ISSUE 12 July 22, 2004
SOYBEANS ARE SLOW TO GREEN UP
Soybeans have been chlorotic for the past month; far deeper into the summer than normal. The major factors that result in iron-deficiency chlorosis in soybean are soil pH higher than 7 with carbonates present. Once those conditions are present, a number of factors contribute to severity of the condition, including soluble salts, cool weather, wet soil conditions, high soil nitrates and any other stress condition. This year has been exceptionally cool. Remember just three weeks ago there was frost in certain areas of North Dakota. This current hot spell is a recent event. In addition to the cool weather, many areas of the eastern and northern parts of the state have been exceptionally wet. The combination of these two climatic conditions has been the main reason why chlorosis lingers on so far into the season. In my experience, the longer the stress is imposed on soybeans, the longer it takes for them to recover. I expect that if the soil dries out, many of these acres will recover and yield decently, but not tremendously, perhaps 25 bu/acre on the top end. Dr. Goos at NDSU has observed that when soybeans turn chlorotic, the top end of yield is already gone even if they recover quickly. If it continues to be wet, even with the warmer weather, the chlorosis will linger. If it continues into August, the possibility of recovery is slim and about 10 bu/acre would be a good yield.
Some growers are applying micronutrients with their herbicide to try to cure the chlorosis. This is not advised for a couple reasons. First, applications of iron amendments do little more than green up some plants sometimes, but do not increase yield very often. Secondly, application of fertilizers with herbicides can either decrease the activity of the herbicide or increase its phytotoxicity to the crop. Before taking such action, be sure to consult with a herbicide company representative and the product label.
NDSU Extension Soil Specialist
SUGARBEET CROP UPDATE
The sugarbeet crop is making optimal use of the sunshine, heat units, and available (sometimes too much) water to maximize growth. Most sugarbeet fiels in southern Minnesota and the southern Minn-Dak factory district have closed canopy. In the American Crystal factory districts, about 70 to 75% of the crop have closed canopy. Dry conditions in April and early May coupled with cold conditions in May and June were not favorable for crop growth early in the season. Should the current favorable weather conditions continue for the remainder of the growing season, it is estimated that sugarbeet yield would average about 18 tons per acre in this region.
Some sugarbeet fields that were under saturated conditions for several days are showing chlorosis. The upper, younger leaves show interveinal yellowing. Some varieties, especially some of the Rhizomania resistant varieties, seem to be more susceptible to chlorosis. In severely affected fields, the entire leaf blade was yellow surrounding a network of green veins. It is suspected that the chlorosis may be a nutrient deficiency symptom. When the soil dries out and conditions become more favorable for root growth, the symptoms are expected to disappear.
Chlorosis on Sugarbeet
Extension Sugarbeet Specialist