Saturday, December 3, 2022

Time To Make End-Of-Season Disease Notes

⋅ BY NICHOLAS DUFAULT ⋅

As the end of the peanut season approaches, there are many things that need to be done; however, do not forget to pay attention to late-season diseases. Leaf spots and rust diseases are always on our minds, but harvest is an excellent time to evaluate many soilborne disease issues, especially in fields with minimum to no crop rotation. Below are three important disease situations that can be assessed before or shortly after digging peanuts.

Cylindrocladium Black Rot

Red perithecia on the stem on the crown at the soil line is a sign of CBR.

This disease is not typically on people’s radars, and it can be an especially devastating disease after a warm winter. Field diagnosis of CBR is possible, but it is highly recommended that a laboratory diagnosis be made as there are many look-a-like diseases, including Neocosmospora foot and pod rot, Tomato Spotted Wilt Virus, the pod rot complex and stem rot/white mold. 

While we do have some late season management options for CBR, the best management of this disease occurs at planting up to 40 days after planting. Early applications of fungicide products containing prothioconazole (e.g., Proline, Provost Silver and Propulse) can effectively reduce the pathogen’s impact on peanuts. The addition to foliar sprays of prothioconazole can also be helpful for CBR management if applied between 40 and 90 days after planting. Later season sprays can help manage the disease but typically do not lead to significant yield savings.

Pod Rot

These peanuts show pod rot caused by Pythium spp.

Peanut pod rot is an issue that is often hard to diagnosis before you dig peanuts as there are no above-ground symptoms or signs of this disease. However, after digging, it is not uncommon to find sections of the field with dark and rotting pods. This issue can be amplified by heavy rains, such as those parts of the state receiving rain from Hurricane Ian. Pod rot can be caused by multiple fungal and oomycete (water mold) pathogens, including CBR. This makes diagnosis critical to a management plan for next season. 

Unfortunately, while this issue can be identified in the field, the pathogen cannot. It is recommended that producers collect a sample of five or more plants from their fields and send it to a diagnostic laboratory for pathogen confirmation. After diagnosis, consult your local Extension office for how to plan for the specific pathogen related to this disease issue in the future.

Stem Rot/White Mold

A plant infected with white mycelia and sclerotia from white mold/stem rot is found by looking down into the crown of the plant at the soil line.

Stem rot/white mold continues to impact peanut production in Florida and throughout the Southeast. However, the extent of the damage from this disease can go unnoticed throughout the season depending on environmental conditions and the peanut’s response to the pathogen. That’s why paying attention at digging is critical to developing and implementing an effective management plan for 2023. 

Sclerotia of stem rot/white mold pathogen appears as white, fuzzy mycelia.

Similar to CBR, there are early season fungicide options available, such as tebuconazole and prothioconazole, to help manage this disease as well as the possibility to improve the timing of typical stem rot applications, (e.g., flutolanil and inpyrfluxam), which occur at 60 and 90 days after planting. Also, there are multiple varieties available with resistance to this disease that should be considered in fields with a history and on a minimal crop rotation.

Final Thoughts

Disease assessments can be time consuming and difficult to complete between harvest and extreme weather events such as hurricanes. However, if the issue is large enough to notice from the cab of a tractor or truck, it’s worth assessing. There are some early season management options available for these pathogens that can be a “game changer” the next season when it comes to disease management. Unfortunately, there is not one management technique available that will manage all of these disease issues, which makes proper diagnosis important. PG


Article by Nicholas Dufault, University of Florida Extension plant pathologist for vegetable and row crops.

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