Aphicide Awareness: Reports of Phytotoxicity on Ornamentals
After my previous post outlining how Ontario growers may be experiencing resistance to Beleaf (flonicamid), several growers are experimenting with alternate aphicides (chemicals that control aphids) this spring. These growers tested products on small batches of crops at high rates, to look for phytotoxicity, and have passed on their results to share with the rest of you.
Keep reading to see which products are affecting which crops, and how you can help mitigate issues with phytotoxicity from insecticides.
Phytotoxicity: The Usual Suspects and Typical Symptoms
For anyone that grows plants commercially, you’re well aware that pesticides, plant growth regulators, and fertilizers can all sometimes cause unwanted effects or damage to crops (phytotoxicity). Products used for greenhouse sanitation, such as those used to clean biofilm from water lines, can also be a source of unexpected phytotoxicity (or “phyto”), if used incorrectly.
Typically, symptoms of phytotoxicity can include:
- Leaf damage: leaf tips, margins, or the entire leaf may appear burned, discolored, or spotted. Leaves may also appear yellowed, cupped, or twisted. Leaf drop can occur.
- Flower damage: flowers or buds may abort, and petals may look bleached or stippled.
- Plant stunting: the plant may be stunted or grow abnormally.
- Root damage: root tissue may be injured, causing stunting or slow plant decline.
Phyto usually occurs fairly quickly on ornamentals (2-4 days), but can take up to 7-10 days, depending on the plant, the chemical agent involved, its application (spray vs. drench) and the environmental conditions (with heat/sun often exacerbating symptoms).
Aphicides and Phyto: What We’re Seeing
Kontos:
Alternate aphicides to Beleaf (flonicamid; Aria in the U.S.) were covered in a recent post. Kontos (spirotetramat), one of the most effective products against aphids, is also a product that growers are familiar with when it comes to potential phyto. Luckily, the manufacturers are aware of this, and the phytotoxicity warning on the Kontos label is quite comprehensive. However, newer chemistries, or those which have not been in heavy rotation until recently, may catch growers by surprise.
This was the case in the last month or so with two products that are being used more frequently now that Beleaf appears to have less efficacy on certain farms.
Altus:
Both Altus (flupyradifurone) and Rycar (pyrifluquinanzon) have shown effects on open blooms of different crops.
At a high spray rate, Altus may cause some spotting on open blooms of Kolanchoe. This was more apparent on dark blooms that light. There have been no reports of effects on other crops as of yet. (BUT, see the section below on how these tests were done). No phytotoxicity was seen on any of the foliage, even on young plants.
Phytotoxicity on Kolanchoe caused by a heavy spray of Altus. Photo by OMAFA.
Rycar
The same grower also saw effects on Kolanchoe with Rycar, but the damage was worse. On the red variety, along with more severe petal streaking, it appeared that some of the unopened buds were burned. As with Altus, however, the damage was confined to the flowers and buds, and did not affect the foliage.
Similar damage was seen recently at another grower’s, where a single application of Rycar (at label rates) caused severe petal streaking when applied to open gerbera flowers. In this case, the grower suspected the damage occurred because Rycar was sprayed during a sunny afternoon. No damage was seen when the grower tried to re-create the damage on a cloudy day.
Phytotoxicity on Kolanchoe caused by a heavy spray of Rycar. Photo by OMAFA.
Rycar has also caused issues on certain tropical plants, such as the Goldfish plant, if used repeatedly at high spray rates. It seems to have a plant growth regular-like effect, causing stunting and branching. (Note: I had never heard of this plant before this issue, and am now in love with it!!!).
So far, Ference (cyantraniliprole) does not seem to be a risky chemical for aphid control. Even with repeated applications, growers are not seeing any phytotoxicity.
However, as many growers have already been using Ference (Exirel) to help suppress thrips, overuse is a real concern, potentially resulting in the development of resistance in thrips AND aphids. Given this, Ference should be saved for aphid control, or for thrips outbreaks only (instead of being used prophylactically, as I’ve been seeing in the industry).
A Method to Test for Phytotoxicity:
Pesticide labels usually include a vague statement on phytotoxicity to the effect of “always test on a small area to confirm tolerance prior to adoption”. But what is the best way to go about this?
The effects above were discovered on Kolanchoe by a grower who always does the same trial with new chemical/crop combinations. His (very smart) approach is to apply the chemical at the high label rate as a “sprench” on a small subset of plants, as a “worst-case scenario”. In his trials, he usually includes:
- Young, vegetative plants
- Mature, flowering plants with light blooms
- Mature flowering plants with dark blooms
The reasoning behind this application is to quickly approximate what would happen under repeated applications, or if a spray applicator got a little “heavy handed” at the end of a row after a long day. If little to no phyto is seen under this scenario, the grower can confidently apply 1-2 applications of the chemical (following label rates/ max. applications) on the whole crop. In this case, he feels comfortable applying at least 1 application of Altus at the high rate, but would do more tests before doing two back-to-back applications of Altus on open blooms.
If he DOES see moderate to heavy phyto, he knows he needs to either a) go with a lower rate on that crop, b) apply only 1 application or c) avoid specific plant life stages. In this case, the grower would feel comfortable doing multiple applications of Rycar on vegetative plants, but would use a different chemical if aphids were to pop up near sale, when plants are flowering.
Precautions to Mediate Phytotoxicity
Not one to reinvent the wheel, I’d recommend this e-Gro alert by Nora Catlin from Cornell University extension, if you want to learn more about recognizing and mediating phytotoxicity. There’s also great tips on avoiding phytotoxicity in this Grower Talks newsletter by JC Chong. JC even suggests that phytotoxicity can be thought of in a similar way to diseases:
I guess, in some way, you can think of phytotoxicity like a disease—its occurrence also depends on the “phytotoxicity triangle.” You’ll need a causal agent (in this case, a pesticide that has formulation or other properties that increases its risk of phytotoxicity), suitable environmental conditions (high temperature, high relative humidity, etc.) and a susceptible plant (either because it’s a sensitive plant species or cultivar, or has a condition that predisposes the plant to damage) to tango.
Hopefully, this year will be the only year where growers experience growing pains with these chemicals, and figure out how to use them safely. (Remember this post, where we also documented phyto when first using Beleaf as a drench). If you DO see phyto from these products (or any other products) that are NOT listed on the label, please let me know. I will make sure to add them to the phyto warnings in Crop Protection Hub (see example, below):
Comments
Post a Comment