CANOLA DISEASE SURVEY
The NDSU Extension Service is conducting a disease survey of commercial canola fields. During August 3-8, ten fields were surveyed in the south-central ND counties of Stutsman, Foster, Wells, and Sheridan. In each swathed field, 40 lower stems were examined for incidence of Sclerotinia (white mold) and blackleg. In addition, plants were examined for aster yellows and pods examined for Alternaria black spot.
Sclerotinia stem rot was found in all 10 fields in Stutsman County and averaged 23% infected plants (range of 2-78%). Aster yellows was present in 9 of 10 fields and plant incidence ranged from 0-7.5%. In Foster County, Sclerotinia was found in all 10 fields and averaged 13% infected plants (range of 2-23%). Aster yellows was present in 8 of 10 fields and plant incidence ranged from 0-7.5%. In Wells County, sclerotina was found in all 10 fields and averaged 19% infected plants (range of 2-45%). Aster yellows appeared in half the fields and plant incidence ranged from 0-10%. In Sheridan County, sclerotina appeared in 6 of 10 fields and averaged 12% infected plants (range of 0-55%). Aster yellows was detected in 9 of 10 fields with plant incidence ranging 0-7.5%.
For each % of sclerotinia stem rot incidence, about 0.5-0.75% yield loss may occur. As an example, the 19% average sclerotinia incidence in Wells County represents a yield loss of 10-14%.
Blackleg incidence generally was low in the four-county area with a range of 0-2.5% affected plants in Stutsman, Foster, and Wells Counties and a range of 0-10% affected plants in Sheridan County.
Blackspot was found in all of the fields checked with incidence ranging from 20-73% in Stutsman County, 23-63% in Foster County, 18-58% in Wells County, and 23-70% in Sheridan County.
Canola growers may want to check their swathed fields for incidence and potential yield loss of these diseases. Another consideration is impact of these diseases as future crop rotations are planned.
Most soybean in the region are in the full pod to beginning seed stages. The following is a brief description for these growth stages:
Full Pod (R4)
This stage shows rapid pod growth. and the beginning of seed development. Dry weight of pods is greatly increased from R4-R5. There is a pod at this stage which is at least ¾- inch long on at least one of the four upper nodes of the main stem. This stage is the most crucial period for seed yield. Any stress from R4-R6 causes more yield reduction than at any other time. Yield reduction at this time is mainly from fewer pods. This is a critical period to consider irrigation, if needed and available, to reduce yield losses. The last flowering will occur at the main stem tip (through R5).
Beginning Seed (R5)
This stage has seed at least 1/8 inch long in one of the pods on one of the four upper nodes of the main stem. Seed filling during this stage requires much water and nutrients from the plant. Redistribution of nutrients in the plant occurs with the soybean providing about a half of needed N, P and K from the plant's vegetative parts and about a half from N fixation and nutrient uptake by the roots. Leaf loss of 100% at this stage will reduce yields by 80%; the plant is less able to compensate from stress and vegetative damage. Stress can actually lower yields by reducing pod number and the number of beans per pod, and to a lesser extent by reducing seed size. About halfway through this stage, the plant attains its maximum height, node number and leaf area. Nitrogen fixation peaks and begins to drop and the seeds continue a steady period of dry weight accumulation. Toward the end of this stage, the nutrient accumulation in the leaves peaks and then begins the process of redistributing to the seed.
Additional information may be found in the NDSU Extension Service circular A-1174 “Soybean growth and management”.