 

 duce larger crops than late plantings. This is i^articularly true 

 where the beans are raised without irrigation. The climate and soil 

 conditions, therefore, as well as the availability of irrigation water, 

 must be taken into consideration in arranging for a delayed planting 

 program. Where late planting can not be practiced because of these 

 conditions, it is especially important that all seed either be unin- 

 fested or treated to kill the weevil before planting; but where con- 

 ditions are favorable, planting should be delayed as late as is com- 

 mensurate with getting a good crop. 



