“The management of corn stunt disease involves the elimination of volunteer corn plants, synchronization of sowing, seed treatment with systemic insecticides…”
Daniel Debona is a professor of agronomy at the Federal University of Technology – Paraná, a researcher, consultant and lecturer in the area of phytopathology.
Debona is an agronomist from the Federal University of Santa Maria, M.Sc. and Ph.D from the Federal University of Viçosa.
Diseases are among the main factors that reduce yields and grain quality in corn, with emphasis on foliar diseases, stem and ear rot and stunt.
The most important foliar diseases are white spot (Pantoea ananatis), gray leaf spot (Cercospora zeae-maydis), northern leaf blight (Exserohilum turcicum), Bipolaris leaf spot, Diplodia leaf streak and rust (common, polysora and tropical). The damage potential of these diseases is quite high, reaching more than 80%, as reported for the gray leaf spot epidemics that occurred in the southwest of the State of Goiás in the 2000s, for example.
The management of foliar diseases mainly involves the use of resistant hybrids and the spraying of fungicides. In the case of fungicides, the choice of product and the moment of application are crucial for successful handling. Among the fungicides used, mixtures of triazoles (cyproconazole, difenoconazole, epoxiconazole or tebuconazole) or triazolinthione (prothioconazole) with strobilurins (azoxystrobin, metominostrobin, picoxystrobin, pyraclostrobin or trifloxystrobin) and carboxamides (benzovindiflupyr, bixafen and fluxapyroxad) stand out.
In some cases, the inclusion of multisite fungicides such as mancozeb is justified. Furthermore, new molecules from the triazoles (mefentrifluconazole) and carboxamides (adepidyn) groups were recently registered for use in maize, raising the bar for disease control.
With regards to the moment of control, it is fundamental to use fungicides in a preventive way, since their effectiveness drops drastically after the manifestation of the symptoms of the disease. Applications of fungicides in pre-tasseling result in greater productive responses, but it is essential to carry out monitoring, since some diseases, such as white spot and northern leaf blight, can start earlier (between V4 and V6), demanding an anticipation of the control program. Applications after tasseling (VT) may also be necessary, depending on disease pressure, environmental conditions and susceptibility level of the hybrid.
Different genera of fungi are associated with stem, ears and/or burned grains rot (Colletotrichum, Fusarium, Diplodia), and some of them (Fusarium) are also responsible for the presence of mycotoxins in grains. The management of these diseases involves choosing hybrids with a higher level of resistance, balanced fertilization (nitrogen and potassium), treatment of seeds in rotation/succession with non-host cultures and sowing under adequate conditions.
Leaf protection with fungicides is also important to minimize stem rot problems. In addition, the use of hybrids with good ear mulch and pest management, especially caterpillars that cause damage to the ears (including the use of Bt corn and insecticide applications) is important in the management of ear rot.
Corn stunt disease (pale and red) is the main phytosanitary challenge of maize today. This problem is caused by two prokaryotic microorganisms (mollicutes), that are transmitted by the corn leafhopper (Dalbulus maidis), that also transmits the stripe virus.
The management of stunt involves the elimination of volunteer corn plants, synchronization of sowing, seed treatment with systemic insecticides (clotianidin, imidacloprid or thiamethoxam) and foliar application of chemical insecticides (carbamates, phenylpyrazoles, neonicotinoids, organophosphates and/or pyrethroids) during the critical periods (V2-V8).
In general, chemical insecticides have a low residual effect and the inclusion of biological products (Beauveria, Isaria, Paecilomyces and Pseudomonas) is essential. In any case, the use of more tolerant hybrids is one of the most important control measures, as we have found differences of more than 80 bags/ha between hybrids because of their variation in stunt tolerance.