ISSUE 11 July 13, 2000
MELANISM vs BLACK CHAFF
The recent heavy rainfall favors the development of several diseases in wheat and melanism which can easily be mistaken for disease. Melanism, a genetically controlled discoloration, is often confused with black chaff a bacterial disease.
Symptoms black chaff (the disease) consist of dark lines or parches on glumes and dark lesions on the awns. The lesions often result in alternating green and brown areas on the awns which aids in identifying the disease. Black strips are also diagnostic of black chaff. Leaf symptoms are dark water soaked longitudinal streaks that result in tan or brown dead tissue.
Melanism, or false black chaff, produces dark purple to black streaks or blotches on the glumes. This dark discoloration is usually more uniform black than black chaff. The awns and peduncle show no symptoms. A dark purple to purple brown ring forms at each joint; it is often necessary to peel away the leaf sheath to see this symptom. These purple rings are diagnostic of melanism.
Melanism is not thought to reduce yield in currently grown varieties. Development of melanism usually occurs with hot humid weather; consequently, the period of hot weather following the recent rains could result in substantial amounts of melanism.
Michael D. Peel
Small Grains Extension Agronomist
BEGINNING BLOOM ON BEANS IS SEEN
Many soybean fields have begun to bloom through the Valley. The
beginning bloom stage or R1 stage in soybeans is marked by the plants having at least one
flower on any node of the main stem. Flowering, unlike maturity on soybeans, begins toward
the bottom of the plant (at the third to sixth node) and then progresses upward and back
downward. Branches off of the main stem will flower a few days later than the main stem.
While flowering begins at the base of the plant and proceeds to the top of the plant,
physiological maturity of the beans will progress in just the opposite direction.
Normally, soybean pods will be mature from the top of the plant and down, thus remember to
check pods toward the bottom of the plant when determining if harvest time has come.
Flowering of soybeans is an important time in bean growth and development. At stage R2,
full bloom, each plant has accumulated about 25% of its total dry weight and nutrients; it
has attained about 50% of its mature height; and, it
has produced 50% of its total mature node number. This later flowering stage begins the period of very rapid N-P-K and dry matter accumulation that will continue through R6. Also, during flowering the soybean plant gears up on its nitrogen fixation in order to provide for the demands of the plant. Keep soybean plants happy during flowering for good yields. Scout for disease and insect problems and maintain good growing conditions.
WEATHER AND FERTILITY STILL FOREMOST IN LATE VEGETATIVE GROWTH
In the later vegetative stages before corn tassels, weather and
yield correlations are significant. The growth stages from late June through July make or
break yield promises. High July temperatures above 86F can negatively affect corn
especially in dry years when transpiration is limited by moisture availability. With ample
moisture, temperatures above 86F simply make the transpiration process a little less
energy efficient. Supplied with ample sunshine as growing degree day units, this may not
a problem unless plants are already severely stressed. With more soil-moisture available, a higher water demand caused by higher temperatures can be met without additional stress occurring.
In the late vegetative stage, corn grows very rapidly. Water use is great and the water balance is important under low rainfall conditions. Corn plants subjected to drought stress for four to six days have been shown to exhibit as much as two to four percent grain yield reduction per day under severe drought stress during July. Part of this yield reduction was due to fertility stress with less nutrient uptake that consequently caused decreased leaf area below the optimum for the corn plants. Preventing this fertility stress reduced the drought induced losses by about two percent per day. Stunted plants from the drought stress also limited yield by limiting leaf area and overall vegetative dry matter.
On the other side of the coin, corn is also affected by flooding. Corn at two and one-half feet tall after 24 hours of flooding with a subsequent low level of nitrogen availability showed reduced yields by 14 percent (Ritter, W.F., and C.E. Beer. 1969. Yield reduction by controlled flooding of corn. Trans. ASAE 12:46-50). This yield reduction can easily be increased to 30 percent with 96 hours of flooding during late vegetative growth in corn. However, some leeway does exist. Contributing to corn s adaptability, soils with a high level of nitrogen showed very little yield reduction even with 96 hours of flooding. Later, when flooding occurred near silking, no reduction in yield occurred at high nitrogen level. Yield reductions up to 16 percent occurred with 96 hours of flooding at the low level of nitrogen. Fields maintained at ample fertility levels for optimum corn growth, even with water-logged soils, will green up quicker, have healthier corn plants and have more of a chance for yield.
FARMING THE NET IS NECESSARY IN THE NEAR FUTURE?
You can auction livestock on-line and purchase your herbicides via
the Web. The new technology is changing the way farming and ranching are done. Today, more
than a half-dozen Net marketplaces let farmers buy seed, fertilizer, tractors and other
equipment at a discount.
Agriculture is expected to become the third-largest Internet business-to-business market by 2004, which represents eight percent of the overall pie according to a recent report by The Goldman Sachs Group (http://www.gs.com). The largest business is expected to be chemicals at 23 percent followed by computer-related products at 15 percent.
This phenomenal growth is why an entrepreneur from Florida started an auction site for farm equipment called Farmbid.com (http://www.Farmbid.com). Already this former hedge fund manager who grew up on a family dairy farm has 100,000 registered users on the site. The site now includes information on ag news, weather and online catalog sales. Listing more than 1,300 items from 12 suppliers, Farmbid.com kicks back a sales commission of 5-15 percent to the company. The site also has a chat room. The developers hope to eventually offer farmers discount rates on insurance, banking and travel.
In addition to Farmbid, several other sites operate similarly to cater to farmers. Some of these include: DirectAg.com; NetSeeds (http://www.netseeds.com); Powerfarm.com and XSAg.com. These sites usually make money by selling advertising on the site, transaction fees or by taking a percentage of each sale made over the site. This is true of the Memphis, TN based site called Farms.com. This site has been online since 1995 and earlier this year purchased Canada s eHarvest.com.
In addition to these sites, agricultural firms such as most seed and chemical companies now have Web sites and some are getting into the online exchange market such as: Cargill (http://www.cargill.com); Cenex Harvest States Cooperative (http://www.cenexharveststates.com); and E.I. du Pont de Nemours (http://www.dupont.com) that now holds Pioneer Seed. Two months ago these three manufacturers launched Rooster.com, an electronic mall where farmers can sell crops and buy goods.
CORN DEVELOPMENT FROM V10 TO VT
Once the corn plant has 10 leaves, it has begun a steady and rapid
increase in nutrient and dry matter accumulation that will continue through most of the
reproductive stages. Demand for both nutrients and water remain high. At V12 up until one
week before silking the number of seed per row on the corn ear will be determined. Any
stresses from V12 through to physiological maturity can limit first the number (until
silking) and then the fill of these kernels. Early maturing hybrids will progress
through the growth stages in less time and will generally have smaller ears than more adapted or later hybrids. Right before silking, the corn plant will have the upper ear shoot development take dominance over that of any existing lower ear shoots. Moisture stress two weeks before or after silking on corn plants can cause large grain yield reductions. Stress can delay silking past pollen shed and result in missing kernels on the ear (especially on the ear tip).
Extension Crop Production Specialist