Soybean Fungicide Selection and Application
The June 18 2016 MCS blog has an article entitled Soybean R3/R4 Fungicide Selection by Dr. Tom Allen, Plant Pathologist at the MSU-DREC. Pertinent points from that article are highlighted below.
● The automatic fungicide application at R3/R4 should be targeted to soybeans in “high-yield” environments. Past experience indicates this automatic fungicide application will result in a 3 to 6 bu/acre yield increase.
● Generic azoxystrobin products should have the same efficacy as Quadris.
● A strobilurin product applied to a frogeye leaf spot (FLS)-susceptible variety may not provide intended results due to widespread strobilurin resistance within the FLS fungal population.
● Know the disease package of a particular variety before making an application of a strobilurin-only product. Click here to check disease ratings of varieties grown in the MSU variety trials.
● If a variety is known to be susceptible to FLS, consider a tank-mix or premix of fungicides with multiple modes of action. Click here for a White Paper that discusses this topic in detail and contains a list of soybean foliar fungicides along with their mode of action and efficacy ratings against prominent soybean diseases.
● Fungicide applications made closer to R4 should provide residual activity past R5, or into the seed filling period. Most fungicides applied at labeled rates should provide 17 to 21 days of residual activity.
● Pay special attention to rate of application since this will determine the length of residual activity.
● The application volume should be chosen to achieve maximum coverage since the systemic activity of both strobilurin and triazole fungicides is limited to movement around the area where the spray droplet is deposited..
Check the above White Paper for the below additional points to consider for control of soybean diseases.
● Several important diseases of soybean, e.g. stem canker, sudden death syndrome, and charcoal rot, have no curative control. They may only be prevented or managed by selecting less-susceptible or resistant varieties, or rotation to a non-host crop.
● Seed and seedling diseases can be effectively prevented by using the appropriate seed-applied fungicide.
● Soybean rust can be managed with applications of preventive and curative fungicides timed according to occurrence of rust in sentinel plots.
● If an FLS-tolerant/resistant variety is grown, applying a stand-alone strobilurin fungicide is an acceptable practice to manage other diseases or as an automatic fungicide application.
Diseases can and do cause economic losses in midsouthern US soybean production. The above information should be considered to prevent those losses.
Composed by Larry G. Heatherly, June 2016, larryheatherly@bellsouth.net