Fig 1.
Conceptual model for the assessment of coffee yield losses caused by pests and diseases.
Ycomp: yield components (productive stems and branches, fruiting nodes and fruits); P&D: pests and diseases; DeadB: dead productive branches; RF: reducing factors (P&D, DeadB); Yatt: attainable yield; Yact; actual yield; Yloss: yield loss; n: a given year. Within each year: (1) Yield components can affect pests and diseases, since it is known that high fruit loads can make the plant more susceptible to pathogens. (2) Pests and diseases can cause defoliation and thus contribute to the death of branches. (3) In turn, this will cause the drying and death of the fruits that were growing on them. (4) Pests and diseases can also reduce the photosynthetic capacity of the branch without causing its death but negatively affecting the development of fruits. (5) Yield components also influence the death of branches, because high fruit loads could cause the exhaustion of plant tissues, especially when the plant does not have enough nutrients to sustain growth and production. (6) The actual yield, then, as an output of the system, depends on yield components, pests and diseases, and dead productive branches. (7) The attainable yield would be the output of the system if there were no influences of pests and diseases (P&D = 0) nor dead branches (DeabB = 0), i.e., reducing factors = 0. Yield loss for a specific year (primary yield loss) is the difference between this attainable yield and the actual yield. Across years: (8) Yield components depend on the yield components of the previous year. A year with yield components achieving high values will be followed by a year with low values, and vice versa (biennial behavior of coffee production). (9) Yield components of the current year also depend on the number of dead branches of the previous year, as those branches will no longer be able to bear fruits. (10) Pest and disease abundance of the previous year will influence their abundance in the current year through its effect on primary inoculum. Secondary yield loss is the difference between the attainable yield (i.e., the yield with no yield-reducing factors in the previous and current years) and the actual yield obtained with reducing factors >0 in the previous year and reducing factors = 0 in the current year.
Fig 2.
Scheme of the treatments applied in the coffee experimental parcel T: Treated with pesticides.
Each year T consisted in: Fungicides: three applications of Opera® (13.3% Pyraclostrobin and 5% Epoxiconazole) with doses = 2 ml lt-1; one of Soprano 25SC® (12.5% Carbendazim and 12.5% Epoxiconazole) with doses: 1.25 ml lt-1; Insecticides (only in 2103): three applications of Sumithion 50EC® (50% Fenithrotion) with doses = 4 ml lt-1; one of Solver 48EC® (48% Chlorpyrifos) with doses = 2.5 ml lt-1 N: No pest and disease control
Table 1.
Variables characterized in the coffee experimental parcel, Turrialba, Costa Rica.
Table 2.
Number of plots and plants considered in the analysis, according to different three-year sequences of chemical treatments and quantification of yield losses.
Table 3.
Basic statistics of the variables studied in the coffee experimental parcel, Turrialba, Costa Rica.
Fig 3.
Yields and primary and secondary yield losses resulting from the sequences of chemical treatments TTT, TTN, TNT, TNN.
T: treated with pesticides; N: no control of pests and diseases. Different lowercase letters between bars indicate significant differences (P<0.05) between coffee yields. Red arrows and numbers in percentages represent the yield losses. Yatt: attainable yield; Yloss: coffee yield loss; I: primary losses resulting from the current-year injuries (year n); II: secondary losses resulting from year n-1 injuries; III: primary and secondary losses (total losses) resulting from years n and n-1 injuries.
Fig 4.
Structural equation models for the estimation of actual coffee yield for Piecewise List 1 (A) and Piecewise List 2 (B) presented in Table 4 Yact: actual coffee yield per plant; NFN: number of fruiting nodes per plant; DeadB: number of dead productive branches per plant; sAUDPC P&D: standardized area under the disease progress curve of all pests and diseases together; sAUPC Sev: standardized area under the progress curve of severity; (n): current year (2015); (n-1): previous year (2014). Arrows represent relationships among variables; black arrows denote positive relationships and red arrows denote negative relationships; arrows for no significant paths (P >0.05) have dashed lines; arrows with significant paths (P <0.05) have continuous lines. The numbers near the arrows are the regression coefficients. The thickness of the significant paths was scaled based on the magnitude of the standardized regression coefficients (not shown in the figures).
Table 4.
Models for the estimation of actual coffee yields in 2015 (g of fresh coffee cherries per plant) with data of 2014 and 2015, through Piecewise structural equation modeling
Fig 5.
Evolution of coffee production in Central America as a percentage of the production in the harvest year 2011/2012.
Curves were constructed with data of the International Coffee Organization [33]; the production in 2011/2012 (before coffee crisis) was taken as the reference, corresponding to 100%.