When growing soybeans, Anne Dorrance, OSU Extension specialist, lists some symptoms and conditions to look for:
1. Early dying due to drought. Yep, drought. Some parts of the state have not had rain in more than two weeks and the leaves on the plants are turning a pale yellow, and leaves are dropping prematurely. If you can dig up the roots – they are white and healthy – no soybean cyst nematode (SCN). However, look at the roots; there are few of them. Many of these plants are in the same fields that were hit with too much water earlier in the season and have poorly developed roots systems, thus making them more prone to drought injury. This just emphasizes that soybeans in Ohio need to be ready to be able to tolerate many, many challenges.
2. Early maturity due to high SCN populations. Based on several recent surveys in the state — one from my lab and the latest work from Laura Lindsey and Terry Niblack’s groups — we have many fields in the state with high SCN populations. Fortunately, these high SCN populations sit in pockets in fields and can be detected by early maturity. If you have an area of a field that consistently turns yellow first, and you know it is not due to flooding – go take a look at the roots or target that site for sampling this fall. Knowing what your SCN numbers are is critical to management and knowing what crop should go in that field in 2016.
3. Phytophthora stem rot. Yes, Phytophthora stem rot is popping up in our historical high Phytophthora fields. We really should not be finding this, but there are a few cultivars out there that are relying too much on the Rps genes to carry the load and our P. sojae populations are too variable. This pathogen in Ohio has adapted to all of the commercially available genes and we must now really look at the variety listings for partial resistance (sensu field resistance, tolerance). Approximately a week after a heavy rain, plants will begin to show symptoms and you can find that classic chocolate brown canker moving up the stem.
4. Sclerotinia stem rot. As predicted, this is beginning to show up in a few spots. The hot dry weather over the past two weeks has set it back a bit, but it is showing up in a few fields. Plants have a dull gray/green appearance and hold their leaves while the fluffy white mold can be observed on the stem.
5. Sudden death syndrome. This one has me a bit confused this year. We found lots of plants with symptoms earlier this summer but, following some rain, the plants reflowered and seemed to recover. As these plants begin to approach growth stage 6 – full pod and beginning to mature — I think we will see the symptoms return and be even more dramatic than what we saw earlier. On some of these plants, the tap root is totally dead but the plants put out large side roots to help make it through the rest of the season. It will be interesting to see what the yield hits will be this year.
6. Frogeye leaf spot. I received some more calls last week about this one in fields which are in the late growth stages (> 5.0). It’s too late to do anything but, since we now know that this pathogen can overwinter here, we need to be careful. I don’t care how you do it, whether it is on a big map of your farms, or in individual field notes, but mark that this disease was present. And for 2016, plant a different crop – corn or wheat, especially if you are a no-tiller. If you till, then some tillage is in order for this one. Then preferably for 2017, plant a variety with resistance to this pathogen. During the 2004/2005 winter, we had many fields with high levels of frogeye at the end of the season and the pathogen overwintered in high numbers, and got off to a very early start in 2005. We had substantial losses on almost ½ million acres, so let’s not repeat that one.
Rob Leeds is the Ohio State University Extension educator for agriculture and natural resources in Delaware County.