Springtails Suppress Weeds
New research from Virginia Tech University shows that small insects called springtails (Collembola species) help farmers fight herbicide resistant weed species in the soil. These tiny wingless insects are about the size of small rice kernel. They live in soil residue and feed on weed seed. There are more than 6,500 species of springtail (Collembola species) world-wide. Results vary by weed seed species depending upon the thickness of the seed coat.
Two Virginia Tech researchers (Jernigan & Sonoskie) found that in a 4-week greenhouse study, springtails reduced weed biomass by 23%. Unfortunately, at first the springtail affected weed seed seemed to increase weed germination for the first two weeks followed by a dramatic reduction in the last two weeks. The researchers think the springtails increased weed seed germination initially by breaking open the seed coat so that the weed seed could germinate faster. In the last two weeks, the germination was drastically reduced, probably because the springtails were eating the germ (middle of the seed), reducing weed seed germination. It appears that the thickness of the weed seed coat has a big impact on how effective the springtail are at reducing weed seed germination.
Weed seed with thicker coats were less affected like yellow foxtail and common lambsquarters than weed seed with thinner seed coats like pig weed species. Thinner seed coats with just a small nick or bit might be able to germinate faster but if feeding continued, the germ would be harmed, reducing seed germination. The study found that springtail reduced yellow foxtail emergence by 41%, Powell Amaranth by 67% and waterhemp by 43%. Powell Amaranth is not the same as Palmer, however; both species are herbicide weed resistant. For this research, the Powell seed was easier to study. The researchers noted that pigweed and amaranth weed species total biomass were reduced by 55% and 32% on waterhemp as the springtail population increase doubled (from 100 springtail to 200 springtail per plastic container).
Several factors might be affecting weed seed germination including seed coat thickness, nutrient availability, the type of crop grown, the type of weed seed, springtail feeding preferences, and overall soil insect diversity. Understanding the results in this first of its kind research in a greenhouse should help researchers understand better what is happening in the field.
How can farmers use this information to fight weeds in their fields? First, springtails (Collembola species) flourish in healthy soils. NRCS’s Four Principles of Soil Health apply here. First, springtails thrive in undisturbed soils. Tillage reduces springtail populations. Second, they live in the soil residue which is their home. They need good macropores to move around so tillage destroys both the soil structure and the residue. Third, they live around live roots. They feed off of microbes and weeds seed in the soil. Fourth, they need a lot of diversity. Diverse soil systems supply the foundation for springtails and other higher level beneficial insects to thrive. Springtails thrive from lots of soil organic matter, large soil aggregates formed by lots of live roots, and by live plants which protect the soil from rain drops and reduce soil erosion by keeping the soil in place.
Another way springtails are harmed are using too much insecticides. Many broad spectrum insecticides kill all insect species, good and bad; while targeted insecticides placed in-furrow are better for keeping springtail populations healthy. Another benefit of springtails are that they in a class of insects that make crop residue more nutrient available to the next crop.
On another research note, researchers found that while there are many diverse microbes in the soil, most are inactive or dormant. Penn State researchers found that the active microbes not the dormant microbes are the most important for soil health and plant growth. So microbial abundancy (how many microbes exist regardless of activity state) is not as important as how many microbes are actively growing and living, not only in the soil but even more importantly in the plants themselves.
Endophytes are microbes that live inside the plant. These microbes are 10X more active than microbes that live in the soil, even right around the root. There can be 1,000X to 2,000X more microbes around a live root. However, the ones inside the plant may be even more important for plant health. Only a few species (for example Psuedomonas bacteria) can make it inside the plant, but these species supply many growth hormones, vitamins, and other nutrients to the plant. Researchers at Penn State are looking for ways to increase microbial activity to increase crop yields.
