*update as of April 1, 2025: active EHS crawlers found in fields in Upper Mountain Research Station, Avery County, and West Jefferson 

Spring is Breaking Records

We are on track for another very warm April. This past weekend, our NC State Climate Office Growing Degree Day Explorer calculated the highest growing degree days in 30 years for both Newland, NC, and Laurel Springs, NC, for April 27^th.

Growing degree days (GDD) are a measure of heat accumulation and are used to predict growth and development rates of crops and pests. While complicated methods exist to calculate GDD, the simplest applications use temperature averaging, a threshold temperature for the pest or crop of interest, and a specific starting date. For the GDD given in this post, I’ll be using a threshold of 50 degrees F and a starting date of January 1.

The GDD data for Laurel Springs, NC for April 27, 2025 displayed 242 GDD which is 59 GDD higher than last year’s April 27 Laurel Springs calculation, 105 GDD higher than the 30-year Laurel Springs average, and 34 GDD higher than the GDD accumulation for any April 27 in Laurel Springs collected in 30 years.

The GDD Explorer tells a similar story for April 27 in Newland. The 189 GDD calculated for April 27, 2025 is 60 GDD higher than last year’s April 27 Newland calculation, 80 GDD higher than the 30 year April 27 Newland average, and 1 GDD higher than the GDD accumulation for any April 27 collected in Newland in 30 years.

If we look at the data in terms of dates, we are 11 days ahead of last year’s GDD rates in Laurel Springs, as Laurel Springs did not reach above 242 GDD until May 8 in 2024. We are four days ahead of last year’s GDD rates in Newland.

Growing Degree Days (50°F) from Jan 1, 2025 to April 27, 2025

GDD and Insect Emergence

To predict what these earlier GDD data mean for insect emergence, we can look to research that examines emergence time of elongate hemlock scale (EHS) in other states in relation to GDD. Researchers in Rutgers have noted that elongate hemlock crawlers (EHS) in New Jersey begin emerging at 360-700 GDD, while cryptomeria scale begins emerging around 600 GDD.

It’s important to note that geographically distinct populations of the same insect species often have different phenological indications. In other words, EHS populations in New Jersey might emerge at a different time than WNC populations of EHS. We are working to collect WNC-specific data now and do not have WNC data from last year. Furthermore, it’s important to note that GDD emergence data are estimations, and microclimates and regional differences can play important roles in insect life cycles. Keeping track of your own field using traps is the best way to predict scale active crawler peak and other insect activity. However, if we follow Rutger’s phenological patterns, last year’s first EHS crawlers would have begun emerging around May 22, 2024 in Newland and May 16, 2024 in Laurel Springs. These data underline the extreme nature of last year’s weather; when examining 30 year mean GDD trend lines, the EHS crawlers normally would have begun emerged May 31 in Newland and May 25 in Laurel Springs. According to the GDD data, we are on track to have an even earlier emergence than last year.

Cryptomeria data extrapolations with Rutger’s GDD calculations in WNC are similar. The cryptomeria scale would have begun emerged around June 5 in 2024 in Laurel Springs. When examining 30 year mean GDD trend lines, June 12 is historically the average date of crawler emergence in Laurel Springs.

Mating male cryptomeria scale. Richard Cowles, Connecticut Research Station CC BY-NC-ND 4.0

Male cryptomeria scale. Richard Cowles, Connecticut Research Station CC BY-NC-ND 4.0

Captured Scales in WNC

Blake Williams, Ashe County horticultural agent, captured almost 600 male, winged cryptomeria on a sticky card in the last week; these likely developed from overwintering earlier-instar stages such as pupae or settled crawlers. I have had tape traps set up since winter 2024 in two cryptomeria infested fields in Ashe County, and have yet to pick up any active cryptomeria crawlers. Even with the extreme warmth, it’s still early for active crawlers. In the coming weeks, we expect to capture the first active crawlers of 2025 emerging from overwintering eggs, eggs laid by overwintering mated females, and/or newly laid eggs.

In other scale systems, such as the white peach scale in tea plantations, the optimum time to spray chemically-controlling materials was found to be two to five days after the peak number of first generation crawlers were captured on sticky traps. Last year’s four-county WNC acetamiprid study showed significantly higher EHS control near the end of May, which lines up with Rutger’s estimation of EHS peak crawler peaks around 360 GDD, or May 16-22, 2024. Once we have WNC-specific GDD data regarding our pest populations, it’s likely we will be better able to predict emergence for WNC cryptomeria and EHS and thus possibly predict effective spray windows. It’s important to note, however, that both EHS and cryptomeria are known to have overlapping and extended generations (meaning all developmental stages may be observed throughout much of the growing season), so isolating a 100% effective spray window on the more vulnerable active crawler stage may always be out of reach. Furthermore, tree phenology and systemic uptake/mobility of the pesticide also likely play a role in the best timing for pesticide application, as research in Connecticut suggested effective control of EHS with acetamiprid applications two weeks before and until budbreak (Cowles, 2023. Armored Scale Management, presentation to Jackson County Christmas Tree Association). Complete bud break in Fraser fir plantations varies widely across WNC, but often occurs earlier than mid May.

As mentioned earlier in this post, GDD data is just one way to predict insect population and life cycle swings. Steve Rettke, Agriculture & Natural Resources Program Associate at Rutgers Nursery/Greenhouse IPM Program, likes to remind farmers that photo periods and chilling effects affect insect phenology as well. “On-site traps will always give the most accurate information,” Mr. Rettke emphasizes.

Please get in touch with me or any Extension staff if you have any questions. Along with the tape trap examinations, for 2025, I have studies examining the 1. Effect of basal applications against cryptomeria scale on basal pruned trees vs foliar applications; 2. Effect of foliar and soil injections of imidacloprid and Bassiana beauveria against root aphid populations; 3. Effect of foliar applications, root drench, and plug drench using dinotefuran (Safari) against cryptomeria populations; 4. Effect of pyriproxyfen (Esteem), acetamiprid (Tristar), and afidopyropen (Ventigra) foliar applications against EHS; and 5. Interactions between fertilizer rates and EHS populations in nursey and field settings. I’ll be updating this page with results from these studies in the coming year.

Over 300 male cryptomeria scale on one side of a sticky trap captured in one week in mid April. 598 total cryptomeria male scale were counted on both sides. Blake Williams, Ashe County Extension Horticultural Agent CC BY-NC-ND 4.0