Various maize foliar diseases are causing major yield losses in maize fields across South Africa. Identifying these diseases early can reduce the risk of widespread damage to your crops and can help farmers to develop the correct fungicide treatment programme. The key is starting early and putting preventative measures in place before it is too late. The different fungicide diseases vary greatly between different regions as the geography plays a significant role in determining the nature of the predominant species. Let’s take a look at some of the foliar diseases that has a significant effect on farming practices across South Africa.
Common rust (Puccinia sorghi) is a foliar maize disease, favoured by wet, humid and cold environmental conditions. If left untreated, this fungal disease can lead to incomplete grain filling and yield losses. When leaves are exposed to moisture for periods longer than 6 hours, they are at risk of being infected.
The symptoms of common rust normally appear after silking. Common rust appears scattered as reddish-brown pustules of large, circular to elongated shape and can easily be observed on both leaf surfaces of maize plants, but generally not before tasseling.
Uredospores are produced in pustules of common rust during summer and released from the fruiting bodies and dissipated in the canopy infecting new leaf tissue. Yellowing of the leaf occurs around pustules. As the maize plant grows, pustules turn into a dark-brown colour as the fungus starts producing teliospores.
Control measures include planting tolerant hybrids together with early fungicide application to prevent the production of pustules. Nativo® can be applied as a preventative spray. Nativo is a systemic suspension concentrate fungicide with mesostemic properties that offers broad-spectrum disease control and yield and quality improvement.
NORTHERN CORN LEAF BLIGHT
Northern Corn Leaf Blight (Exserohilum turcicum) (NCLB) is one of the most common maize leaf diseases on the African continent and has been seen to cause consistent yield loss year on year. This fungal disease can cause yield losses of between 5% and 30%. When NCLB co-occur with common rust, it can result in yield losses of more than 50%. Infection can take place during any growth stage of the maize plant which is why the leaves of maize plants should be continuously monitored for any signs of this disease.
Conditions that are conducive to the development of NCLB, include moderate temperatures (18 - 27 °C), high humidity or heavy dews. The incubation period lasts about 8 – 12 days under these favourable conditions. E. turcicum overwinters as mycelium or conidia on infected crop debris which serves as a primary inoculum source in following crop seasons. The dark-greyish spores are blown either by wind or rain splashing/droplets onto new/lower leaves from the plant or to other plants, causing infection. Once the pathogen gets into contact with the leaf, it requires about 6 – 18 hours of leaf wetness. Once infection has occurred, the pathogen will grow in the plant tissue causing blights – initially, they have a grey-green colour and later adopt a brown/straw colour. When lesions merge, they can form large areas of dead leaf tissue – these lesions are typically long and cigar-shaped. Should conditions be ideal, sporulation under the lesions will occur. From this sporulation, the conidia blow from there, causing more infection.
NCLB usually starts from the bottom of the maize plant – lower leaves going to upper leaves. It can blight the whole leaf/plant so that it looks as if it has been hit by frost. Therefore, it is important to stop the development of the disease on the lower leaves before it affects the upper leaves. Despite the devastating effects of this fungal disease on yield, it can be easily controlled. Control measures include planting disease tolerant maize hybrids or the early application of fungicides to protect the upper leaves. Nativo can be applied, followed by Zantara®. Zantara compliments Nativo's dual spectrum through its alternative way of disease control. With its combination of two unique modes of action, Zantara disrupts the cell wall of the disease-causing fungi and ceases energy production in the fungicide cell for the unparalleled control of NCLB and Grey Leaf Spot in maize.
GREY LEAF SPOT
In South Africa, Grey leaf spot (GLS) (Cercospora Zeina) was first identified in KwaZulu-Natal in 1989/1990 and has since spread to neighbouring provinces and countries, resulting in significant yield losses. GLS’s dire effect on the development of a maize plant holds various challenges for farmers if not treated correctly. GLS reduces the amount of photosynthetic-active area on the leaf and eventually leads to premature grain filling which ultimately results in yield losses.
The symptoms of GLS, are first noticed on the lower leaves of the plant where it appears as small, irregular tan spots with yellow chlorotic halo’s. Should the disease progress, lesions can merge and form large lesions that appear elongated and rectangular and run parallel to the leaf veins. This happens when conditions are extremely favourable for the spread of GLS. Conducive conditions include several days of high humidity and favourable temperatures during which the conidia formed on infested maize residues are spread within and among fields through wind and/or rain. Should the favourable environmental conditions persist, the original lesions can spread spores to the upper leaves by means of wind or rainfall, resulting in the spread of the disease.
Control measures include the early application of fungicides (Nativo) to protect the maize foliage. This should be followed by Zantara.
Head smut (Sphaecelotheca reiliana) is a fungal disease that can cause extensive yield losses of up to 80% if left untreated.
The teliospores that cause head smut, overwinters in the maize soil and can be dormant for at least four years. Environmental factors that are conducive to the survival of the fungal disease, are low soil moisture, cold planting conditions, hot temperatures and soil that is nitrogen deficient.
The teliospores present in the soil, infect the maize seedling. The symptoms of head smut are only presented when the male (tassel) and the female (ear) flower parts of the maize plant emerges. The spores appear as a compact mass of dark teliospores covered by a thin greyish-white tissue layer.
In the processes of controlling this disease in your maize fields, it is important to clean equipment thoroughly after leaving an infected field, as the spores can easily be transmitted to a field that has not been infected. Farmers should also refrain from planting in cold conditions as this may stimulate the development of the disease.
The flowable systemic fungicidal seed dressing, Baytan® 150 FS can be used to arrest the development of the disease.
For more information on the foliar diseases in your maize field, please contact your nearest Bayer representative for assistance.
The following products are trademarks of Bayer AG, Germany:
Nativo® Reg. No. L8942 (Act No. 36 of 1947)
Zantara® Reg. No. L10011 (Act No. 36 of 1947)
Baytan® 150 FS Reg. No. L1697 (Act No. 36 of 1947). Contains the active ingredient Triadimenol (triazole)150 g/l.
Baytan® is a registered trademark of the Bayer Group.