Row Crop Disease Update
Kemerait and Brenneman
Over the next week, temperatures in southern Georgia as expected to be near 100 degrees for several days. Such very warm conditions can bring a greater urgency to early-season disease control in the peanut crop with regards to Aspergillus crown rot and white mold. Risk to losses from these diseases can be more severe when conditions are hot early in the season. First, both fungal pathogens (Aspergillus niger and Sclerotium rolfsii) thrive in warm environments. Second, hot soils (temperatures well above 100 degrees) will scorch the young seedlings just below soil surface, creating wounds that can be exploited by the A. niger pathogen, increasing risk to Aspergillus crown rot. This has also been shown to be a factor with Diplodia collar rot which can also be an issue on peanuts both early and later in the season in Georgia. Diplodia is often seedborne, and the good growing conditions for last years seed should help minimize that problem for this years crop. Lastly, lesser corn stalk borers are often more problematic in hot and dry soils; lesser corn stalk borers also increase the risk to Aspergillus crown rot.
Who is at most risk to Aspergillus crown rot?
From above, Aspergillus crown rot is more of a threat during early-season periods of hot and dry weather. Once the tap-root of the peanut plant “hardens off” and becomes less succulent, the peanut plant is less susceptible to this disease. Aspergillus crown rot occurs more commonly in non-irrigated fields where irrigation cannot be used to cool the soil; Aspergillus crown rot also occurs more commonly where poor seed quality is an issue.
Management of Aspergillus crown rot
- Use high quality seed. Saved- seed may be at increased risk to Aspergillus crown rot.
- Use a good fungicide seed treatment (preferably Rancona over Dynasty PD specifically for Aspergillus crown rot).
- Consider use of an in-furrow fungicide. Azoxystrobin is more effective on Rhizoctonia seedling disease and less effective against Aspergillus crown rot. Products that contain fluopyram (Velum and Propulse) have better activity against Aspergillus crown rot than does azoxystrobin.
- Take steps to control lesser corn stalk borers.
- When available, use irrigation to reduce threat from Aspergillus crown rot. Growers sometimes fear that irrigation will spread the disease, but in reality there is little if any “in field” spread. Irrigation to reduce stress on the plant and help them develop as quickly as possible is a positive step toward control. It also helps reduce damage from lesser corn stalk borers.
Who is most at risk to early-season outbreaks of White mold?
Hot soil temperatures early in the growing season predispose the peanut crop to white mold even before a foliar canopy has developed. Early season white mold can be identified by white, thread-like fungal growths along the developing taproot of the peanut plant and subsequent wilt and death. Early-season threat from white mold may also be more problematic in conservation tillage than in conventional tillage as the sclerotia that initiate infection are more likely to be in the upper few inches of the soil surface. Obviously, growers who plant peanuts on short rotations (every year or every other year) are at risk to early-season outbreaks.
Management of early-season white mold (when appropriate)
- Apply Proline fungicide in a concentrated band ( 6 inches for single rows and 10 inches for twin rows)3-5 weeks after emergence.
- Include a fungicide effective against white mold in the 30 and 45 days after planting broadcast applications instead of chlorothalonil only (which has no activity on white mold). For example, Priaxor and Lucento have both shown activity on white mold when applied during that spray timing for leaf spot.
- Use of Proline as an in-furrow application at planting may have some benefit, though limited, in the management of early-season white mold.