RED SPIDER AND POWDERY MILDEW 293 



age. Thus, if the label reads "Active ingredient — Copper — 12.5%'", the quan- 

 tity of that material to use should be 2.5/12. .5 or 2 pounds in 50 gallons of 

 water. 



Combination Treatments 



The effective control of different pests on cucumber vines may involve the 

 use of several insecticides and fungicides. Alone, these materials can be 

 used with safety but in combination or when following one anotiier at short 

 intervals, some of these same treatments may cause severe injury to the vines. 



Under certain conditions, previously discussed, it is advisable to combat 

 cucumber powdery mildew with copper sprays. These sprays leave a copper 

 residue on the leaves which causes severe burning of cucuml)er foliage when 

 reacted upon by hydrocyanic acid gas generated from sodium or calcium 

 cyanide. Fumigation with this gas for the control of plant lice, thrips, or 

 white fly, therefore, should always be made before spraying with copper 

 fungicides; otherwise these pests should be combated with nicotine fumes or 

 sprays. 



The highly refined white mineral oil emulsion which effectively controls the 

 red spider is not so toxic to plant lice and thrips as is desirable. However, 

 concentrated nicotine solutions, the standard insecticides used for the control 

 of these pests, can be safely mixed with it. When lice or thrips are present 

 with red spider, tlie addition of one pint of 40 per cent nicotine sulfate or 

 40 per cent free nicotine liquid in 100 gallons of diluted highly refined white 

 mineral oil emulsion, or 1^ teaspoonful in a gallon, will control all of these 

 pests. In fact, this combination spray is one of the best insecticides known 

 for use on greenhouse cucumber vines. 



If, in addition, mildew is present, Bordeaux mixture or other copper sprays 

 may be safely mixed with the oil-nicotine spray or with the oil spraj'. The 

 addition of Bordeaux mixture to the oil spray greatly improves its wetting 

 and spreading qualities. This is an advantage for controlling both red spider 

 and powdery mildew. A convenient method for mixing this combination 

 spray is to add one-half gallon of the lubricating oil emulsion to the fully 

 diluted copper spray and agitate until the oil is tiioroughly dispersed. The 

 nicotine may be added at any time. 



When both powdery mildew and red spider are present, the use of highly 

 refined white mineral oil emulsion and a potassium sulfide spray or high grade 

 sulfur dust, as is recommended for tlie control of these pests specifically, 

 may cause severe injury to cucumber foliage, especially in warm weather. 

 The oil spray makes the foliage more susceptible to sulfur injury and pro- 

 hibits the use of dusts containing a large amount of free sulfur or sulfur 

 sprays. Experiments with dusts of low free sulfur content have shown that 

 they may be used safely either before or after the oil spray, and, although 

 only mildly fungicidal to mildew, if the sulfur content is 10 per cent or less, 

 they will control tiie fungus during briglit warm weather. In milder weather 

 sulfur dusts containing 15 and 20 per cent free sulfur have given good con- 

 trol. In cool, damp weather when sulfur dust is less effective, and if the use 

 of the oil emulsion is necessary, mildew outbreaks should be suppressed with 

 copper sprays. 



Among commercial dusts, Slug Shot, having a free sulfur content of 6 per 



