Certified Professional Horticulturist (CPH) Practice Exam

What lawn management strategy is likely to promote lawn disease?

1. Under fertilization, overwatering

2. Overfertilization, overwatering

3. Under fertilization, underwatering

4. Overfertilization, underwatering

The correct answer is: Overfertilization, overwatering

Overfertilization combined with overwatering creates an environment conducive to lawn diseases. When there is an excess of nutrients, especially nitrogen, it stimulates lush, rapid growth in grass. While healthy growth is desirable, too much nitrogen can lead to a soft, succulent tissue that is more susceptible to diseases. The combination of overwatering exacerbates this problem by keeping the soil consistently moist and creating ideal conditions for pathogens to thrive. Saturated soil can hinder air exchange and promote fungal growth, leading to issues like root rot or various blights that are prevalent in overly moist environments. This means that lawns that receive too much fertilizer and water are often plagued by a greater incidence of lawn diseases, such as dollar spot, brown patch, and pythium blight, which thrive in such nutrient-rich and wet conditions. The other choices highlight scenarios of either underfertilization or underwatering, both of which tend to lead to weaker grass that is not as susceptible to diseases as over-enriched and overwatered grass.