New Perspectives on the Epidemiology of Citrus Stubborn Disease in California Orchards

Fig. 2. Field sampling techniques used to estimate citrus stubborn disease in two commercial sweet orange orchards in Kern Co., CA. (A) Stat sampling: Every fifth tree in every fifth row was sampled; each black square represents one sampled tree. (B) Hierarchical sampling (HS), each group of 4 black squares represents 4 trees pooled as a single sample. Reprinted with permission from A. F. S. Mello, et al. (10).



Image from Plant Health Progress article:
New Perspectives on the Epidemiology of Citrus Stubborn Disease in California Orchards