Causes of Corn Ear Smut and Control Measures

Corn tip sterility refers to the phenomenon where the top of the ear fails to set kernels, resulting in poorly filled grains—commonly known as “bald tip” or “bare tip.” It is one of the major factors that compromise stable corn yields; in severe cases, it can lead to yield losses of 20% to 30%. Therefore, effective measures should be implemented in production to reduce and prevent this issue. Below, the editor of HuoBao Agricultural Inputs will explain the causes of corn tip sterility and corresponding control methods.

I. Causes of Baldness

The differentiation of female florets, silk extrusion, and kernel formation in maize begin in the middle to lower portion of the female inflorescence; thereafter, these processes proceed simultaneously both upward and downward from that region, culminating at the tip. Under unfavorable environmental conditions, the apical florets or fertilized embryos often undergo abortion due to insufficient nutrient supply. Aside from the genetic characteristics of maize varieties, the main causes of barren tip include the following:

First, nutrient deficiency. Phosphorus deficiency in the soil inhibits cell division. Particularly during the filament elongation stage, insufficient phosphorus leads to slow filament growth, thereby impairing pollination. If the grains at the tip of the ear are shriveled and abnormally white, this indicates a deficiency of both phosphorus and potassium, with potassium deficiency being especially pronounced.

Second, spikelet degeneration occurs. At the tip of the ear, the spikelets become degenerate and malformed; occasionally, hermaphroditic flowers appear, or male flowers develop while female flowers fail to do so. This impairs normal pollination in maize, making seed set difficult.

Third, silk development is delayed. At the top of the ear, silk filaments mature late, resulting in a delayed tasseling and anthesis; this often leads to a mismatch between male and female flowering, preventing successful pollination and seed set.

Fourth, drought and water stress. The optimal temperature for maize flowering is 22–26°C, with a preferred relative humidity of 65%–90%; when temperatures exceed 30°C and relative humidity falls below 60%, flowering is significantly reduced; and at temperatures above 38°C, the tassel fails to produce pollen. During the flowering and pollination period, drought can prolong the interval between male and female flower emergence, causing the silk to emerge too late to coincide with the peak of pollen shed from the tassel, thereby impairing pollination and reducing grain set. Additionally, drought or nutrient deficiency during the differentiation of apical florets may lead to their degeneration into sterile flowers.

Fifth, excessive planting density. Overly dense planting leads to poor ventilation and inadequate light penetration in the later stages of corn growth, thereby hindering normal development.

Sixth, the soil is deficient in micronutrients. Boron deficiency adversely affects both the formation of pollen in maize tassels and its viability during pollination. Zinc deficiency causes white spots to appear on the leaves of older seedlings, which rapidly expand into localized white patches and necrotic lesions; internodes shorten, and ear development often becomes deformed, resulting in a bare tip.

Seventh, the severity of pest and disease incidence: Various leaf spot diseases in maize, as well as seedling blight, sheath blight, and basal stem rot, can all impair normal growth and development, leading to poor plant performance. In particular, corn aphids proliferate extensively during the tasseling stage, preventing proper flowering and pollination and resulting in barren tips and reduced grain set.

II. Prevention and Control Measures

First, select superior varieties. Choose coated seeds that are high-yielding, have plump kernels, and exhibit strong viability, and ensure they are properly treated before sowing through methods such as sun-drying and seed dressing.

Second, apply fertilizer appropriately. Fertilization should balance nitrogen, phosphorus, and potassium, with the addition of micronutrients as needed. On low‑fertility soils, prioritize topdressing, but ensure a heavier application early in the season followed by lighter doses later to avoid excessive vegetative growth and late maturity. During the seedling stage, limit irrigation to promote spikelet differentiation and shorten the interval between tasseling and silk emergence, thereby increasing pollination opportunities. In terms of fertilization, emphasize base application: apply sufficient farmyard manure and phosphate‑potash fertilizers in a single application whenever possible. For fields of moderate fertility, apply 750–1000 kg of high‑quality farmyard manure, 6 kg of urea, 50–60 kg of superphosphate, and 1.5–2 kg of zinc sulfate per mu. On poorer or richer soils, adjust the rates accordingly—increasing or decreasing slightly as needed. Apply ear‑stage fertilizer judiciously: about 10 days before tasseling, during the so‑called “large trumpet mouth” stage, topdress with 25–30 kg of ammonium bicarbonate per mu; when the female ears begin to shed silk, apply an additional 3 kg of urea per mu. Foliar spray with zinc fertilizer: during the jointing stage, evenly spray the foliage with a 2% zinc sulfate solution.

Third, irrigate during the tasseling and flowering stage. Corn is highly sensitive to water 15 days before tasseling; when soil moisture falls below 80% of field capacity, immediate irrigation is required to promote pollination and grain filling. Fourth, conduct artificial assisted pollination. During the peak flowering period, promptly carry out this practice in the morning after the dew has dried and when male flowers begin to release pollen in large quantities. Use either the rope‑pulling method or the plant‑shaking method, repeating every 2–3 days for 2–3 consecutive sessions to help prevent barren tips.

Fourth, practice appropriate planting density to enhance resistance. Taking into account the variety, soil conditions, cultivation practices, and climatic factors, aim to establish a high‑efficiency light‑capture canopy by optimizing plant spacing—ensuring both adequate ear‑bearing density and favorable ventilation and light penetration. A typical planting density is around 4,000 plants per mu; on fields with good fertility, increase the number of plants slightly, while on less fertile fields, reduce it accordingly. Additionally, it is advisable to adopt a wide–narrow row planting pattern to prevent weak seedlings caused by uneven distribution of nutrients, water, and light.

Fifth, implement moderate tasseling removal: based on field growth conditions and the overall tasseling status, selectively remove tassels from every other row or plant to reduce water and nutrient consumption, improve ventilation and light penetration in the upper canopy, and enhance photosynthetic efficiency. This approach not only helps minimize the occurrence of bare tops but also mitigates damage caused by the European corn borer.

Sixth, implement drought‑resistance and flood‑drainage measures to enhance plant resilience. By promptly addressing drought and waterlogging, we can mitigate adverse factors that hinder corn growth, improve the microclimate within the field, strengthen the plants’ stress tolerance, accelerate the synthesis and accumulation of photosynthetic products, and reduce the incidence of barren tips.

Seventh, for the prevention and control of diseases and pests—specifically corn seedling blight, sheath blight, and stem base rot—apply either a 30% Miaojun Di wettable powder at 0.3% of the seed weight, or treat the seeds with a 12% triazolyl alcohol emulsifiable concentrate or a 12.5% epoxiconazole emulsifiable concentrate, each at 0.02% of the seed weight. Alternatively, upon detecting diseased plants in the field, spray with an 800‑fold dilution of 30% Miaojun Di wettable powder, an 800‑fold dilution of 50% methyl tobuzin wettable powder, or a 700–800‑fold dilution of 80% Lvheng No. 2, mixed with a 1,000‑fold dilution of Tianda 2116; these treatments provide good control of corn seedling blight, sheath blight, and stem base rot.

Control of various leaf spot diseases: In the mid-to-late growth stages of maize, once leaf spot disease appears, apply a spray using either a 50% thiophanate‑methyl wettable powder diluted at 800 times or a 50% carbendazim wettable powder diluted at 800 times.

For the control of corn borers, apply 3 kg of 3% furadan granules during the late stage of the corn heart leaf development. Alternatively, following the onset of corn aphids, spray with a 1,000‑fold dilution of 40% omethoate emulsifiable concentrate, an 800‑fold dilution of 50% monocrotophos emulsifiable concentrate, or a 3,000‑fold dilution of 10% imidacloprid wettable powder.