It is time to consider preventative applications for soilborne diseases. Two different fungi (Rhizoctonia solani and Pythium spp.) are the primary components of the pod rot complex. These fungi may occur alone but are often found together. Positive disease identification is necessary to ensure maximum economic returns for chemical applications.
Subtle differences between symptoms caused by the two can be observed. Pythium infections may include blackened decay with a greasy appearance; whereas, Rhizoctonia infections may have more of a dry textured appearance. Laboratory confirmation is often required for a complete diagnosis.
Preventative fungicide applications are generally administered 60 to 90 days after planting; however, early initial applications may result in the need for an additional application late in the season if conducive environmental conditions persist.
Several factors must be considered when applying pod rot fungicides:
1. Growth Stage – Applications made before the formation of pegs and development of pods may limit the amount of product that is ultimately deposited in the pegging zone. Therefore, it is important to monitor peg development and delay applications accordingly.
2. Pathogen Pressure – The identification of which pod rot pathogen you are dealing with will dictate fungicide selection.
3. Fungicide Selection – Pod rot fungicides with activity against Rhizoctonia consist primarily of Abound, Artisan, and Convoy. Other fungicides such as Folicur (and other generic formulations of tebuconazole) and Provost are labeled for Rhizoctonia pod rot; however, their labels specify that applications are made in a 4-block regime (that is more congruent with practices in the Southeastern US).
AgFax Weed Solutions
Additional fungicides are labeled for use against Rhizoctonia; however, efficacy data of these products is limited. Fungicide options for Pythium are limited to Ridomil (several formulations including a liquid and a granule are available), and Abound (suppression only, at the maximum label rate of 24.5 fl oz/A).
4. Application Method – The activity of these products can be increased substantially when applied via chemigation; however, the banding of initial applications is often more cost effective. Broadcast applications result in fungicide treating bare ground which may be wasteful.
Increasing carrier volumes (>20 gallons per acre) will improve deposition into the lower canopy, especially when applying liquid Ridomil formulations (as that product binds very quickly to the leaf). Administering irrigation soon after fungicide applications will also help to redistribute fungicides deposited on the foliage and increase concentrations delivered to the pegging zone.