BỆNH PHẤN TRẮNG – AGRICULTURE
bệnh phấn trắng trên cây chôm chôm
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BỆNH PHẤN TRẮNG

Posted On May 29, 2017 at 12:54 am by / 92 Comments

BỆNH PHẤN TRẮNG


Tác nhân:

Do nấm Oidium sp gây ra.

Triệu chứng: 

Nấm chủ yếu gây hại trên hoa, trái non và lá non trên các vườn chôm chôm. Trên bề mặt lá bị bao phủ một lớp nấm màu trắng xám.

Bệnh có  thể nhiễm vào trái  ở mọi giai đoạn  phát triển của trái. Trái bệnh  bị nhỏ hay không  phát triển được. Bệnh  nặng làm trái bị thối  khô và gây thiệt hại nặng  đến năng suất. Trái bệnh bị đóng phấn trắng xám trên khắp vỏ làm các chóp gai bị cháy khô, vỏ trái bị thối nâu đen.

Trên lá non: Trên bề mặt lá bị bao phủ một lớp nấm màu trắng xám, nấm phát triển trên cả hai mặt lá, làm cho lá bị xoăn, còi cọc và cuối cùng là chết khô.

Trên hoa: tương tự như trên lá, cả hoa phát hoa bị bao phủ bởi một lớp nấm màu trắng xám, làm cho hoa bị khô, đen và rụng đi.

Trên trái non:
Trái non cũng bị một lớp phấn màu trắng xám bao phủ, trái bị khô đen và rụng đi. Nấm cũng tấn công ở giai đoạn trái hơi lớn, làm cho trái khô có thể rụng đi hoặc treo trên cây. Nếu nấm tấn công vào giai đoạn trái lớn sẽ làm cho râu trái bị khô, đổi màu đen, gây hiện tượng râu kẽm trên trái chôm chôm, trái bị nhiễm sẽ kém phát triển, cơm mỏng.

Theo Goerge (2000) nấm gây hại trên nhiều loại cây trồng như xoài, chôm chôm, nhãn, đu đủ và trên một số cây trồng khác như đậu, các loại ngũ cốc, một số loại cải trong họ thập tự, một số cây trong họ cà và cả hoa hồng.

Điều kiện phát sinh phát triển:

Theo Johnson, Mayers và Cooke (1993) nấm phát triển mạnh trong điều kiện có ẩm độ cao, nhiệt độ thấp. Nhiệt độ thích hợp cho nấm phát triển là: 20 – 250C (Jun Imada, 1995). Cũng theo Goerge (2000) nấm phát tán chủ yếu nhờ gió và nẩy mầm trong điều kiện có giọt sương.

Khả năng gây hại:

Trong điều kiện thuận lợi nấm có khả năng gây hại đến 90%.

Qui trình phòng trừ bệnh phấn trắng:

Biện pháp cơ học:
Sau khi thu hoạch trái thì tiến hành cắt tỉa những cành già cỏi, cành mang mầm bệnh, phát hoa, trái khô đen bị nhiễm bệnh còn sót lại của vụ trước, tỉa cành giúp vườn cây thông thoáng.

Bón phân tưới nấm đối kháng Trichoderma:

Xới nhẹ gốc, tiến hành bón phân hữu cơ hoai mục càng nhiều càng tốt, tưới hoặc rải nấm đối kháng Trichoderma giúp nhanh hoai mục xác bã thực vật, diệt nấm gây hại trong đất, bón phân N-P-K liều lượng theo khuyến cáo của quy trình kỹ thuật canh tác, tuỳ theo tuổi cây. Mục đích nhằm tạo cho cây có bộ lá xanh tốt. Sau đó bón phân lần 2 với liều lượng ít hơn, mục đích cho lá mau thành thục và trổ hoa sớm.

Biện pháp hóa học:
Vụ thuận:

Phun ngừa khi những phát hoa bắt đầu nở, vì vào vụ thuận thời tiết không thuận lợi cho sự bộc phát của nấm gây bệnh phấn trắng như nhiệt độ cao, ẩm độ thấp. Ta có thể phun ngừa bằng Kumulus nồng độ 40g/ 10 lít nước, Anvil nồng độ 20 ml/ 8l nước. Khi bệnh phát triển mạnh thì nên dùng Kumulus, Anvil, thuốc gốc Defenoconazole, Propiconazole, nồng độ theo khuyến cáo.

Phòng trị  bệnh bằng cách  phun thuốc lên  cây khi trái  còn non, bằng một trong các loại thuốc như Ridomyl 72 WP, Topsin-M 50 WP hoặc bằng bột lưu huỳnh (nồng độ 0,2%).

Vụ nghịch:
Thời gian phun ngừa nên sớm hơn, khi những phát hoa bắt đầu bung chà, vì vào thời điểm này thường mưa nhiều, ẩm độ cao, thuận lợi cho bệnh phát triển. Khi bệnh phát triển mạnh thì nên phun trị bằng Kumulus, Anvil, Propiconazole, Defenoconazole, nồng độ theo khuyến cáo.

Phân bố các lần phun:

Tiến hành phun lần 1 khi phát hoa vừa bung chà, phun lần 2 cách lần 1 là 7 ngày, lần 3 khi trái đã kết thúc giai đoạn rụng sinh lý. Lần 1 và lần 2 phun nên phun thuốc gốc lưu huỳnh, lần 3 phun Anvil. Hoặc phun lần 1 với Defenoconazole hay Propiconazole, lần 2 với thuốc gốc lưu huỳnh và lần 3 khi trái đã kết thúc giai đoạn rụng sinh lý bằng thuốc Anvil.

 

 

 

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