WHEAT DISEASE UPDATE

According to the NDSU small grain disease forecasting model for the Carrington site, tan spot infection was likely every day but two based on weather conditions during the period of July 8 to 19. Leaf rust infection was likely during July 8 to 14, but not during recent days. The disease forecasting model may be accessed at the following website:

         

The NDSU Extension Service small grain disease survey continues for south-central North Dakota. Thirty-five HRS wheat fields in post-anthesis to soft dough stages of growth were checked in Emmons, McIntosh, Logan, Burleigh, Kidder, Stutsman, Foster, Griggs, Eddy, and Benson counties during July 13-14 and 17. Tan spot was found in at least 37% of the fields surveyed, leaf rust in 89% of the fields, and Septoria leaf blotch in 74% of the fields. Scab (Fusarium head blight) was found in 74% of the fields surveyed with incidences of infected main stem heads ranging from 2 to 18%.

 

SOYBEAN DEVELOPMENT

Most soybean in the region are in the full bloom to beginning pod stages. The following is a brief description for these growth stages:

Full Bloom (R2)

Soybean are about 17-22 inches in height. An open flower is seen at one of the two top nodes of the main stem. At least one of these two upper nodes shows a fully developed leaf. At this stage, the soybean has accumulated about 25% of its total dry weight and nutrients and has obtained about 50% of its mature height. About 50% of the total mature node number have been established. Very rapid N, P, K and dry matter accumulation is now occurring. The appearance of new flowers on the plant begins to slow between R2.5-R3 and will be complete by R5. Major lateral roots have turned downward in the soil and nitrogen fixation by root nodules is increasing rapidly. Defoliation of the plant of 50% at this stage will reduce yield by 6%.

Beginning Pod (R3)

Plants can be up to 23-32 inches tall. A pod on the upper four nodes is 3/16 inch long. Temperature or moisture stress at this time can affect yield through total pod number, bean number per pod or seed size. Partial compensation with only temporary stress can occur in soybean, but as the plant matures from R1 to R5.5 this ability to compensate will decrease. Very favorable conditions will result in greater pod number per plant at this time. Since 60-75% of most flowers typically abort on soybean, any stress that increases this abortion will greatly influence yield. Half of most flowers are lost before pods begin developing and the other half are due to pod abortion. However, the long flowering period of soybeans is one reason these plants can compensate so well.

 

Additional information may be found in the NDSU Extension Service circular A-1174 “Soybean growth and management”.