Effect of cover crops and tillage system on symphylan (Symphlya: Scutigerella immaculata, Newport) and Pergamasus quisquiliarum Canestrini (Acari: Mesostigmata) populations, and other soil organisms in agricultural soils

Abstract

The garden symphylan ( Scutigerella immaculata: Newport) is a common myriapod soil pest of vegetable crops in the Pacific Northwest and other regions of the US. Symphylans consume germinating seeds, plant roots, and above-ground plant parts in contact with the soil. Factors regulating symphylan populations in agricultural soil systems are poorly understood, particularly the effects of farming practices such as cover cropping and reduced-tillage. Cover crops were planted in the fall of 1994 through 1996 and either incorporated into the soil in the spring with tillage or killed with glyphosate and the residue left on the soil surface. Fewer symphylans were recovered with Berlese funnels from soil under cereal cover crops than soil in mustard cover crops, regardless of tillage system. Fewer symphylans were recovered from soil under the spring oat cover crop than soil under the barley cover crop. Eliminating spring tillage may have increased symphylan populations but the effect of reduced tillage on symphylan populations was less important than cover cropping. Predaceous mites were more abundant in soil under large amounts of cover crop residue but these predators were not correlated with lower populations of symphylans. Spring tillage dramatically reduced populations of Pergamasus quisquiliarum, a known predator of symphylans. Cover crops increased both the ratio of predaceous mites to symphylans and the total population of potential prey, thereby, reducing the capacity of predaceous mites to regulate symphylan populations.