09-04-2017, 09:31 AM
There are 2 classes of fungicides - contact and systemic fungicides. Contact fungicide will remain on the plant surface and prevent fungi from entering the plant. So with this class of fungicide, it is important that you cover the whole plant surfaces - cover both top and bottom surfaces of leaves.
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Systemic fungicides on the other hand will enter the plant system and work from inside the plant. So total coverage is not that important.
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When there is constant rain, contact fungicides are not effective because rain can wash them off. So systemic fungicides are better in that situation.
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As for best time to spray, here is what I find out: apply contact fungicides when the leaves are dry and when it is sunny. Under this atmospheric condition, the contact fungicide will strongly attach itself to the leaves and resist wash-off by light rains. I've experienced this in my cucumber farm. For systemic fungicides, apply them when the weather is wet and humid. Under this condition, the waxy layer covering the plant surfaces will be swelled up, allowing the fungicide to easily enter the plant. Under dry conditions the waxy coating is less permeable. Any systemic fungicide that is not absorbed will breakdown under the sun, washed off by rain or destroyed by microbes.
..
Systemic fungicides on the other hand will enter the plant system and work from inside the plant. So total coverage is not that important.
..
When there is constant rain, contact fungicides are not effective because rain can wash them off. So systemic fungicides are better in that situation.
...
As for best time to spray, here is what I find out: apply contact fungicides when the leaves are dry and when it is sunny. Under this atmospheric condition, the contact fungicide will strongly attach itself to the leaves and resist wash-off by light rains. I've experienced this in my cucumber farm. For systemic fungicides, apply them when the weather is wet and humid. Under this condition, the waxy layer covering the plant surfaces will be swelled up, allowing the fungicide to easily enter the plant. Under dry conditions the waxy coating is less permeable. Any systemic fungicide that is not absorbed will breakdown under the sun, washed off by rain or destroyed by microbes.