Late blight forecasters from the cropsim package

LB_forecasters.R

# cropsim
# https://r-forge.r-project.org/scm/?group_id=335
#
# Potato late blight forecast models
# Model name: Hyre
# Hyre, R. A. 1954. Progress in forecasting late blight of potato and tomato. Plant Disease Reporter. 38: 245-253.

# R implementation by Robert Hijmans, r.hijmans@gmail.com
# October 2009

# Days are considered blight favorable when the 5-day average temperature
# is below 25.5 C and the total rainfall for the last 10 days is 3 cm or greater.
# Days with minimum temperatures below 7.2 C are considered unfavorable.

# Source: http://www.ipm.ucdavis.edu/DISEASE/DATABASE/potatolateblight.html#hyre

.subsetwth <- function(wth,
                       emergence = "2000-05-15",
                       duration = 120) {
  emergence <- as.Date(emergence)
  wth@w <- subset(wth@w, wth@w$date >= emergence)
  if (dim(wth@w)[1] < duration) {
    stop("Incomplete weather data")
  }
  wth@w <- wth@w[1:duration, ]
  wth
}


.cumulate <- function(x) {
  xx <- vector(length = length(x))
  xx[1] <- x[1]
  for (i in 2:length(x)) {
    xx[i] <- xx[i - 1] + x[i]
  }
  xx
}


Hyre <- function(wth,
                 emergence = "2000-05-15",
                 duration = 120) {
  w <- .subsetwth(wth, emergence, duration)@w
  t5 <- raster::movingFun(w$tavg,
                          n = 5,
                          type = "to",
                          na.rm = TRUE) / 5
  p10 <- raster::movingFun(w$prec,
                           n = 10,
                           type = "to",
                           na.rm = TRUE)
  blightFavorable <- t5 < 25.5 & w$tavg > 7.2 & p10 > 30
  cbind(as.data.frame(w$date), blightFavorable)
}


Wallin <- function(wth,
                   emergence = "2000-05-15",
                   duration = 120) {
  wth <- .subsetwth(wth, emergence, duration)
  leafwet <- leafWet(wth)
  w <- wth@w
  t1 <- w$tavg > 7.2 & w$tavg <= 11.6
  t2 <- w$tavg > 11.6 & w$tavg <= 15.0
  t3 <- w$tavg > 15.0 & w$tavg <= 26.6
  lw16 <-
    severity <- vector(length = duration)
  severity[leafwet < 16 & t1]  <- 0
  severity[leafwet < 13 & t2]  <- 0
  severity[leafwet < 10 & t3]  <- 0
  severity[leafwet < 19 & t1]  <- 1
  severity[leafwet < 16 & t2]  <- 1
  severity[leafwet < 13 & t3]  <- 1
  severity[leafwet < 22 & t1]  <- 2
  severity[leafwet < 19 & t2]  <- 2
  severity[leafwet < 16 & t3]  <- 2
  severity[leafwet <= 24 & t1] <- 3
  severity[leafwet < 22 & t2]  <- 3
  severity[leafwet < 19 & t3]  <- 3
  severity[leafwet >= 22 & t2] <- 4
  severity[leafwet >= 19 & t3] <- 4
  cumSeverity <- .cumulate(severity)
  x <- which(cumSeverity > 19) + 10
  x <- subset(x, x <= duration)
  action <- vector(length = length(severity))
  action[] <- FALSE
  action[x] <- TRUE
  cbind(as.data.frame(w$date), severity, cumSeverity, action)
}


blitecast <- function(wth,
                      emergence = "2000-05-15",
                      duration = 120) {
  wth <- .subsetwth(wth, emergence, duration)
  hyre <- Hyre(wth, emergence, duration)
  wallin <- Wallin(wth, emergence, duration)
  first <- hyre$blightFavorable | wallin$action
  spray <- first
  spray[] <- FALSE
  if (sum(first) > 0) {
    first <- min(which(first))
  } else {
    return(cbind(as.data.frame(wth@w$date), spray))
  }

  rainfav7 <-
    raster::movingFun(wth@w$prec > 3,
                      n = 7,
                      type = "to",
                      na.rm = TRUE)
  severity7 <-
    raster::movingFun(wallin$severity,
                      n = 7,
                      type = "to",
                      na.rm = TRUE)

  second <- first
  second[] <- -1

  second[rainfav7 < 5 & severity7 == 4] <- 0
  second[rainfav7 < 5 & (severity7 == 5 | severity7 == 6)] <- 1
  second[rainfav7 < 5 & severity7 > 5] <- 2
  second[rainfav7 > 4 & severity7 == 3] <- 0
  second[rainfav7 > 4 & severity7 == 4] <- 1
  second[rainfav7 > 4 & severity7 > 4] <- 2

  spray[first] <- TRUE
  sprayed <- 0
  for (i in first:length(second)) {
    if ((second[i] == 1 &
         sprayed == 7) |  (second[i] == 2 & sprayed == 5)) 	{
      spray[i] <- TRUE
      sprayed <- 0
    }
    sprayed <- sprayed + 1
  }
  return(cbind(as.data.frame(wth@w$date), spray))
}