58 MASS. EXPERIMENT STATION BULLETIN 427 



of power spraying equipment. Frequent and thorough coverage of the plants 

 with a dense driving mist of spray is needed to control the disease. Hand spray- 

 ers are both impractical and inefficient. Dusting has never given satisfactory 

 results. The disease is not a problem if the grower will dispense with field culture, 

 at least for his susceptible class of stock. If the grower must field the plants even 

 for the months of May and June only, frequent protection with fungicides would 

 be desirable, particularly in areas along the sea coast or where field culture is 

 prolonged into July. 



On the basis of studies at Waltham, growers have been encouraged to use 

 homemade Bordeaux mixture 4-4-50 plus a suitable spreader, such as fish oil, 

 linseed oil, or Penetrol, which have been used at the rate of 1 pint to 100 gallons 

 of spray. Where serious outbreaks of the disease have occurred, the addition of 

 1 pound of calcium arsenate to 50 gallons of Bordeaux spray has been recom- 

 mended to strengthen the fungicide. Without the spreader the control of the 

 disease can be unsatisfactory. It is emphasized that good results may be ex- 

 pected only from thorough plant coverage and frequent application. 



The applications should begin shortly after the plants are established in the 

 field and continue at 7-10 day intervals until the plants are housed. Spraying 

 the plants in the flats just before fielding is practical and can be very desirable. 

 If rainfall is not too frequent the interval between treatments may be extended 

 to two weeks. One or two additional applications may be desirable after the 

 plants are established in the benches. This schedule of treatments has given 

 increases in, yields of cut flowers in both blight and non-blight years, and no 

 injurious effect upon the plants has been apparent. 



SANITATION BETWEEN PLANTINGS IN THE GREENHOUSE 



The sanitary disposal of the carnation stock and litter at the end of the pro- 

 ducing season is an important pest control measure. Diseased plants dispersed 

 among the litter are loaded with the inoculum of various pathogenes and at the 

 end of the year the stock usually harbors thrips, red spider mite, and other 

 miscellaneous pests. 



In the removal of the old plants a considerable population of insect pests and 

 fungous spores is left behind or redistributed in the houses making it possible 

 for infestations to become established in the new planting. Too frequently the 

 carnation rubbish is deposited outside the greenhouse and left there after the 

 houses are replanted, thus providing a source from which the pests are redis- 

 tributed throughout the newly planted stock. 



The plants and the adhering pests can be destroyed reasonably well just before 

 the cleaning-out operations are started by fumigating with strong concentrations 

 of sulfur dioxide generated from burning sulfur; naphthalene base vapors; hydro- 

 cyanic acid gas; or chlorpicrin. Both sulfur dioxide and chlorpicrin are complete 

 pesticides. Naphthalene and hydrocyanic acid gas are more specifically insecti- 

 cidal and not fungicidal. The use of these fumigants is recommended only for 

 individual isolated houses. The seepage of the fumigant into adjoining or at- 

 tached houses containing plants can cause damage in spite of all reasonable pre- 

 cautions taken to avoid it. Growers who may be interested in disinfecting the 

 old stock with chemical fumigants between plantings should first consider all 

 of the particulars and hazards involved in their use. After a fumigation of twenty- 

 four hours or longer and the complete destruction of the growth, the houses 

 should be aired well and the litter removed and burned. Such disinfestation of 

 the greenhouse would help greatly in preventing sudden infestations of pests in 

 the newly planted stock. 



