A network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests.
PestNet is a network that helps people worldwide obtain rapid advice and information on crop protection, including the identification and management of plant pests. It started in 1999. Anyone with an interest in plant protection is welcome to join. PestNet is free and is moderated, ensuring that messages are confined to plant protection.
Two members replied: The first said that the downward curling and crinkling of the leaves suggested thrips, possibly Sirtothrips dorsalis. The plants could also be showing symptoms of mite infestation. Sprays of wettable sulphur were recommended. If spider mites are the the cause then overhead irrigation is likely to keep populations in check. The yellowing of the leaves might be due to poor nutrition, but also it could be due to nematodes, and roots should be checked for galls of root knt nematodes. If so, then crop rotation has to be considered for long-term control.
Another member wrote the following:
1) 5947, 5948 and others – necrotic leaves. Fungal lesions, but probably secondary with infections occurring as the leaves senesce from other causes. Probably not important.
2) 5949, possibly mite. Look at the shoot at the top right corner. The bunched crinkled leaves are typical of mite damage, and if in the Pacific, this would be Polyphagotarsonema. Spray a few plants with chemicals that are active against mites and see what happens.
3) 6089, are these showing scale insects? Difficult to see clearly, but if scale insects are present in numbers, the leaf yellowing could be caused by them. (Soil also looks very dry, so lack of water could also be the cause of the symptoms, or could lack of nutrients. The corn looks a bit yellow, too, in 5944, but it’s more difficult to diagnose symptoms when the photos are taken in bright sunlight – try taking them early in the morning or towards evening next time).