Mulches can control pests, boost soil and plant health

Mulches can play a surprising role in pest control and soil health.

Organic mulch, such as wood chips, can cover crop residues, or straw can reduce thrips and leaf miner numbers significantly. Additionally, organic mulch can reduce fungal pathogens by preventing soil splashing and therefore preventing spores from reaching the leaves.

For example, purple blotch (Alternaria porri), a fungal disease of green onions, can be significantly reduced by using mulch. Organic mulches also help to conserve soil water and increase beneficial soil organisms that play a role in nutrient cycling and biocontrol. This results in a significantly greater yield.

Synthetic mulches can also play an important role in pest control. Reflective silver plastic mulch significantly reduces arthropod pests such as thrips, spider mites and whiteflies. The light reflection repels and confuses these pests, and the pest control levels can be higher than insecticides.

Additionally, reflective mulch increases plant growth by increasing photosynthesis, and it reduces plant heat and water stress by keeping the plant and soil cooler. These benefits resulted in a more than 50 percent increase in marketable yield in a University of Hawaii tomato field trial.

Solarization mulch, or clear synthetic mulch that covers the soil, traps solar heat to kill off the weed seed bank in the top soil layer. Additionally, the high temperatures generated by this treatment reduce nematodes and many pathogens. Solarization mulch is an effective weed control strategy.

Mulches can be an effective and sustainable pest control strategy that can reduce chemical inputs, improve yield and increase soil and plant health. So use mulch in your garden or farm to obtain multiple benefits.

Marisol Quintanilla is a nematologist and board-certified entomologist in the sustainable agriculture and soil health extension office of the University of Hawaii Tropical Plant and Soil Science department.