Where does knotty smut in corn come from?
Let's start from the source. Where does the knotty smut of corn come from on the plantation? How does it develop? So the development of the disease caused by the fungus Ustilago maydis is facilitated by pests, i.e. the fungus develops in the first two generations primarily on those plantations that have been infected by the corn fly (first generation) or aphids (second generation). What's more, this fungus thrives primarily in high temperature conditions, around and above 30 ºC. At the same time, the infection is facilitated by conditions when plants struggle with water shortages, but also nutrient deficiencies. We will observe a particularly high intensity of the development of the disease after a period of drought, when humid conditions appear.
The nodular smut is quite characteristic and relatively easy to recognize. As a result of infection, we will notice growths in white and cream shades, at this time most often on developing cobs.
read more
Will drought reduce corn yields?
Three generations of blades
Currently, we are dealing with the second (and in some cases the third – depending on the region, earliness of the variety and sowing date) generation of knotty smut of corn. The last one is the least dangerous and usually appears relatively late, at the time of kernel filling and during milk maturity. In the case of the third generation, there are no longer any yield losses, and the kernels themselves have less protein (and therefore worse quality in the nutritional context). Studies show that the third generation of knotty smut develops particularly intensively on plants previously infected by the feeding of the European corn borer.
The first two generations of knotty smut are definitely more dangerous in terms of yield. The most dangerous is the smut that appears in the initial stages, usually in the BBCH phase 14 – 16. In extreme cases, infected plants die (this can happen if knotty smut appears in the growth cone).
The second generation occurs around flowering, and is usually the time of panicle shedding. The growth resulting from infection is mainly visible on young cobs. Generally, we can encounter a situation where the cob is partially grained and only a fragment is infected, but there are also cases where the cob remains without grain due to infection.
Can knotty smut cause significant yield losses? Theoretically, we are talking about an average loss of no more than 10 percent (from 3 to 10 percent). It all depends on when the infection occurred. It is worth noting that usually we observe greater intensity of knotty smut in the marginal strips of plantations.
read more
How much does corn on the stand cost?
Knotted smut and silage
And what about feeding animals with silage made from corn where smut has appeared? Generally, there are no obstacles to making silage from infected plants, as confirmed by German studies, among others. However, there is a caveat. While the fungus causing knotty smut in corn does not produce mycotoxins, Fusarium fungi do. Therefore, you need to be a little careful, because there is a possibility that the smut itself will also be infected, precisely with fusarium fungi. Then we will also notice clusters of fusarium fungi spores on the surface of the smut (pink, slightly orange, salmon). So we are talking about a situation where the smut itself is infected. To sum up: if we notice the presence of knotty smut on a plantation, this alone does not disqualify it from being used for silage, however, if it is secondary infected with fusarium diseases, fungi from this group are able to produce mycotoxins. Interestingly, if animals are fed silage from a plantation infected with knotweed, there is a greater risk of the disease appearing on the next plantation (after fertilization with manure from animals eating such feed).
