Should You Treat ThryvOn Cotton With Insecticide?
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Collapse ▲The short answer for thrips is no, and for plant bugs, yes, if it hits threshold. We covered this in a 2023 article, but here is some more justification.
Thrips
ThryvOn cotton is an egg-laying and feeding deterrent for thrips. Because it only deters, but doesn’t eliminate them, we can expect to find larval thrips on ThryvOn cotton. However, numbers on ThryvOn will be greatly reduced relative to non-ThryvOn cotton. In my experience, there are generally 5-10x fewer thrips on ThryvOn cotton relative to non-ThryvOn cotton. This varies greatly with environment.
In North Carolina, we have evaluated the effect of ThyrvOn for thrips in multiple small-plot experiments since 2014. We also tested this on-farm in 2022 and 2023 in Nash and Edgecombe counties using whole fields instead of small plots. Numbers were very high in 2022 and they provided an excellent estimate for how ThryvOn could perform. We treated some ThryvOn fields with 5lbs. AgLogic and left other ThryvOn fields untreated.
At 28 days after planting, thrips numbers soared to an average of 6.5 per plant in ThryvOn + AgLogic and 21.2 per plant in ThryvOn alone. Keep in mind our economic threshold (when it pays to spray) is 2 larval thrips per plant.
Injury was high at this point, as well. On a scale of 1-5 (1 = no injury, 2.5 = yield loss likely, 5 = dead plant), injury averaged 1.25 in ThryvOn + AgLogic and 2.25 in ThryvOn alone.
This persisted during the early season. In fact, plants treated with AgLogic had a higher vigor and were taller. However, at the end of the season, yields were statistically the same (ThryvOn + AgLogic = 1162 lbs. lint and ThryvOn alone = 1166 lbs. lint). We have seen this phenomenon time and again in small plots as well.
For example, because cotton did not grow quickly in May and early June, 2023 was a high pressure year across the state. Despite this, ThryvOn + AgLogic yielded 1595 lbs. lint and ThryvOn alone yielded 1527 lbs. lint in small plot trials at Plymouth, NC. Note that these yields were statistically the same, just like the on-farm tests.
To my knowledge, no university extension trial in the Cotton Belt has shown a yield benefit to treating thrips in ThryvOn cotton. You can reduce thrips and improve appearance, vigor, and even plant height, but not yield. Therefore, you should not treat thrips in ThryvOn cotton.
Tarnished plant bug
Similar to thrips, ThryvOn cotton is an egg-laying and feeding deterrent to tarnished plant bug. However, it will need to be treated if the economic threshold (when it pays to spray) is reached.
A good example of the benefit of ThryvOn alone, and the benefit of ThryvOn protected from the insecticide, is from our 2021 trial. Note that ThryvOn does not need protected with weekly sprays. Our current economic thresholds work fine. In fact, we have experiments in place to see if we can relax our thresholds for ThryvOn cotton. However, check out the benefit of spraying when tarnished plant bug pressure is high.
Lint yield for non-ThryvOn and ThryvOn cotton, both sprayed weekly (5x) and unsprayed for tarnished plant bug. Letters that are different mean yields are significantly different. Dollar figures represent net gain for treating tarnished plant bug, including lint yield profit, minus the cost of the insecticide application and cost of the ThryvOn trait.
Unsprayed non-ThryvOn left and weekly-sprayed ThryvOn right from 2021 trial.
This trial clearly demonstrates that ThryvOn alone provides some protection from tarnished plant bug. However, under moderate to high-pressure tarnished plant bug scenarios, yield can be improved with foliar insecticides.