By David Jones, CropNuts BroadAcre Agronomist
Having toured several farms in the North Rift, Nakuru and Naivasha lately, it is apparent that Maize Lethal Necrosis Disease (MLND) is still alive and kicking. The concerns over Fall Armyworm last season perhaps overshadowed the importance of the disease which certainly appeared less than I saw in 2016..
Maize Lethal Necrosis Disease (MLND)
It is important not to lose sight of MLND as it clearly remains a real threat to maize production.
It is caused by two viruses being present in the plant at the same time; Maize Chlorotic Mottle Virus and one of either Maize Dwarf or Wheat Streak Mosaic viruses.
The viruses are transmitted by a wide range of vectors including Cereal Leaf Beetles, Thrips, Rootworms and Aphids, which means a range of control measures are required:
Early detection of infected plants is crucial, although infection can occur very early on in the crops life so spraying early with a neonicotinoid insecticide will give good systemic protection as the seed dressing wears off from the 3-4 leaf stage.
For those who have not planted yet, my first consideration would be to make absolutely certain that the soil structure is in good order, and secondly that any issues identified in the soil test have been addressed.
On continuous maize fields that have had bad infection in previous years, I would question whether the risk of planting maize is sensible in view of the infection levels that I am seeing this season. If absolutely necessary to plant maize, I would look at whether a variety with a degree of tolerance to the disease would be appropriate.
DK 777 and KATEH 01 for example show tolerance (NOT resistance) so in high risk situations can reduce the potential for yield loss due to MLND considerably. Nonetheless, this has to be weighed against the yield potential of these varieties compared to the very best varieties for your region – a tolerant variety is not worth growing if it is already 20% lower yielding than Pannar 691 or Western Seed Company’s 505 for example.
Good field hygiene is the final step to reducing the damage of MLND. Weeds act as hosts to many insects (some beneficial!) but overall they compete with the crop for light, nutrients and water so must be well controlled. Just do not stress the plant by applying when the crop is stressed.
Fall Armyworm Update
One of my key observations so far this year is that when spraying to control Fall Armyworm, keeping the intervals tight (i.e. 7 days) early in the crops life is key.
Any larvae that fail to die from the first spray in particular (around 5-6 leaf stage) will reach the 5th/6th instar while the crop is still small (10 leaves). Larvae of this size are bad news at any stage of the crop but they do any awful lot more damage when the plant is small.
The lesson is to keep spray intervals tight in the early stages, especially when you have seen surviving larvae. Any patches of badly affected plants should be noted and immediately targeted with knapsack spraying.
Till next time,
David Jones is the Broad Acre Specialist at Crop Nutrition Laboratory Services Ltd. (CROPNUTS). David has a keen interest in soils and no till farming systems where he has undertaken work looking into weed levels and changes in soil structure, and has extensive experience in field trials and in the development of precision farming techniques. In his spare time he enjoys playing rugby.