In This Issue:
- Can warm nights reduce grain yield in corn?
- Western Bean Cutworm Update: Eggs and Larvae Found
- Foliar Diseases Showing up in Corn
- Evaluation of three commercial mycotoxin inhibitors added to Vomitoxin (DON) contaminated corn diets for weanling pigs
- Inoculum for Sclerotinia apothecia is present in some fields
- Foliar diseases are absent in soybeans
- Scab Resistant Soft Red Winter Wheat Varieties are Available for Fall Planting
- Wheat Seed Treatments 2010
Western bean cutworm larvaeWestern Bean Cutworm Update: Eggs and Larvae Found
For the first time, we have found western bean cutworm egg masses in Ohio. Last Tuesday, July 13, a field in Fulton county was inspected where egg masses were found. Pictures from this field including the egg masses and newly hatched larvae can be found on our Agronomic Crops Insects website: http://entomology.osu.edu/ag/pageview3.asp?id=1150.
Remember, egg masses are first white, then tan, and then turn a deep purple color immediately before they hatch.
(Be sure not to confuse western bean cutworm eggs with stink bug eggs. Stink bug eggs are first white, then turn a dark brown before hatch—images of stink bug eggs are at the above website for comparison). Western bean cutworm eggs of all stages were found in this Fulton county field. In addition, some 1st instar larvae were found feeding on the unemerged tassel within in the whorl. However, the good news is that this particular field was under economic threshold (threshold is 5% of corn inspected with egg masses or larvae). These observations indicate that oviposition and egg hatch is underway. Corn fields should continue to be inspected for both eggs and larvae, especially in pre-tassel corn. Once tasselling is complete, these corn plants are less preferred hosts for western bean cutworm. In pre-tassel corn, the top-most 1-3 leaves that are still mostly vertical in orientation should be searched for egg masses on the upper surface of the leaf. Often time you might see the shadow of the egg mass on the underside of the leaf when viewed facing the sun (a picture of this is also at the web site). In corn that has tasseled, inspection should also include the possibility of larvae. Larvae can be found feeding on the leaves or on the silk. These next few weeks will be critical as, if chemical application is needed, it must be applied after egg hatch and before larvae enter the ear.
It is difficult to determine if we have reached peak flight yet. Counts are increasing in some areas (northwest and northeast Ohio), while more southern and central locations are seeing a decrease. Previous years have seen peak flight during the 3rd or 4th week of July, and, because of the warm June and July, we may be in peak flight now. Our total count as of July 19 is 1,659. Please see our updated trap counts for Ohio at http://entomology.osu.edu/ag/pageview3.asp?id=1390. Again, if you find what you think are western bean cutworm egg masses or larvae, please contact entomology specialists at michel.70@osu.edu or hammond.5@osu.edu.
Inoculum for Sclerotinia apothecia is present in some fields
Sclerotinia white mold, also known as Sclerotinia stem rot has a very interesting disease cycle. The inoculum comes from very small fruiting bodies called apothecia that form from the sclerotia. There are several papers that have looked at the formation of these, but they tend to be from lab conditions. Last week, we found apothocia in fields in north east Ohio (Figure 1). 
This was a bit of a surprise as the 2 weeks prior to this were dry, but rains did fall 3 to 4 days prior, the night time temperatures hit below 70 a couple of nights and more importantly – there was still heavy dew on the plants at noon. My pants were soaked. In addition to apothecia from Sclerotinia we also found birds’ nest fungus (Figure 2)
and another yellow fungus (Figure 3).
Both the Bird’s nest fungus and the Yellow one, were on the decaying residue and not found with sclerotia. Neither of these contribute to white mold but do help in degrading the soybean residue. When it is wet, there are lots of different fungi found on the residue of soybean fields (and corn and wheat as well) but only those that germinate from sclerotia (the rat turds) are associated with development of Sclerotinia stem rot.
These fields are those that always have some white mold in them – this disease does not occur in every field across the state – for those historically positive fields – this is a year to watch. Fungicides (Topsin M) needs to be applied at the R1-R2 growth stage for any management of this disease. We have soybeans at just about every growth stage from V1 to R4 – so it will be interesting. Monitor the growth and development of soybeans – fields that have been historically positive for Sclerotinia, form a dense canopy prior to flowering and have consistent moisture and a few cool nights are at the highest risk for this disease.
Note: whenever you apply a fungicide – always leave a control strip or 2 (not the edge of the field) to evaluate if the treatment worked. If it didn’t then, a) reassess if you truly needed the treatments or b) double check the timing of the application. All fungicide applications work best when applied prior to arrival of fungal spores, as protectants on the leaves or stems depending on the disease in question.
- Glen Arnold (Nutrient Management Field Specialist),
- Roger Bender, ret. (Shelby),
- Bruce Clevenger (Defiance),
- Justin Petrosino (Darke),
- Gary Wilson (Hancock),
- Les Ober (Geauga),
- Mike Estadt (Pickaway),
- Matt Davis (Northwest ARS Manager),
- Wes Haun (Logan),
- Ed Lentz (Hancock),
- Suzanne Mills-Wasniak (Montgomery),
- Greg LaBarge (Agronomy Field Specialist),
- Steve Prochaska (Agronomy Field Specialist),
- Mike Gastier (Huron)