It goes without saying that plant diseases can be ruinous for your crops. That is why AECI Plant Health helps Food For Mzansi readers to understand why their plants get sick, and how to better manage it. E-mail your questions and pictures to info@foodformzansi.co.za.
Siphokazi Gobeni from Butterworth in the Eastern Cape writes: I’m really worried about my tomato plants. The leaves are covered in what looks like flour or white powder. Please help!
Dr André Cilliers, marketing manager at AECI Plant Health, writes:
Thanks for reaching out, Siphokazi. It sounds like your tomatoes are being attacked by what we call “powdery mildew”. Just as the name suggests, the symptoms of powdery mildew look like a fine white powder on the leaf surface. However, this fungal disease begins as pale yellow spots on the leaves, which soon begin to produce spores. It is these spores that cause the white powdery symptom. The white areas of the leaf soon turn brittle and brown. The disease may also occur on the stems of the tomato plant. There are actually two fungi that can cause powdery mildew on tomatoes. These are Oidium neolycopersici and Leveillula taurica.
Infection of the leaves
Most fungal pathogens require conditions of high humidity and leaf moisture to cause infection on the plant foliage. This is not the case with powdery mildew of tomatoes, however. The fact is that powdery mildew can develop on leaves under a wide range of conditions, which makes it a difficult disease to predict. This also means that it spreads very rapidly. Even though powdery mildew can infect under almost any conditions, it does develop best under conditions of high humidity.
Losses due to powdery mildew
As is the case with many plant pathogens, the leaves are infected. These are either killed off completely or lesions develop that affect the green area of the leaves. Either way, the leaf area which is meant to photosynthesise is either reduced or the leaf is completely lost, obviously also reducing photosynthetic potential. Remember that the leaves are the engine of the plant which keeps all systems going, and are therefore critical for optimal yield. Any reduction to the photosynthetic potential of the plant therefore leads to yield loss.
What can you do?
Fortunately, powdery mildews are reasonably easy to control. Again, as is the case with many diseases of crops, the plant is most susceptible to infection if it is in a state of stress. Stress may be either biotic (caused by living factors) or abiotic (caused by non-living factors). Examples of biotic factors are insects, diseases, and nematodes. Examples of abiotic factors are heat, drought, wind, and too much water.
The first step in controlling the disease is the planting of a resistant variety, if these are available. The stress can be addressed by a unique product of AECI Plant Health called Alexin. This product increases the natural resistance of a plant, making it better equipped to deal with stress.
Other products from AECI Plant Health that are very effective in controlling the disease are CungFu, Chloroflo, and Flowable Sulphur. Note, however that none of these are registered on the crop against this disease.
Visit aeciph.com to find your closest crop adviser for advice.
ALSO READ: Early blight: How to protect your potatoes
Sign up for Farmer’s Inside Track: Join our exclusive platform for new entrants into farming and agri-business, with newsletters and podcasts.
