298 Diseases of Greenhouse Crops 



Petal Blight 



Caused by ScJeroti/iia fuckeliana (De By.) Fckl. 



Greenhouse growers are often troubled with a 

 petal blotch of orchids. This disfigures the blos- 

 soms, and consequently ruins their market value. 

 The disease appears as small spots over the entire sur- 

 face area of the petals. Frequently the spots are bor- 

 dered by a delicate ring of pink. Perhaps another 

 stage of this disease is marked by the large spots 

 which cause the petals to become disorganized. Af- 

 fected petals either drop off or stick to the now 

 worthless blossom. On examination of the spotted 

 petals, there will be noticed a gray mold growing on 

 the surface of the affected tissue. This is but the 

 fruiting stalks of the causal organism. This gray 

 mold will also be found on faded blossoms, and if 

 allowed to remain in the greenhouse will saturate 

 the place with the spores of the fungus. 



Control. All affected blossoms should be cut off 

 and destroyed. This simple precaution will remove 

 the host upon which the fungus is able to thrive as 

 a saprophyte. 



Rot 



Caused by Nectria huJhicoJa Henn. 



This trouble is manifested as a rot on the pseudo 

 bulbs of Macillaria rufescentis. It was originally 

 found by Hennings"^ on orchids brought in from 

 Venezuela or Trinidad. 



* Hennings, P., Xotizbl. K. Bot. Gasten u. Mus. Berlin. 



