The following update was prepared by Clemson peanut specialist Dan Anco.
60 DAP Fungicide Application: Peanuts planted May 1st will be at 60 DAP next week on June 30th. This is around when we get full size pods and when pod-fill may be beginning. This is also the beginning of the critical soil disease management period (foliar disease management typically begins around 45 DAP). For high risk situations (susceptible varieties, field history, short rotations, inadequate volunteer control during rotation years…), programs that include multiple premium fungicide applications can be greatly beneficial. However, if we only use one premium fungicide application, 60 DAP is the time to use it. Outside the standard chlorothalonil + tebuconazole (Bravo + Folicur), premium fungicide options include Elatus, Priaxor, Fontelis, Bravo + Convoy, and Provost.
While many of us are familiar with peanut diseases, it doesn’t hurt to remind ourselves about a couple points. First, while we often manage diseases and insects using many of the same basic methods (resistant varieties, pesticides, planting time…) the differences in how we use some of these methods can be very important. Take pesticides for example. With insects, we have insecticide chemistries with knockdown action to kill insects that are currently there (not forgetting that we also have important preventative insecticides). With diseases, while we have some chemistries that have some reach-back activity, the majority of our products act to prevent the growth of fungi. Because of this, even though we may not see a disease problem when we are deciding which fungicide to use (especially during earlier fungicide applications), this doesn’t mean we are in the clear. When managing diseases, it is critical to prevent the disease from building up in the crop, and this is much easier to do if we plan for it early on rather than trying to compensate for it after the fact. It takes time for a spore of a disease-causing fungus to germinate, to enter the peanut plant, and grow enough to finally be visible as disease symptoms. The whole disease process can go even more unseen with soil diseases, where we sometimes might not see anything until inversion. By the time we actually see disease symptoms, how many more infection do we have that is just not yet showing symptoms? While it’s usually “more”, the answer to this is not always so clear, but what is clear is the importance of disease prevention: we don’t want to wait till it’s too late.
Manganese: If our soil tests indicated we need manganese (Mn), or if the new peanut leaves are showing Mn deficiency as yellow between the leaf veins, we should include manganese with our 60 DAP and 75 DAP fungicide sprays. Copied here is the section from the Peanut Money-Maker:
Mn deficiency shows up as yellowing between leaf veins in the top of the plant. Mn deficiency is most prevalent on soils limed to 6.4 or higher. Prevent or correct with two foliar applications of 0.5 lb elemental manganese per acre (2 lb/A manganese sulfate 25% or 1.5 lb/A Tecmangam 32%, or 1.5 lb/AManGro DF 31%). Only foliar treatment is effective and new growth will remain deficient, so repeated applications of 0.5 lb elemental manganese are recommended.
Liquid manganese applications are more convenient but not any more available to the plant than dry formulations. Make sure liquid formulation use rates are adequate to meet the nutrient requirement. See table below for equivalent liquid rates.
|Amounts needed to supply 0.5 lb elemental manganese/A.|
|Manganese sulfate 25%||2 lb|
|Tecmangam 32%||1.5 lb|
|ManGro DF 31%||1.6 lb|
|Liquid 10%||2 quarts|
|Liquid 5%||1 gal|
|Liquid 1%||5 gal|
|*Assumes weight of approximately 10 lb/gal.|
Peanut manganese sufficiency levels for soil pH (from soil test).
pH Mn lb/A
For pH values above 6.5, the Mn lb/A sufficiency level increases by 1 lb for each 0.1 pH increase (for example, a soil pH of 6.8 would have a Mn sufficiency level of 15 lb/A).