Plants have the capacity to kill insects and mites feeding on them when they are healthy enough. These potential pests don’t show up in fields at random, but only when the plant has a nutritional profile they can utilize as a food source. When you change the plants nutritional integrity with agronomy management practices, you also change the crops susceptibility to insects and pests of all types.
Spider mites are often associated with hot and dry conditions. Spider mites are not attracted to high temperatures specifically. They are attracted to plants with abundant levels of free ammonium in the plant sap.
Elevated levels of ammonium often occur in high temperature environments when plants shift from photosynthesis dominant to photorespiration dominant. When this shift to high photorespiration occurs, plants are no longer getting enough energy (sugars) from the photosynthesis process (which has slowed down or halted). To sustain themselves, they begin catabolizing proteins to use as an energy source.
The protein catabolism during photorespiration in high temperature environments usually results in the accumulation of ammonium in the leaf, which can result in the crop being susceptible to spider mites, only when the plant does not have the needed nutrients and enzyme cofactors to convert the ammonium back into proteins at night, or as soon as carbohydrate energy become available. The critical nutrients for this conversion process are magnesium, sulfur, boron, molybdenum, adequate carbohydrates in the plant, and occasionally nickel.
In these photos, you can observe the results of a nutritional correction applied through an overhead pivot on a corn crop in SW Kansas in 2015. Spider mites were present in large numbers, and the local crop scout recommended a miticide application immediately.
The pivot took 48 hours to treat the entire circle with nutrients. In the sections that had been treated 24 hours earlier the spider mites were noticeably sluggish and moving slowly. In the section that had been treated 48 hours earlier, the spider mites were completely dead. The local crop scout assumed a miticide had been applied, but this was not the case.
Healthy plants can be completely resistant to all diseases and all insects when supported with the correct nutrition and the correct microbiome.
Of course, applying more ammonium fertilizer than plants can convert to proteins in a few days is also a great attractant for spider mites, thrips, and other related pests that are thought to like ‘warm conditions’.