|Phosphorus deficiency causes purple corn|
|Wednesday, June 12, 2013 10:59 PM|
BY JAMES J. HOORMAN
Mississippi State University offers the following explanation on purple corn. “Corn growth is often stunted and lower corn leaves turn purple as a result of phosphorus (P) deficiency. Phosphorus’s primary role in a plant is to store and transfer energy produced by photosynthesis for use in growth and reproductive processes. Adequate P levels encourage vigorous root and shoot growth and promote early maturity. These effects often increase water use efficiency and potential grain yield. Thus, phosphorus deficiency stunts plant vegetative growth and reduces grain development.
Purple leaf tissue is symptomatic of P deficiency. Phosphorus deficiency symptoms appear on lower leaf tips and progress along leaf margins until the entire leaf shows purpling. Lower leaves often die when P deficiency is severe, especially when hot, dry, windy conditions persist. New leaves emerging from the whorl are usually green, because the plant mobilizes available P to the youngest leaves.
Phosphorus deficiency symptoms often occur as young plants are exposed to growing conditions following cool and often wet conditions. These conditions result in a lag phase where vegetative growth exceeds the roots’ ability to supply P. Young plants are especially vulnerable because their root systems are small and P is immobile in the soil solution. Any cultural or environmental factors which limit root growth will aggravate deficiency symptoms. Examples of such conditions include: cool temperatures, too wet or dry soil, compacted soil, herbicide damage, insect damage, and root pruning by side-dressing knives or cultivators. Acidic soil can also intensify P deficiency symptoms. Low soil pH severely limits P availability to plants, which may cause deficiency symptoms even where high soil test P levels exist.
Leaves normally regain green coloration when further root exploration occurs, especially when favorable growing conditions prevail. However, P deficiency will reduce yield by delaying maturity, stunting growth, and restricting energy utilization. Warmer temperatures, sunlight, and rain help plants obtain more P because these conditions promote both plant and root growth. Good growing conditions move sugars blocked in the plant leaves, which is causing the purple leaf color.
Treatment options to remedy P deficiency have modest short-term effectiveness, since P is immobile in the soil solution. Thus, root exploration into the amended area is required for plant uptake. Surface application of P fertilizer will limit availability to the top couple inches of soil. Thus, plant uptake would be more probable in no-tillage cropping systems, since these systems encourage root exploration near the soil surface. Phosphorus injected as a side-dress treatment would increase availability to the root system; however, be careful not to prune roots” (Mississippi State University). In most cases, a good rain and warmer temperatures are the best cure.
“Bagworms are starting to hatch in southwest Ohio”, says Joe Boggs, Ohio State University horticulturalist, “so people in Northwest Ohio should start looking for signs of bagworms on their trees, especially pine trees.” However, bagworms eat not only evergreens but also about 130 different species of deciduous (plants that grow and live more than one year) trees and shrubs.
Bagworms use a process called “ballooning” to transport themselves to new locations. Some of the first caterpillars (first instar) that hatch will produce a strand of silk and if the wind catches this strand, they can be transported to a new location. This is how bagworms find new hosts to infect each year. The first instar caterpillars make a bag like a dunce cap while the second batch (second instar) forms a downward balloon like a pine cone. The later-hatched instars are highly destructive, especially to pine trees. To control bagworms and their damage, try to target the early instar caterpillars that are hatching. The best product to use on early instar hatching caterpillars is a biological insecticide call Bacillus thuringienis(Btk) found in products like Dipel®, Thuricide®, etc. which kill the pest but not the beneficial predators. Btk is a stomach poison insecticide that must be ingested so the effect is short-lived and two applications may be required to control the emerging bagworms. Once the bagworms get more than 0.75 inches long, the Btk efficiency declines, so spray early and often. A soil drench application of dinotefuran (e.g. Safari) or products containing clothianidin are also effective against early instar bagworms and do not harm beneficial predators and parasitoids (Taken from Buckeye horticultural newsletter).