Categories: Vegetables

How to ensure effective crop spraying

Non-systemic products have to be sprayed thoroughly to be effective. This applies particularly to fungicides.

With insecticides, you might get away with less than full coverage, depending on the mobility of the pest.

For example, with caterpillars that eat through the leaf, it is not essential to obtain full coverage on both sides, provided you apply the correct rate of active ingredient.

READ Biotechnology: how it can help farmers

Fungal diseases are more of a challenge as they usually develop on the underside of leaves, so you need to spray these areas thoroughly.

In fact, wetting the underside usually gives fairly good coverage of the top of the leaves as well.

Admittedly, it takes considerable effort to reach the underside of leaves, especially in the case of Brassicaceae (the cabbage family) in the nursery.

Here, wetting the underside of the leaves close to the ground is awkward, yet this is where downy mildew starts off and has to be controlled.

All seedling growers experience downy mildew on their plants at some stage, and most resort to systemic products.

In doing so, they reduce the working life of the product. Systemic products should be used only as an emergency measure, not for routine spraying.

Seedling growers should rather employ contact products to stop the fungus from entering the leaf (prophylactic coverage).

This invariably uses air and fine droplets to reach the underside of the leaves. I find, however, that few farmers check under the leaves to ensure that full coverage has been achieved, as they assume that the misting does the job.

Physically inspecting the underside of the leaves is the only way to be sure.

If you get your spraying right, you can use cheaper fungicides very effectively. This will not only save you money, but ensure that you still have effective systemic products ready for emergencies – such as when climatic conditions are especially favourable for the development of diseases.

Use common sense!
Tomatoes are prone to leaf diseases; be especially vigilant here. With tall-growing varieties, the leaves hang down. Spraying from the side means that the force of the spray often pushes the outer leaves flat, preventing penetration to the areas where diseases usually start.

I recall visiting a tomato farmer who proudly showed me his new spray rig. It consisted of a vertical pipe with nozzles equally spaced all the way up. The outer leaves glistened with water. I pulled up a leaf and showed him that those underneath were dry.

He was stunned.

If he had angled the nozzles to face 45° upwards, the spray would have caused the leaves to open outwards, enabling it to penetrate as far as the back of leaves on the other side. Even the distance from nozzle to plant makes a difference – it takes trial and error to get the set-up correct.

Beans are also a problem. They are low to the ground and usually sprayed from above. Unless you have a wind-assisted sprayer to wave the leaves around, the undersides will remain dry.

To ensure effective spraying on crops such as these, ensure that the crop is uniformly planted and fit drop arms to the spray boom with nozzles angled up on either side. All this takes effort, but it’s worth it.

Coverage is everything!

Bill Kerr is a vegetable specialist and a breeder of a range of vegetables.

Share
Published by

Recent Posts

‘Growing the agri value chain through partnerships’

Partnership linkages are required throughout the agricultural value chain to ensure that the sector contributes to the growth of the…

6 hours ago

Reviving generations of Brangus genetics

Harrismith breeder Dr Elsie Campher’s Helpmekaar Brangus herd embodies generations of top-quality genetics. She says the stud, founded by her…

11 hours ago

‘No clarity on gun licences for the foreseeable future’

Parliament’s Portfolio Committee on Police has referred the draft notice declaring an amnesty on firearms back to Police Minister Bheki…

1 day ago

Towards climate-smart livestock farming

Natural selection is pivotal in adapting livestock farming to climate change inAfrica and beyond,says Prof Charles T Kadzere of the…

1 day ago

SA farmers concerned about live cattle exports from Botswana

The South African Red Meat Producers' Organisation (RPO) has expressed serious concern about the announcement by the Ministry of Agriculture…

2 days ago

Hans Rosling’s gift to the world

In today’s world, surrounded by ‘fake news’ and hampered by our own brains, we need to know how to separate…

3 days ago