Effects of moldboard plowing, chisel plowing and rotation crops on the Rhizoctonia disease of white potato

Abstract

Two tillage practices, chisel plowing (30 cm) and deep moldboard plowing (22 cm), and five rotation crops (oats, lupine, buckwheat, broccoli and peas) were studied for their effects on the soil population ofRhizoctonia solani AG-3 and on Rhizoctonia disease on potato. All rotation crops were harvested except buckwheat, which was treated as a green manure crop. Chisel plowing significantly reduced (p = 0.05) the incidence and severity of stem lesions on potato caused byR. solani AG-3. In 1990, oats after moldboard plowing significantly increased disease when compared to other crops and broccoli after chisel plowing decreased disease severity. Soil populations ofR. solani AG-3 were significantly lower with chisel plowing. No interactions between tillage and rotation crops were observed.

Rhizoctonia solani Kühn is a soil inhabiting plant pathogen found worldwide that affects many plant species including white potato (Solanum tuberosum L.).R. solani attacks potato at one or more stages in development resulting in distinct disease symptoms (25) often termed the Rhizoctonia disease complex of potato. In Maine, only strains AG-3 and AG-5 ofR. solani (4, 5) have been identified as attacking potato and causing four distinct types of symptoms: 1) black scurf (sclerotia) on tubers, 2) stem cankers, 3) aerial tubers and top rosetting, and 4) killing of sprouts.

Crop rotation has been reported to reduce the incidence and severity ofR. solani on potato, but no single rotation method controls completely or to a high degree of reliability (11, 23, 24, 26). Deep moldboard plowing has been shown to reduce diseases caused byR. solani andSclerotium rolfsii Sacc. in crops other than potatoes (2, 7, 15, 19, 20). However, Gudmestadet al. (6) reported that deep moldboard plowing increased the severity ofR. solani on stems and stolons of potatoes.

The reduction of diseases caused byR. solani andS. rolfsii by moldboard plowing is attributed to low inoculum densities in the upper soil layer by the burial of sclerotia to depths where germination and infection were prevented (14, 15, 19, 20). However, disking to a depth of 5–7 cm did not affect disease as the inoculum remained in the root zone (14, 15). Gurkin (7) states that the rationale for deep moldboard plowing is to promote decay of organic matter, remove organic matter from the infection court and to bury the sclerotia below the infection court. Cultural control techniques are largely preventive and are designed to reduce the quantity or the activity of inoculum by means of crop rotation, tillage practices, green manure crops, etc. (22).

This study was conducted to determine individual effects and possible interactions of deep moldboard plowing versus chisel plowing in various rotation crops on the presence ofR. solani AG-3 in the soil and on the incidence of Rhizoctonia disease complex of potato.

Compendio

Dos prácticas de labranza, aradura con arado de púas (30 cm) y aradura profunda con arado de vertedera (22 cm), y rotatión con cinco cultivos (avena, lupino, trigo sarraceno, brócoli, y arvejas) fueron estudiadas para determinar sus efectos en la población de Rhizoctmia solani AG-3 en el suelo y sobre la Rhizoctoniosis de la papa. Todos los cultivos en rotación fueron cosechados con exceptión del trigo sarraceno, que fue tratado como un cultivo de abono verde. La aradura con pũas redujo significativamente (p = 0.05) la incidencia y severidad de las lesiones en el tallo de la papa causadas por R. solani AG-3.

En 1990, la enfermedad se incrementó significativamente cuando se produjo avena después de la aradura con arado de vertedera en comparación con los otros cultivos, y el brócoli después de una aradura con arado de púas disminuyó la intensidad de la enfermedad. Las poblaciones de R. solani AG-3 en el suelo fueron significativamente más bajas al usarse la aradura con púas. No se observaron interacciones entre la labranza y los cultivos en rotatión.