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| Seedling corn is susceptible to injury from frost, hail, herbicides and insects. LSU AgCenter researchers simulated defoliation at various growth stages to find out how corn plants would recover. Photo by Rhett Gable. |
Rhett H. Gable, Roger Leonard, Donald R. Cook and Karla T. Emfinger
Several physical, chemical and biological factors can influence corn seedling development and reduce maximum yield potential. Adverse weather conditions, such as frost and hail, can destroy the shoot portions of corn seedlings depend-ing on the time of seeding and growth stage of the plant. Improper herbicide selection or drift from adjacent fields can damage or kill corn seedlings and lower yields. Foliage injury from insect pests can range from minimal leaf injury to complete destruction of the above-ground portion of seedlings.
In Louisiana, producers have adopted practices that reduce the emphasis on tillage and rely heavily on pre-plant burndown herbicide applications to establish clean seedbeds. The shift to these conservation tillage systems has allowed several insect pests to become more consistent problems. The black cutworm and the variegated cutworm are significant pests of field corn and a common problem in no-till fields. Cutworms damage plants by severing the plant stem near the soil line. Another caterpillar pest, the true armyworm, feeds on corn seedlings, completely defoliating the leaf tissue and occasionally feeding on the stems.
Insect injury to the shoot tissue of corn seedlings can result in abnormal plant development, seedling death or a barren stalk. Seedling defoliation also can delay crop maturity and decrease grain yield. During early spring in Louisiana, the field environment is usually not conducive to optimal plant development; therefore, corn plants usually have difficulty compensating for this type of injury and recovering to produce optimal yields.
During 1999 to 2002, studies were conducted at the LSU AgCenter’s Macon Ridge Research Station to determine the effect on grain yield of foliage injury to field corn seedlings. To simulate seedling injury caused by caterpillar pests, corn seedlings were defoliated with a gas-powered weed trimmer. Plants were severed within one inch of the soil surface at selected growth stages, ranging from first leaf (V1) through fifth leaf (V5). Each treatment was only applied one time, and the injured plants were allowed to recover for the duration of the growing season. These studies were conducted in several environments (conventional and conservation tillage systems) using multiple varieties of field corn. The test areas were managed in accordance with practices recommended by t
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| The split stem of two corn seedlings shows the growing point at the V3 (left) and V5 growth stages. Defoliation or stalk injury can kill a corn plant when the growing point is injured. Photo by Rhett Gable. |
he LSU AgCenter to optimize crop development and manage pests. Each plot was mechanically harvested to determine treatment effects on grain yield. All defoliation treatments were compared to non-defoliated control plots.
During the four-year test period, seed yields from plants defoliated at growth stage V1 and V2 were not significantly different from yields of the nondefoliated plants. However, significant yield losses were observed when plants were defoliated at the V3 through the V5 growth stages. In 1999, only plants defoliated at the V5 growth stage had significantly lower yields than the nondefoliated plants. In subsequent years, defoliation of the plants at the V3 to V5 growth stages significantly reduced yield compared to the nondefoliated plants. During the testing period, yield losses ranged from 16.7 to 67.3 bushels per acre in defoliated plots compared to the nondefoliated plots.
Early-season defoliation will decrease plant populations when the apical meristem (the growing point in which the leaves and eventually the tassel are initiated) is above the soil line compared to plants with the meristematic tissue below the soil line. Seedling defoliation can kill the primary stalk and cause the plant to produce a secondary stalk (sucker), which usually produces less yield compared to nondamaged plants. Defoliation also may delay crop maturity because of the time required for the plant to compensate for foliage loss.
Early-season seedling defoliation can make replant decisions difficult. Producers typically underestimate the resilience of corn plants after they undergo early-season injury. The studies reported h
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| These corn plants had recovered 18 days after nearly complete defoliation. This study was conducted at the LSU AgCenter’s Macon Ridge Research Station in Winnsboro. Photo by Rhett Gable. |
ere indicated that plants defoli-ated at the V1 and V2 growth stage should recover and produce normal yields following nearly complete defoliation before the apical meristem emerges above the soil line. Regardless of the factors causing the injury (frost, hail, herbicides, insects), early-season seedling injury will not always result in a significant yield loss. Corn seedlings will often recover if environmental conditions are favorable.
Rhett H. Gable, research associate, and Roger Leonard, professor, Macon Ridge Research Station, Winnsboro, La.; Donald R. Cook, research associate, Department of Entomology, LSU AgCenter, Baton Rouge, La.; and Karla T. Emfinger, research associate, Macon Ridge Research Station, Winnsboro, La.
(This article appeared in the winter 2005 issue of Louisiana Agriculture.)