Crop Progress

 

With less than a month to go before school starts, summer is winding down. Most farms have had plenty of moisture, so crops on the surface look good. However, there may be some hidden nutrient deficiencies, hidden yield losses, and even insect and disease issues starting to surface. On corn, sometimes too much rain at pollination may cause a problem. Tight tassels may occur which may limit or delay pollination of corn kernels. Sometimes the kernels get pollinated but at different times so the kernels grow at different rates. It creates different size corn kernels and funky looking corn. Some corn varieties are worse than others. Sometimes it is also caused by drought or nutrient imbalances. Yield losses may range from 15% to 40% depending upon how long and tight the tassel wrap occurs.

On soybeans, too much moisture often causes poor rooting. Some areas have received twice as much moisture as usual and the soybeans are suffering due to anaerobic (lack of oxygen) soil conditions due to ponding water and a lack of roots. In other areas, on sandy soils especially, the soybeans may be yellowing due to soybean cyst nematodes and sudden death syndrome. Insect pests are also being noticed in soybeans. Grasshopper and Japanese beetle appear to be chewing on some leaves, however; most of the damage, so far has been relatively minor. Farmers should be checking their fields though for further damage.

Right around August 1st and thereafter; it is easy to see symptoms of what I call the soybean mystery disease. It is not actually just one soybean limiting disease, it may be a whole slew of soybean diseases that start to show up that may reduce soybean yields 10–30 bushels. Generally, this complex of diseases is worse during dry years but it can affect yields in wet years. Here are some soybean symptoms to watch out for this year.

Usually, low areas or compacted areas show up first but also hilltops with sandy soils. It starts on lower leaves which turn pale, yellow, then brown and fall off. Usually, bean pods start aborting from the bottom third of the plant. Often, Manganese (Mn) deficiency signs characterized by dark green veins with yellow leaves occurs. Some leaves have yellow and brown halos that look like septoria leaf spot on steroids.

In severe cases, the top soybean leaves thin out. I say it looks like a Charlie Brown Xmas tree. Small top leaves, aborted blossoms, and aborted pods signal Calcium (Ca) deficiency. Another odd characteristic: On the top trifoliate leaves, the middle leaf stands almost perpendicular to the sun. (Almost looks like a middle finger sticking up.) In some cases, the leaf is bent over so much that the bottom of the leaf is pointed to the sun rather than the top of the leaf. Severely impacted plants are at least 6 to 8 inches, even a foot shorter than healthier plants nearby. Plants start maturing 2–3 weeks early.

Some of these symptoms line up with charcoal stem rot, sudden death, soybean cyst nematode, and septoria. Sometimes it’s Phytophthora stem root and Sclerotinia (white mold disease) or even Fusarium. The key point, it can be several diseases showing up at the same time. The most telltale sign is one upright leaf, bent straight up on the petiole, on trifoliate leaves at the top of the plant. The bad news is that as the season progresses, it may get worse.

Last year, soybean plants started showing stems with no leaves and no pods. Almost like deer nipping the top leaves off, except it was too widespread for deer damage (Ca deficiency, aborted blossoms, no leaves). On healthy soybean plants, leaves can sometimes be almost the size of your palm on your hand. On infected plants, leaf size is very small.

This year, again, there was a lot of spraying, especially with glyphosate (Roundup). Sometimes several applications. Glyphosate chelates many nutrients (Manganese, calcium, iron, zinc, copper, nickel) and most diseases occur when nutrient deficiencies are occurring. Glyphosate is not the cause of diseases; it just may enhance the symptoms and increase the occurrence of multiple diseases. When nutrients are lacking, insects and diseases attack stressed plants and yields decline.

Tips: Try to reduce glyphosate applications especially after soybeans bloom (R1). Do not tank mix Mn with glyphosate because it gets tied up. It should be applied separately, if possible, perhaps with a drone. If you plan to plant soybeans back to soybeans, try planting a cover crop to increase microbial activity and reduce diseases. Scout fields now to look for the damage described above before the crop totally matures.