They say, “You are what you eat”, and for your crops that means NPK: Nitrogen, Phosphorus, and Potassium. These three macronutrients greatly influence the health of your plants, which in turn can directly impact the effectiveness of your pest management plan. Knowing the effect of each will ensure that the bugs don’t get an unfair advantage when you’re trying to control them.
Nitrogen is king when it comes to the nutrients your plants crave. It is a vital component for proteins, which are the raw materials they need to grow. For those fields that were planted later this season, we’re closing in on one of the most critical times for applying nitrogen. More than half of the nitrogen uptake for the season occurs between the V8 and VT stages. If your fields are around this stage, you may already be planning on an application. And it’s understandable that you might be tempted to give your plants an extra boost after our slow start this season.
Be warned, insects love it when you over-spray nitrogen on your fields. That little extra ammonia that helps your plants flourish also helps insects thrive. Studies that treated plants with higher-than-recommended doses of nitrogen found greater numbers of insects on treated plants. That elevated nitrogen causes the plants to focus on growth, putting out lush, green leaves rather than focus on defense. This attracts insects and gives them the nitrogen they need to produce lots of babies. Pest populations explode as a result, increasing the rate of damage. Therefore, try to avoid the impulse to spray a little extra N in your field. It might help the bugs more than your corn.
Phosphorus has a different effect on insects when compared to nitrogen. Greater phosphorus concentrations reduce the number of insects on crop plants and may lower the survival rate for those insects that feed on them. This is due to phosphorus being an important component for a number of plant defensive compounds that can suppress feeding or kill insects.
But phosphorus’ protective properties are not universal. Additional phosphorus can attract some types of insects due to the greater overall health of the plants or because some species can tolerate the defensive compounds that deter their more-aggressive competitors. But even so, the benefits of adequate phosphorus can outweigh the impact of these pests.
Plants treated with potassium are more tolerant of stress (drought, heat, etc.), which makes them resistant to infection and insect feeding. Part of this response is due to potassium acting as a competitor to nitrogen. When present in the soil, potassium can slow plant the uptake of nitrogen, preventing the high-nitrogen content scenario that helps pest insects thrive. Potassium is also incorporated into several defensive compounds, limiting damage and allowing the plant to invest resources into general defenses and tissue repair. When plants are deficient in potassium, insects like soybean aphids take advantage of this weakness to attack.
Despite the benefits of having adequate potassium for your crops, potassium-deficient plants are not always defenseless. A study focused on thrips damage to potassium-deficient plants found that damage was reduced even without potassium. The low potassium forced the plants to produce more defensive compounds, helping them deter feeding damage.
One of the most crucial tasks on your plate each season is to make sure your plants get the right amount of nutrition. How you handle this responsibility can play an important role in your management strategy. Carefully-balanced nutrient inputs can help you avoid pest outbreaks and costly control methods.