Pest monitoring:
A survey of growers, in all Victorian production areas, demonstrated that more than 92% of growers used pest monitoring to inform their spraying decisions and 57% used consultants for advice on pest management based on their monitoring results.
More than 84% were prepared to balance pest control with the value of maintaining predator populations by selecting pesticides on the basis of compatibility with predators.
Prior to 1990, spraying for mites was based either on direct counts of the number of mites/leaf, or the percentage of leaves infested by mites (with an adjustment for the percentage of leaves with predatory mites present).
More accurate and reliable threshold
Agriculture Victoria research conducted in the Goulburn Valley developed a more accurate and reliable threshold, based on the cumulative number of leaf-infested days (that is, the number of days leaves were infested multiplied by the average percentage of leaves infested).
The research compared the cumulative leaf-infested days (CLIDs) with yield losses in the current and subsequent growing seasons and concluded that for WBC pears the threshold value, above which some yield losses would occur, was 1500 CLIDs. For Packhams the threshold was around 2000 CLIDs, and most apples had thresholds greater than 2500 CLIDs.
This allowed for quicker, more cost-effective monitoring of mite populations by using simple presence/absence assessments of leaves, and the graphical output allowed growers and consultants to use the trend line to predict when the mite population would exceed the threshold well in advance of the event.
To calculate the leaf-infested days between two sample dates (D1 and D2) the formula is:
(number of days between D1 and D2) times (% leaves infested on D1 plus % leaves infested on D2)/2
A worked example is given in Table 1 for weekly samples.
To get good mite control: (cont next issue)
See this article in Tree Fruit April 2019
