The rains we received a couple of weeks ago were both beneficial and detrimental, depending on whether you received 1-inch or 3-inches plus your neighbor's runoff from out west. Fields along some of our major creeks, like Petronila Creek, were under water for several days, thus drowning or severely stressing crops from super saturated conditions. Our recent warm temperatures have helped move along our degree day units, in fact for grain sorghum and corn we are back up to about 93 percent of normal, while our cotton degree day units are about 98 percent of normal. Our wheat crop continues to develop well with some reports of rice stinkbug damage occurring on grain that was in the milk to soft dough stage.
Our grain sorghum crop growth stages range from just a few leaves to reaching the stage of growth at which time many things begin to happen with the plant. For the older sorghum plants, the total number of leaves has been determined and the grain head size is being determined at this time. Now is also the time that rapid nutrient uptake is occurring, and yes, we are seeing some nutrient deficiencies.
These nutrient deficiencies tend to be more obvious in situations with adequate soil moisture, when the plant is growing rapidly, and in many cases has a small root system, so it can not capture all of the nutrients that it needs. Until grain sorghum develops an extensive root system, young plants may not be able to obtain enough ferrous iron to maintain normal growth on some soils. Although iron is not a part of the chlorophyll molecule, it is required to supply enough chlorophyll to support the growth of new leaf tissue.
High-pH, calcareous soils not only reduce the availability of soluble iron in the soil; they also change the soil's cation-exchange capacity so that less iron is present and available for exchange overall. The result is a more slowly growing plant and subsequent uneven flowering dates. This not only delays ripening of grain and harvest, but the uneven pollination undermines an effective insecticide spray program for controlling sorghum midge.
Mild chlorosis ranges from a lighter green leaf color that progresses to increasing interveinal striping, to almost no visual symptoms. Moderate chlorosis is seen where sorghum plants are yellow or yellow-green in strips, or irregularly shaped areas of the field.
Fields may have intermittent blotches of chlorotic plants scattered in a salt-and-pepper (random) arrangement. Iron chlorosis is often sporadic throughout the field, or it may be associated with some land-moving event.
Visual symptoms are often the best indicator of whether or not to treat chlorotic fields or parts of fields for iron chlorosis.
Applying iron as a foliar spray is effective in restoring the green color and they are most effective when repeated at 10-day to two-week intervals. Several products are available for field use to correct iron chlorosis. Iron sprays require a spreader-sticker or detergent in order to be effective. If a commercial spreadersticker is not available, ordinary household detergent may be used at rates of 1/4 to 1/2 pint per 50 gallons of solution. Thorough coverage and wetting of the entire leaf surface is necessary for good results. Avoid too much detergent to minimize the chances of leaf burn.
Jeffrey Stapper is the Agricultural and Natural Resources Agent for Nueces County. Readers may contact him at (361) 767-5217.