Corn Stalk Rots and White Mold In Soybeans
After spending the last few days wandering around in some corn I have noticed a fair amount of stalk rots. I don't think it is a great surprise to many that stalk rots may be more common this year. Stalk rots (of which there are many different kinds) are caused by certain soil borne or air borne pathogens that can manifest themselves after good growing conditions followed by later season stresses. These stresses could be anything from N deficiency, other foliar diseases, hail, drought and a whole host of other things. One thing for sure is that we did have good early season growing conditions and less than ideal conditions after tassel. The pathogens that cause stalk rots are normally present every year and this year brought just the right conditions for them to propagate. Your only real defense against stalk rots are to select hybrids with good stalk strength and do what you can to limit late season stress by making sure of adequate weed control, fertility and so fourth.
If you see any stalk rots there are a couple of rules of thumb to remember when trying to identify which type it is. The reddish internal coloring is indicative of gibberella stalk rot, a dark coloration will probably be anthracnose and the absence of any discoloration could be fusarium. These three are by no means the only types of stalk rot but can be a useful tool when trying to determine which type you may be facing.
Knowing the type of stalk rot may be irrelevant if not expecting it. I will be trying to get a look at more fields in the near future but if a wind shows up now it could still be very devastating. You should be prepared to take corn early if needed.
Many of you have been noticing random dead soybeans in many fields. This, as expected, is white mold. Some fields don't seem to have much at all while others will probably lose a high percentage of yield to it. As you know, the warm, wet conditions we have seen at flowering this year is very much favorable to the development of white mold and fields with a variety of bean without good white mold tolerance is being hit hard. Like stalk rot, the pathogen that causes white mold is ever present and in this year found favorable conditions to increase.
The first picture below is that of the white mold apothecia, the structure that produces the white mold spores. What is important about that now is that I took this picture in a corn field and the apothecia were very easy to find. This is a good indication that this particular field will be at risk for white mold next year if conditions favor it. This should be something else you should be looking for in your fields.
To identify white mold, split open a suspected soybean stem. Inside you will find the sclerotia, these are the 'rat turd' looking structures that many of you have heard talked of in the past. (second picture) It is also these sclerotia that can spread via your combine to non infested fields so remember when moving from one field to the next that you could be helping spread this disease to your other fields.
Weed control is also important for control of white mold. Certain weeds are known hosts. These are lambsquarter, ragweeds, pigweed, velvelteaf and others. Chemical control has proven inconsistent and since no variety is completely resistant to white mold, choosing multiple soybean varieties may prove to be a good way to lesson your susceptibility to infection.