ISSUE 9 June 26, 2003
LODGING OF SMALL GRAINS
Wet weather in the east has caused some small grain fields to lodge. There are several possible factors that contribute to small grain lodging. The first factor that most people consider is excessive nitrogen. It is unlikely that this is the main factor this year, since N rates were relatively modest due to high N prices last fall and this spring and because of soil N losses that have likely occurred during the last month due to wetness. I have seen evidence that within fields, differences in lodging may have been due to excessive N. In some fields, semi-circular lodging shaped patterns on end-rows suggest that as a fertilizer applicator turned, some nitrogen fell off the fans or out of the pneumatic tubes behind the applicator, at rates much higher than the rest of the field application.
There are varietal differences in lodging susceptibility. Shorter varieties are generally more resistant to lodging than taller varieties. Other possible causes of lodging are higher seeding rates, and higher plant moisture content and taller plants due to cloudy and humid weather. This spring, it has been especially cool and cloudy, making me think that this is a more likely environmental cause of increased lodging susceptibility in the east than excessive fertility or nitrogen timing.
The ultimate cause of lodging this summer is the wet leaves from dew and rain during the past week that have made the top parts of the plants heavy, combined with wind.
Plants that are lodged prior to heading will have an opportunity to stand back up if the weather dries out soon. Continued rain will hinder recovery. Any lodging tends to lower yield potential, although lodging prior to heading is less harmful than lodging during pollination.
CONTINUED REPORTS OF YELLOW CROPS
Reports of yellow small grains and corn continue to come in from across the state. If the lower leaves are yellow and new leaves are green, it is most likely a nitrogen problem. Nitrogen can be a problem, especially on hilltops with sandier textures, due to rainfall experienced during the last month regardless of the initial rate of N used, or whether it was applied last fall or early this spring. In sandy soils, small rains can move soluble nutrients, like nitrogen, sulfur and chloride, to deep depths rapidly. It is unlikely that once moved out of the root system by rainfall the plants will be able to recover it later in the season. On our precision farming field at Valley City, the sandy hilltops are usually deficient in N by mid-late June regardless of whether the application was fall or spring applied, and sampling in September or October revealed little residual N down to 4 feet in depth. So if the crop is still at a stage when topdressing or sidedressing would be helpful, an additional application in these areas would help to save some yield.
Another cause of yellowing of small grains and corn might be sulfur. A sulfur deficiency would appear on upper, newer leaves, while the leaves below would be greener. A sulfur deficiency would be most common on low organic matter sandy soils, but in areas with a great deal of precipitation this spring, deficiencies might also be seen in loamy soils on slopes and recharge areas. It is not likely that sulfur would be seen in most depressional landscapes. If the crop is still in a growth stage that would benefit from a sulfur application, it should be applied as soon as practical. Fertilizers to use would include ammonium sulfate (dry) or ammonium thiosulfate (liquid applied with streamers). Other sulfur sources might also be possible, but not elemental sulfur.
Sugarbeets have been in the 6-10 leaf stage during the last week, and in areas with low organic matter, sandy soils have been showing what has been referred to as "sand syndrome".
Affected plants begin to show symptoms about the 5-6 leaf stage and always appear on lighter soils within a field. Most of the areas tend to be lower in pH (less than pH 7), but some areas have shown the symptoms at pH’s higher than 7. Researchers at Crookston appeared to lessen symptoms with starter application of P on lower testing soils. However, research out of Fargo at Larimore and Galchutt showed symptoms, but no effect of starter P applications on medium or higher testing soils. Application of potassium magnesium sulfate at 50 lb magnesium/acre and beet lime at 2 tons/acre resulted in yield increases at one site in 2002, but not at the other site.
The site with responses experienced heavy root rot in July, and all treatments, including boron and dolomite applications, reduced the root rot severity and increased plant survival. So it is not known whether the yield increases were due to alleviation of the sand syndrome, or from helping out the root rot. With only one site responding, it is not possible to draw recommendations from the study.
At this date, we have no solution for this problem. The plan is to identify new sites for research this coming year, but the problem appears to be expanding, rather than going away.
NDSU Extension Soil Specialist
ROOT ROT DISEASES OF SUGARBEET
The combination of saturated fields and warm soils, currently about 74EF at the four inch depth, is a recipe for fungal pathogens root infections. In sugarbeet, current soil conditions are very favorable Aphanomyces and Rhizoctonia root rot. Aphanomyces root rot is caused by the fungus Aphanomyces cochlioides. In older plants, disease results in a chronic root rot. Infected plants become yellow and wilt in the afternoons of hot, sunny days. Optimum conditions for infection occurs in high soil moisture at temperatures of 72-82E F. Aphanomyces can be managed by using tachigaren pelleted seeds, tolerant varieties, planting early when possible to avoid the early acute phase, and improved drainage to keep soils dry. Rhizoctonia root rot is caused by Rhizoctonia solani. Infected plants become yellow and wilt and the outer, older leaves often lay flat on the ground. The point of attachment of the petioles to the crown has a characteristic black color. Optimum conditions for infection occurs in wet or dry soils at 68-86EF. Rhizoctonia can be managed by using tolerant varieties, applying Quadris just before infection, planting early, and rotate with nonhost crops such as corn and wheat.
Extension Sugarbeet Specialist