What are the methods for controlling Phytophthora disease in carnations?

Symptoms The stems and roots are affected. When infected at the seedling stage, it causes root rot and the plants die. After planting out, the main stem and branches become infected; the affected areas appear water-soaked and turn grayish-white when dry, and the stems and leaves above the affected area wither.

The pathogen Phytophthora nicotianae Breda is called tobacco Phytophthora and belongs to the fungal subdivision Mastigomycotina. The sporangiophores emerge from the stomata and measure 10-744 microns long; the sporangia are borne singly, long elliptical or oval, measuring 28.8-67.5 x 12.5-30 microns, with a prominent papilla at the tip; the oospores are spherical, pale yellow or golden yellow, 20-22.5 microns in diameter. The chlamydospores are slightly yellow, spherical, 20-40 microns in diameter. The pathogen develops within a temperature range of 12-36°C, with 25-32°C being optimal. The mycelium is killed at 50°C after 5 minutes.

Transmission route and disease conditions The oospores overwinter in diseased plant residues in the soil. When conditions are suitable the following year, they produce sporangia and zoospores, which infect the host and cause disease. When humidity is high, sporangia are again produced from the diseased parts and spread by wind and rain, causing repeated infection.

Control methods

1. Build raised beds to prevent rain damage and drain excess water.

2. Chemical control Apply chemicals before the diseased plant rate exceeds 1%.

1) Spraying: Commonly used sprays include 25% metalaxyl wettable powder at 600 times dilution, 40% phosethyl-Al wettable powder at 250 times dilution; 64% oxadixyl-mancozeb wettable powder at 500 times dilution or 77.2% propamocarb aqueous solution at 800 times dilution, and 72% cymoxanil or cymoxanil-cyanide wettable powder at 800 times dilution. In areas where resistance to the above fungicides has developed, 69% dimethomorph-mancozeb wettable powder or water-dispersible granules at 1000 times dilution may be used, applied once about every 10 days, for 2-3 applications.

2) Smoke: In greenhouses, smoke agents may be used; 45% chlorothalonil smoke agent can be used, at 250 grams per mu each time.

3) Dust: For dust application technology, use 5% chlorothalonil composite dust, at 1 kilogram per mu each time.

4) Root drenching: Use 50% metalaxyl-copper wettable powder at 600 times dilution, or 60% fosetyl-Al wettable powder at 400 times dilution for root drenching, applying 300 grams of solution per plant.