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Growing Degree Days for Insect Pests

Encyclopedia Article

Humans and other warm-blooded animals can generate their own heat to regulate their body temperature. In contrast, insects are ectotherms, which means they cannot generate their own heat and their development is driven by the temperatures they experience in their environment. This is the same for plants, fish, amphibians, and reptiles. Most people in agriculture are familiar with using growing degree days (GDD; also called “heat units”) to monitor and predict crop development.

Start Scouting for Stalk Borers in Southern Iowa

June 2, 2020

In 2019, numerous field edges were infested with common stalk borer. Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications, if needed, are only effective when larvae are migrating and exposed to the insecticide. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Much of Iowa has reached this important benchmark (Figure 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions.

Crop: 

Stalk Borers Moving in Central and Southern Iowa

June 6, 2018
Degree day map of stalk borer

Tracking degree days is a useful tool to estimate when common stalk borer larvae begin moving into cornfields from their overwintering hosts. Foliar insecticide applications, if needed, are only effective when larvae are migrating and exposed. Start scouting corn for larvae when 1,300-1,400 degree days (base 41°F) have accumulated. Counties south of I-80 in Iowa reached this important benchmark this week (Figure 1), and therefore scouting for migrating larvae should begin now to make timely treatment decisions. Stalk borer larvae in northern counties will migrate later in June.

Crop: 

Corn Rootworm Egg Hatch Peaking Around Iowa

June 12, 2017
Predicted corn rootworm egg hatch in 2017

Corn rootworm egg hatch in Iowa typically occurs from late May to the middle of June, with an average peak hatching date of June 6 in central Iowa. In 2017, the average hatching date will be about the same time as the 2014-2016 growing seasons. Development is driven by soil temperature and measured by growing degree days. Research suggests about 50 percent of egg hatch occurs between 684-767 accumulated degree days (base 52°F, soil). Most areas in Iowa have reached peak corn rootworm egg hatch or will within a few days (Figure 1).

Crop: 

An update on 2017 degree days

May 30, 2017 9:25 AM
Blog Post

Last summer, I wrote a blog about how the spring started off warm compared to most summers. I was curious to know about accumulated temperatures for 2017. According to the ISU Agronomy Mesonet, southern counties are about 100 degree days ahead of 2016; central counties are about 100 degree days behind 2016 and northern counties are 200 degree days behind 2016. Most interesting!


Alfalfa Weevils Active Throughout Southern and Central Iowa

April 10, 2017
alfalfa weevil adult

Adult alfalfa weevils become active and start laying eggs as soon as temperatures exceed 48°F. Alfalfa weevil eggs develop based on temperature, or accumulating degree days, and hatching can start around 200-300 degree days. Start scouting alfalfa fields south of Interstate 80 at 200 degree days and fields north of Interstate 80 at 250 degree days. Based on accumulated temperatures since January, weevils could be active throughout southern and central Iowa (Figure. 1).

Alfalfa weevils active throughout southern Iowa

April 11, 2016 1:53 PM
Blog Post

In March, I posted a blog about alfalfa weevils laying eggs in SE Iowa. Degree days have been slowly accumulating in April. I've updated the degree day map for 2016 and alfalfa weevils should be actively laying eggs throughout southern Iowa. Important temperature benchmarks are 200 degree days in southern Iowa and 250 degree days in northern Iowa.

Alfalfa weevils start moving in SW Iowa

March 24, 2016 11:37 AM
Blog Post

Adult alfalfa weevils begin moving as soon as temperatures exceed 48°F and begin laying eggs in alfalfa. Alfalfa weevil eggs develop based on temperature, or accumulating degree days, and hatching can start around 200-300 degree days. Start scouting alfalfa fields south of Interstate 80 at 200 degree days and fields north of Interstate 80 at 250 degree days. Based on accumulated temperatures since January, alfalfa weevil larvae could be active in southwest Iowa now.

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