Fungicide Control of Rot and Mildews in Crop Plants
Wilts, necrosis, rots, mildews and degeneration are common in humid season crops. These diseases can be identified by a sort of dusty, wilted or boiled type of appearance. They also produce some sort of bad smell. Once affected, complete devastation, loss of crop and plants are a big blow to the growers. When it comes to crop protection, farmers are worried about two things. One should not lose his crop and the control measures taken should not harm the consumer, because of loss of quality or residue. Cost of treatment and duration of effects are also important. Therefore, it is a matter of discussion among the farm-related people throughout.
At present, the rot diseases caused by Phytophthora genus of fungi on garden and crop plants are the focal points here, since there are vast varieties of fungal plant diseases troubling the crops worldwide. Rot diseases form wet areas in the affected places, later it will rot and then ultimately wilt and wither off the parts. Sometimes entire plant might die due to the disease.
For long, the Bordeaux mixture, incidentally discovered by Prof. Millardet in 1882 as a control against downy mildew of grapes in France, is in use as rot control fungicide. It is a 1:1 mixture of copper sulphate and calcium hydroxide (also known as hydrated lime) in water, prepared on-site, at the time of use. Even today, it is the simplest, effective and prophylactic fungicide in use for a variety of crops.
In recent years, copper oxychloride is also effectively used as a copper fungicide to control mildews and rots. Copper hydroxide is also used in some crops. Unlike Bordeaux mixture, these have extended keeping quality in agrochemical stores.
A kilogram of copper sulphate and a kilogram of calcium hydroxide (also called as quick lime) are needed to prepare Bordeaux mixture. Depending on the type of use, Bordeaux mixture is prepared as paste, solution or as paint. In any case, it should be used on the same day of mixing.
One kilogram of copper sulphate is mixed in 5 litres of water and one kilogram of calcium hydroxide is mixed in 5 litres of water in separate wooden or plastic containers. Use a net pouch or a strainer to dissolve copper sulphate in water. These are then mixed by pouring together and simultaneously stirring with a wooden stick or stirrer in a third container to make 10 litres of Bordeaux paste. This can be brushed to highly disease affected plant parts. It is good practice to maintain a neutral pH with the addition of slightly less lime solution.
This is the chemical reaction taking place in the mixture, which forms effective copper fungicide.
Add 90 litre of water to Bordeaux paste to make 100 litres of solution, which is suitable for spraying by means of different sprayer pumps.
Bordeaux painting solution
Here double the quantity (2 kilogrammes) of calcium hydroxide is used to smear in cut surfaces of plants or grafted areas of plants after joint healing, quick-drying requirements, etc. This also can be sprayed using a sprayer pump.
Preparation of Bordeaux mixture
Prevention is better than cure
- Good field practices such as removal of dead and the decaying crop matter from the location and avoiding water stagnation are helpful for keeping the plants away from the disease-causing pathogen.
- Growing hardy and resistant crop varieties will not succumb to disease pathogens quickly.
- The proper bordering of the cropping area helps in easy exposure to diseases. If possible, high tech greenhouses and poly houses for crops keep the diseases at bay.
Pathogens are everywhere
- Due to easy dispersal of spores of fungi by water, wind or soil and harbouring in alternate host plants, diseases survive in the environment.
- Spores remain dormant in soil or dried plant parts for many years and suddenly emerge when favourable conditions.
- The only hope is that, if the crops can grow well with sufficient nutrients and climate and the pathogen load in the environment is not sufficient to cause disease symptoms, the crops will survive.
- If the pathogen life cycle and cropping season will not clash together, then also crops will survive.
Recently, some of the alkaloids and other chemicals are found imparting resistance to plants, thereby they become capable of remaining disease-free. Some of the growth retarders, phosphorus acid, some alkaline mild substances help to avoid the disease.
Some of vegetable spray oils such as palm oil, neem oil, Pongamia oil, etc are having fungicidal properties. Some of the other spray oils of mineral oil category also are useful in controlling the disease spread.
Biological control of the fungi causing disease is possible by making use of certain microorganisms and antibiotics also judiciously. Composting of organic matter promotes these helpful microorganisms grow well, thereby giving competition and suppressing of disease-causing pathogens.
The synergic occurrence of different microorganisms often does not cause any disease to crop plants. Those organisms live their life at an optimum level without harming the plants.
Trichoderma and Pseudomonas suppress the disease pathogens considerably. Identifying these properties, mass multiplication of these microorganisms and supplying them in easily usable liquid form or flow dust form are manufactured by agro suppliers.
Recently, new chemicals such as Mancozeb, Chlorothalonil, Mandipropamid, etc., are also effectively used to control rot and mildew diseases in different crops.
Always act well in time
As far as fungal diseases, especially rots are considered, they cause epidemic conditions very quickly. Therefore, control measures have to be taken prophylactically, every season well in advance. This will help the crops grow and yield for giving happiness and prosperity for the growers. So, always consult an agro service professional for appropriate control measures.
This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.
© 2019 Halemane Muralikrishna