Tomato potato psyllid and degree days for the New Zealand potato growing regions
TPP and degree days 2016/17 season
The graphs above show the accumulated degree days (DD) for Pukekohe, Hawke's Bay, Matamata, Manawatu, Mid-Canterbury and South Canterbury from 1 July 2016. The graph for each region also contains accumulated degree days for a hot and cold year in that region, to allow you to make comparisons with the current season. The number of TPP generations for the current season so far is indicated on the graph with a yellow arrow. These graphs will be updated weekly until early May 2017. Previous seasons' graphs can be found at the bottom of this page.
Things to consider:
- Psyllids are active throughout the year and therefore 1 July is an arbitrary starting point.
- It is important to be aware of other plants near your crop that can sustain TPP and act as a source of infestation. These include nightshade weeds, African boxthorn, poroporo but also volunteer potatoes.
- Since the psyllid research is a work in progress, we strongly advise you to use the degree day graphs in conjunction with crop monitoring using sticky traps and plant sampling. Crop monitoring provides valuable information on TPP arrival, population build up and the life stages present in your crop (see the links below for a sticky trap monitoring brochure).
What do you need to know about insects and degree days?
Insect growth and development
Since insects are cold-blooded, temperature plays a major role in their growth and development. Insects require a certain amount of heat to develop from one stage in their life to another i.e. eggs – nymphs – adults. Insects have a lower development threshold below which insect development is negligible and an upper development threshold which is the maximum temperature before development stops. These thresholds can be used in predicting insect development.
What are degree days and what are they used for?
A degree day is a measure of the amount of heat that accumulates between a lower and upper development threshold during a 24-hr period. One degree day accumulates for each degree the average temperature remains between the lower and upper development threshold over those 24hrs, and several degree-days can accumulate during a 24-hr period.
The lower development threshold for TPP is estimated at 7.1oC and the upper development threshold at 33.6oC. These two values are used to calculate the number of degree days for a specific day. One degree-day accumulates for each degree the temperature remains above 7.1oC for 24 hours. It takes TPP 358 degree days to develop from an egg to an adult i.e. to complete 1 generation (Tran, L.T., et al., Estimating development rate and thermal requirements of Bactericera cockerelli (Hemiptera: Triozidae) reared on potato and tomato by using linear and nonlinear models. Environmental Entomology, 2012. 41(5): p. 1190-1198).
Degree days are a measure of insect growth and development in response to "heat" accumulated during each growing season and are commonly used to measure and predict insect development. Accumulated degree days are an important decision support tool in Integrated Pest Management (IPM) programmes. Weather varies hugely between years and locations, which can make it difficult to time spray applications accurately. For example, insect development can be two to three weeks faster in a year with warm spring weather than in a year with cold spring weather. Similarly, insect development may be several weeks faster in Pukekohe than Chertsey. Growers can use degree days to improve the timing of their insecticide applications rather than relying on calendar dates.
Degree days are most useful early in the season, as insecticide applications, rain and irrigation may alter psyllid populations. Additionally as the season progresses you will have all TPP life stages in your crop. Once eggs are found in your crop, 358 degree days later those eggs will potentially be adults. With the development of more targeted insecticides, timing and insecticide selection is very important. For example, as soon as TPP nymphs are found in your crop it is essential to use an insecticide which is active against nymphs. You need be aware of which life stages the insecticide you are using is targeting.
Degree days information
Sticky trap monitoring brochure
TPP and degree days 2015/16 season
TPP and degree days 2014/15 season