Reduced usage of synthetic chemical fungicides while preserving the crop against late blight. It is one of the problems in applying more ecological farming practices in potato production. Phytophthora infestans, a fungus-like organism, causes potato late blight. Despite its odd nature, the fungus is capable of completely killing an unprotected potato crop in one or two weeks if the weather circumstances are favourable. The potential reproductive consequences and increased cancer risk posed by several synthetics and their breakdown products are particularly concerning. Fungicide for seed potatoes, on the other hand, can considerably lower the likelihood of fungus on your potatoes.

Late blight is the most researched plant disease on the planet. However, there are few alternatives to synthetic chemical fungicides, and the usage of these pesticides is increasing the fungicide resistant population. However, with a thorough understanding of the fungus’ life cycle and the conditions that favour its growth.The late blight prevention and control programme can be developed, potentially reducing the need for synthetic chemical fungicides in potato-growing areas. 

Understanding Fungus

Understanding the biology of the organism you’re dealing with and its disease cycle is the first step toward achieving a more ecological strategy to protect your potato crop from late blight. The sporangiophore is the structure that bears the sporangia, which can number in the millions, which are the fruit of the fungus. Each sporangium contains eight zoospores, which are similar to seeds but can swim. When sporangia discharge their zoospores, blight spreads quickly in cool, damp weather. These “swimming seeds” move quickly throughout the field in rainwater, germinate, and infect the crop under such conditions. The sporangia can be borne by the wind and infect plants directly, which happens most often when the weather is milder.

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The Lifecycle of the Late Blight Fungus

  • Sporangia are transferred to leaf surfaces by wind and rain from cull piles, volunteer potato plants, or contaminated seeds. Infection occurs when the moisture and temperature conditions are ideal. The first symptoms develop three to seven days later.
  • The fungus’s mycelium infiltrates plant cells and kills them, creating blight. It keeps growing till it emerges from the underside of the leaves. The fungus then produces sporangiophores, which release more sporangia for wind and rain to carry elsewhere in the field.
  • When the fungus is washed off the leaves and the sporangia and zoospores are brought down into the soil by the water, tubers get infected. Tubers that have been exposed to the elements are more likely to become infected. If uninfected tubers come into contact with sporangia in the soil while being dug, they can become infected.
  • Because the blight pathogen overwinters on tubers rather than in the soil. An infection can be spread the following year through cull piles, volunteer plants, and sick seeds. Blight requires living plant tissue to survive. 

Symptoms of Potato

Late blight symptoms usually emerge after flowering, later in the growing season. A musty-fishy odour emanates from the rotting leaves of blight-infected plants. I

  • On Leaves: Olive to dark green dots form on the upper surface of the leaves, close to the leaf tip or leaf margins, as the initial symptom. They can be dry, yet they frequently appear wet. The infected leaf zone margins will appear watery and light green when exposed to light, indicating that the fungus is still progressing. As the disease proceeds, these spots spread, turn brown, and die. Except in extremely damp conditions, these symptoms develop initially on the plant’s lower leaves. Blighted leaves twist and shrivel in dry weather, becoming black and crisp.
  •  Infected areas of the stem will turn brown just below the growth point, forming dark strips that run the length of the stem. The infected spots on the stem do not appear to be as wet as the leaves. In severe situations, infection of the stem will result in the death of the leaves just above the infection site.
  • Purplish-brown sunken patches of uneven size and shape will form on tubers as symptoms. Infected potatoes decay in storage due to a dry reddish brown rot that spreads beneath the peel.

 Conditions that Favour Blight

  • Late blight spreads faster in cool, moist weather than in hot, dry weather because its spores require water and a specific temperature range to germinate. However, if the blight circumstances are favourable for long periods of time earlier in the season, there is a high danger of late blight.
  • Weather is cool and humid: The spores will germinate and form mycelium when the relative humidity is over 80%, the air temperature is between 10 and 18°C, and water is present on the leaves. As long as the temperatures remain cool, no reproduction will take place.
  • When the temperature is over 30°C and the relative humidity is below 80% or there is no water on the leaves, the fungus stops growing and cannot reproduce. High temperatures, on the other hand, will not destroy the fungus.

Fungicidal Spraying

Fungicidal sprays are used as a preventative measure before late blight attacks the crop. This is to safeguard the lower leaves, which will be difficult to reach if the foliage becomes too dense later.

Blight Forecasts: By determining the optimum timing for the first spray application and the frequency of spraying required, late blight forecasts can assist prevent unnecessary sprays.

Blight prediction software installed on your home computer and an on-farm weather station can help you identify properly and quickly when you should spray for your specific farm, reducing the number of sprays even more. As a result, rather than using more generalised area data, you’d be working from your own on-farm conditions.Its forecasts are based on long-term cumulative readings, as well as cumulative rainfall over a 10-day period and average temperature over 5 days. It also takes into account the vulnerability of the cultivars in question.

Schedule Spraying: If you farm in an area with a lot of disease pressure or if you’re producing vulnerable cultivars, you probably spray on a regular basis. Spray every 10-12 days if you’re growing very blight tolerant cultivars, every 8-10 days if they’re moderately tolerant to blight, and every 7 days if they’re sensitive to blight, all else being equal. When it’s rainy or raining, don’t spray.

Spray Equipment: You can plant low-growing plants between the potato rows to provide for easier access with minimal damage. By charging the spray particles, newer spraying technologies such as electrostatic sprayers prevent drift and substantially reduce the amount of water required. This also allows more spray to reach the budding leaves. Because of the considerable quantity of drift caused by aviation applications, this method is unsuitable for the environment.

What to Spray

Copper-based fungicides and compost extracts are the safest sprays to use.While some of these sprays, such as the Bordeaux mixture, are more phytotoxic to potatoes than newer synthetic fungicides, they do not cause late blight resistance. When it rains, they are also more effective in staying on the plants. Copper also outperforms other sprays in terms of preventing tubers from illness as the season progresses.

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How to spray fungicides

To avoid illnesses, the best way to ensure a big harvest of potatoes is to treat them before planting and consistently during the growth season.

  • Cut seed potatoes into portions with one to two sprouts or eyeballs in each. Leave potatoes whole if they are little and only have one or two eyes.
  • Place a layer of newspaper on top of the seed potatoes, both sliced and whole. Mix 2 to 4 teaspoons of mancozeb-containing fungicide with a gallon of water in a garden sprayer. To thoroughly combine the materials, swirl the sprayer around. Spray the seed potatoes with the fungicide, rotating them to coat both side
  • Place the potatoes in a room with a high humidity level and a temperature of 60 to 70 degrees Fahrenheit. For one to two days, store them in a single layer on dry newspaper. The cuts on seed potatoes will heal as a result of this procedure, increasing viability.
  • If you water your potatoes more than one inch per week, they will rot in the moist ground.
  • When the plant stems reach a height of 6 inches, pull the soil up around them. This shields the tubers underground from the sun, resulting in a larger yield and preventing the potatoes from becoming green.
  • When the potato plants reach 4 to 6 inches tall, sprinkle the stems, undersides, and topsides of all leaves with mancozeb fungicide at the same rate as the seed potatoes.
  • Depending on the variety of potato, repeat the fungicide application every five to ten days or after a big rain during the growing season, which lasts 90 to 120 days. 14 days before harvesting potatoes, stop using fungicide.
  • When the tops of the plants turn brown and wilt, harvest the potatoes. FUNGICIDES^ HERBIDICES