Friday, July 31, 2009
Thursday, July 30, 2009
- Genetics: There is a wide range in test weight among the common wheat varieties grown in WI. In a "good" year these differences may not appear significant however in a "bad" year these differences can cost growers significant dollars. The University of Wisconsin Variety Test Program not only provides growers with yield information, but we also report test weight differences. Our variety trial results will be published in the next two weeks. Go to www.coolbean.info for these results.
- Weather: The wetting and drying action of frequent rainfalls on dry wheat can drop test weight quickly. Thus timeliness of harvest is critical. Wheat can also swell following a rainfall and remain swollen even after the grain has dried back down. This increased kernel size displaces space and leads to lowered test weight.
- Thin stands: Thin stands due to winterkill in parts of WI have led to late tillering, green stems and immature heads in the field. This may be causing a resource allocation issue in some fields (e.g. some photosynthates maybe going to growth instead of grain fill). If possible avoid these parts of the field if you are experiencing low test weight.
Tuesday, July 28, 2009
Soybean aphid infestations remain at sub-economic levels throughout Wisconsin. Will they stay there, or will we have a repeat of last year’s late season aphid buildup? We will have to wait to see what aphid populations do over the next several weeks. However, one thing we do know - that soybean fields with suboptimal potassium levels are at greater risk of soybean aphid population increase and yield loss.
Following the 2000 discovery of the soybean aphid in Wisconsin, entomologists and agronomists noticed that soybean aphid infestations seemed to be more severe in K deficient soybeans. [The below photo of a soybean field in Grant County (taken by John Wedberg in August, 2000) illustrates this. The yellow beans on the left were literally dripping with soybean aphids and were presumed to be K deficient, whereas the healthy beans on the right had few aphids and were thought to have adequate K. The demarcation line follows the field contour.]
Subsequent research has proved this observation to be correct, plus we now have a better understanding of why this occurs. What happens is that low K actually makes soybean more nutritious for soybean aphids, promoting higher aphid reproduction and leading to more rapid aphid population increase. To give an idea of how this might work, under field conditions in a K deficient field an aphid infestation can increase from 10 per plant to 230 per plant in 10 days; in a field with adequate K, that same population would increase from 10 to 150 aphids per plant. Further research suggests that K deficient beans have a greater percentage of asparagine in the plant phloem where the aphids are feeding. Asparagine is known to be an important amino acid for aphid nutrition.
Finally, we think the yellowing of K deficient soybean leaves may preferentially attract migrating soybean aphids, placing K deficient fields at a further disadvantage. The color yellow has been shown to be highly attractive to a number of aphids.
Bottom line, maintaining adequate K levels in soybean goes a long way toward managing soybean aphid.
Monday, July 27, 2009
Image by Tim Wood
As growers, county extension agents, and crop consultants walk fields and assess crop damage it is important to remember the following key points.
1. Do not do anything to the field before you call your hail adjuster and have the claim inspected.
2. Remember in soybean the crop injury often looks worse than it really is. A soybean can add a new trifoliate ever 3-5 days so canopy coverage will reoccur in ~2 weeks.
3. Most of the soybean crop in Wisconsin is in the R3 growth stage or earlier. If defoliation only occurred expected yield loss ranges from 0 to 33% (33% yield loss may occur at 100% defoliation). If stem breakage or node removal occurred then the following yield losses may be encountered (Table 1).
4. There is no evidence to suggest a fungicide application to hail damaged soybean will prove beneficial.
Table 1.Yield loss from simulated hail injury.
Crop Growth Stage when Injury Occurred Percent main-stem node removal V2 V6 R3 ---------------Yield Loss--------------- 20 5% 7% 15% 40 11% 14% 24% 60 12% 22% 37% 80 17% 40% 59% 100 19% 99% 100% *Conley, S. P., Pedersen, P., and Christmas, E. P. 2009. Main-stem node removal effect on soybean seed yield and composition. Agronomy Journal: 101:1-4.
Crop Growth Stage when Injury Occurred
Percent main-stem node removal
*Conley, S. P., Pedersen, P., and Christmas, E. P. 2009. Main-stem node removal effect on soybean seed yield and composition. Agronomy Journal: 101:1-4.