Lodging (Stalk Rot) and Corn Fungicides

The impact of the cool temperatures leads to many questions, including the impact on stalk rots (lodging) in corn, and would a fungicide application benefit? When it comes to stalk rot, stress conditions are important contributors to infection and stalk strength. These stresses may include excessively wet or dry conditions, cool temperatures, lack of solar radiation (sunshine), the presence of leaf diseases (such as rust, Northern leaf blight and gray leaf spot), leaf and ear damage (from hail, birds or frost), incomplete pollination, unbalanced fertility, insect damage, excessively high plant populations, poor soil conditions, and hybrid susceptibility to all of these stresses. All of these factors can increase the incidence of stalk rots and impact stalk strength

Trials in 2008 (and again in 2009) by the University of Guelph Ridgetown Campus and OMAFRA were established to answer some of these questions. In 2008, we observed an association between reduced lodging and a fungicide application (Headline) at the tassel to silking stage in 21-hybrid trials (see one trial in Figure 1). Due to limited space and resources we did not apply any other fungicides in this trial. Although 4 of the 21 hybrids had a significant increase in standability (25% or more), the majority had more modest increases. It is important to note that these improvements in stalk stength were realized even when overall leaf disease pressure at this location (and others) was relatively low at less than 5%.

In other trials from 2008, 4 hybrids were chosen that ranged from tolerant to very susceptible to two pathogens that cause northern leaf blight and eyespot disease in corn. At both Ridgetown and the Huron Research Station, the greatest lodging occurred in the hybrid which was most susceptible to the foliar diseases, and as expected, it had the greatest amount of disease in the trial. These results are similar to other studies which often associate less lodging (stalk rot) with control of leaf diseases.

What is the Impact of Stalk Rots?

The distribution and prevalence of stalk and ear rot diseases vary from year to year, but the diseases are present in most years even though it may be at low levels. The majority of stalk rot damage in Ontario is caused by four fungi, namely Anthracnose, Gibberella, Fusarium and Diplodia. However, Pythium have also been observed in Ontario. Although these fungi cause different symptoms, their ultimate effect on the corn plant is the same. They reduce grain fill and stalk integrity and accelerate senescence. Stalk rot fungi affect the nutrient movement of the corn plant in three main ways.

1. Sugars (photosynthates) produced through photosynthesis and carbohydrates in the root and stalk are diverted to the fungus and not to the ear. These nutrients allow stalk rot fungi to grow and flourish.
2. There is a reduction in stalk integrity. To meet the nutrient needs of both the developing ear and the stalk rot organisms, the corn plant will begin to cannibalize itself by moving soluble carbohydrates from the root and stalk. Problems arise when the plant is unable to meet the nutrient requirements of the developing ear. The result is a weaker stalk (prone to lodging) and less resistance to stalk rot fungi.
3. Finally, the infection and colonization process inhibits or blocks many of the pathways that the plant would ordinarily use to move nutrients. Yield losses (generally 10%-20%) arise from poorly filled ears and harvest losses from lodging.

Figure 1. Increased Hybrid standability After Headline

Each response average of 4 replications
Standability assessed after a push test before harvest

Hooker, Tenuta and Stewart (2008)
University of Guelph, Ridgetown campus, OMAFRA

Figure 2. Impact of Fungicide and High Leaf Disease Pressure on Corn Hybrid Standability