Landscape and Irrigation is read by decision makers throughout the landscape and irrigation markets — including contractors, landscape architects, professional grounds managers, and irrigation and water mgmt companies and reaches the entire spetrum.
Issue link: https://read.dmtmag.com/i/120372
culture) tends to be higher when mixtures are used, and mixtures may be less expensive than do-it-yourself tank mixes. Another reason to use a mixture or pesticide combination is to slow down the development of resistance in some pests. However, this is not the typical motivation of applicators, and I would appeal to you to weigh the pros and cons of this when choosing your pesticide inventory. I was amazed that in agriculture, a lot of insecticide mixtures have been used over the last 50-plus years — e.g., abamectin (Avid) plus thiamethoxam (Meridian) on pears against psyllids and aphids. The list was so long, I couldn't write down all of the combinations. Mixing products is not as easy as it sounds. With any kind of mixture, there are some things to watch out for. It is possible to get "antagonism" between compounds, which means that the mixture is less effective than when the single products are used alone. There is also the risk of plant damage or "phytotoxicity," which is more likely to occur when mixtures are applied to stressed plants (e.g., drought-stress), but separate applications of the compounds would not hurt a plant. And "physical incompatibility" can happen if two compounds or formulations react to each other or physically can't combine (an issue of compatible solubility). The result could be a big glob of goo in your spray tank. Some cautions Avoid mixing insecticides that have the same "mode of action" or are in the same chemical class. From a resistance management perspective, if an insect is resistant to one insecticide (e.g., bifenthrin), then what good would it do to add another pyrethroid (e.g., permethrin, deltamethrin, lambda-cyhalothrin, etc.) to the mix? There could be cross-resistance within the same chemical class or even across other classes, so you would only be exerting the same selection pressure to the pest. For example, carbamates and organophosphates act essentially the same way on an insect, and pyrethroids and DDT similarly have some cross-resistance. Hopefully, you remember that a mode of action is how an insecticide acts (e.g., interferes with the sodium channel) at its target site (e.g., the nervous system) within the insect. Also avoid using the same mode of action (single product or mixture) against the same generation or life stage of the target pest. This may be easier said than done in the southeastern United States, especially Florida and the Caribbean, where we have overlapping life stages of pests nearly yearround. Ideally, one treatment could be used to knock out most of one pest generation, then, if needed, you could come back to treat the next generation or whenever damage reoccurs. Similarly, if a treatment of some product doesn't work the first time, don't keep applying it again in the hopes that attempt number 2 or 3 might be more worthwhile. Doing the same thing over and over again when you know it doesn't work is insane (and arguably unethical if you're getting paid for the job). Be aware that treating with a brand name product and at the same time with a generic product at the highest labeled rates equals a 2X application, which is illegal. Again, the goal is to reduce selection pressure and use products wisely, not nuke everything. Modes of action can be determined by finding the "Group" number on a product label or by looking up the active ingredients on the IRAC website (http://www.irac-online.org). The last caution is that premixes should not be used unless all components within the product are needed. Say that an insecticide premix is used on residential turf in June in north central Florida. Which pests might be present at that time that could be killed by both a pyrethroid and a neonicotinoid, without even doing any monitoring? Maybe grubs, mole cricket nymphs, chinch bugs, twolined spittlebugs (in north Florida); but how often are multiple pests really present and causing damage? So, is it even necessary to use two insecticides if one can effectively do the job? How would you justify the treatment or ever know without doing any monitoring? It reminds me of when my kids get sick. I have to wait 10 to 14 days to make sure the virus has run its course before taking them to the doctor to get an antibi- otic, because by then, the infection has become bacterial and is treatable. Advantages and disadvantages of mixes Commercial premixes have the advantages of being convenient to use, the active ingredient rates are unchangeable, the component rates and formulations are optimized during development, no mixing or stability issues should exist, and at least one component is usually applied at a lowerthan-labeled rate. Some disadvantages include the inability of an applicator to change the active ingredients, all target pests should be present at the same time, and premixes may have been designed for specific pests or regions of the United States but could be used outside of the optimal treatment zone. From an economic standpoint, premixes may be created by manufacturers as part of a post-patent marketing plan to obtain a licensing extension. Some advantages of tank mixtures include giving the applicator some flexibility to provide treatments that fit the pest control need at that time, and they help to reduce any excess pesticide inventory that might exist. However, the flip side is that creating a tank mixture is less convenient, it's potentially hazardous to people who are not trained to properly mix products, "homemade" tank mixes may not be as stable as a premix, and the products being combined tend to be mixed at the highest labeled rates. According to IRAC, which is a highlyregarded committee of pesticide experts (pesticide manufacturers must pay dues to belong to this group), there are some requirements for a mixture to be considered effective. First, all toxins should persist the same length of time where the mixture is applied. Complete coverage of the treated plant is essential. There should be no cross-resistance between the toxins. In effect, both compounds should each be able to kill the target pest, which is called "redundant killing." As turfgrass managers, we are not chemists, and we don't know if only one of the compounds in the mix is doing all the heavy lifting or if there is really a benefit to having both compounds in the mix. It is possible to get "antagonism" between compounds, which means that the mixture is less effective than when the single products are used alone. www.landscapeirrigation.com Landscape and Irrigation 13