Weather requires close monitoring and is a primary driver for crop disease and pest issues. Kansas has a unique tool called the Kansas Mesonet (weather station network) which can provide weather information assisting with agriculture management decisions. Using Mesonet data, we can evaluate the presence and stage of a primary pest of alfalfa -- the alfalfa weevil.
The Kansas Mesonet has launched a new tool just in time for 2017 spring weevil concerns. Our “Degree Day Calculator” (mesonet.ksu.edu/agriculture/degreeday) can help with alfalfa weevil detection and scouting. This tool utilizes weather data from 56 stations across the state. The data can be used to estimate the stage of alfalfa weevils in alfalfa fields. This article briefly summarizes the Degree Day Calculator and will describe how to use it with weevil scouting.
1. To utilize the tool, first determine your proximity to a nearby station. While there are many stations in the state, they aren’t evenly spread and there are some spatial gaps. Therefore, keep in mind a) stations south of your location may overestimate the number of degree days, north may underestimate; and b) station siting/location may greatly differ from your field level and have a resulting impact on the data. Select the closest station to you (or several stations if you want to get an average) from the map and/or list (if accessing on a mobile phone, only list is available).
2. Since we are focusing on alfalfa weevil, be sure to select “Alfalfa Weevil” from the calculation menu.
3. Weevil eggs hatch in spring, usually at anywhere between 25-300 Degree Days with scouting recommended once the number of Degree Days reaches 150-180. Degree Days begin accumulation after January 1st. Therefore, for a current analysis of estimated Days so far in 2017, we want to enter the following dates into the boxes: 2017 01 01 TO: 2017 03 27. Select “Alfalfa Weevil” in the calculation menu.
4. Press the submit button.
When to scout…
1. Upon pressing submit, the table below will populate with the station(s) you selected and the associated data. “Actual” column is the current Degree Days which have accumulated since the beginning of the period.
2. The far right column contains a “Graph” button for each station. Selecting this button will display the associated chart below the table.
3. Using the graph, the black line terminates on the right side representing the current Degree Day value. Pair the color coding of the graph with that of the legend below. Values still in the white are under recommended scouting values, however, as values increase and approach blue (150 Degree Days) the probability that eggs will start hatching increase. This is when scouting programs should be initialized. Blue or above suggests that scouting should already be occurring.
Comparing to normal…
Using “Normal” values (climatology of 1981-2010), we can estimate when the initial period may begin for weevil scouting in a “normal” or “average” year. The second data column in the table is the calculated normal for the period you entered. The “Departure” column to the right of Normal is the difference between the Actual versus the Normal. Positive values indicate that weevil progression is occurring sooner than normal and scouting will be required ahead of what “normal” climatology would indicate. Negative values indicate the opposite. This comparison to normal can also be viewed on the graph and is represented by a blue line.
2017 Conditions (as of 3/27/17)
Currently, after a very warm late winter/early spring the entire state of Kansas is averaging 400+ Degree Days. The average climatology for March 27th is 100 Degree Days over the whole state. To be more than 300 Degree Days ahead of normal at this point in the year is an incredible feat. Typically in Kansas, the climatological normal for alfalfa weevil scouting recommendations would be early April. However, with a 300 Degree Day surplus, most locations are already likely seeing leaf pinholing as a result of weevil feeding. Some consistency and variability needs to be considered in these values. Although, with such high values, it is recommended that a scouting program should be ongoing statewide at this time.
For more information, see:
Alfalfa Weevils, K-State Research and Extension publication MF2999.
Kansas Mesonet (March 2017). Degree Day Calculator, Department of Agronomy Weather Data Library. http://mesonet.k-state.edu/agriculture/degreedays
Christopher Redmond, Assistant Scientist/Mesonet Manager
Mary Knapp, Weather Data Library
Dan Regier, Weather Data Library Web and Database Developer
Jeff Whitworth, Extension Entomology