33 



Methods of Control. 

 The widely differing life histories and habits of the various insects 

 found in greenhouses prevent the use of any single method for their 

 control. The treatment in each case must depend upon the kind of 

 insect to be treated, and in many cases as well upon the kind of plant 

 it is on. For some plants the cultural methods necessary to obtain 

 the best results are those most favorable to the increase of their insect 

 pests, while with others a treatment strong enough to destroy all the 

 pests would certainly destroy or at least seriously injure the plants. 



Preventive Measures. 



It is almost needless to state that an empty greenhouse should have 

 no pests present, and this will be the case if the house has been thor- 

 oughly cleared out and then fumigated, directions for which are given 

 below. 



The first step in starting a new crop in a house is to be certain that 

 no pests are brought in with the soil. This can be made sure of by 

 sterilizing the earth thoroughly. Probably cutworms are the insects 

 most likely to be brought in with the earth, and they have located 

 in this while it was outside. Therefore, early in the season select the 

 soil to be used, and throw it into piles. If no grass or other vegetation 

 is allowed to grow on such piles, no cutworm eggs will be laid there, 

 and any cutworms present will go elsewhere in order to get food. In 

 this way where sterilization is impossible at least a considerable degree 

 of protection against the introduction of pests with the soil can be 

 secured. 



If the new plants are to be started in pots, these should be fumigated 

 with the house while it is empty. If the plants themselves are grown 

 from seed, they should be free from pests. The real danger under 

 these conditions would be either that the fumigation of the empty 

 house was not sufficiently thorough, or that pests might be brought 

 in on cuttings or in some such way, and spread to the originally clean 

 plants. 



All cuttings or potted plants brought into a clean house should be 

 themselves fumigated, or at least dipped into a solution of one pound 

 of laundry soap in a gallon of water for a few moments. The pots 

 should also be thoroughly washed with the soap, as many pests feeding 

 on the plants are often found on the pots as well. Where scales are 

 present on the plants this treatment is not usually a success, and their 

 fumigation must be resorted to. 



Treatment for Houses already infested. 

 Syringing with water is of some value for this purpose, if the pressure 

 of the water is sufficient to knock the insects off the plants. Many 

 of the insects crawl back afterwards, however ; many are not removed ; 

 and many others are not even reached at all by this method, which 

 must be repeated at least once or twice a week. Frequently the 

 amount of water it is necessary to use for effective results in this way 

 is injurious to the plants, the liability of the carnation to develop rust 

 when too much water is used being an example. For these reasons, 

 therefore, the use of water as an insecticide in greenhouses is not 

 particularly desirable where better methods can be employed, unless 

 the plants concerned can stand considerable water, as much more of 

 this is necessary than would be the case in ordinary watering. 



