By Melissa Bartels and Tamra Jackson-Ziems et.al
With harvest quickly wrapping up around the state, now is the perfect time to think about how you can minimize diseases next growing season. Reviewing diseases and the level they were present in your fields can help you select more disease-resistant corn hybrids and soybean varieties for the upcoming season.
This is an important concept when you consider most of the diseases of corn and soybean in Nebraska are caused by pathogens that overwinter (survive) in fields year after year. Most of these pathogens survive in infested residue or crop debris from the previous growing season(s). For example, if susceptible corn hybrids are planted in a field with a history of gray leaf spot, or another disease caused by a residue-borne pathogen, you can expect to see disease development when weather conditions are favorable. Planting disease-resistant hybrids and varieties may be a more economical way to manage certain diseases, reduce disease severity and reduce dependence on pesticides, like fungicides, thereby cutting input costs. In some cases, selecting resistant varieties can be the best way to reduce disease such as sudden death syndrome of soybean (Figure 1) and Goss’s bacterial wilt of corn (Figure 2).
Figure 1. Leaf symptoms of sudden death syndrome of soybean.
Figure 2. Goss’s bacterial wilt of corn.
The word “resistance” seldom suggests plants are immune to a specific disease. Instead, it implies a reduction in disease severity. The degree of hybrid resistance to a particular disease can range from high to low. For instance, under low disease pressure a low level of disease resistance in a seed selection could be adequate, but a moderate or high level of resistance may be needed in a seed selection for fields with a history of severe disease presence. This is also the case in fields in production systems that are at greater risk for disease, such as those in continuous corn or soybean production, or those in minimum or no-tillage regimes where more infested residue (and the pathogen) is maintained on the soil surface.
It is important to refer to your company's seed catalog to understand their rating scale. Be aware, not all companies evaluate their hybrids for their reaction to diseases as evaluation of hybrids and varieties can be costly, time consuming, difficult, and/or impossible due to the nature of the pathogen(s). Table 1 lists some of the diseases for which companies have provided ratings in their seed catalogs for their corn hybrids or soybean varieties. Remember when comparing hybrids and varieties across different companies, their scales might be unique. For instance, 1-9 might mean “high to low” resistance for one company but “low to high” for another. To avoid misinterpretation, pay close attention to the rating scale and their exact meaning, and contact your local company representative for clarification or if you have questions.
Table 1: Seed companies in Nebraska provide ratings to some of the following diseases.
|Corn diseases||Soybean diseases|
|Gray leaf spot||Soybean cyst nematode|
|Bacterial leaf streak||Phytophthora root and stem rot|
|Northern corn leaf blight||Frogeye leaf spot|
|Goss’s wilt||White mold|
|Tar spot||Sudden death syndrome|
|Southern corn leaf blight||Brown stem rot|
|Southern rust||Southern stem canker|
|Common rust||Charcoal rot|
|Tar spot|| |
|Fusarium crown rot|| |
|Anthracnose stalk rot|| |
|Diplodia ear rot|| |
|Fusarium ear rot|| |
|Gibberella ear rot|
Source : unl.edu